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Chapter 9 EIGRP

TECI 185 Routing Protocols and Concepts Jack Yon Western Colorado Community College jyon@mesastate.edu Last Updated: 4/14/2009. Chapter 9 EIGRP. Topics. EIGRP Metric Calculation EIGRP Composite Metric and the K Values EIGRP Metrics Using the bandwidth Command

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Chapter 9 EIGRP

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  1. TECI 185 Routing Protocols and Concepts Jack Yon Western Colorado Community College jyon@mesastate.edu Last Updated: 4/14/2009 Chapter 9EIGRP

  2. Topics • EIGRP Metric Calculation • EIGRP Composite Metric and the K Values • EIGRP Metrics • Using the bandwidth Command • Calculating the EIGRP Metric • DUAL • DUAL Concepts • Successor and Feasible Distance • Feasible Successors, Feasibility Condition, and Reported Distance • Topology Table: Successor and Feasible Successor • Topology Table: No Feasible Successor • Finite State Machine • More EIGRP Configurations • The Null0 Summary Route • Disabling Automatic Summarization • Manual Summarization • EIGRP Default Route • Fine-Tuning EIGRP • Introduction to EIGRP • EIGRP: An Enhanced Distance Vector Routing Protocol • EIGRP Message Format • Protocol-Dependent Modules • RTP and EIGRP Packet Types • Hello Protocol • EIGRP Bounded Updates • DUAL: An Introduction • Administrative Distance • Authentication • Basic EIGRP Configuration • EIGRP Network Topology • Autonomous Systems and Process IDs • The router eigrp Command • The network Command • Verifying EIGRP • Examining the Routing Table

  3. EIGRP: An Enhanced Distance Vector Routing Protocol EIGRP Message Format Protocol-Dependent Modules RTP and EIGRP Packet Types Hello Protocol EIGRP Bounded Updates DUAL: An Introduction Administrative Distance Authentication Introduction to EIGRP

  4. Introduction to EIGRP • Enhanced Interior Gateway Routing Protocol (EIGRP) • Distance vector • Classless routing protocol • Released in 1992 with Cisco IOS Software Release 9.21. • Enhancement of Cisco Interior Gateway Routing Protocol (IGRP). • Both are Cisco proprietary • Operate only on Cisco routers.

  5. Introduction to EIGRP • The term hybrid routing protocolis sometimes used to define EIGRP. • Misleading, not a hybrid between distance vector and link-state • Solely a distance vector routing protocol.

  6. Introduction to EIGRP • Instead of hop count, both IGRP and EIGRP use metrics composed of bandwidth, delay, reliability, and load. • Only bandwidth and delay are used by default.

  7. EIGRP Message Format • EIGRP Header field • Data field = Type/Length/Value, or TLV. • Encapsulated in an IP packet. • Protocol field = 88 (EIGRP) • Destination IP address = multicast 224.0.0.10. • If the EIGRP packet is encapsulated in an Ethernet frame: • Destination MAC, multicast address: 01-00-5E-00-00-0A

  8. EIGRP Message Format Note: All fields are shown to provide an accurate picture of the EIGRP message format. However, only the fields relevant to the CCNA candidate are discussed. • Opcode specifies the EIGRP packet type as one of the following: • Update • Query • Reply • Hello

  9. EIGRP Packet Header Message Format Note: All fields are shown to provide an accurate picture of the EIGRP message format. However, only the fields relevant to the CCNA candidate are discussed. • Autonomous system number • Specifies the EIGRP routing process. • Unlike RIP, Cisco routers can run multiple instances of EIGRP. (more later) • EIGRP packet types are discussed later in this chapter.

  10. EIGRP TLV Message Format • EIGRP uses weightsfor its composite metric. • Default, only bandwidth(K1) and delay(K3) are weighted (used) • Set to 1. • OtherK values are set to 0 (affect load and reliability). • More later. • The hold time • Amount of time the EIGRP neighbor receiving this message should wait before considering the advertising router to be down. • More later

  11. IP Internal Routes TLV • Metric fields: • Delay and Bandwidth • Reliability and Load • (more later) • Subnet mask field (Prefix Length): • Example, the prefix length for 255.255.255.0 is 24 (/24) • Destination field: • The destination network.

