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Ccna day3


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Ccna day3

  1. 1. 1 Distance Vector Link State Hybrid Distance Vector vs. Link State Route table Topology Incremental Update Periodic UpdateRouting by rumor A B C D X E
  2. 2. 2 Distance Vector vs. Link State Distance VectorDistance Vector • Updates frequently • Each router is "aware" only of its immediate neighbors • Slow convergence • Prone to routing loops • Easy to configure Link State • Updates are event triggered • Each router is "aware" of all other routers in the "area" • Fast convergence • Less subject to routing loops • More difficult to configure
  3. 3. 3 Comparison Continued Distance VectorDistance Vector • Fewer router resources required • Updates require more bandwidth • Does not "understand" the topology of the network Link StateLink State • More router resource intensive • Updates require less bandwidth • Has detailed knowledge of distant networks and routers
  4. 4. 5 Link State Example OSPF IS-IS OSPF is used for corporate networks IS-IS is used for ISP’s
  5. 5. 6
  6. 6. 7 Open Shortest Path First (OSPF)  OSPF is an open standards routing protocol  This works by using the Dijkstra algorithm  OSPF provides the following features: Minimizes routing update traffic Allows scalability (e.g. RIP is limited to 15 hops) Has unlimited hop count Supports VLSM/CIDR Allows multi-vendor deployment (open standard)
  7. 7. 8 Link State There are two types of Packets Hello LSA’s
  8. 8. 9 OSPF Hello • When router A starts it send Hello packet – uses • Hello packets are received by all neighbors • B will write A’s name in its neighbor table • C also process the same way A B C
  9. 9. 10 "Hello" Packets • Small frequently issued packets • Discover neighbours and negotiate "adjacencies" • Verify continued availability of adjacent neighbours • Hello packets and Link State Advertisements (LSAs) build and maintain the topological database • Hello packets are addressed to
  10. 10. 11 Link State Advertisement (LSA) An OSPF data packet containing link state and routing information that is shared among OSPF routers LSAs are shared only with routers with whom it has formed adjacencies LSA packets are used to update and maintain the topology database.
  11. 11. 12 Link State There are three type of tables Neighbor Topology Routing
  12. 12. 13 Tables  Neighbor Contain information about the neighbors Neighbor is a router which shares a link on same network Another relationship is adjacency Not necessarily all neighbors LSA updates are only when adjacency is established
  13. 13. 14 Tables  Topology Contain information about all network and path to reach any network All LSA’s are entered in to topology table When topology changes LSA’s are generated and send new LSA’s On topology table an algorithm is run to create a shortest path, this algorithm is known as SPF or dijkstra algorithm
  14. 14. 15 Tables  Routing Table Also knows as forwarding database Generated when an algorithm is run on the topology database Routing table for each router is unique
  15. 15. 16 OSPF Terms Link Router ID Neighbours Adjacency OSPF Area Backbone area Internal routers Area Border Router (ABR) Autonomous System Boundary Router (ASBR)
  16. 16. 17 Link  A network or router interface assigned to a given network  Link (interface) will have "state" information associated with it Status (up or down) IP Address Network type (e.g. Fast Ethernet) Bandwidth Addresses of other routers attached to thisAddresses of other routers attached to this interfaceinterface
  17. 17. 18 OSPF Term: Link A link is a network or router interface assigned to any given network This link, or interface, will have state information associated with it (up or down) as well as one or more IP addresses
  18. 18. 19 OSPF Term: Link State Status of a link between two routers Information is shared between directly connected routers. This information propagates throughout the network unchanged and is also used to create a shortest path first (SPF) tree.
