Your SlideShare is downloading. ×
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Ccent notes part 3
Upcoming SlideShare
Loading in...5
×

Thanks for flagging this SlideShare!

Oops! An error has occurred.

×
Saving this for later? Get the SlideShare app to save on your phone or tablet. Read anywhere, anytime – even offline.
Text the download link to your phone
Standard text messaging rates apply

Ccent notes part 3

495

Published on

70-802

70-802

0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total Views
495
On Slideshare
0
From Embeds
0
Number of Embeds
0
Actions
Shares
0
Downloads
46
Comments
0
Likes
0
Embeds 0
No embeds

Report content
Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
No notes for slide

Transcript

  • 1. CCENT Notes Part 3 – IP Routing Ref : CCENT/CCNA ICND1 Official Exam Certification Guide, Second Edition by Wendell OdomIt is highly recommended that you read at least once the above study guide to make fulluse of this notes, it is expected that there may be minor errors in this notes, pleasealways refer the study guide for accurate information. (Jojo Jacob - CCENT)
  • 2. TABLE OF CONTENTSChapter 12 – IP Addressing and Subnetting........................................................................3Chapter 13 – Operating Cisco Routers..............................................................................38Chapter 14 – Routing Protocol Concepts and Configuration............................................47Chapter 15 – Troubleshooting IP Routing.........................................................................58 2
  • 3. Chapter 12 – IP Addressing and SubnettingList of all possible valid network numbers….reference table for the number of network,size of the network part, size of the host part, for Class A,B and C ip networks. Class A Class B Class CFirst Octect range 1 to 126 128 - 191 192 – 223Valid Network Numbers 1.0.0.0 to 128.0.0.0 192.0.0.0 to 126.0.0.0 191.255.0.0 223.255.255.0Number of networks in this Class 2^7–2 2 ^ 14 = 2 ^ 21= = 128 16,384 2,097,152Number of hosts per network 2 ^ 24 – 2 = 2 ^ 16 – 2 = 2^8–2= 16,777,214 65,534 254Size of network part of the address 1 2 3(bytes)Size of hosts part of the address 3 2 1(bytes)^ raised toCLASS A (7 Network Bits)0 N N N N N N N H H H H H H H H H H H H H H H H H H H H H H H H1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 CLASS B (6 + 8 = 14 Network Bits)1 0 N N N N N N H H H H H H H H H H H H H H H H H H H H H H H H1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8CLASS C (5 + 16 = 21 Network Bits)1 1 0 N N N N N H H H H H H H H H H H H H H H H H H H H H H H H1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8Class A , B and C network, network and host parts and default maskClass of Size of network part of Size of host part of Default mask forAddress address in bits address in bits each class of networkA 8 24 255.0.0.0.B 16 16 255.255.0.0C 24 8 255.255.255.0 3
  • 4. RFC 1918 Private IP Address SpacePrivate IP Networks Class of Networks Number of Networks10.0.0.0 through 10.0.0.0 A 1172.16.0.0 through 172.31.0.0 B 16192.168.0.0 through 192.168.255.0 C 255IPv6 – 128 bit IP address : can provide 10 ^ 38 IP Addresses.Currently in the earth there are 10 ^ 10 people living.IPv4 vs IPv6Feature IPv4 IPv6Size of address 32 bits , 4 octects 128 bits , 16 octectsExample address 10.1.1.1 0000:0000:0000:0000:FFFF:FFFF:0A01:0101Same address ---- ::FFFF:FFFF:0A01:0101abrreviatedNumber of possible 2 ^ 32 2 ^ 128 , or roughly 3.4 x 10 ^ 38addresses, ignoring Approx 4 billionreseved addressesBitwise Boolean AND example Decimal BinaryAddress 150.150.2.1 10010110 10010110 00000010 00000001Mask 255.255.255.0 11111111 11111111 11111111 00000000Result of AND 150.150.2.0 10010110 10010110 00000010 00000000255.255.255.0 – 11111111 11111111 11111111 00000000Is written as a /24 subnet mask.Binary process to convert between Dotted decimal and prefix notationStep 1. Covert the dotted decimal mask to binaryStep 2. Count the number of binary 1s in the 32 bit binary mask, this is the value of theprefix notation maskEg. 255.255.240.0 converts to….11111111 11111111 11110000 00000000The mask has 20 binary 1s, so the prefix notation of the same mask is /20.Convert prefix notation to a dotted decimal format…Step 1. write down x binary 1s, where x is the value listed in the prefix notation of themask 4
  • 5. Step 2. Write down binary 0s after binary 1s until you have written down all the 32 bitsStep 3. Convert this binary number, 8 bit at a time to dotted decimal format.Eg. /20 converts to11111111 11111111 11110000 00000000255.255.240.0Nine possible Decimal Numbers in a subnet maskSubnet mask’s Binary Equivalent Number of Binary Number of BinaryDecimal Octect 1s 0s0 00000000 0 8128 10000000 1 7192 11000000 2 6224 11100000 3 5240 11110000 4 4248 11111000 5 3252 11111100 6 2254 11111110 7 1255 11111111 8 0Convert a dotted decimal subnet mask format to a prefix format….Step 1. Start with a prefix value of 0Step 2. For each dotted decimal octect, add the number of binary 1s, listed for thatdecimal value in the table aboveStep 3. Prefix length is /x , where x is the sum calculated in Step 2.Eg. 255.255.240.0Start from 0First octect 255 add 8Second octect 255 add 8Third octect 240 add 4Fourth octect 0 add 0Prefix is 20Converting a /20 subnet into dotted decimal format….Step 1. Divide x by 8 ( x / 8) , noting the number of times 8 goes fully into x , thedividend represented as d, and the number left over, the reminder represented as r.Step 2. write down d octets of 255, 5
  • 6. Step 3. for the next octet, find the decimal number that begins with r, binary 1s,Followed by all binary 0s.Step 4. for any remaining octets write down value 020 / 8 = 2 and a reminder of 42 octects with all binary 1s , third octed with 1 birary 1 and 4 binary 0 , and last one withall binary 0s.255.255.240.0Appendix D. Problem Set 1.255.240.0.0 - 8+4+0+0+ = /12255.255.192.0 – 8+8+2+0 = /18255.255.255.224 – 8+8+8+3 = /27255.254.0.0 – 8+7+0+0 = /15255.255.248.0 - 8+8+5+0 = /21/30 - 255.255.255.252/25 - 255.255.255.128/11 - 255.224.0.0/22 - 255.255.252.0/24 - 255.255.255.0255.240.0.0 - 11111111 11110000 00000000 00000000 - /12255.255.192.0 – 11111111 11111111 11000000 00000000 /18255.255.255.224 – 11111111 11111111 11111111 11100000 /27255.254.0.0 – 11111111 11111110 00000000 00000000 /15255.255.248.0 - 11111111 11111111 11111000 00000000 /21/30 - 11111111 11111111 11111111 11111100 255.255.255.252/25 - 11111111 11111111 11111111 10000000 255.255.255.128/11 - 11111111 11100000 00000000 00000000 255.224.0.0/22 - 11111111 11111111 11111100 00000000 255.255.252.0/24 - 11111111 11111111 11111111 00000000 255.255.255.0 6
  • 7. ANALYSING AND CHOOSING SUBNET MASKSSLSM – Static Length Subnet MaskVLSM – Variable Length Subnet MaskHow to find the size of the Network , Subnet and Host part of an IP Address…• The network part of the address is always defined by the class rule• The host part of the address is defined by the subnet mask, the number of binary zeros in the subnet mask defines the number of host bits.• Subnet part of the address is what is left over in the 32 bit addressIP Address : 8.1.4.5Mask : 255.255.0.0Class : ANetwork Bits : 8Host bits : 16Subnet bits : 32 – 24 = 8IP Address : 130.4.102.1Mask : 255.255.255.0Class : BNetwork Bits : 16Host bits : 8Subnet bits : 32 – 24 = 8IP Address : 199.1.1.100Mask : 255.255.255.0Class : CNetwork Bits : 24Host bits : 8Subnet bits : 32 – 32 = 0Facts about how the subnet mask identifies part of the structure of an IP address• A subnet masks binary 1s define the combined network and subnet part of an IP address• The masks binary 0s define the hosts part of the IP address• Class rules define the size of the network part 7
  • 8. Finding the Network, Subnet and Host part using binary…..Step 1. Compare the first octet of the address to the table of Class A,B or C addresses,write down the number of network bits depending on the address class.Step 2. Find the number of hosts bits by a. Converting subnet masks to binary b. Counting the number of binary 0s in the maskStep 3. Calculate the number of subnet bits by subtracting the combined network andhosts bits from 32.Decimal Process : Finding the Network, Subnet and Hosts bits in a subnet maskStep 1. Compare the first octet of the address to the table of Class A,B or C addresses;write down the number of network bits based on the address class.Step 2. If the mask is in dotted decimal format, convert the mask to prefix formatStep 3. To find the number of host bits, subtract the prefix length from 32Step 4. Calculate the number of subnet bits by subtracting the combined network andhosts bits from 32Given a class full network number and a single subnet mask is used throughout theclassfull network.Number of subnets :- 2 ^ s , where s is the number of subnet bitsNumber of hosts :- 2 ^ h , where h is the number of host bitsWhen to use which formula for number of subnetsUse the 2 ^ s – 2 formula, and avoid using Use the 2 ^ s formula, and use the zero andthe zero subnet and broadcast subnet if… broadcast subnet if…Classful routing protocol Classless routing protocolRIP version 1 or IGRP as the routing RIP Version 2, EIGRP or OSPF as theprotocol routing protocolThe no ip subnet zero command is The ip subnet zero command is configuredconfigured or ommited (default) VLSM is used No other clues provided 8
