A COMPLETE PACKAGE FOR EASY CCNA LEARNING

2.  Host A sends a TCP SYNchronize packet to
Host B
 Host B receives A's SYN
 Host B sends a SYNchronize-
ACKnowledgement
 Host A receives B's SYN-ACK
 Host A sends ACKnowledge
 Host B receives ACK.
TCP socket connection is ESTABLISHED.

5. ROUTER
MANUFACTURER
TYPES
ISR VS NORMAL ROUTER
SONET
CISCO, NORTEL, MULTICOM, CYCLADES, JUNIPER, DLINK,
LINKSYS etc.
Access Layer Router (800, 1600, 1700, 1800, 2500, 2600, 2800)
Distribution Layer Router (2600, 2800, 3600, 3700, 3800)
Core Layer Router (64000, 7200, 7300, 7400, 7500, 7600, 10000, 12000)
ISR router will do lot of services compared with normal router. For
example terminating VPN Sections, VoIP support, and bridging
LAN/WAN cards. Basically ISR routers are modular routers, you can
insert WAN T1/E1, SONET, etc
Synchronous Optical Networking (SONET) or Synchronous Digital
Hierarchy (SDH) are standardized multiplexing protocols that
transfer multiple digital bit streams over optical fibre using lasers or
light-emitting diodes (LEDs).

6. INTERFACES
ROUTER MODES
CLI
LAN Interface (Ethernet, Fast Ethernet, Gigabyte Ethernet) – RJ 45
WAN Interface (Serial Interface) DB -50
Modem Interface - RJ 11
AUX Port
Console Port
Router> User mode
Router# Privileged mode
Router(config)# Global configuration mode
Router(config-if)# Interface mode
Router(config-subif)# Sub interface mode
Router(config-line)# Line mode
Router(config-router)# Router configuration mode
The CLI is the medium that allow interacting with the system by
typing commands.

7. Connecting to a Cisco Router Using Console
Step 1: Attach a console cable to the console port (Rj-45) located at the back of the
router.
Step 2: Open a new HyperTerminal instance from Start-All Programs-Accessories-
Communications-HyperTerminal, enter a random name to this connection and
choose the com port to use for connecting to the router. Adjust the following port
settings to the com port:
Bits per second: 9600
Data bits: 8
Parity: none
Stop bits: 1
Flow control: Hardware
Step 3: After pressing [Enter] a few times you will see the Router> prompt. Go to
menu view-font of the HyperTerminal and select courier font with font size 14.
Write enable to enter into privileged mode (after issuing the correct enable secret).
Here are the steps:
[Router name]>
[Router name]>enable
Password: ……….
[Router name]#

8. Connecting to a Cisco Router Using Telnet
Note that in order to be able to telnet onto a router, a telnet password must have
been configured on the router and also telnet access should not be disabled on the
specific router.
Before installing a new router you must provide a password for the telnet access
on the router, otherwise you will not be able to telnet to it.
Use the console to connect to the router:
[Router name] enable
Password: ……….[insert enable secret here]
[Router name]# sh run
Press [enter] until you see a sentence like: line vty 0 4 (see the example below).
Below this sentence you should see a password. If not then you should provide a
password. If a password is set but no exec line is seen like in the example below,
then telnet is blocked and you should unblock it.
Example:
Line vty 0 4
Password surpass
No exec

9. a. To Provide a telnet Password
Router#config t
Router(Config)#line vty 0 4
Router(Config)#login
Router(Config)#password [password name]
Press [Ctrl][z] and issue sh run to ensure that password has been set
b. To Unblock telnet Access on Router
Router#config t
Router(Config)#line vty 0 4
Router(Config)#exec
C:>telnet 10.176.100.2
Password: ……….
[Router name]>enable
Password: ……….
[Router name]#

10. BackingUpRouterConfiguration
TocopytheconfigurationfromtheroutertotheTFTPserveryoucanusethecopyrun
tftpcommand.ItwillbackuptherouterconfigurationthatsstoredinDRAM.Thenyouwillbeaskedto
entertheaddressoftheTFTPserverandthenameofthedestinationfileonTFTPserverlikethis:
[Routername]#copyruntftp—tocopytherunningconfigurationtoTFTPserver
Addressornameofremotehost[]?172.16.10.2—theipaddressofTFTPserver
Destinationfilename[routername-confg]?/Backup/Router01.cfg—thefolderpathontheserver
wheretheconfigurationfilewillbestored)