  19. 19. 20 Router ID  The Router ID (RID) is an IP address used to identify the router  Cisco chooses the Router ID by using the highest IP address of all configured loopback interfaces  If no loopback interfaces are configured with addresses, OSPF will choose the highest IP address of all active physical interfaces.  You can manually assign the router ID.  The RID interface MUST always be up, therefore loopbacks are preferred
  20. 20. 21 Neighbours Neighbours are two or more routers that have an interface on a common network E.g. two routers connected on a serial link E.g. several routers connected on a common Ethernet or Frame relay network Communication takes place between / among neighbours neighbours form "adjacencies"
  21. 21. 22 Adjacency A relationship between two routers that permits the direct exchange of route updates Not all neighbours will form adjacencies This is done for reasons of efficiency – more later
  22. 22. 23 OSPF Design Each router connects to the backbone called area 0, or the backbone area. Routers that connect other areas to the backbone within an AS are called Area Border Routers (ABRs). One interface must be in area 0. OSPF runs inside an autonomous system, but can also connect multiple autonomous systems together. The router that connects these ASes together is called an Autonomous System Boundary Router (ASBR).
  23. 23. 24 OSPF Areas  An OSPF area is a grouping of contiguous networks and routers Share a common area IDarea ID  A router can be a member of more than one area (area border router)  All routers in the same area have the same topology database  When multiple areas exist, there must always be an area 0 (the backbone) to which other areas connect
  24. 24. 25 Why areas?  Decreases routing overhead Compare to multiple smaller broadcast domains instead of one large one  Speeds convergence  Confines network instability (e.g. route "flapping") to single area of the network  Adds considerably to the complexity of setting up OSPF CCNA certification deals only with single-area OSPF
  25. 25. 26 Area Terminology
  26. 26. 27 LSA’s in Area • LSAs communicate with adjacent routers in the same OSPF area • Subsequently, a change in a link state is "flooded" to all area routers via LSAs • In larger networks, multiple areas may be created – LSAs are sent only to adjacent routers in the same area – "Area border routers" connect areas, passing summarized route information between
  27. 27. 28 Path Calculation  Changes to the topological database of a router trigger a recalculation to re-establish the best route(s) to known networks Uses the SPF (shortest path first) algorithm developed by a computer scientist named Dijkstra This is done by each individual router using its detailed "knowledge" of the whole network Leads to rapid and accurate convergence Based on detailed knowledge of every link in the area and the OSPF "cost" of each builds an OSPF treeOSPF tree with itself at the route
  28. 28. 29 Terminology: Cost • Various criteria can be selected by the administrator to determine the metric • Usually, OSPF cost=108 /bandwidth Do not forget to configure the bandwidth`bandwidth` command on serial links to ensure correct default OSPF cost
  29. 29. 30 Pros and Cons  Note that OSPF is a more sophisticated routing protocol Converges rapidly and accurately Can use a metric calculation that effectively selects the "best" route(s) primarily based on bandwidth, although an OSPF cost can be administratively assigned  Use of OSPF requires More powerful routing hardware More detailed knowledge by the administrator, especially when large multi-area networks are used
  30. 30. 31 Types of Neighbors • OSPF can be defined for three type of neighbors – Broadcast Multi Access (BMA) ex- Ethernet – Point to Point – Non-Broadcast Multi Access (NBMA)
  31. 31. 32 OSPF Network Types
  32. 32. 33 Adjacencies  Point to Point all routers form adjacencies  BMA & NBMA one router is elected as DR  DR establish adjacency with every neighbor router  LSA updates are exchanged only to DR  DR is the router which has highest priority  All CISCO routers has priority 1  If priority is same then router id is seen  The RID is highest IP address of all interfaces
  33. 33. 34 Point-to-Point Links  Usually a serial interface running either PPP or HDLC No DR or BDR election required  OSPF autodetects this interface type  OSPF packets are sent using multicast All routers form adjacencies
  34. 34. 35 Multi-access Broadcast Network • Generally LAN technologies like Ethernet and Token Ring • DR and BDR selection required • All neighbor routers form full adjacencies with the DR and BDR only • Packets to the DR use • Packets from DR to all other routers use
  35. 35. 36 Electing the DR and BDR  Hello packets are exchanged via IP multicast.  The router with the highest priority is selected as the DR. If Priority is same then Router ID is seen  Use the OSPF router ID as the tie breaker.