  • 9. Analysing the subnet mask8.1.4.5 /16Hosts bits : 32 – 16 = 16Class A network bits : 8Subnet bits : 32 – 24 = 8Number of subnets = 2 ^ 8 = 256Number of host = 2 ^ 16 – 2 = 65,534130.4.102.1/24Hosts bits : 32 – 24 = 8Class B network bits : 16Subnet bits : 32 – 24 = 8Number of subnets = 2 ^ 8 = 256Number of host = 2 ^ 8 – 2 = 254199.1.1.100/24Hosts bits : 32 – 24 = 8Class C network bits : 24Subnet bits : 32 – 32 = 0Number of subnets = 2 ^ 0 = 1Number of host = 2 ^ 8 – 2 = 254130.4.102.1/22Hosts bits : 32 – 22 = 10Class B network bits : 16Subnet bits : 32 – 26 = 6Number of subnets = 2 ^ 6 = 64Number of host = 2 ^ 8 – 2 = 1022 9
  • 10. 199.1.1.100/27Hosts bits : 32 – 27 = 5Class C network bits : 24Subnet bits : 32 – 29 = 3Number of subnets = 2 ^ 3 = 8Number of host = 2 ^ 5 – 2 = 30Number of bits in the host Maximum number of hosts Maximum number ofor subnet field (2 ^ h – 2) subnets (2 ^ s )1 0 22 2 43 6 84 14 165 30 326 62 647 126 1288 254 2569 510 51210 1022 102411 2046 204812 4094 409613 8190 819214 16,382 16,384Finding the only possible MASKWith a Class B network 130.1.0.0 , what is the only subnet mask you can use to haveupto 200 subnets and 200 hosts per subnets???To have 200 subnets you need to have atleast 8 subnet bits( 2 ^ 8 = 256) , (2 ^ 7 is only 128)Only possible subnet so is…(16 bits for network part as it is a Class B network).NNNNNNNN NNNNNNNN SSSSSSSS HHHHHHHH11111111 11111111 11111111 00000000255.255.255.0 or a /24 mask. 10
  • 11. Finding the multiple possible MASKsWith a Class B network, what are the subnet masks you can use to have upto 50 subnetsand 200 hosts in the largest subnet???To have 50 subnets you need to have atleast 6 subnet bits( 2 ^ 6 = 64) , (2 ^ 5 is only 32)To have 200 hosts you need to have atleast 8 host bits( 2 ^ 8 - 2 = 254) , (2 ^ 7 is only 128)Possible subnet format is …(16 bits for network part as it is a Class B network).NNNNNNNN NNNNNNNN SSSSSSXX HHHHHHHHXX – can be either subnet or host bitsThat mean you may get 2 ^ 2 = 4 possible combination of subnet masks, howeverAll masks must start with one unbroken consecutive string of binary 1s, followed by oneunbroken consecutive string of binary 0s.So the possible mask are listed below but only three are valid.11111111 11111111 11111111 00000000 (8 subnets , 8 hosts)11111111 11111111 11111110 00000000 (7 subnets, 9 hosts)11111111 11111111 11111100 00000000 (6 subnets, 10 hosts)11111111 11111111 11111101 00000000 (INVALID MASK)255.255.255.0 prefix format /24255.255.254.0 prefix format /23255.255.252.0 prefix format /22Choosing the subnet that maximizes the number of subnets or hostsThe mask with the most subnet bits : the mask with the wildcard bits set to binary 1s,there by increasing the subnet bits, maximizes the number of subnets and minimizes thenumber of hosts per subnet.The mask with most host bits : the mask with the wildcard bits set to binrary 0s, therebymaking the host part of the subnet address larger, maximizes the number of hosts persubnet and minimizes the number of subnets. 11
  • 12. Choosing a subnet mask steps …..Step 1. Find the number of network bits (N) based on the Class A,B or C rulesStep 2 : Find the number of subnet bits (S) based on the formula 2 ^ s , such that 2 ^ s >or = the number of required subnets.Step 3. Find the number of host bits (H) based on the formula 2 ^ h – 2, such that 2 ^ h –2 is >= the number of required hosts.Step 4. Write down starting from the left N+S binary 1sStep 5. Write down starting from right H binary 0sStep 6. If the binary 1s and 0s together adds up to less than 32 a. fill in the remaining ‘wildcard’ bit positions with X between binary 1s and 0s. b. find all combination of bits for the wildcard bit positions, meeting the requirement ofhaving one unbroken consecutive string of binary 1s on left.Step 7. convert the mask to decimal or prefix formatStep 8. To find the mask that maximizes the number of subnets pick the mask with mostbinary 1s init, and to find the mask that maximizes the number of hosts pick the maskwith most binary 0s.Problem set 2. Analysing unsubnetted IP addresses10.55.44.3Class of the address : ANumber of octets in the network part : 1Number of octets in the host part : 3Network number : 10.0.0.0Network broadcast number : 10.255.255.255128.77.6.7Class of the address : BNumber of octets in the network part : 2Number of octets in the host part : 2Network number : 128.77.0.0Network broadcast number : 128.77.255.255192.168.76.54Class of the address : CNumber of octets in the network part : 3Number of octets in the host part : 1Network number : 192.168.76.0Network broadcast number : 192.168.76.255 12
  • 13. 190.190.190.190Class of the address : BNumber of octets in the network part : 2Number of octets in the host part : 2Network number : 190.190.0.0Network broadcast number : 190.190.255.2559.1.1.1Class of the address : ANumber of octets in the network part : 1Number of octets in the host part : 3Network number : 9.0.0.0Network broadcast number : 9.255.255.255200.1.1.1Class of the address : CNumber of octets in the network part : 3Number of octets in the host part : 1Network number : 200.1.1.0Network broadcast number : 200.1.1.255Problem Set 3. Interpreting existing subnet masks10.66.5.99 255.255.254.0StepsMask in prefix format /23Class : AResultsNetwork bits 8Subnet bits 32 – (8+9) = 15Host bits 9Number of subnets in the network 2 ^ 15 = 32,768Number of hosts per subnet 2 ^ 9 – 2 = 510 13
  • 14. 172.16.203.42 255.255.252.0StepsMask in prefix format /22Class : BResultsNetwork bits 16Subnet bits 32 – (16+10) = 6Host bits 10Number of subnets in the network 2 ^ 6 = 64Number of hosts per subnet 2 ^ 10 – 2 = 1022192.168.55.55 255.255.255.224StepsMask in prefix format /27Class : CResultsNetwork bits 24Subnet bits 32 – (24+5) = 3Host bits 5Number of subnets in the network 2 ^ 3 = 8Number of hosts per subnet 2 ^ 5 – 2 = 3010.22.55.87 /30StepsClass : AResultsNetwork bits 8Subnet bits 32 – (8+2) = 22Host bits 2Number of subnets in the network 2 ^ 22 = 4,194,304Number of hosts per subnet 2 ^ 2 – 2 = 2172.30.40.166 /26 14
  • 15. StepsClass : BResultsNetwork bits 16Subnet bits 32 – (16+6) = 10Host bits 6Number of subnets in the network 2 ^ 10 = 1024Number of hosts per subnet 2 ^ 6 – 2 = 62192.168.203.18 /29StepsClass : CResultsNetwork bits 24Subnet bits 32 – (24+3) = 5Host bits 3Number of subnets in the network 2 ^ 5 = 32Number of hosts per subnet 2 ^ 3 – 2 = 6Problem set 4 : Choosing Subnet MasksNetwork 10.0.0.0 needs 50 subnets and 200 hosts/subnetsClass : ANetwork bits : 8Min. Subnet bits 6Min. Host bits 8NNNNNNNN SSSSSSXX XXXXXXXX HHHHHHHH10.0.0.0 /14 (Maximum number of hosts)10.0.0.0 /1510.0.0.0 /1610.0.0.0 /1710.0.0.0 /18 15
  • 16. 10.0.0.0 /1910.0.0.0 /2010.0.0.0 /2110.0.0.0 /2210.0.0.0 /2310.0.0.0 /24 (Maximum number of subnets)Network 172.32.0.0 need 125 subnets and need 125 hosts/subnetClass : BNetwork bits : 16Min. Subnet bits : 7Min. Host bits : 7NNNNNNNN NNNNNNNN SSSSSSSX XHHHHHHH172.32.0.0 /23 255.255.254.0 (Maximum number of hosts)172.32.0.0 /24 255.255.255.0172.32.0.0 /25 255.255.255.128 (Maximum number of subnets)Network 192.168.44.0 need 15 subnets and 6 host/subnetClass : CNetwork bits 24Min. subnet bits : 4Min. host bits : 3NNNNNNNN NNNNNNNN NNNNNNNN SSSSXHHH192.168.44.0 /28 255.255.255.240 (Maximum number of hosts/subnet)192.168.44.0 /29 255.255.255.248 (Maximum number of subnets)10.0.0.0 300 subnets and 500 hosts/subnetClass : ANetwork bits : 8Min. subnet bits : 9Min. host bits : 9NNNNNNNN SSSSSSSS SXXXXXXH HHHHHHHH10.0.0.0 /17 255.255.128.0 Maximum hosts/subnets 16
  • 17. 10.0.0.0 /18 255.255.192.010.0.0.0 /19 255.255.224.010.0.0.0 /20 255.255.240.010.0.0.0 /21 255.255.248.010.0.0.0 /22 255.255.252.010.0.0.0 /23 255.255.254.0 Maximum subnets172.32.0.0 500 subnets and 15 hosts/subnetClass : BNetwork bits : 16Min. subnets bits : 9Min. host bits : 5NNNNNNNN NNNNNNNN SSSSSSSS SXXHHHHH172.32.0.0 / 25 255.255.255.128 Maximum hosts/subnet172.32.0.0 / 26 255.255.255.192172.32.0.0 / 27 255.255.255.224 Maximum subnetsNetwork 172.16.0.0 2000 subnets 2 hosts/subnetClass : BNetwork hosts : 16Min. subnet bits : 11Min. host bits : 2NNNNNNNN NNNNNNNN SSSSSSSS SSSXXXHH172.16.0.0 /27 255.255.255.224 Maximum number of hots/subnet172.16.0.0 /28 255.255.255.240172.16.0.0 /29 255.255.255.248172.16.0.0 /30 255.255.255.252 Maximum number of subnetsANALYSING EXISTING SUBNETS : BINARYLearning resident subnet number using Boolean AND operation….Step 1. Convert the IP address from decimal to binaryStep 2. Convert the subnet mask to binary and write it down under the binary ip addressStep 3. Perform a bit wise Boolean AND operation of the two numbers…Step 4. Convert the resulting binary number back to decimal, to get the subnet number 17
  • 18. Address 8.1.4.5 00001000 00000001 00000100 00000101Mask 255.255.0.0 11111111 11111111 00000000 00000000Subnet Number 8.1.0.0 00001000 00000001 00000000 00000000Address 130.4.102.1 10000010 00000100 01100110 00000001Mask 255.255.255.0 11111111 11111111 11111111 00000000Subnet Number 130.4.102.0 10000010 00000100 01100110 00000000Address 199.1.1.100 11000111 00000001 00000001 01100100Mask 255.255.255.0 11111111 11111111 11111111 00000000Sub. Number 199.1.1.0 11000111 00000001 00000001 00000000Address 130.4.102.1 10000010 00000100 01100110 00000001Mask 255.255.252.0 11111111 11111111 11111100 00000000SubnetNumber 130.4.100.0 10000010 00000100 01100100 00000000Address 199.1.1.100 11000111 00000001 00000001 01100100Mask 255.255.255.224 11111111 11111111 11111111 11100000SubnetNumber 199.1.1.96 11000111 00000001 00000001 01100000Binary Short cut….• Record decimal mask in the first row of the table, and decimal IP address below it• For any mask octect of value 255, copy the IP address’s octet value for the same octet of the decimal subnet number• Similarly for any mask octet value of 0, write down decimal 0 for the same octet of the subnet number• If the subnet number has still has one remaining octet to be filled in, then o Convert the remaining octet of the ip address to binary o Convert the remaining octet of the mask to binary o AND the two 8-bit numbers together o Covert the 8 bit number to decimal, and place the value in the remaining octet of the subnet numberAddress 199.1.1.100Mask 255.255.255.0Sub. Number 199.1.1.0Address 130.4.102.1 01100110Mask 255.255.252.0 11111100SubnetNumber 130.4.100.0 01100100 18