11. Restoring Router Configuration
In this section I’ll show you how to restore a running router with basic configuration and also how to
restore a new router with no basic configuration — both of which scenarios you’ll probably run into.
1. Restoring a Running Router with Basic Configuration
In case the router has the basic configuration (i.e. router ports are assigned to subnet), use the
command copy TFTP run and then complete the rest of the requirements like this:
[router name]# show run — to see the running configuration
[router name]#copy tftp run — to copy the configuration file from TFTP server to the running
configuration of the router
Address or name of remote host []?172.16.10.2 — TFTP server address
Source filename[]?/Backup/Router01.cfg — the configuration file to be copied to the router
[router name]#show run
[router name]#show interfaces
[router name]#copy run start
We issue show run command to verify that the configuration has been copied to the router.
Useshow interfaces command to ensure that the interfaces where we have cables connected to
them are up. Issue the command copy run start to copy the configuration from running
configuration (DRAM) to Startup configuration (NVRAM).

12. Restoring a New Router with No Basic Configuration
a. Provide basic router configuration
In case we install a new router with no configuration, then we have to incorporate this router into the
subnet before restoring the final configuration. We have to assign an IP address and subnet mask to
interface Vlan1.
First we have to go through the old configuration files either from the old router or from the tfrp
server and look for the IP address and subnet that the router was configured with, on its previous
location. This information will look like this:
interface vlan1
ip address [ip address] [subnet]
Make a note of both IP address and subnet and then log onto your new router with the console
cable using a hyperterminal. Issue passwords and then issue the following:
[Router name]#config t
[Router name](Config)#int vlan1
[Router name](Config-if)#ip address [ip address] [subnet]
[Router name](Config-if)#no shutdown
Press [CTRL][Z]
[Router name]# show run — to see that IP address on vlan1 has been set
b. Copy configuration from TFTP server to the router
[Router name] #copy TFTP run
Address or name of remote host []?172.16.10.2
Source filename[]?/Backup/Router01.cfg
[router name]#show run
[router name]#show interfaces
[router name]#copy run start

13. BACKING UP IOS
RESTORE IOS IN PRIVILEGED MODE
router# copy flash: tftp:
Source filename []? c2600-i-mz.122-28.bin
You can check the file name using command show flash in user privilege mode
Address or name of remote host []? 1.0.0.1
Destination filename [c2600-i-mz.122-28.bin]? Xyz.bin
DONE………….
Router#copy tftp: flash:
Address or name of remote host []? 1.0.0.1
Source filename []? xyz.bin
Destination filename [xyz.bin]? myrouter.bin
DONE……………

14. RESTORE IOS IN ROMMON MODE
rommon 1> IP_ADDRESS=x.x.x.x
rommon 2> IP_SUBNET_MASK=x.x.x.x
rommon 3> DEFAULT_GATEWAY=x.x.x.x
rommon 4> TFTP_SERVER=x.x.x.x
rommon 5> TFTP_FILE=myrouter.bin
rommon6> tftpdnld
Do you wish to continue? y/n: [n]: y
Done ………….

15. The administrative functions include:
– Hostname
• Assigns a name to the Router.
• Does not affect the functioning of the Router.
• Router(config)# hostname George
– Banner
• Warns an unauthorized user who is trying to connect to the
Router.
• Router(config)#banner motd .
• welcome to Cisco .
– Password
• Secures the Router from unauthorized access.
• Is categorized into five types namely, console, auxiliary,
telnet, enable password, and enable secret.
• Service password encryption is the command to encrypt
password

16. Console Password
Telnet password To encrypt password
Auxillary Password
Line console 0
Password nopass
Login
Exit
Line vty 0 4
Password nopass “Service password-encryption”
Login use it after exit cmd
Exit
Line aux 0
Password nopass
Login
Exit

17. ROUTER INTERFACE
BRINGING UP AN INTERFACE
• Assist a Router to communicate with other devices in the
network.
• Act as ports.
• Require network address and media type for configuration.
• Are configured using the interface [type][slot/port]
command.
• Bringing up an interface means enabling an interface and
involves assigning an IP address to it.
• The no shutdown command is used to enable an interface and
the shutdown command is used to disable an interface.
• The show interface command in the privileged mode allows
checking the status of a specific interface.
• The ip address command is used to assign an IP address for
an enabled interface.