  36. 36. 37 Terminology: DRs and BDRs  The designateddesignated router (DR)router (DR) is responsible for generating LSAs on behalf of all routers connected to the same segment
  37. 37. 38 DR Responsibility  When a router sees a new or changed link-state, it sends an LSA to its DR using a particular multicast address  The DR then forwards the LSA to all the other routers with whom it is adjacent Minimizes the number of formal adjacencies that must be formed and therefore the amount of LSU (link state update) packet traffic in a multi-router network
  38. 38. 39 OSPF Summary  AD -100  Hop count is unlimited  Metric = Cost – 108 /BW  Classless, VLSM  Load balance up to SIX routers  Require more processing power
  39. 39. 40 Basic OSPF Configuration Router(config)# router ospf 1Router(config)# router ospf 1  The number 1 in this example is a process-id #process-id # that begins an OSPF process in the router More than one process can be launched in a router, but this is rarely necessary Usually the same process-id is used throughout the entire network, but this is not required The process-id # can actually be any value from 1 to "very large integer“ The process-id # cannot be ZERO This is NOT the same as the AS# used in IGRP and EIGRP
  40. 40. 41 Configuring OSPF Areas  After identifying the OSPF process, you need to identify the interfaces that you want to activate OSPF communications Lab_A#config t Lab_A(config)#router ospf 1 Lab_A(config-router)#network area ? <0-4294967295> OSPF area ID as a decimal value A.B.C.D OSPF area ID in IP address format Lab_A(config-router)#network area 0 • Every OSPF network must have an area 0 (the backbone area) to which other areas connect  So in a multiple area network, there must be an area 0  The wildcard mask represents the set of hosts supported by the network and is really just the inverse of the subnet mask.
  41. 41. 42 OSPF Configuration • OSPF Process ID number is irrelevant. It can be the same on every router on the network • The arguments of the network command are the network number ( and the wildcard mask ( • Wildcards - A 0 octet in the wildcard mask indicates that the corresponding octet in the network must match exactly • A 255 indicates that you don’t care what the corresponding octet is in the network number • A network and wildcard mask combination of would match only, and nothing else. • The network and wildcard mask combination of would match anything in the range–
  42. 42. 43 OSPF Configuration -1 R2 R1 R3 S0 S1 E0 S0 E0 S0 A B
  43. 43. 44 OSPF Configuration -1 R2 R1 R3 S0 S1 E0 S0 E0 S0 R1#config t Enter configuration commands, one per line. End with CNTL/Z. R1(config)#router ospf 1 R1(config-router)#network area 0 R1(config-router)#network area 0 R1(config-router)#^Z A B
  44. 44. 45 OSPF Configuration -2 R2 R1 R3 S0 S1 E0 S0 E0 S0 A B
  45. 45. 46 OSPF Configuration -2 R2 R1 R3 S0 S1 E0 S0 E0 S0 A B
  46. 46. 47 OSPF Configuration -2 R2 R1 R3 S0 S1 E0 S0 E0 S0 R1#config t Enter configuration commands, one per line. End with CNTL/Z. R1(config)#router ospf 1 R1(config-router)#network area 0 R1(config-router)#network 200.0.0. 8 area 0 R1(config-router)#^Z A B R3#config t Enter configuration commands, one per line. End with CNTL/Z. R3(config)#router ospf 1 R3(config-router)#network 200.0.0. 32 area 0 R3(config-router)#network 200.0.0. 12 area 0 R3(config-router)#^Z
  47. 47. 48 OSPF and Loopback Interfaces  Configuring loopback interfaces when using the OSPF routing protocol is important  Cisco suggests using them whenever you configure OSPF on a router  Loopback interfaces are logical interfaces, which are virtual, software-only interfaces; they are not real router interfaces  Using loopback interfaces with your OSPF configuration ensures that an interface is always active for OSPF processes.  The highest IP address on a router will become that router’s RID  The RID is used to advertise the routes as well as elect the DR and BDR.  If you configure serial interface of your router with highest IP Address this Address becomes RID of t is the RID of the router because e router  If this interface goes down, then a re-election must occur  It can have an big impact when the above link is flapping
  48. 48. 49 Configuring Loopback Interfaces R1#config t Enter configuration commands, one per line. End with CNTL/Z. R1(config)#int loopback 0 R1(config-if)#ip address R1(config-if)#no shut R1(config-if)#^Z R1#
  49. 49. 50 show ip protocolsshow ip protocols Router# • Verifies the configured IP routing protocol processes, parameters and statistics Verifying OSPF Operation show ip route ospfshow ip route ospf Router# • Displays all OSPF routes learned by the router show ip ospf interfaceshow ip ospf interface Router# • Displays the OSPF router ID, area ID and adjacency information