  • 19. Calculating the Broadcast address – BinaryAddress 8.1.4.5Mask 255.255.0.0 nnnnnnnn nnnnnnnn hhhhhhhhh hhhhhhhSubnetAddress 8.1.0.0 00001000 00000001 00000000 00000000BroadcastAddress 8.1.255.255 00001000 00000001 11111111 11111111Address 130.4.102.1Mask 255.255.255.0SubnetAddress 130.4.102.0BroadcastAddress 130.4.102.255Address 199.1.1.100Mask 255.255.255.0SubnetAddress 199.1.1.0BroadcastAddress 199.1.1.255Address 130.4.102.1 01100110Mask 255.255.252.0 11111100SubnetAddress 130.4.100.0 01100100BroadcastAddress 130.4.103.255 01100111Address 199.1.1.100 0110 0100Mask 255.255.255.224 1110 0000SubnetAddress 199.1.1.96 0110 0000BroadcastAddress 199.1.1.127 0111 1111Steps to determine Subnet Broadcast Address…..• Step 1. Write down the subnet number (IP address), and subnet mask in binary form,• Step 2. Separate the network/subnet and host bits by a vertical line• Step 3. To find the subnet broadcast address in binary 19
  • 20. o Copy the bits of the subnet number (IP address) that are to the left of the vertical line o Write down binary 1s for the (HOST) bits to the right of the vertical line• Step 4. Convert the 32 bit binary subnet broadcast address to decimal, 8 bits at a time, ignoring the vertical lineSteps to find the first and last IP address in a subnetStep 1. To find the first IP address, Copy the subnet number but add 1 to the fourth octetStep 2. To find the last IP address, Copy the subnet broadcast address but substract1 fromthe fourth octetAddress 8.1.4.5Mask 255.255.0.0 nnnnnnnn nnnnnnnn hhhhhhhhh hhhhhhhSubnetAddress 8.1.0.0 00001000 00000001 00000000 00000000BroadcastAddress 8.1.255.255 00001000 00000001 11111111 11111111FirstAddress 8.1.0.1LastAddress 8.1.255.254Address 130.4.102.1Mask 255.255.255.0SubnetAddress 130.4.102.0BroadcastAddress 130.4.102.255FirstAddress 130.4.102.1LastAddress 130.4.102.254Address 199.1.1.100Mask 255.255.255.0SubnetAddress 199.1.1.0Broadcast 20
  • 21. Address 199.1.1.255FirstAddress 199.1.1.1LastAddress 199.1.1.254Address 130.4.102.1 01100110Mask 255.255.252.0 11111100SubnetAddress 130.4.100.0 01100100BroadcastAddress 130.4.103.255 01100111FirstAddress 130.4.100.1LastAddress 130.4.103.254Address 199.1.1.100 0110 0100Mask 255.255.255.224 1110 0000SubnetAddress 199.1.1.96 0110 0000BroadcastAddress 199.1.1.127 0111 1111FirstAddress 199.1.1.97LastAddress 199.1.1.126Finding subnet address, broadcast address and range of address using Decimal– Difficult MaskSubnet Chart 130.4.102.1 / 255.255.252.0Octet 1 2 3 4 CommentsMask 255 255 252 0Address 130. 4 102 1Subnet Address 130 4 100 0 Magic number = 256 – 252 = 4 100 is the multiple of 4 closes to but not higher than 102First Address 130 4 100 1 Add 1 to the subnets last octetLast Address 130 4 103 25 Subtract 1 from broadcast 4 address’s fourth octetBroadcast Address 130 4 103 25 Subnet’s interesting octet + 5 magic number – 1 (100+4 – 1) 21
  • 22. Summary of decimal process to find the subnet, broadcast and rangeStep 1. Write down the subnet mask in the first empty row of the subnet chart, and the IPaddress in the second empty row.Step 2. Find the octet for which subnet mask’s value is not 255 or 0. This octet is calledthe interesting octet. Draw a dark rectangle around the interesting octet’s column of thetable, top to bottom.Step 3. Record the subnet numbers value for the uninteresting octets as followsa. for each octet to the left of the rectangle, drawn in step 2, copy the IP address value inthe same octet.b. for each octet to the right of the rectangle: write down decimal 0Step 4. To find the subnet numbers value for this interesting octeta. calculate the magic number by subtracting the subnet mask’s interesting octet valuefrom 256b. calculate the multiple of magic number starting from 0 through to 256c. write down the interesting octet value, calculated as follows, Find the multiple ofmagic number that is closest to, but not higher than the IP Address’s interesting octetvalue.Step 5 : Find the subnet broadcast address as followsa. for each subnet mask octet to the left of the rectangle, copy the IP address octet valueb. for each subnet mask octet to the right of the rectangle, write down 255c. find the value for the interesting octet by adding the subnet number’s value in theinteresting octet to the magic number and subtract 1.Step 6. To find the first IP address, copy the decimal subnet number, but add 1 to thefourth octet.Step 7. To find the last IP address, copy the decimal subnet broadcast address, butsubtract 1 from the fourth octet. 22
  • 23. Problem 110.180.10.18 255.192.0.0Size of Network Part 8Size of Subnet Part 2Size of Host part 22Number of hosts per subnet 2 ^ 22 – 2 = 4,194,302Number of subnets 2^2=4 255.192.0.0 10.180.10.18 (256 – 192 ) = 64 64 x 3 = 192 64 x 2 = 128Subnet Number 10.128.0.0Broadcast Address 10.191.255.255Range of valid IP addressesFirst Address 10.128.0.1Last Address 10.191.255.254Problem 210.200.10.18 255.224.0.0Size of Network Part 8Size of Subnet Part 3Size of Host part 21Number of hosts per subnet 2 ^ 21 – 2 = 2,097,150Number of subnets 2^3=8 255.224.0.0 10.200.10.18 (256 – 224 ) = 32 32 x 6 = 192Subnet Number 10.192.0.0Broadcast Address 10.223.255.255Range of valid IP addressesFirst Address 10.192.0.1Last Address 10.223.255.254 23
  • 24. Problem 310.100.18.18 255.240.0.0Size of Network Part 8Size of Subnet Part 4Size of Host part 20Number of hosts per subnet 2 ^ 20 – 2 = 1,048,574Number of subnets 2 ^ 4 = 16 255.240.0.0 10.100.18.18 (256 – 240 ) = 16 16 x 6 = 96Subnet Number 10.96.0.0Broadcast Address 10.111.255.255Range of valid IP addressesFirst Address 10.96.0.1Last Address 10.111.255.254Problem 410.100.18.18 255.248.0.0Size of Network Part 8Size of Subnet Part 5Size of Host part 19Number of hosts per subnet 2 ^ 19 – 2 = 524,286Number of subnets 2 ^ 5 = 32 255.248.0.0 10.100.18.18 (256 – 248 ) = 8 8 * 12 = 96Subnet Number 10.96.0.0Broadcast Address 10.103.255.255Range of valid IP addressesFirst Address 10.96.0.1Last Address 10.103.255.254 24
  • 25. Problem 510.150.200.200 255.252.0.0Size of Network Part 8Size of Subnet Part 6Size of Host part 18Number of hosts per subnet 2 ^ 18 – 2 = 262,142Number of subnets 2 ^ 6 = 64 255.252.0.0 10.150.200.200 (256 – 252 ) = 4 37 * 4 = 148Subnet Number 10.148.0.0Broadcast Address 10.251.255.255Range of valid IP addressesFirst Address 10.148.0.1Last Address 10.251.255.254Problem 610.150.200.200 255.254.0.0Size of Network Part 8Size of Subnet Part 7Size of Host part 17Number of hosts per subnet 2 ^ 17 – 2 = 131,070Number of subnets 2 ^ 5 = 32 255.254.0.0 10.150.200.200 (256 – 254 ) = 2 75 * 2 = 150Subnet Number 10.150.0.0Broadcast Address 10.151.255.255Range of valid IP addressesFirst Address 10.150.0.1Last Address 10.151.255.254 25
  • 26. Problem 710.220.100.18 255.255.0.0Size of Network Part 8Size of Subnet Part 8Size of Host part 16Number of hosts per subnet 2 ^ 16 – 2 = 65,534Number of subnets 2 ^ 8 = 256 255.255.0.0 10.220.100.18 (256 – 255 ) = 1 220 * 1 = 220Subnet Number 10.220.0.0Broadcast Address 10.220.255.255Range of valid IP addressesFirst Address 10.220.0.1Last Address 10.220.255.254Problem 810.220.100.18 255.255.128.0Size of Network Part 8Size of Subnet Part 9Size of Host part 15Number of hosts per subnet 2 ^ 15 – 2 = 32,766Number of subnets 2 ^ 9 = 512 255.255.128.0 10.220.100.18 (256 – 128 ) = 128 0 * 128 = 0Subnet Number 10.220.0.0Broadcast Address 10.220.127.255Range of valid IP addressesFirst Address 10.220.0.1Last Address 10.220.127.254 26
  • 27. Problem 9172.31.100.100 255.255.192.0Size of Network Part 16Size of Subnet Part 2Size of Host part 14Number of hosts per subnet 2 ^ 14 – 2 = 16,382Number of subnets 2^2=4 255.255.192.0 172.31.100.100 (256 – 192 ) = 64 1 * 64 = 64Subnet Number 172.31.64.0Broadcast Address 172.31.127.255Range of valid IP addressesFirst Address 172.31.64.1Last Address 172.31.127.254Problem 10172.31.100.100 255.255.224.0Size of Network Part 16Size of Subnet Part 3Size of Host part 13Number of hosts per subnet 2 ^ 13 – 2 = 8,190Number of subnets 2^3=8 255.255.224.0 172.31.100.100 (256 – 224 ) = 32 3 * 32 = 96Subnet Number 172.31.96.0Broadcast Address 172.31.127.255Range of valid IP addressesFirst Address 172.31.96.1Last Address 172.31.127.254 27
  • 28. Problem 11172.31.200.10 255.255.240.0Size of Network Part 16Size of Subnet Part 4Size of Host part 12Number of hosts per subnet 2 ^ 12 – 2 = 4,094Number of subnets 2 ^ 4 = 16 255.255.240.0 172.31.200.10 (256 – 240 ) = 16 12 * 16 = 192Subnet Number 172.31.192.0Broadcast Address 172.31.207.255Range of valid IP addressesFirst Address 172.31.192.1Last Address 172.31.207.254Problem 12172.31.200.10 255.255.248.0Size of Network Part 16Size of Subnet Part 5Size of Host part 11Number of hosts per subnet 2 ^ 11 – 2 = 2,046Number of subnets 2 ^ 5 = 32 255.255.248.0 172.31.200.10 (256 – 248 ) = 8 25 * 8 = 200Subnet Number 172.31.200.0Broadcast Address 172.31.207.255Range of valid IP addressesFirst Address 172.31.200.1Last Address 172.31.207.254 28