  12. IP External Routes TLV • In this chapter, we import or redistribute a default static route into EIGRP. • Additional fields • All the fields used by the IP Internal TLV

  13. Note on MTU • Some EIGRP literature might incorrectly state that the maximum transmission unit (MTU) is one of the metrics used by EIGRP. • MTU is not a metric used by EIGRP. • The MTU is included in the routing updates, but it is not used to determine the routing metric.

  14. Protocol-Dependent Modules • EIGRP uses protocol-dependent modules (PDM). to route different protocols, including: • IP, Internetwork Packet Exchange (IPX) • AppleTalk, • PDMs are responsible for the specific routing tasks for each network layer protocol. • Example The IP-EIGRP module is responsible for: • Sending and receiving EIGRP packets that are encapsulated in IP. • Using DUAL to build and maintain the IP routing table.

  15. RTP and EIGRP Packet Types • Reliable Transport Protocol (RTP) • Delivery and reception of EIGRP packets. • Cannot use the services of UDP or TCP • IPX and AppleTalk do not use protocols from the TCP/IP protocol suite. • RTP includes both reliable delivery and unreliable delivery of EIGRP packets: • Reliable RTP requires an acknowledgment (like TCP). • Unreliable RTP does not require an acknowledgment (like UDP). • RTP can send packets either as a unicast or a multicast (224.0.0.10).

  16. EIGRP Packet Types – Hello Packet • Hello packets are used by EIGRP to: • Discover neighbors • Form adjacencies with those neighbors • EIGRP hello packets: • multicasts • unreliable delivery

  17. EIGRP uses triggered updates X EIGRP Packet Types – Update and Acknowledgement Packets • Update Packets • Contains only the routing information needed (a change occurs) • Sent only to those routers that require it. • Uses reliable delivery. • Multicast when sent to multiple routers • Unicast when sent to a single router • Acknowledgment (ACK) Packets • Sent when reliable delivery is used (update, query, and reply packets). • Sent as an unreliable unicast.

  18. Why Query? Another router could be attached to the same LAN. X EIGRP Packet Types – Query and Reply Packets • Used by DUAL when searching for networks and other tasks. • Queries and replies use reliable delivery. • To keep this example simple, acknowledgments were omitted in the graphic. • All neighbors must send a reply regardless of whether they have a route to the downed network. • Queries can use multicast or unicast, whereas replies are always sent as unicast. • DUAL is discussed in a later section. • Queries and replies packets are discussed in more detail in CCNP.

  19. HelloProtocol • Before any EIGRP packets can be exchanged between routers, EIGRP must first discover its neighbors. • EIGRP routersdiscover neighbors and establish adjacencies with neighbor routers using the hello packet.

  20. Hello Protocol • Most networks, EIGRP hello packets are sent every 5 seconds. • On multipoint nonbroadcast multiaccess (NBMA) networks such as X.25, Frame Relay, and ATM interfaces with access links of T1 (1.544 Mbps) or slower, hellos are unicast every 60 seconds. • An EIGRP router assumes that as long as it is receiving hello packets from a neighbor, the neighbor and its routes remain viable.

  21. Hello Protocol • Hold time - maximum time the router should wait to receive the next hello before declaring that neighbor as unreachable. • Default hold time - 3 times the hello interval, • 15 seconds on most networks • 180 seconds on low-speed NBMA networks • If the hold timeexpires: • EIGRP declares the route as down • DUAL searches for a new path in the topology tableor by sending out queries. • More later.

  22. EIGRP Bounded Updates • EIGRP uses the terms partial and boundedwhen referring to its update packets. • EIGRP sends its updates only when the metric for a route changes. • The term partialmeans that the update only includes information about the route changes. • The term boundedrefers to the propagation of partial updates sent only to those routers that are affected by the change. • This minimizes the bandwidth required to send EIGRP packets.

  23. DUAL: An Introduction J. J. Garcia-Luna-Aceves • Diffusing Update Algorithm (DUAL) is the convergence algorithm used by EIGRP. • First proposed by E. W. Dijkstra and C. S. Scholten. • The most prominent work with DUAL has been done by J. J. Garcia-Luna-Aceves. • Routing loops, even temporary ones, can be extremely detrimental to network performance. • Distance vector routing protocols such as RIP prevent routing loops with hold-down timers and split horizon. • Although EIGRP uses both of these techniques, it uses them somewhat differently; the primary way that EIGRP prevents routing loops is with the DUAL algorithm.