  50. 50. 51 show ip ospfshow ip ospf Router# • Displays the OSPF router ID, timers, and statistics Verifying OSPF Operation (Cont.) show ip ospf neighbor [detail]show ip ospf neighbor [detail] Router# • Displays information about the OSPF neighbors, including Designated Router (DR) and Backup Designated Router (BDR) information on broadcast networks
  51. 51. 52 The show ip route ospf Command RouterA# show ip route ospf Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP, D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area, E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP, i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default Gateway of last resort is not set is subnetted, 2 subnets O [110/10] via, 00:00:50, Ethernet0
  52. 52. 53 The show ip ospf interface Command RouterA# show ip ospf interface e0 Ethernet0 is up, line protocol is up Internet Address, Area 0 Process ID 1, Router ID, Network Type BROADCAST, Cost: 10 Transmit Delay is 1 sec, State DROTHER, Priority 1 Designated Router (ID), Interface address Backup Designated router (ID), Interface address Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 Hello due in 00:00:04 Neighbor Count is 1, Adjacent neighbor count is 1 Adjacent with neighbor (Designated Router) Suppress hello for 0 neighbor(s)
  53. 53. 54 The show ip ospf neighbor Command RouterB# show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 1 FULL/BDR 00:00:31 Ethernet0 1 FULL/- 00:00:38 Serial0
  54. 54. 55 show ip ospf neighbor detail show ip ospf database
  55. 55. 56 Setting Priority for DR Election ip ospf priority numberip ospf priority number This interface configuration command assigns the OSPF priority to an interface. Different interfaces on a router may be assigned different values. The default priority is 1. The range is from 0 to 255. 0 means the router is a DROTHER; it can’t be the DR or BDR. Router(config-if)#
  56. 56. 57
  57. 57. 58 EIGRP • IGRP – DV – Easy to configure – Neighbor – Advanced Metric – Periodic – Broadcast • OSPF – LS – Incremental Updates – Multicast – Open Standard • EIGRP – Hybrid – DUAL – Topology Database – Rapid Convergence – Reliable
  58. 58. 59 Overview Enhanced Interior Gateway Routing Protocol (EIGRP) is a Cisco- proprietary routing protocol based on Interior Gateway Routing Protocol (IGRP). Released in 1994, Unlike IGRP, which is a classful routing protocol, EIGRP supports CIDR and VLSM.  it is probably one of the two most popular routing protocols in use today. Compared to IGRP, EIGRP boasts faster convergence times, improved scalability, and superior handling of routing loops. EIGRP is often described as a hybrid routing protocol, offering the best of distance vector and link-state algorithms.
  59. 59. 60 Comparing EIGRP with IGRP IGRP and EIGRP are compatible with each other. EIGRP offers multiprotocol support, but IGRP does not. Communication via Reliable Transport Protocol (RTP) Best path selection via Diffusing Update Algorithm (DUAL) Improved convergence time Reduced network overhead
  60. 60. Introducing EIGRP EIGRP supports: Rapid convergence Reduced bandwidth usage Multiple network-layer protocols
  61. 61. 62 EIGRP Tables • EIGRP maintains 3 tables – Neighbor table – Topology table – Routing table
  62. 62. 63 Neighbor Discovery There are three conditions that must be met for neighborship establishment Hello or ACK received AS numbers match Identical metrics (K values) Hello ? AS ? K K1 – BW K2- Delay K3-Load K3-Reliability K5-MTU
  63. 63. 64  The metrics used by EIGRP in making routing decisions are (lower the metric the better):  bandwidth  delay  load  Reliability  MTU  By default, EIGRP uses only:  Bandwidth  Delay Analogies: Think of bandwidth as the width of the pipe and delay as the length of the pipe.  Bandwidth is the carrying capacity  Delay is the end-to-end travel time. Metric Calculation
  64. 64. 65 Neighbor Table  The neighbor table is the most important table in EIGRP  Stores address and interface of neighbor
  65. 65. 66 Topology Table Give me information about all routes Network
  66. 66. 67 Topology Table The topology table is made up of all the EIGRP routing tables in the autonomous system. DUAL takes the information and calculates the lowest cost routes to each destination. By tracking this information, EIGRP routers can identify and switch to alternate routes quickly. The information that the router learns from the DUAL is used to determine the successor route, which is the term used to identify the primary or best route. Every EIGRP router maintains a topology table. All learned routes to a destination are maintained in the topology table.