  • 29. Problem 13172.31.50.50 255.255.252.0Size of Network Part 16Size of Subnet Part 6Size of Host part 10Number of hosts per subnet 2 ^ 10 – 2 = 1022Number of subnets 2 ^ 6 = 64 255.255.252.0 172.31.50.50 (256 – 252 ) = 4 12 * 4 = 48Subnet Number 172.31.48.0Broadcast Address 172.31.51.255Range of valid IP addressesFirst Address 172.31.48.1Last Address 172.31.51.254Problem 14172.31.50.50 255.255.254.0Size of Network Part 16Size of Subnet Part 7Size of Host part 9Number of hosts per subnet 2 ^ 9 – 2 = 510Number of subnets 2 ^ 7 = 128 255.255.254.0 172.31.50.50 (256 – 254 ) = 2 25 * 2 = 50Subnet Number 172.31.50.0Broadcast Address 172.31.51.255Range of valid IP addressesFirst Address 172.31.50.1Last Address 172.31.51.254 29
  • 30. Problem 15172.31.140.14 255.255.255.0Size of Network Part 16Size of Subnet Part 8Size of Host part 8Number of hosts per subnet 2 ^ 8 – 2 = 254Number of subnets 2 ^ 8 = 256 255.255.255.0 172.31.140.14Subnet Number 172.31.140.0Broadcast Address 172.31.140.255Range of valid IP addressesFirst Address 172.31.140.1Last Address 172.31.140.254Problem 16172.31.140.14 255.255.255.128Size of Network Part 16Size of Subnet Part 9Size of Host part 7Number of hosts per subnet 2 ^ 7 – 2 = 126Number of subnets 2 ^ 9 = 512 255.255.255.128 172.31.140.14 256 – 128 = 128 0 * 128 = 0Subnet Number 172.31.140.0Broadcast Address 172.31.140.127Range of valid IP addressesFirst Address 172.31.140.1Last Address 172.31.140.126 30
  • 31. Problem 17192.168.15.150 255.255.255.192Size of Network Part 24Size of Subnet Part 2Size of Host part 6Number of hosts per subnet 2 ^ 6 – 2 = 62Number of subnets 2^2=4 255.255.255.192 192.168.15.150 256 – 192 = 64 2 * 64 = 128Subnet Number 192.168.15.128Broadcast Address 192.168.15.191Range of valid IP addressesFirst Address 192.168.15.129Last Address 192.168.15.190Problem 18192.168.15.150 255.255.255.224Size of Network Part 24Size of Subnet Part 3Size of Host part 5Number of hosts per subnet 2 ^ 5 – 2 = 30Number of subnets 2^3=8 255.255.255.224 192.168.15.150 256 – 224 = 32 4 * 32 = 128Subnet Number 192.168.15.128Broadcast Address 192.168.15.159Range of valid IP addressesFirst Address 192.168.15.129Last Address 192.168.15.158 31
  • 32. Problem 19192.168.100.100 255.255.255.240Size of Network Part 24Size of Subnet Part 4Size of Host part 4Number of hosts per subnet 2 ^ 4 – 2 = 14Number of subnets 2 ^ 4 = 16 255.255.255.240 192.168.100.100 256 – 240 = 16 6 * 16 = 96Subnet Number 192.168.100.96Broadcast Address 192.168.100.111Range of valid IP addressesFirst Address 192.168.100.97Last Address 192.168.100.110Problem 20192.168.100.100 255.255.255.248Size of Network Part 24Size of Subnet Part 5Size of Host part 3Number of hosts per subnet 2^3–2=6Number of subnets 2 ^ 5 = 32 255.255.255.248 192.168.100.100 256 – 248 = 8 12 * 8 = 96Subnet Number 192.168.100.96Broadcast Address 192.168.100.103Range of valid IP addressesFirst Address 192.168.100.97Last Address 192.168.100.102A NOTE : In the above examples, Number of subnets means, maximum number ofsubnets possible for the subnets mask (eg. 255.255.255.248), 32
  • 33. Subnet address and Broadcast address are the subnet and broadcast address for thesubnet the given IP addresss 192.168.100.100 belongs to. (see the binary version inappendix d for more details)Problem 21192.168.15.230 255.255.255.252Size of Network Part 24Size of Subnet Part 5Size of Host part 3Number of hosts per subnet 2^3–2=6Number of subnets 2 ^ 5 = 32 255.255.255.248 192.168.100.100 256 – 248 = 8 12 * 8 = 96Subnet Number 192.168.100.96Broadcast Address 192.168.100.103Range of valid IP addressesFirst Address 192.168.100.97Last Address 192.168.100.102Problem 2210.1.1.1 255.248.0.0Size of Network Part 8Size of Subnet Part 5Size of Host part 19Number of hosts per subnet 2 ^ 19 – 2 = 524,286Number of subnets 2 ^ 5 = 32 255.248.0.0 10.1.1.1 256 – 248 = 8 0*8=0Subnet Number 10.0.0.0Broadcast Address 10.7.255.255Range of valid IP addressesFirst Address 10.0.0.1Last Address 10.7.255.254 33
  • 34. Problem 23172.16.1.200 255.255.240.0Size of Network Part 16Size of Subnet Part 4Size of Host part 12Number of hosts per subnet 2 ^ 12 – 2 = 4094Number of subnets 2 ^ 4 = 16 255.255.240.0 172.16.1.200 256 – 240 = 16 0 * 16 = 0Subnet Number 172.16.0.0Broadcast Address 172.16.15.255Range of valid IP addressesFirst Address 172.16.0.1Last Address 172.16.15.254Problem 24172.16.0.200 255.255.255.192Size of Network Part 16Size of Subnet Part 10Size of Host part 6Number of hosts per subnet 2 ^ 6 – 2 = 62Number of subnets 2 ^ 10 = 1024 255.255.255.192 172.16.0.200 256 – 192 = 64 3 * 64 = 192Subnet Number 172.16.0.192Broadcast Address 172.16.0.255Range of valid IP addressesFirst Address 172.16.0.193Last Address 172.16.0.254 34
  • 35. Problem 2510.1.1.1 255.0.0.0Size of Network Part 8Size of Subnet Part 0Size of Host part 24Number of hosts per subnet 2 ^ 24 – 2 = 16,777,214Number of subnets 2^0=1Subnet Number 10.0.0.0Broadcast Address 10.255.255.255Range of valid IP addressesFirst Address 10.0.0.1Last Address 10.255.255.254Finding all subnets with fewer than 8 subnet bitsGeneric list All Subnet ChartOctect 1 2 3 4Mask 255 255 252 0Magic Number 4Network number/Zero subnet 130 4 0 0Next subnet 130 4 4 0Next subnet 130 4 8 0Last subnet 130 4 248 0Broadcast subnet 130 4 252 0Out of range (used by process) 130 4 256 0Step 1. Write down the subnet mask in decimal, in the first empty row of the tableStep 2. Identify the interesting octet, which is the octet with value other than 255 or 0,and draw a rectangle around the column of the interesting octet.Step 3. Calculate the magic number by subtracting the mask’s interesting octet from 256Step 4. Write down the classful network number (zero subnet number)Step 5. To find each successive subnet number a. for the three un-interesting octets copy the previous subnet numbers value b. for the interesting octet add the magic number to the previous subnet numbers interesting octet value.Step 6. Once the sum calculated in stp 5.b becomes 256, stop the process, the numberwith 256 in it is out of range, and previous subnet number is the broadcast subnetnumber. 35
  • 36. Finding all subnets with exact 8 subnet bitsThe subnet octet is the interesting octet, to find all the subnets add 1 to the interestingoctet till it reaches 256.Finding all subnets with more than 8 subnet bitsThe process follows the same five steps as with fewer than 8 subnet bits.Step 6. When any steps addition results is in sum of 256a. for the octet whose sum would have been 256 write down 0b. for the octet to the left add 1 to the previous subnet’s value in that octetc. for any other octet copy the value of the same octet in the previous subnet numberd. start again with step 5Step 7. each time the process results in a sum of 256, repeat step 6 of this processStep 8. Repeat the steps until the addition in step 6b, would actually change the value ofthe network portion of the subnet numberOctect 1 2 3 4Mask 255 255 255 192Magic Number 64Network number/Zero subnet 130 4 0 0First non-zero subnet number 130 4 0 64Next subnet 130 4 0 128Next subnet 130 4 0 192Next subnet (add 1 to the third octet, and 130 4 1 0write 0 in the fourth octet)Next subnet 130 4 1 64Next subnet 130 4 1 128Next subnet 130 4 1 192Broadcast subnet 130 4 255 192Definitions….Bitwise Boolean AND : A Boolean AND between two numbers of the same length wherethe first bit in each number is ANDed and the second bit and so onBoolean AND : A math operation performed on a pair of one digit binary numbers, theresult is another one digit binary number, binary 1 and 1 yields a result of binary 1, allother combinations yielding binary 0. 36
  • 37. Broadcast subnet : When subnetting a Class A, B or C network, the one network in eachclassful network, for which all subnet bits have a value of binary 1s. The subnetbroadcast address in this subnet has the same numeric value as the classful network’snetwork wide broadcast address.Classful network : An IPv4 Class A,B or C network, called classful network, becausethese networks are defined by the class rules for IPv4 addressing.Default Mask : The mask used in Class A,B or C network, that does not create anysubnets, specifically mask 255.0.0.0 for Class A, 255.255.0.0 for Class B, and255.255.255.0 for a Class C network.Prefix notation , CIDR notation : A shorter way to write subnet mask, in which number ofbinary 1s in the mask is simply written in decimal. For instance /24 denotes the subnetmask with 24 binary 1 bits in the subnet mask.Private IP address : IP addresses within Class A,B and C, networks that are set aside foruse within a private organization. These addresses are defined by RFC 1918, and are notroutable through internet.Public IP Address : An IP address that is part of a registered network number, as assignedby an Internet Assigned Numbers Authority (IANA) member agency. Routers in theinternet forward (route) publicly assigned network numbers.Subnet : Sub division of Class A, B or C network as configured by the networkadministrator. Subnets allow single Class A,B or C network to be used, instead ofmultiple networks but still allow multiple groups of ip addresses.Subnet Mask : A 32 bit number that numerically represents the format of an IP address,by representing the network and subnet part with a mask bit value of 1, and host part witha mask bit value of binary 0s.Subnet number/ Subnet address : In IPv4 a dotted decimal number that represents alladdresses in a single subnet. Numerically smallest value in the range of numbers in asubnet, reserved so that it cannot be used as a uni cast IP address by a host.Zero Subnet : For every class ful IPv4 network that is subnetted, the one subnet whosesubnet number has all binary 0s in the subnet part. In decimal zero subnet can be easilyidentified, because it is the same number as the classful network number. 37