18. VIEWING AND SAVING CONFIGURATION
DELETING COFIGURATION AND RELOADING THE ROUTER
• The copy running-config startup-config command is used to
save the configuration file manually.
• The show running-config command is used to display the current
configuration.
• The show startup-config command is used to display the
configuration that will be used when the Router would be reloaded.
• The erase startup-config command is used to delete the saved
configuration in the Router.
• The reload command is used to reboot the Router in EXEC
privileged mode.

19. SHOW COMMANDS
Router#show clock Displays time set on device
Router#show hosts Displays local host-to-IP address
cache. These are the names and
addresses of hosts on the network to
which you can connect
Router#show users Displays all users connected to
device
Router#show history Displays history of commands used
Router#show flash Displays info about Flash memory
Router#show version Displays info about loaded
software version
Router#show arp Displays the ARP table
Router#show protocols Displays status of configured Layer
Router#show startup-config Displays configuration saved in
NVRAM
Router#show running-config Displays configuration currently
running in RAM

20. ENHANCED EDITING COMMANDS
Ctrl-A - Moves the cursor to the beginning of the line.
Ctrl-B - Moves the cursor back one character.
Ctrl-D - Deletes the character at the cursor.
Ctrl-E - Moves the cursor to the end of the command line.
Ctrl-F - Moves the cursor forward one character.
Ctrl-K - Deletes all characters from the cursor to the end of the command line.
Ctrl-L and Ctrl-R - displays the system prompt and command line.
Ctrl-T - Transposes the character to the left of the cursor with the character
located at the cursor.
Ctrl-U and Ctrl-X - Deletes all characters from the cursor back to the beginning
of the command line.
Ctrl-W - Deletes the word to the left of the cursor.
Ctrl-Y - Recalls the most recent entry in the delete buffer. The delete buffer
contains the last ten items you have deleted or cut. Ctrl-Y can be used in
conjunction with Esc Y.
Ctrl-Z - Ends configuration mode and returns you to the EXEC prompt.
Ctrl-P or Up Arrow Recalls commands in the history buffer in a backward
sequence, beginning with the most recent command. Repeat the key sequence to
recall successively older commands.
Ctrl-N or Down Arrow Returns to more recent commands in the history buffer
after recalling commands with Ctrl-P or the Up Arrow. Repeat the key sequence
to recall successively more recent commands.

21. Serial interface (S0, S1 etc) - 60 pin/26 pin(smart
serial)
ISDN interface(BRI0 etc) - RJ45
AUI (Attachement Unit Interface) (E0) - 15 pin
10baseT - RJ45
Console - RJ45 – Local
Auxiliary - RJ45 – Remote
A bootstrap program is located here. It is same as the BIOS of the PC.
Bootstrap program current version is 11.0. POST , Mini –IOS and rom
Monitor also found here in rom
Internetwork Operating System (IOS) developed by Cisco is stored
here. IOS is Command line interface.
WAN interfaces
LAN interfaces – Ethernet
Administration interfaces
INTERNAL COMPONENTS
Rom
Flash

22. NVRAM
RAM
Processor
Non volatile RAM, similar to Hard Disk It is also known as Permanent
Storage or Start-up Configuration. Generally size of NVRAM is 32 KB.
It is also known as Temporary Storage or running configuration.
Minimum size of RAM is 2MB. The size of RAM is greater than NVRAM
in the Router.
Motorola Processor 70 MHz, RISC based processor
(Reduced Instruction Set Computer)

23. Power on Self Test (verifies) the hardware
Contact the ROM Loads the Bootstrap Program
IOS found in Flash Loading IOS
Flash contacts the NVRAM
NVRAM configuration copied into RAM
BOOT SEQUENCE

24. COLLISION DOMAIN
BROADCAST DOMAIN
VLSM
A collision domain is a physical network segment where data packets can
collide with one another when being sent on a shared medium, in
particular, when using the Ethernet networking protocol. A network
collision occurs when more than one device attempts to send a packet on a
network segment at the same time.
A broadcast domain is a logical division of a computer network, in which
all nodes can reach each other by broadcast at the data link layer. A
broadcast domain can be within the same LAN segment or it can be bridged
to other LAN segments.
A variable length subnet mask (VLSM) allows you to subnet Class A, B, or C
addresses using different length masks for the various subnets. It is
beneficial because it allows more efficient use of an assigned address space.