  67. 67. 68 Routing Tables  A successor is a route selected as the primary route to use to reach a destination.  DUAL calculates Successor (Primary Route) and places it in the routing table (and topology table)  Can have up to 4 successors of equal or unequal value  DUAL calculates Feasible Successor (Backup Route) and places it in the Topology Table.  Promoted to successor if the route goes down if it has a lower cost than current successor  If no FS in Table - Send query  Multiple feasible successors for a destination can be retained in the topology table although it is not mandatory
  68. 68. 69 EIGRP Concepts & Terminology  EIGRP routers that belong to different autonomous systems (ASes) don’t automatically share routing information  The only time EIGRP advertises its entire routing table is when it discovers a new neighbor and forms an adjacency with it through the exchange of Hello packets  When this happens, both neighbors advertise their entire routing tables to one another  After each has learned its neighbor’s routes, only changes to the routing table are propagated
  69. 69. 70 1.544Mbps 56Kbp s 1.544Mbps Dist to =100Dist to =100 Dist to =350 10Mbp s 10Mbps – 100 1,544Mbps – 250 56Kbps -1000 Chennai receives an update from Mumbai with a cost of 100, which is Mumbai's cost to reach, This cost is referred to as the reported distance (RD) Bangalore will report its cost to reach Bangalore's RD is 350 Chennai will compute its cost to reach via Mumbai and Bangalore and compare the metrics for the two paths Chennai's cost via Mumbai is 1100. Chennai's cost via Bangalore is 600. The lowest cost to reach a destination is referred to as the feasible distance (FD) for that destination Chennai's FD to is 600. The next-hop router in the lowest-cost path to the destination is referred to as the successor. A feasible successor is a path whose reported distance is less than the feasible distance, and it is considered a backup route.
  70. 70. 71 EIGRP Terms  Feasible distance (FD) - This is the lowest calculated metric to reach destination. This is the route that you will find in the routing table, because it is considered the best path  Reported distance (RD) - The distance reported by an adjacent neighbor to a specific destination.  Interface information - The interface through which the destination can be reached.  Route status - The status of a route. Routes are identified as being either passive, which means that the route is stable and ready for use, or active, which means that the route is in the process of being recomputed by DUAL
  71. 71. 72  Successor – Current Route  A successor is a route selected as the primary route to use to reach a destination.  Successors are the entries kept in the routing table.  Feasible Successor - A backup route  A feasible successor is a backup route.  These routes are selected at the same time the successors are identified, but they are kept in the topology table.  Multiple feasible successors for a destination can be retained in the topology table. EIGRP Terminology and Operations
  72. 72. 73 Reliable Transport Protocol (RTP)  Used by EIGRP for its routing updates in place of TCP  EIGRP can call on RTP to provide reliable or unreliable service  EIGRP uses reliable service for route updates  Unreliable for Hellos  Reliable Transport Protocol (RTP) is a transport layer protocol that guarantees ordered delivery of EIGRP packets to all neighbors.  On an IP network, hosts use TCP to sequence packets and ensure their timely delivery. RIP uses UDP  However, EIGRP is protocol-independent and does not rely on TCP/IP to exchange routing information the way that RIP, IGRP, and OSPF do.  EIGRP uses RTP as its own proprietary transport layer protocol to guarantee delivery of routing information.  With RTP, EIGRP can multicast and unicast to different peers simultaneously.