  24. DUAL: An Introduction X X 1. A directly connected network on R2 goes down. • R2 sends an EIGRP update message to its neighbors indicating the network is down . 2. R1 and R3 return an EIGRP acknowledgment indicating that they have received the update from R2.

  25. DUAL: An Introduction X X 3. R2 does not have an EIGRP backup route known as a feasible successor. (more later.) • So, R2 sends an EIGRP query to its neighbors asking them whether they have a route to this downed network. 4. R1 and R3 return an EIGRP acknowledgment indicating that they have received the query from R2 5. R1 and R3 send an EIGRP reply message in response to the query sent by R2. • In this case, the reply would state that the router does not have a route to this network. 6. R2 returns an acknowledgment indicating that it received the reply. Note: Much more later!

  26. Administrative Distance • When compared to other interior gateway protocols (IGP), EIGRP is the most preferred by the Cisco IOS software because it has the lowest AD. • Later in this chapter, you learn how to configure EIGRP summary routes.

  27. Authentication • Like other routing protocols, EIGRP can be configured for authentication. • It is good practice to authenticate transmitted routing information. • This practice ensures that routers will accept routing information only from other routers that have been configured with the same password or authentication information. • When authentication is configured on a router, the router authenticates the source of each routing update packet that it receives. • However, authentication does not encrypt the router’s routing table.

  28. EIGRP Network Topology Autonomous Systems and Process IDs The router eigrp Command The network Command Verifying EIGRP Examining the Routing Table Basic EIGRP Configuration

  29. Topology • Includes the addition of the ISP router. • R1 and R2 routers have subnets that are part of the 172.16.0.0/16.

  30. R1’s running-config hostname R1 ! interface FastEthernet0/0 ip address 172.16.1.1 255.255.255.0 ! interface Serial0/0/0 ip address 172.16.3.1 255.255.255.252 clock rate 64000 ! interface Serial0/0/1 ip address 192.168.10.5 255.255.255.252

  31. R2’s running-config hostname R2 ! interface Loopback1 ip address 10.1.1.1 255.255.255.252 description Simulated ISP ! interface FastEthernet0/0 ip address 172.16.2.1 255.255.255.0 ! interface Serial0/0/0 ip address 172.16.3.2 255.255.255.252 ! interface Serial0/0/1 ip address 192.168.10.9 255.255.255.252 clockrate 64000 • ISP router does not physically exist in our configurations. • The connection between R2 and ISP is represented with a loopback interface on Router R2.

  32. R3’s running-config hostname R3 ! interface FastEthernet0/0 ip address 192.168.1.1 255.255.255.0 ! interface Serial0/0/0 ip address 192.168.10.6 255.255.255.252 clockrate 64000 ! interface Serial0/0/1 ip address 192.168.10.10 255.255.255.252

  33. Autonomous Systems and Process IDs • An autonomous system (AS) is a collection of networks under the administrative control of a single entity that presents a common routing policy to the Internet. • Described in RFC 1930. • AS numbers are assigned by IANA and its RIR. • Same authority that assigns IP address space.

  34. Autonomous Systems and Process IDs • Who needs an autonomous system number? • ISPs • Internet backbone providers • Large institutions connecting to other entities that also have an autonomous system number. • Uses exterior gateway routing protocolBGP. • The vast majority of companies and institutions with IP networks do not need an autonomous system number because they come under the control of a larger entity such as an ISP. BGP

  35. Process ID Router(config)# router eigrp autonomous-system Must be same on all routers in EIGRP routing domain Router(config)# router eigrp 1 • Both EIGRP and OSPF use a process ID to represent an instance of their respective routing protocol running on the router. • Although EIGRP refers to the parameter as an “autonomous-system” number, it actually functions as a process ID. • AS parameter is between 1 and 65,535. • All routers in this EIGRP routing domain must use the sameprocess ID number (autonomous system number).

  36. The router eigrp Command R1(config)# router eigrp 1 R1(config-router)# R2(config)# router eigrp 1 R2(config-router)# R3(config)# router eigrp 1 R3(config-router)# • EIGRP is enabled on all three routers using the process ID of 1.