  • 38. Chapter 13 – Operating Cisco RoutersPhysical installationSteps required to install a router…..Step 1. Connect any LAN cables to LAN portsStep 2. If using an external CSU/DSU connect the router’s serial interface to CSU/DSUand the CSU/DSU to the line from telco.Step 3. If using internal CSU/DSU connect the routers’ serial interface to the line fromtelcoStep 4. connect the router’s console port to a pc using a rollover cable as needed toconfigure the routerStep 5. Connect the power cable to power port on the routerStep 6. Turn on the routerComparison between Switch CLI and Router CLIThe configuration commands used for the following features are the same on both routersand switches…Similarities between switch CLI and router CLI…• Use and Enable (privileged) mode• Entering and exiting configuration mode, using configure terminal, end and exit commands, and ctrl z key sequence• Configuration of console, telnet and enable secret password• Configuration of SSH encryption keys, and username/password login credentials.• Configuration of host names and interface descriptions• Speed and Duplex commands• Shutdown and no shutdown commands to administratively disable and enable an interface respectively• Navigation through different configuration context modes, using commands like line console 0 , and interface• CLI help, command editing and command recall• The meaning and use of start-up config in NVRAM, running config in RAM, external servers like TFTP, along with copy commands.• The process of reaching a setup mode either by re-loading the router with an empty start-up config, or by using setup commandDifferences….• The configuration of IP address differ in someway between switches and routers• Questions asked in setup mode differ 38
  • 39. • Routers have an auxiliary port, intended to be connected to an external modem and phone line, to allow remote users to dial into the router and access the CLI, by making a phone call.There is no show mac address-table dynamic command in a router, but a router hasshow ip route command.Router InterfacesRouters generally have two types of physical interfaces : Ethernet Interfaces and SerialInterfaces.Ethernet Interfaces…Interface Ethernet numberInterface fastethernet numberInterface gibabitethernet numberSerial Interfaces…For PPP links and Frame relay links and uses HDLC or PPP protocols HDLC being thedefault.Valid configuration command formats….Interface Ethernet 0Interface fastethernet 0/1Interface serial 1/0/1Commands to view information about interfaces….Show ip interface briefShow protocols fa0/0Show interfaces s1/0/1Please refer to page 413 for a detailed listing example 39
  • 40. Router Interface status codes and their meaningName Location General MeaningLine Status First Status Refer to the layer – 1 status, eg. If the cable is code installed, is it the right/wrong cable, is the device on the other end powered on.Protocol Status Second Status Refer generally to the layer – 2 status, It is always code down if the line status is down. If the line status is up and protocol status is down, usually is caused by mismatch in the data link layer protocol configurations.Typical combinations of two interface status codes and likely reasons….Line and protocol status Typical ReasonsAdministratively down, The interface has shutdown command configured on itdownDown, down The interface has no shutdown command configured but the physical layer has a problem. Eg. No cable has been connected to the interface, or with Ethernet, the switch interface on the other end of the cable is shutdown, or the switch is powered off.Up, down Almost always refer to data link layer problems, most often configuration problems. Eg. Serial link have this combination when one router was configured to use PPP and the other default to use HDLC.Up, Up All is well, interface is functioningRouter Interface IP AddressRouters need an IP address on each interface.Router1# configure terminalRouter1 <config> # interface fa0/1Router1 <config-if> # ip address 10.1.1.1 255.255.255.0Router1 <config-if> # ^zRouter1# show ip interface briefPlease refer to page 415 for the command output listingBandwidth and clock rate on serial interfaces 40
  • 41. The clock rate speed sub command sets the rate in bits per second on the router that hasthe DCE cable plugged into it. Show controllers serial 0/1/0 command will show if aDCE/DTE cable is connected to a router interface. IOS accepts the clock rate commandon an interface only if it has a DCE cable attached to it, or if no cable is installed. If aDTE cable is installed IOS silently rejects the clock rate command.Bandwidth speed command tells the IOS the speed of the link, in kilobits, which aremainly used by routing protocols (EIGRP, OSPF) etc in their default routing matrices.For serial link the default bandwidth is 1544 , 1544 kbps, 1.544 Mbps, (a T1 line).Router ethernett interface default to a bandwidth setting that reflects the current speed ofthe interface. If router’s fasterethernet interface is running at 100 Mbps then thebandwidth is 100,000 Kbps.Clock rate uses a unit of kbps, whereas bandwidth command uses a unit of KbpsAuxiliary Port can be configured using theLine aux 0 command to reach the aux line configuration mode.Summary of facts about Initial configuration Setup Mode dialogue.• Setup mode is intended to allow basic configurations by prompting the CLI user via a series of questions.• You can reach the setup mode, either by booting the router after erasing the startup- config file, or by using the setup enable mode EXEC command.• At the end of the process you get three options (0,1,2), to either ignore the answers and go back to the CLI (0), ignore the answers but begin again in setup mode (1), or to use the resulting config (2).• Ctrl C key combination to eject the user out of the setup mode• If the user selects to use the resulting config, the router writes the configuration file to the startup-config file as well as the running-config file.The questions asked differ between switches and routers especially on IP configurations.Cisco IOS Software boot sequence…When a router first powers on, it follows these four steps…1. The router performs Power On Self Test (POST) , to discover hardware components,and to verify that all components work properly. 41
  • 42. 2. The router copies the bootstrap program from ROM into RAM, and runs the bootstrapprogram3. Bootstrap program decides which IOS (or other OS) to load into the RAM, and loadsthe OS. After loading the IOS the bootstrap program hand over the control of the routerhardware to the newly loaded OS.4. If the bootstrap program loads IOS, IOS find the configuration file typically thestartup-config from the NVRAM and loads it into the RAM as running-config.Loading the Cisco IOS RAM ROM Step 2 Bootstrap Flash TFTP Step 3 Cisco IOS ROM NVRAM Running TFTP Step 4 Config File ConsoleRouter can get the Cisco IOS image from three different locations, and running configfile from other three different locations. 42
  • 43. The Three Router Operating SystemsComparison of ROMMON and RxBoot Operating Systems…Operating Common Name Stored in Used inEnvironmentROM Monitor ROMMON ROM Older and new routersBoot ROM Rx Boot, Boot helper ROM Only in older routersCisco routers use different OSs to perform some troubleshooting, to recover routerpasswords, and to copy new IOS into the flash when the flash has been erased orcorrupted.The configuration registerThe configuration register is a special 16 bit number, that can be set on any cisco router.Eg. The console speed, what IOS iamge to load etc are set using the configurationregister bits.Config-register global configuration command sets the configuration register values.Eg. Config-register 0x2100 sets the value to hex 2100, which causes the router to loadROMMON OS, instead of IOS - a common practice when recovering lost passwords.Config-register values are automatically saved, to both running config and startup-config,but these new values will not be used until the router is re-loaded.The show version command lists the configuration register’s current value, if differentthe value that will be used once the router is re-loaded.In most cisco routers the default configuration register setting is Hex 2102.How routers choose which OS to loadA router chooses the OS to load based on the low order 4 bits in the configurationregister, and the details configured in any boot system global configuration commandfound in start-up configuration command. The low order 4 bits, (the 4th hex digit) is theconfiguration register are called boot-field.Steps a routers uses to choose which IOS to load…Step 1. If boot field = 0 , use the ROMMON OSStep 2. If boot field = 1, load the first IOS file found in Flash memoryStep 3. If boot field = 2-Fa. try each boot system command in the startup-config file, in order until one worksb. if none of the boot system commands works, load the first IOS file found in the flashmemory 43