  73. 73. 74 Diffusing Update Algorithm (DUAL)  All route computations in EIGRP are handled by DUAL  One of DUAL's tasks is maintaining a table of loop-free paths to every destination.  This table is referred to as the topology table  DUAL saves all paths in the topology table  The least-cost path(s) is copied from the topology table to the routing table  In the event of a failure, the topology table allows for very quick convergence if another loop-free path is available  If a loop-free path is not found in the topology table, a route recomputation must occur  DUAL queries its neighbors, who, in turn, may query their neighbors, and so on...  Hence the name "Diffusing" Update Algorithm
  74. 74. 75 VLSM Support • EIGRP supports the use of Variable- Length Subnet Masks • Can use 30-bit subnet masks for point-to-point networks • Because the subnet mask is propagated with every route update, EIGRP also supports the use of discontiguous subnets • Discontiguous network is the one that has two or more subnetworks of a classful network connected together by different classful networks
  75. 75. 76 Discontiguous Network
  76. 76. Configuring EIGRP outer(config-router)#network network-number • Selects participating attached networks Router(config)#router eigrp autonomous-system • Defines EIGRP as the IP routing protocol
  77. 77. EIGRP Configuration Example
  78. 78. 80 EIGRP Configuration R2 R1 R3 S0 S1 E0 S0 E0 S0 R1#config t Enter configuration commands, one per line. End with CNTL/Z. R1(config)#router eigrp 10 R1(config-router)#network R1(config-router)#network 200.0.0. 8 R1(config-router)#^Z A B R3#config t Enter configuration commands, one per line. End with CNTL/Z. R3(config)#router eigrp 10 R3(config-router)#network 200.0.0. 32 R3(config-router)#network 200.0.0. 12 R3(config-router)#^Z
  79. 79. 81 Verifying the EIGRP Configuration To verify the EIGRP configuration a number of show and debug commands are available. These commands are shown on the next few slides.
  80. 80. 82 show ip eigrp topology show ip eigrp topology [active | pending | successors]
  81. 81. 83 show ip eigrp topology all-links show ip eigrp traffic
  82. 82. 84 Administrative Distances
  83. 83. 85 TELNET  Getting information about remote device  Can connect to remote device and configure a device  Password must be set R1(config)# line vty 0 4 Password cisco login
  84. 84. 86 © 2002, Cisco Systems, Inc. All rights reserved. 86 Discovering Neighbors on the Network
  85. 85. Cisco Discovery Protocol CDP is a proprietary utility that gives you a summary of directly connected switches, routers, and other Cisco devices. CDP discovers neighboring devices regardless of which protocol suite they are running. Runs on the Data link layer Physical media must support the Subnetwork Access Protocol (SNAP) encapsulation. Only give directly connected device By default enabled, you can enable or disable
  86. 86. Discovering Neighbors with CDP CDP runs on routers with Cisco IOS® software Release 10.3 or later and on Cisco switches. Show CDP ? Summary information includes:  Device ID  Local Interface  Port ID  Capabilities list  Platform
  87. 87. 89 CDP  CDP timer is how often CDP packets are transmitted to all active interfaces. Router(config)#cdp timer 90  CDP holdtime is the amount of time that the device will hold packets received from neighbor devices. Router(config)#cdp holdtime 240
  88. 88. 90 Using CDP
  89. 89. 91 Using the show cdp neighbors Command The show cdp neighbor command (sh cdp nei for short) delivers information about directly connected devices.
  90. 90. 92 CDP show cdp neighbor detail This command can be run on both routers and switches, and it displays detailed information about each device connected to the device
  91. 91. 93 Using the show cdp entry Command The show cdp entry * command displays the same information as the show cdp neighbor details command.
  92. 92. 94 Additional CDP Commands The show cdp traffic command displays information about interface traffic, including the number of CDP packets sent and received and the errors with CDP.
  93. 93. 95 CDP Commands To disable the CDP on particular interface use the "no cdp enable" command To disable CDP on the entire router use the "no cdp run" in global configuration mode.