  37. The network Command Router(config-router)# networknetwork-address • The networkcommand in EIGRP has the same function as in other IGP routing protocols: • Any interface on this router that matches the network address in the networkcommand will be enabled to send and receive EIGRP updates. • This network (or subnet) will be included in EIGRP routing updates.

  38. The network Command Adjacency R1(config-router)# network 172.16.0.0 R2(config-router)# network 172.16.0.0 %DUAL-5-NBRCHANGE: IP-EIGRP 1: Neighbor 172.16.3.1 (Serial0/0) is up: new adjacency • The network-address is the classful network address for this interface. • 172.16.0.0 includes both 172.16.1.0/24 and 172.16.3.0/30 subnets. • When EIGRP is configured on R2, DUAL sends a notification message to the console stating that a neighbor relationship with another EIGRP router has been established. • This new adjacencyhappens automatically because both R1 and R2 are using the same EIGRP 1 routing process and both routers are now sending updates on the 172.16.0.0 network.

  39. The network Command with a Wildcard Mask Router(config-router)# networknetwork-address[wildcard-mask] • Network command – When uses classful network address: • All interfaces on the router that belong to that classful network address will be enabled for EIGRP. • To include only specific interface(s), subnets, to be enabled for EIGRP: • Use the wildcard-mask option.

  40. The network Command with a Wildcard Mask 255.255.255.255 - 255.255.255.252 Subtract the subnet mask --------------- 0. 0. 0. 3 Wildcard mask R2(config-router)# network 192.168.10.8 0.0.0.3 Or R2(config-router)# network 192.168.10.8 255.255.255.252 • Think of a wildcard mask as the inverse of a subnet mask. • The inverse of subnet mask 255.255.255.252 is 0.0.0.3. • To calculate the inverse of the subnet mask, subtract the subnet mask from 255.255.255.255. • Some Cisco IOS software versions also let you just enter the subnet mask. • However, Cisco IOS software then converts the command to the wildcard mask format, as can be verified with the show running-config

  41. The network Command with a Wildcard Mask R2(config-router)# network 192.168.10.8 0.0.0.3 Or R2(config-router)# network 192.168.10.8 255.255.255.252 R2# show running-config <some output omitted> ! router eigrp 1 network 172.16.0.0 network 192.168.10.8 0.0.0.3 auto-summary

  42. The network Command with a Wildcard Mask • The passive-interface command should not be used with EIGRP. • When the passive-interface command is configured, EIGRP stops sending hello packets on that interface. • Will not form an adjacency • Unable to send or receive routing updates. R2(config-router)# network 192.168.10.8 0.0.0.3

  43. Network configurations R1 router eigrp 1 network 172.16.0.0 network 192.168.10.4 router eigrp 1 network 172.16.0.0 network 192.168.10.8 0.0.0.3 router eigrp 1 network 192.168.1.0 network 192.168.10.0 R2 R3

  44. Verifying EIGRP • EIGRP routers must first establish adjacencies with their neighbors before any updates can be sent or received. • show ip eigrp neighbors- view the neighbor table and verify that adjacencies with its neighbors. • If a neighbor is not listed: • Check the local interfaces to make sure it is activated with the show ip interface briefcommand. • Try pinging the IP address of the neighbor.

  45. Verifying EIGRP Verifying EIGRP • If the ping is successful and EIGRP still does not see the router as a neighbor, examine the following configurations: • Are both routers configured with the same EIGRP process ID? • Is the directly connected network included in the EIGRP networkstatements? • Is the passive-interface command inappropriately configured, thus preventing EIGRP hello packets on the interface?

  46. R1# show ip protocols Routing Protocol is “eigrp 1” Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Default networks flagged in outgoing updates Default networks accepted from incoming updates EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0 EIGRP maximum hopcount 100 EIGRP maximum metric variance 1 Redistributing: eigrp 1 Automatic network summarization is in effect Automatic address summarization: 192.168.10.0/24 for FastEthernet0/0, Serial0/0/0 Summarizing with metric 2169856 172.16.0.0/16 for Serial0/0/1 Summarizing with metric 28160 Maximum path: 4 Routing for Networks: 172.16.0.0 192.168.10.0 Routing Information Sources: Gateway Distance Last Update (this router) 90 00:03:29 192.168.10.6 90 00:02:09 Gateway Distance Last Update 172.16.3.2 90 00:02:12 Distance: internal 90 external 170 Some items to make note of. These will be explained later.