  • 44. ROM Bootstrap and ROMMON BOOT = 0 RAM FLASH IP Network BOOT = 1 1st IOS File TFTP ND 2 IOS File 3rd IOS File BOOT = 2...F … NVRAM (Startup Config) …. Last IOS File Boot System command 1 Boot System command 2 …. Boot system command lastIf all three steps fails, as it may be possible that flash memory is erased, the router sendbroadcasts looking for tftp server and guessing IOS file name to load, if that fails, routerloads the ROMMON which provides the tools to recover.From the factory Cisco routers have not boot system command configured, and comeswith a configuration register value of 0x2102, meaning boot field hex 2, the process tiresstep 3, finds no boot system commands and loads the first IOS image from the flashmemory.Boot System commandsBoot system command ResultBoot system flash The first file from flash memory is loadedBoot system flash filename IOS with name filename is loaded from flash memoryBoot system tftp filename IOS with name filename loaded from TFTP server10.1.1.1 44
  • 45. The SHOW VERSION commandShow version command supplies a wide variety of information about the router,including the current and future configuration register.1. IOS Version2 The uptime – the length of time passed since the last reload3. The reason for the last reload of the IOS (reload command, power off/on, softwarefailure)4. The time of the last loading of IOS (if the router’s clock has been set)5. The source from which the router has loaded the current IOS6. The amount of RAM memory7. The number and types of interfaces8. The amount of NVRAM memory9. The amount Flash memory10. The configuration register’s current and future settings (if different)Please refer to page 430 for a detailed listing of the show version commandBandwidth : A reference to the speed of a network link. Its origins come from earliercommunication technologies where the range or width of frequency bands dictated howfast communication could occur.Boot field : Low order 4 bits of the configuration register in a cisco router. The value inthe boot field in part tells the router where to look for the cisco IOS image to load.Clock Rate : The speed at which a serial link encodes bits on the transmission mediumConfiguration register : In cisco route a 16 bit use configurable value that determines howrouter the router functions during initialization. In software, the bit position is set byspecifying a hex value using configuration commands.IOS Image : A file that contains IOS – Cisco operating system that provides majority ofthe router’s or switch’s features with the hardware providing the remaining features.Power On Self Test (POST) : The process on any computer, including routers andswitches , in which computer hardware first runs hardware diagnostics on requiredhardware before even trying to load a bootstrap program.ROMMON : A shorter name of ROM Monitor , which is a low level operating system,that can be into cisco routers for several seldom needed maintenance tasks, includingpassword recovery, and loading new IOS when flash memory has been corrupted. 45
  • 46. RxBoot : A limited function version of IOS stored in the ROM, in some older models ofCisco routers, for the purpose of performing seldom needed low level functions includingloading new IOS into flash memory, when flash memory has been corrupted or erased.Configuration Command refernce…Bandwidth kbps Interface command that sets the router’s perception of bandwidth in kpbsClock rate rate Interface command that sets the speed at which the router supplies a clocking signal, applicable when the router has a DCE cable installed. The unit is bit/secondConfig-register value Global command that sets the hexadecimal value of the configuration registerBoot system {file-url | filename} Global command that identifies an externally located IOS image using a URL.Boot system flash [flash:fs:] Global command that identifies the location of an[filename] IOS image in flash memoryBoot system rom Global command that tells the router to load RxBoot OS found in ROM, if one exitsts.Boot system {rcp|tftp|ftp} Global command that identifies an external server,filename [ip address] protocol and file name to use to load IOS from an external serverEXEC Command reference….Command PurposeShow interfaces type number Lists a large set of information about each interface, or about the one, if one is specifiedShow ip interface brief List a single line of information about each interface, including the IP address, line and protocol status, and the method with which address was configured. (manual or DHCP).Show protocols type numebr Lists a single line of information about the specified interface including ip address, line,protocol status.Show controllers type number List many line of information per interface, or for the specified interface, for the hardware contoller of the interface. On serial interfaces, this command identifies the cable as either a DCE or DTE cable.Show version Lists IOS version as well as a lots of other usefil informationsetup Starts the setup dialogueCopy url-from url-to Copies the file from source url to destination urlShow flash List the contents of the flash memory, including used and available memoryreload Enable mode command to reboot the router 46
  • 47. Chapter 14 – Routing Protocol Concepts and Configuration ` 10.1.1.0/24 Fa0/0 10.1.1.251 10.1.128.251 S0/0/0 S0/1/0 10.1.130.251 Albequerque 10.1.128.0/24 10.1.130.0/24 10.1.130.253 10.1.128.252 S0/0/1 S0/0/1 10.1.2.252 10.1.3.253 ` ` ` ` 10.1.2.0/24 10.1.3.0/24A router adds routes to its routing table for the subnets connected to each of the router’sinterfaces. For this to occur the router must have an ip address and mask configured onthe interface, and the interface must be in an up/up status.Show running config – will show the ip address and mask on each interfaceShow ip interface brief – will show the interface status (line/protocol)Show I p route – will show the routing table entries10.0.0.0/24 is subnetted , 3 subnetsc 10.1.1.0 directly connected, Fastethernet 0/0c 10.1.128.0 directly connected, serial 0/0/0c 10.1.130.0 directly connected, serial0/1/0terminal ip netmask-format decimal – will change the mask format to decimal 47
  • 48. Static RouteAdding a static route to router alberquerque for the subnet 10.1.2.0/24 and 10.1.3.0/24Albuquerque# configure terminalAlbuquerque(config)# ip route 10.1.2.0 255.255.255.0 10.1.128.252Albuquerque(config)# ip route 10.1.3.0 255.255.255.0 10.1.130.253Albuquerque# show ip route static10.0.0.0 /24 is subnetted , 5 subnetsS 10.1.3.0 [1/0] via 10.1.130.253S 10.1.2.0 [1/0] via 10.1.128.252Ip route global configuration command supplies the subnet number, mask and the nexthop id address.If the outgoing interface of a router (Albuquerque’s s0/0/0 or s0/1/0) interface is not inup/up state the static route will not be listed in the routing table.Extended PING - a router enable mode command allows the CLI user to change manyoption on Ping command, including the source ip address, which enables to issue a pingcommand from a router which resembles more closely to a ping command issues by anend user.Cisco ping command by default uses the output interface’s ip address as the packet’ssource address, unless otherwise specified in an extended ping.Default Routes Subnet 1 172.16.3.2 Subnet 2 Fa0/0 Rest of the enterprises network S0/1 172.16.3.0 R1 R2 Subnet 3As part of the routing process a router compares a packet’s destination ip address to itsrouting table, if a no matching route is found the router discards the packet. A default 48
  • 49. route is a route that matches all destination ip addresses, and the router forwards using thedefault route, when no other route is matched with packets destination ip address.In the above example the router R1 can be configured in three ways…..• Configure hundreds of static routes on R1, but all with an outgoing interface of s0/1 and next hop id address 172.16.3.2 (R2).• Enable routing protocols on routers to learn routes• Add a default route on R1 with outgoing interface as S0/1R1(config)# ip route 0.0.0.0 0.0.0.0 172.16.3.2R1# show ip route172.16.0.0/24 is subnetted, three subnetsC 172.16.3.1 directly connected fa0/0C 172.16.3.2 directly connected s0/1S* 0.0.0.0/0 [1/0] via 172.16.3.2S* - statically configured default route 49
  • 50. Routing Protocol OverviewRIP2 – Basic Concepts.Example of how RIP-2 advertises routes ` 3 R3 IP Routing Table 5 172.16.5.253 Fa0/0 Subnet Out.Int Next hop Metric ------------------------------------------------------------ I have a route to 172.16.3.0 s0/1 172.16.6.252 1 172.16.3.0/24 , Metric 2 S0/0 S0/1 R3 2 5 I have a route to I have a route to 172.16.3.0/24 , Metric 1 172.16.3.0/24 , Metric 2 S0/1 172.16.6.252 172.16.2.252 S0/1 S0/0 S0/0 172.16.1.251 R1 2 R2 Fa0/0 Fa0/1 172.16.3.252 1 I have a route to 172 .16.3.0/24 , Metric 1 ` ` ` ` 4 R1 IP Routing Table Subnet Out.Int Next hop Metric ------------------------------------------------------------ 172.16.3.0 s0/0 172.16.2.252 11. Router r2 learns a connected route for subnet 172.6.3.02. R2 sends routing updates to its neighbors’ listing subnet, mask and a distance , metric3. R3 hears the routing updates and add a route to its routing table for the subnet172.16.3.0/24 with R2 as the next hop router.4. At the same time R1 also hears the routing update sent directly from R2 to R1 and addsthe route to its routing table5. R1 and R3 then send routing updates to each other for the subnet 172.16.3.0/24 withmetric value 2.RIP routers send periodic routing message about every 30 seconds. 50