  94. 94. 96 Summary Cisco Discovery Protocol is an information-gathering tool used by network administrators to get information about directly connected devices. CDP exchanges hardware and software device information with its directly connected CDP neighbors. You can enable or disable CDP on a router as a whole or on a port-by-port basis. The show cdp neighbors command displays information about a router’s CDP neighbors. The show cdp entry, show cdp traffic, and show cdp interface commands display detailed CDP information on a Cisco device.
  95. 95. 97
  96. 96. Manage IP traffic as network access grows Filter packets as they pass through the router Why Use Access Lists?
  97. 97. 99 What are ACLs? ACLs are lists of conditions that are applied to traffic traveling across a router's interface.  These lists tell the router what types of packets to accept or deny. Acceptance and denial can be based on specified conditions. ACLs can be configured at the router to control access to a network or subnet. Some ACL decision points are source and destination addresses, protocols, and upper-layer port numbers.
  98. 98. 100 Reasons to Create ACLs The following are some of the primary reasons to create ACLs: Limit network traffic and increase network performance. Provide traffic flow control. Provide a basic level of security for network access. Decide which types of traffic are forwarded or blocked at the router interfaces For example: Permit e-mail traffic to be routed, but block all telnet traffic. If ACLs are not configured on the router, all packets passing through the router will be allowed onto all parts of the network.
  99. 99. 101 ACL’s  Different access list for Telnet  When configuring ISDN you need to use access list  Implicit deny at bottom  All restricted statements should be on first  There are two types  Standard  Extended
  100. 100. 102 Network N1 N2 N3 N4 N5 N6 A B C
  101. 101. 103 IP Packet SRC IP Address DEST IP Address Protocol type SRC Port DEST Port The first 2 bytes in the TCP/UDP header are the source port number The next 2 bytes in the TCP/UDP header are the Destination port number
  102. 102. 104 Standard Checks source address Permits or denies entire protocol suite Extended Checks source and destination address Generally permits or denies specific protocols Types of Access Lists
  103. 103. How to Identify Access Lists  Standard IP lists (1-99) test conditions of all IP packets from source addresses.  Extended IP lists (100-199) test conditions of source and destination addresses, specific TCP/IP protocols, and destination ports.  Standard IP lists (1300-1999) (expanded range).  Extended IP lists (2000-2699) (expanded range).
  104. 104. 106 Standard ACLs The full syntax of the standard ACL command is: Router(config)#access-list access-list-number {deny | permit} source [source-wildcard ] The no form of this command is used to remove a standard ACL. This is the syntax: Router(config)#no access-list access-list-number Config# Access-list 1 deny Config# access-list 1 permit any
  105. 105. 107 Wildcard Mask Access-list 99 permit wildcard mask All 32 bits of an IP Address can be filtered Wildcard inverse mask 0=must match 1= ignore MASK ( Matching IP (host) 192.168.0-255.0-255 192.0-255.0-255.0-255 0-255.0-255.0-255.0-255 (any)
  106. 106. 108 The ANY and HOST keyword Access-list 1 permit Or permit host Access-list 1 permit Or permit any
  107. 107. Testing Packets with Standard Access Lists
  108. 108. Outbound ACL Operation • If no access list statement matches, then discard the packet.