25. DCE
DTE
Data Communication Equipment
Generate clocking (i.e. Speed).
Master
Example of DCE device in Leased line setup : V.35 & G.703 Modem &
Exchange (Modem & MUX)
Example of DCE device in Dial up setup : Dialup Modem
Data Termination Equipment
Accept clocking (i.e. Speed).
Slave
Example of DTE device in Leased line setup : Router

26. PPP
HDLC
Point to Point Protocol
Open Standard Protocol works with same and different company Routers
i.e. Cisco-Nortel, Cisco-Multicom.
Supports Authentication
Supports Compression
High level Data link control
Vendor proprietary Protocol (works with same company Router only, i.e.
Cisco-Cisco, Nortel-Nortel, etc.)
No Support for Authentication
No Support for Compression

27. ROUTING TYPES
STATIC ROUTING
DYNAMIC ROUTING
DEFAULT ROUTING
With static routing, you -- as the administrator -- manually enter the routes
and tell the router, for each IP network, what next hop that traffic should
be delivered to.
With dynamic routing, you -- as the administrator -- configure a routing
protocol on your network interfaces. Your routing protocol learns about
other routers automatically. Your router and the other routers exchange
routes, and each learns about the networks that the other is connected to.
When new networks are added or removed, the routers update each other.
A default route is a static route that simply says all traffic to go through
the interface and not network specific. The routing command is :-
ip route 0.0.0.0 0.0.0.0 next-hop-router-IP address

28. ROUTING PROTOCOLS
FUNCTIONS
Route learning and building Routing tables
Best Path Selection
Convergence
Routing Loop Prevention
Route Validation
ROUTING METRICS
Used by a router to find out the best path amongst all the available paths. A
routing metric stores the following details:
Bandwidth
Network Delay
Hop Count
Load (measured by x/255)
MTU
Reliability (measured by x/255)
Routing Types
Classful
Classless

29. Protocol Basics
Loop Prevention Mechanism
Administrative Distance (AD)
Routing Loop
Autonomous System (AS)
Split Horizon:-
Split Horizon with Poison Reverse :-
Triggered updates :-
Route Poisoning :-
Is a method to select the best route in a particular network using the distance
range from 0-255. The value 0 means the route is more trusted and 255 means
the route is unreachable.
Is the condition when the routing table is not updated properly, due to failed
synchronization between two nodes. And the endless loop is known as count-
to-infinity problem.
Consists of different network which are managed by administrative domain.
Interior gateway protocols work within a AS and exterior gateway protocols
(BGP) work between AS to AS.
A mechanism prevent a router from advertising the route
back to the interface from which it learnt about.
This mechanism involves advertising
all the routes by a routing protocols in an interface.
This mechanism sent an update as soon as a route is
failed instead of waiting until the update timer expires.
This mechanism broadcast a failure subnet information
with an infinite distance metric to avoid loop in a network.

30. Administrative Distance
Administrative distance defines the reliability of a routing protocol.
when there are two or more different routes to the same destination
from two different routing protocols.

31. DISTANCE VECTOR PROTOCOL
LINK STATE PROTOCOL
This type of routing protocol requires that each router simply inform its
neighbours of its routing table. For each network path, the receiving
routers pick the neighbour advertising the lowest cost, then add this entry
into its routing table for re-advertisement. Ex – RIP, IGRP
Using this type of routing protocol when a network link changes state (up
to down, or vice versa), a notification, called a link state advertisement (LSA)
is flooded throughout the network. All the routers note the change, and
recompute their routes accordingly. This method is more reliable, easier to
debug and less bandwidth-intensive than Distance-Vector. It is also more
complex and more compute- and memory-intensive. Ex- OSPF, EIGRP
PROTOCOL TYPES

32. RIPv1
RIPv2
RIPng
RIP TIMERS
Classful routing protocol
Slow convergence
Unsuitable for large network
Routing loops
No route authentication
Supports maximum 15 hops
Support CIDR
Route authentication is possible
Extended version of RIPv2
Supports IPv6
UDP based protocol
Does not support authentication
Update timer – 30 seconds
Invalid timer – 180 seconds
Hold-down timer – 180 seconds
Flush timer – 240 seconds

33. IGRP
EIGRP
Type of IGP invented by Cisco to overcome the limitations of RIP, as it
supports maximum 255 hops and can use in large network.
Update time – 90 seconds
Hold-down time -280 seconds
Invalid rime – 270 seconds
Flush time - 630 seconds
Cisco proprietary protocol
Classless routing protocol
Administrative distance is 90
Updates are sent through multicast IP address
Maximum hop count is 224
Supports IP, IPX, and AppleTalk protocols.
Hello packets are send in every 5 seconds
Convergence rate is fast.