  • 51. Interior and Exterior Routing ProtocolsInterior Gateway Protocol (IGP) : A routing protocol that was designed and intendedfor use inside a single autonomous systemExterior Gateway Protocol (EGP) : A routing protocol that was designed and intendedfor use between different autonomous systems.BGP – Border Gateway Protocol is the used to exchange routes between routers indifferent autonomous systems and is an EGP.ICANN – assigns an ASN – Autonomous System NumberRouting protocols classes/algorithms and Protocols that use themClass/Algorithm IGPsDistance vector RIP-1, RIP-2, IGRPLink-state OSPF , Integrated IS-ISBalanced Hybrid (also called advanced EIGRPdistance verctor)MetricsEach routing protocol defines a metric that gives an objective numeric value to thegoodness of each route. The lower the metric the better the route.RIP uses a metric called hop count, which counts the number of routers (hops) between arouter and a subnet.EIGRP uses a metric which by default considers both the interface bandwidth andinterface delay settings as input into the mathematical formula to calculate the metric. ROUTERS generally perform routing more quickly with smaller routing table, RouteSummarization (Auto summarization and Manual Summarization) helps shorten therouting table while retaining all the needed routes in the network. 51
  • 52. Routing protocol that must consider Class (A,B,C) rules are called Classful RoutingProtocols, and that do not need to consider Class rules are called Classless RoutingProtocols.Comparing Classful and Classless Routing ProtocolsFeature Classless ClassfulSupport VLSM Yes NoSend subnet masks in routing updates Yes NoSupport manual route summarization Yes NoThe process used by routing protocols to recognize changes in a network (a link comesup or fail, a router is added or removed), to figure out now-best route to each subnet, andto change each routers routing table is called Convergence.Summary of Interior Gateway (routing) ProtocolsFeature RIP-1 RIP-2 EIGRP OSPF IS-ISClassless No Yes Yes Yes YesSupports VLSM No Yes Yes Yes YesSends mask in updates No Yes Yes Yes YesDistance Vector Yes Yes No No NoLink-state No No No Yes YesSupport No Yes Yes No NoautosummarizationSupport Manual No Yes Yes Yes YesSummarizationProprietary No No Yes No NoRouting updates send to No Yes Yes Yes n/aa multi cast ip addressSupport Authentication No Yes Yes Yes YesConvergence Slow Slow V.Fast Fast FastConfiguring and Verifying RIP-2RIP-2 ConfigurationStep 1. Router RIP configuration command to move into the RIP configuration modeStep 2. Version 2 RIP subcommand to tell the router to use RIP Version 2Step 3. Use one or more network net-number to enable RIP on the correct interfaceStep 4. passive-interface type number to disable RIP on an interfaceThe RIP network command uses a classful network number as its net-number parameters. 52
  • 53. For any of the router’s interface ip address within that clasful network, the router does thefollowing three things…• The router multicast routing updates, to a reserved IP multicast address 224.0.0.9• The router listens for the incoming routing updates on the same interface• The router advertises about the subnet connected to the interfaceSample RIP configuration….. 10.1.1.2. Fa0/0 199.1.1.1 S0/0 Fa0/1 S0/1 199.1.2.1 R1 10.1.4.2.R1# configure terminalR1(config)# router ripR1 (config-router)# version 2R1(config-router)# network 199.1.1.0R1(config-router)# network 199.1.2.0R1(config-router)# network 10.0.0.0S0/0 – 199.1.1.1. is in a class C network 199.1.1.0S0/1 – 199.1.2.1. is in a class C network 199.1.2.0Fa0/1 and fa0/0 10.1.4.2. and 10.1.1.2 are in class A network 10.0.0.0To disable RIP on fa0/1 interface….R1(config-router)# passive-interface fa0/1 53
  • 54. RIP-2 VerificationRIP Operational commands…Command PurposeShow ip interface brief List one line per interface, including ip address and interface status; an interface must have an ip address and up/up status for the RIP protocol to workShow ip route [rip] List the routing table, including RIP learned routes, and optionally just RIP learned routesShow ip protocols Lists information about the RIP configuration, plus IP addresses of neighbouring RIP routers, from which local router has learned the routes.Show ip routeShow ip route ripShow ip route 10.1.2.1Please refer to page 460 for a detailed listing of show ip route command.Show ip route … listing contains…..• Subnet number with the mask at the heading line• Next hop router’s ip address• Local router’s outgoing interface• Length of time since the router heard a routing update about this route• The RIP metric for this route, second number in the square brackets [120/1]• Administrative Distance of the route first number in the bracket [120/1]Administrative Distance : is numeric number representing the routing protocol, which isused to determine the lower number (best route) in a network that uses multiple routingprotocols.IOS defaults for administrative distanceRoute Source Administrative DistanceConnected Route 0Static routes 1EIGRP 90IGRP 100OSPF 110IS-IS 115RIP (V1 and V2) 120 54
  • 55. Unknown or unbelievable 255Normally a static route has lower administrative distance than a RIP learned route,however a backup static route can be configured with an administrative status higherthan any default administrative distances say 150, so that this static route will be added tothe routing table only if no route is learned by any routing protocols.Show ip protocolPlease refer to page 464 for a detailed listing…..Q. How it can be used to trouble shoot RIP problems???Ans. By checking the Version Information and Routing Information Sources of the showip protocol command output. It is possible that one Router is configured as RIP Version 2and other one default Version 1. Also you could verify the router is getting RIP messagesfrom all the expected sources in the network.Examining RIP messages using debugDebug ip ripUndebug allShow processService timestampsPlease refer to page 465 for a detailed listingRIP2 routing messages are sent to multicast IP address : 224.0.0.9RIP1 routing messages are sent to broadcast IP address : 255.255.255.255Definitions…Administrative Distance : In cisco routers a mean for a router to choose betweenmultiple routes to reach the same subnet, when those routes learned by different routingprotocols. The lower the administrative distance, the better the source of the routinginformation.Autonomous Systems : An internetwork in the administrative control of a singleorganization., in side which that organization typically runs a Interior Gateway Protocol(IGP).Backup Static Route : A static route configured with an administrative status higher thanany of the default routing protocol administrative statuses. 55
  • 56. Balanced Hybrid : A general type of routing algorithm, other than distance vector andlink state, EIGRP is the only routing protocol that uses Balance Hybird algorithm.Classful Routing Protocol : Does not transmit mask information along with the subnetnumber, and therefore must consider Class A, B or C network boundaries, and performautosummarization at those boundaries. Does not support VLSM.Classless Routing Protocol : An inherent characteristic of a routing protocol, specificallythat routing protocols send subnets masks in it routing updates, thereby removing anyneed to make assumptions about the addresses in a particular network or subnet. Makingit able to support VLSM and manual route summarization.Covergence : Time required for a routing protocol to react to a change in the network,removing bad routes, and adding new, better routes so that the current best routes are inall routers’ routing tables.Default Route : On a router, the route that is considered to match all packets that are nototherwise matched some more specific routes.Distance Vector : Logic behind some of the Interior Routing Protocols such as RIP.Distance Vector algorithm calls for each router to send its entire routing table in eachupdate, but only to its neighbours. Distance vector algorithm can be prone to routingloops but are computationally simpler than the link state algoritm.Exterior Gateway Protocol (EGP) :A routing protocol that was designed to exchangerouting information between two different autonomous systems.Interior Gateway Protocol (IGP) : A routing protocol designed to use within anorganization (autonomous system).Link State : A classification of underlying algorithm used in some routing protocols. Linkstate protocols build a detailed database that lists links (subnets) and their states(up/down) from which the best route is calculated.Metric : A unit of measure used by routing protocol algorithms, to determine the bestroute, for the traffic to use to reach a particular destination, in RIP-2 it is the hop-counts.Routing Updates : A generic reference to any routing protocol message, in which it sendsthe routing information to its neighbours.Variable Length Subnet Masking (VLSM) : The capacity to specify different subnetmasks for the same Class A,B, or C network number on different subnets. VLSM canhelp optimize available address space. 56
  • 57. Configuration command reference…Command DescriptionRouter rip Global configuration command that moves the user to the RIP configuration mode.Network network-number RIP subcommand that lists a clasful network number, enabling RIP on all of that router’s interfaces in that classful network.Version {1|2} RIP subcommand that sets the RIP versionPassive-interface [default] RIP subcommand that tells the RIP to no longerinterface type, number advertise RIP updates on the listed interfaceIp address ip-address mask Interface subcommand that sets the routers inteface’s ip address and maskIp route prefix mask {ip-address | Global command that defines a static routeinterface type, interface number}(eg. Ip route 10.102.0255.255.255.0 10.1.128.252)Service timestamp Global command that tells the router to put a timestamp on log messages, including the debug messagesEXEC command reference…Command DescriptionShow ip interface brief Lists one line per router interface, including ip address and interface statusShow ip route [rip|static| Lists the routing tableconnected]Show ip route ip-address List the details of the routes the router would match for a packet sent to the listed ip-addressShow ip protocols Lists information about RIP configurations, plus the IP address of the neighbouring routers from which the local router has learned routes.Show process Lists information on processes running in IOS, and also overall CPU utilization statusTerminal ip netmask-format For the length of the user session, causes the routerdecimal to display mask information in dotted decimal instead of prefix formatDebug ip rip Tells the router to generate detailed message logs for each send and received RIP updates. 57