  109. 109. 111 Reading an ACL  First Hit or Best Fit? 1. Access-list 99 deny host access-list 99 permit any 2. Access-list 99 permit Access-list 99 deny host access-list 99 permit any 3. Access-list 99 deny host  Implicit deny at the end of every ACL
  110. 110. 112 Creating ACLs ACLs are created in the global configuration mode. There are many different types of ACLs including standard, extended, IPX, AppleTalk, and others. When configuring ACLs on a router, each ACL must be uniquely identified by assigning a number to it. This number identifies the type of access list created and must fall within the specific range of numbers that is valid for that type of list. Since IP is by far the most popular routed protocol, addition ACL numbers have been added to newer router IOSs. Standard IP: 1300-1999 Extended IP: 2000- 2699
  111. 111. 113 The ip access-group command { in | out }
  112. 112. 114 Exercise – Standard Access List A B Account should be denied access to Sales To steps to configure •Create a standard Access list •Apply ACL to proper interface inbound or outbound S0 S0 E0 E0 S0 S1192.168.0.17
  113. 113. 115 Exercise – Standard Access List A B S0 S0 E0 E0 S0 S1192.168.0.17 Config# Access-list 1 deny Config# access-list 1 permit any Config#int e 0 Config-if# ip access-group 1 out
  114. 114. 116 Extended ACLs Extended ACLs are used more often than standard ACLs because they provide a greater range of control. Extended ACLs check the source and destination packet addresses as well as being able to check for protocols and port numbers. At the end of the extended ACL statement, additional precision is gained from a field that specifies the optional Transmission Control Protocol (TCP) or User Datagram Protocol (UDP) port number. Logical operations may be specified such as, equal (eq), not equal (neq), greater than (gt), and less than (lt), that the extended ACL will perform on specific protocols. Extended ACLs use an access-list-number in the range 100 to 199 (also from 2000 to 2699 in recent IOS).
  115. 115. 117 Configuration • Access-list acl# {permit/Deny} • Protocol • Src IP src WCM • Dst IP dst WCM • Opetrator port • Protocol – OSPF – EIGRP – ICMP – TCP – UDP RP If you need to Block a routing protocol IP • Operator – eq – gt – lt – neq
  116. 116. Testing Packets with Extended Access Lists
  117. 117. 119 Extended ACL Syntax
  118. 118. 121 Extended ACL LAB -2 S0 S0 E0 E0 A B should be denied FTP of On Router R1 Config# Access-list 100 deny tcp eq 21 Config# access-list 100 permit IP any any Config#int s0 Config-if# ip access-group 100 IN should be denied website of On Router R3 Config# Access-list 100 deny tcp 192.168. 0.18 eq 80 Config# access-list 100 permit IP any any Config#int s0 Config-if# ip access-group 100 IN S1 S0
  119. 119. 122 Deny FTP access-list 101 deny tcp any any eq 21 access-list 101 permit ip any any or access-list 101 deny tcp any any eq ftp access-list 101 permit ip any any
  120. 120. 123 Rules For extended access list apply near to the source For standard access list apply near to the destination
  121. 121. 124 Named ACLs IP named ACLs were introduced in Cisco IOS Software Release 11.2, allowing standard and extended ACLs to be given names instead of numbers. The characteristics of named accesslist:  Identify an ACL using an alphanumeric name.  You can delete individual statements in a named access list  Named access lists must be specified as standard or extended  You can use the ip access-list command to create named access lists. Named ACLs are not compatible with Cisco IOS releases prior to Release 11.2. The same name may not be used for multiple ACLs.
  122. 122. 125 Named ACL’s  Numbered Access list did not give you any hint, What is filtered  Named ACL’s are both basic and advanced filtering tool  Name cannot start with a number or !  Cannot have space in the name  Should not have ? Character anywhere in the name  Name is case sensitive
  123. 123. 126 Named ACL Example R1(config)#ip access-list standard blocksales • R1(config-std-nacl)#deny • R1(config-std-nacl)#permit any • R1(config-std-nacl)#exit • R1(config)#^Z • R1# #Int e 0 #Ip access-group blocksales out
  124. 124. 127 Verify Access List
  125. 125. 128 Basic Rules for ACLs  Standard IP access lists should be applied closest to the destination.  Extended IP access lists should be applied closest to the source.  Use the inbound or outbound interface reference as if looking at the port from inside the router.  Statements are processed sequentially from the top of list to the bottom until a match is found, if no match is found then the packet is denied.  There is an implicit deny at the end of all access lists. This will not appear in the configuration listing.  Access list entries should filter in the order from specific to general. Specific hosts should be denied first, and groups or general filters should come last.  Never work with an access list that is actively applied.  New lines are always added to the end of the access list.  A no access-list x command will remove the whole list. It is not possible to selectively add and remove lines with numbered ACLs.  Outbound filters do not affect traffic originating from the local router.