34. EIGRP
For LAN
5 Sec(Hello)
3*Hello(hold-timer)
For WAN
60 Sec(Hello)
3*Hello(hold-timer)
OSPF
10 Sec(Hello)
4*Hello(Dead-interval)

35. EIGRP TABLES
EIGRP Terminology
Neighbor Table
Topology Table
Routing Table
Feasible Distance : -
Reported Distance :-
Successor :-
Feasible Successor :-
Contains information about directly neighbors.
Contains entries for all the destination along with feasible distance and the
calculated metric.
Entries with the best path for each destination from the topology table are moved
into the routing table.
Is the metric of the best route to a destination
The cost of the route advertised by the neighbor.
The neighbor with the best metric to the destination.
The neighbor with the 2nd best metric to the destination.

36. OSPF
OSPF Table
Neighbor Table
Database Table
Routing information Table
Open standard protocol
Successor of RIP
Classless routing protocol
Unlimited hop count
Fast convergence
Routing authentication possible
Use multicast IP address to update information. (224.0.0.5)
Administrative Distance is 110
Hello packets are sent at every 10 seconds.
Hierarchical design with multiple areas and area 0 is called the backbone area.
Contains information about directly connected adjacent routers.
Contains information about entire view of the topology with respect to each
other.
Contains information about the best path calculated by the shortest path first
algorithm.

37. OSPF packet types
OSPF Areas
ROUTER ID
Hello
DBD(Database Descriptor)
LSR(Linkstate Request)
LSU( Linkstate Update)
LSACk(Linkstate Acknowledgement)
It contains a group of network and routers, which share the same Area ID. The
area ID is used to identify area to which the OSPF packet belongs.
Is an IP address configured on the Cisco routers that uniquely identifies the
router in the network

38. Access Control List
TYPES
Ip access control lists is used in router to identify and control traffic. They are a
Sequential list of permit and deny conditions that apply to ip address or upper
Layer protocol.
The access control list can be of two types 1) Standard access control list
2) Extended access control list
And are available in two ways 1) Numbered Acl
2) Named Acl
And filter the traffic in two ways 1) Inbound Filter
2) Outbound Filter

39. STANDARD ACCESS CONTROL LIST
EXTENDED ACCESS CONTROL LIST
A standard access control list can only define the source ip of the traffic.
and is the older one.
They have the format : access_list [number] [permit or deny] [source_address]
The number can be 1-99 in case standard Acl
An extended access control list can define the source and destination ip
Of the traffic, as well as port no .
They have the format :
access_list [number] [permit or deny] [protocol ] [source] [destination] [port]
The number can be 100-199 in case extended Acl

40. FRAME RELAY
DLCI
LMI
Frame Relay is a standardized wide area network technology that specifies the
physical and logical link layers of digital telecommunications channels using a
packet switching methodology. Originally designed for transport across
Integrated Services Digital Network (ISDN) infrastructure.
Data link connection identifiers (DLCIs) are numbers that refer to paths through
the Frame Relay network. They are only locally significant, which means that
when device-A sends data to device-B it will most-likely use a different DLCI
than device-B would use to reply.
Local Management Interface (LMI) is a signaling standard used between routers
and frame relay switches. Communication takes place between a router and the
first frame relay switch it's connected to. Information about keepalives, global
addressing, IP Multicast and the status of virtual circuits is commonly exchanged
using LMI.