  47. Examining the Routing Table: R1 R1# show ip route Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, D - EIGRP, EX - EIGRP external, O - OSPF, <Output omitted> 192.168.10.0/24 is variably subnetted, 3 subnets, 2 masks D 192.168.10.0/24 is a summary, 00:03:50, Null0 C 192.168.10.4/30 is directly connected, Serial0/0/1 D 192.168.10.8/30 [90/2681856] via 192.168.10.6,00:02:43, S0/0/1 172.16.0.0/16 is variably subnetted, 4 subnets, 3 masks D 172.16.0.0/16 is a summary, 00:10:52, Null0 C 172.16.1.0/24 is directly connected, FastEthernet0/0 D 172.16.2.0/24 [90/2172416] via 172.16.3.2, 00:10:47, S0/0/0 C 172.16.3.0/30 is directly connected, Serial0/0/0 D 192.168.1.0/24 [90/2172416] via 192.168.10.6, 00:02:31, S0/0/1 • Notice that EIGRP routes are denoted in the routing table with a D, which stands for DUAL.

  48. Examining the Routing Table: R2 R2# show ip route <Output omitted> 192.168.10.0/24 is variably subnetted, 3 subnets, 2 masks D 192.168.10.0/24 is a summary, 00:04:13, Null0 D 192.168.10.4/30 [90/2681856] via 192.168.10.10,00:03:05,S0/0/1 C 192.168.10.8/30 is directly connected, Serial0/0/1 172.16.0.0/16 is variably subnetted, 4 subnets, 3 masks D 172.16.0.0/16 is a summary, 00:04:07, Null0 D 172.16.1.0/24 [90/2172416] via 172.16.3.1, 00:11:11, S0/0/0 C 172.16.2.0/24 is directly connected, FastEthernet0/0 C 172.16.3.0/30 is directly connected, Serial0/0/0 10.0.0.0/30 is subnetted, 1 subnets C 10.1.1.0 is directly connected, Loopback1 D 192.168.1.0/24 [90/2172416] via 192.168.10.10, 00:02:54, S0/0/1 • EIGRP is a classless routing protocol (includes the subnet mask in the routing update), it supports variable-length subnet masks (VLSM) and classless interdomain routing (CIDR).

  49. Examining the Routing Table: R3 R3# show ip route <Output omitted> 192.168.10.0/24 is variably subnetted, 3 subnets, 2 masks D 192.168.10.0/24 is a summary, 00:03:11, Null0 C 192.168.10.4/30 is directly connected, Serial0/0/0 C 192.168.10.8/30 is directly connected, Serial0/0/1 D172.16.0.0/16 [90/2172416] via 192.168.10.5, 00:03:23, S0/0/0 [90/2172416] via 192.168.10.9, 00:03:23, S0/0/1 C 192.168.1.0/24 is directly connected, FastEthernet0/0 • By default, EIGRP automatically summarizes routes at the major network boundary. • You can disable the automatic summarization with the no auto-summarycommand, just as you can for RIPv2. • Null0 summary routes will be explained next.

  50. Introducing the Null0 Summary Route R2# show ip route <Output omitted> 192.168.10.0/24 is variably subnetted, 3 subnets, 2 masks D 192.168.10.0/24 is a summary, 00:04:13, Null0 D 192.168.10.4/30 [90/2681856] via 192.168.10.10,00:03:05,S0/0/1 C 192.168.10.8/30 is directly connected, Serial0/0/1 172.16.0.0/16 is variably subnetted, 4 subnets, 3 masks D 172.16.0.0/16 is a summary, 00:04:07, Null0 D 172.16.1.0/24 [90/2172416] via 172.16.3.1, 00:11:11, S0/0/0 C 172.16.2.0/24 is directly connected, FastEthernet0/0 C 172.16.3.0/30 is directly connected, Serial0/0/0 10.0.0.0/30 is subnetted, 1 subnets C 10.1.1.0 is directly connected, Loopback1 D 192.168.1.0/24 [90/2172416] via 192.168.10.10, 00:02:54, S0/0/1 • The 192.168.10.0/24 and 172.16.0.0/16 routes do not actually represent a path to reach the parent networks. • If a packet does not match one of the level 2 child routes, it is sent to the Null0 interface. • In other words, if the packet matches the level 1 parent, but none of the subnets, the packet is discarded.

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