  • 58. Chapter 15 – Troubleshooting IP RoutingIP Troubleshooting Tips and ToolsAvoiding reserved IP addresses• Addresses that are always reserved• Two addresses that are reserved in each subnet (subnet number and subnet broadcast address)• Addresses in two special subnets of each classful network, namely zero subnet and broadcast subnetFirst octet values of addresses that are always reserved, and that cannot be assigned tohosts. Reserved IP addresses….as recognized based on the value of the first octect….• 0 (because network 0.0.0.0 is always reserved)• 127 (because network 127.0.0.0 is always reserved)• 224 – 239 (all Class D – Multicast IP Addresses)• 240 – 255 (all Class E – Experimental IP Addresses)Summary of reasons why an exam question should or should not allow the use of the zeroand broadcast subnets. Determine whether a question allows the use of the Zero andBroadcast subnetsClue in the question Subnet reserved?Says nothing about it (default for the exam) NoList the ip subnet-zero configuration command NoUse a classless routing protocol (RIP-2, EIGRP, OSPF) NoList the no ip subnet-zero configuration command YESUse a classful routing protocol (RIP-1) YESSummary of 4 tips when approaching IP Addressing related questions on the exam…• Check the mask used on each device in the same LAN; if different then the devices cannot have the same view of the range of addresses in the subnet.• On a point-to-point WAN link, check the IP addresses and masks on both end of the link, and confirm that the two ip address are in the same subnet.• When checking to confirm that hosts are in the same subnet, do not just examine the subnet number. Also check the subnet mask and the implied range of IP addresses.• Be ready to quickly use the commands in the table below, to find the ip address, masks, and subnet numbers. 58
  • 59. Host NetworkingSummary of how hosts think about routing, address assignment, name resolution andARP…Routing : If the packet’s destination is in the same subnet, send the packet directly, if notsend the packet to the default gateway.Address Assignment : Before sending any packets, the host may use DHCP clientservices to learn its IP address, mask, default gateway, and DNS ip address. The hostcould also be statically configured with the same details.Name resolution : When the user directly or indirectly when a host references a hostname, the host typically uses DNS name resolution request to ask DNS to identify thehost’s ip address, unless the host already has the information in its name cache.IP-to-MAC resolution: The host uses ARP requests to find the other host’s MACaddress, or the default gateway’s ip address, unless the information is already in thehost’s ARP cache.Command FunctionIpconfig/all Displays detailed IP configuration information for all interface, including IP address, mask, default gateway, and DNS IP address.Ipconfig/release Releases any DHCP leased IP addressesIpconfig/renew Acquires an IP address and related information using DHCPNslookup name Sends a DNS request for the listed nameArp –a Lists the host’s ARP cacheIpconfig/displaydns List host’s name cacheIpconfig/flushdns Remove all dns-found name cache entriesArp -d Flushes (removes) the host’s ARP cacheNetstat -rn Displays host’s routing tableTroubleshooting Host Routing Problems.Two typical reasons why a hosts cannot ping other hosts in the same subnet.If a ping of a same subnet host fails, the root cause typically falls into two categories…• The two hosts have incorrect ip address, and mask configuration, so that at least one of the two hosts thinks it is in a different subnet.• The two hosts have correct ip address and mask configuration, but the underlying Ethernet has a problem 59
  • 60. When a host can ping hosts in the same subnet, but not the hosts in a differentsubnet…..the root cause could be…..• There is a mismatch between the host’s default gateway configurations and the router acting as the default gateway. The problems include mismatched masks between hosts and the router, which impacts the perceived range of addresses in the subnet, or the host simply referring the wrong router IP address.• If the default gateway settings are correct but the ping of the default gateway still fails, then probably there is a layer 1 or 2 problem in the LAN.• If the default gateway setting are correct, and ping works, but if ping of one of the other router interface fails, then the router’s other interface must have failed.Tips regarding how a router matches a packet’s destination IP address as part of therouting process. Finding the matching route on a router…key points to remember…..• When a destination IP address matches more than one route in a router’s routing table, the router uses the most specific route, the route with the longest prefix length.• Although the router uses binary maths to match the destination IP address to the routing table entries, you can simply compare the destination address to each subnet in the routing table. If a subnet’s implied address range include the packet’s destination address, the route matches packet’s destination.• If the question include a simulator, you could easily find the matched route by issuing a command show ip route address command, which lists the route matched for the IP address listed in the command.Please see a listing of show ip route rip , in page 484 , and determine the matching routefor a list of destination ip address from page 487.Troubleshooting CommandsShow ip arp – lists the contents of a router’s ARP cache.R1# show ip arpProtocol address age(min) hardware address type InterfaceInternet 172.161.1.1 8 0013.197b.2f58 ARPA Fa0/1Please refer to command output in page 485 60
  • 61. It lists the ip-address, mac address and interface. The age heading if lists a number, thevalue represents the number of minutes since the router last received a packet from thehost and the timer is reset each time a matching packet is received. If the age heading listsa – the arp entry represents the ip address assigned to the router.Traceroute command list the ip addresses of the routers in the routePlease refer to the listing on page 486telnet newYorkCtrl + Shift + 6 and x (to exit/suspend a telnet sessionshow sessionswhere (lists all the suspended telnet sessions)resume 1 (resumes telnet session 1)disconnect 1 (disconnects telnet session 1)show users (lists the users logged in to the telnet session)Routing Troubleshooting Scenarios….please refer to page 491 through to 505. Reminders that are helpful when thinking about source and destination MAC, and IPaddresses that are used at various points in an internetwork.• IP packet flows from the sending host to the destination host• The data link header and trailer that encapsulates the ip packet, do not flow over the complete end-to-end route-instead each data link helps move packet from a host to a router, between routers or from a router to a destination host.• For the process to work, the data link destination lists the next device’s data link address• The IP header lists the sending host’s ip address, and destination hosts IP address, and never changes throughout the journey through the route• Routers discard the received data link header and trailer for received frame, and build a new header and trailer-appropriate for the outgoing interface-before forwarding the frame.• On LANs, hosts and routers use ARP to discover Ethernet MAC address used by other devices on the same LAN• On Point-to-point WAN links ARP is not required, and data link addressing is uninteresting and can be ignored. 61
  • 62. Two key requirements for a router to add a connected route…• The interface’s two status codes are up and up• The interface has an IP address correctly configuredCommand PurposeShow sessions Lists the suspended telent and ssh sessions, from which the telnet and ssh session were createdWhere Does the same thing as show sessionstelnet { hostname| ip Connect the CLI to another host using telnetaddress}Ssh –l username Connects CLI to another host using ssh{hostname | ipaddress}Disconnect Disconnects currently suspended telnet or ssh session, based on[connection number] the connection number as seen with the show sessions commandResume Connects CLI to a currently suspended telnet or ssh session, based[connection number] on the connection number as seen with the show sessions commandTraceroute Discovers if a path from a router to a destination ip address is{hostname|ip working, listing each next hop router in the route.address}Ctrl + Shift + 6 and The key sequence required to suspend a telnet or ssh sessionxShow ip arp Lists the contents of router’s arp casheShow arp Lists the contents of router’s arp casheShow ssh Lists the information about the users logged into the router using sshShow users Lists the information about the users logged into the router, including telnet, ssh , and console users. 62
  • 63. 63

×