41. VIRTUAL CIRCUITS
SVC
PVC
In telecommunications and computer networks, a virtual circuit (VC), synonymous
with virtual connection and virtual channel, is a connection oriented communication
service that is delivered by means of packet mode communication.
A switched virtual circuit (SVC) is a virtual circuit that is dynamically established on
demand and is torn down when transmission is complete, for example after a phone
call or a file download. SVCs are used in situations where data transmission is sporadic
and/or not always between the same data terminal equipment (DTE) endpoints.
A permanent virtual circuit (PVC) is a virtual circuit established for repeated/
continuous use between the same DTE. In a PVC, the long-term association is identical
to the data transfer phase of a virtual call.

43. BREAKING PASSWORD IN CISCO ROUTER
1 - Use the power switch in order to turn off the router, and then turn the
router back on
2- Press Ctrl+Break or Ctrl+Shift+F6+C on the terminal keyboard within 60
seconds of power up in order to put the router into ROMMON
3 - Type confreg 0x2142 at the rommon 1> prompt in order to boot from
Flash.
This step bypasses the start up configuration where the passwords are stored.
4 - Type reset at the rommon 2> prompt.
The router reboots, but ignores the saved configuration.
5 -Type no after each setup question, or press Ctrl-C in order to skip the
initial setup procedure.
6 - Type enable at the Router> prompt.
You are in enable mode and should see the Router# prompt.
7- Type configure memory or copy startup-config running-config in order to
copy the non-volatile RAM (NVRAM) into memory.
Important: Do not type copy running-config startup-config or write. These
commands erase your start-up configuration.
8 - Type configure terminal.
The hostname(config)# prompt appears.

44. 9- Type enable secret <password> in order to change the enable secret password.
For example:
hostname(config)#enable secret Cisco
10- Issue the no shutdown command on every interface that you use.
If you issue a show ip interface brief command in privilege EXEC mode, every
interface that you want to use should display up up. For example:
Router#show ip interface brief
11- Type config-register <configuration_register_setting>. Where
configuration_register_setting is either the value you recorded in step 2 or 0x2102.
For example:
hostname(config)#config-register 0x2102
12-Press Ctrl-z or end in order to leave the configuration mode.
The hostname# prompt appears.
13- Type write memory or copy running-config startup-config in order to
commit the changes.

45. CDP
COMMANDS
Cisco Discovery Protocol (CDP) is a proprietary layer 2 management protocol
for networks. CDP provides network device inventory, connectivity
information, and IP next hop info. It works on LANs and WANs
cdp run and cdp no run - to enable and disable CDP globally
cdp enable and no cdp enable - to enable and disable cdp per interface
show cdp neighbors - to view see what routers and switches are connected to
you on the LAN or WAN.
show cdp interfaces - to see which of your interfaces are participating in the
CDP exchange
show cdp entry - to look at a particular switch or router that is a neighbor

46. SPANNING TREE PROTOCOL
RAPID SPANNING TREE PROTOCOL
Using the spanning tree algorithm, STP provides path redundancy while
preventing undesirable loops in a network that are created by multiple active paths
between stations. Loops occur when there are alternate routes between hosts. To
establish path redundancy, STP creates a tree that spans all of the switches in an
extended network, forcing redundant paths into a standby, or blocked, state. STP
allows only one active path at a time between any two network devices (this
prevents the loops) but establishes the redundant links as a backup if the initial link
should fail.
Same as STP but faster convergence time.

47. To configure Cisco IOS DHCP, follow these steps, which include sample
commands:
Configure an IP address on the router's Ethernet port, and bring up the interface.
(On an existing router, you would have already done this.)
Router(config)# interface ethernet0/0
Router(config-if)#ip address 1.1.1.1 255.0.0.0
Router(config-if)# no shutdown
Create a DHCP IP address pool for the IP addresses you want to use.
Router(config)# ip dhcp pool mypool
Specify the network and subnet for the addresses you want to use from the pool.
Router(dhcp-config)# network 1.1.1.0 /8
Specify the DNS domain name for the clients.
Router(dhcp-config)#domain-name mydomain.com
Specify the primary and secondary DNS servers.
Router(dhcp-config)#dns-server 1.1.1.10 1.1.1.11
Specify the default router (i.e., default gateway).
Router(dhcp-config)#default-router 1.1.1.1
Specify the lease duration for the addresses you're using from the pool.
Router(dhcp-config)#lease 7
Exit Pool Configuration Mode.
Router(dhcp-config)#exit
how to exclude IP addresses .100 and below:
Router(config)#ip dhcp excluded-address 1.1.1.0 1.1.1.100