EIGRP Configuration Example

Configure a two-router EIGRP network with two Frame Relay links between two routers to demonstrate the redundancy mechanism with the EIGRP DUAL algorithm.

Figure 2-15 displays a two-router topology using the same addressing as the RIP example in Figure 2-14.

Figure 2-15 EIGRP Configuration Example

Autonomous System 100 (AS100)

Bandwidth 256

172.108.1.1/24

131.108.3.0/30 Frame Relay

Bandwidth 128

R1's Loopbacks Loopback0 131.108.4.1/24 Loopback1 131.108.5.1/24 Loopback2 131.108.6.1/24

Bandwidth 256

131.108.3.0/30 Frame Relay

131.108.10.0/30 Frame Relay

131.108.10.0/30 Frame Relay

172.108.2.1/24

E0/0

R2's Loopbacks Loopback0 131.108.7.1/24 Loopback1 131.108.8.1/24 Loopback2 131.108.9.1/24

Routers R1 and R2 reside in AS 100, and to enable EIGRP on both routers, you need to start by configuring EIGRP. Example 2-15 displays the EIGRP configuration required on R1 and R2.

Example 2-15 Enabling EIGRP in AS 100

'outer eigrp 100

network 131.108.0.0

The network command in Example 2-15 enables EIGRP to send and receive updates for interfaces configured with the Class B address, 131.108.0.0. EIGRP will automatically summarize.

Example 2-16 displays the IP routing table on R1. Example 2-16 show ip route on R1

R1#show ip route

Codes: C - connected, D - EIGRP, EX - EIGRP external,

131.108.0.0/16 is variably subnetted, 10 subnets, 2 masks C 131.108.10.0/30 is directly connected, Serial0/1

Example 2-16 show ip route on R1 (Continued)

D

131.1

38.9

©

[90/10639872] via 131

138.3.2, 33

34

27,

Serial3/3

D

131.1

38.8

3/24

[90/10639872] via 131

138.3.2, 33

34

27,

Serial3/3

D

131.1

38.7

3/24

[90/10639872] via 131

138.3.2, 33

34

27,

Serial3/3

C

131.1

38.6

3/24

is directly connected

Loopback2

C

131.1

38.5

3/24

is directly connected

Loopback1

C

131.1

38.4

3/24

is directly connected

Loopback3

C

131.1

38.3

3/33

is directly connected

Serial3/3

D

131.1

38.2

3/24

[90/10537472] via 131

138.3.2, 33:

34

28,

Serial3/3

C

131.1

38.1

3/24

is directly connected

Ethernet3/3

Example 2-16 displays four remote EIGRP entries (designated by D in the routing table) via the Serial interface Serial0/0. EIGRP has discovered these networks as the preferred path because the WAN bandwidth is 256 kbps as opposed to 128 kbps via Serial 0/1. To view the alternate paths, use the show ip eigrp topology IOS command to display backup paths.

Example 2-17 displays the output of the show ip eigrp topology command on R1. Example 2-17 show ip eigrp topology on R1

R1#show

ip eigrp

topology

IP-EIGRP

Topology

Table for AS(100)/ID(131.108.6.1)

Codes: P

- Passive,

A - Active, U - Update, Q - Query, R

Reply,

r

- reply

Status, s - sia Status

P

131.13

8.13.3/33,

1 successors, FD is 2169856

via Connected, Serial0/1

via 131.

13

8.3.2 (11023872/1761792), Serial0/0

P

131.13

8.9.3/24,

1

successors, FD is 2297856

via 131.

13

8.3.2 (10639872/128256), Serial0/0

via 131.

13

8.10.2 (20640000/128256), Serial0/1

P

131.13

8.8.3/24,

1

successors, FD is 2297856

via 131.

13

8.3.2 (10639872/128256), Serial0/0

via 131.

13

8.10.2 (20640000/128256), Serial0/1

P

131.13

8.7.3/24,

1

successors, FD is 2297856

via 131.

13

8.3.2 (10639872/128256), Serial0/0

via 131.

13

8.10.2 (20640000/128256), Serial0/1

P

131.13

8.6.3/24,

1

successors, FD is 128256

via Connected, Loopback2

P

131.13

8.5.3/24,

1

successors, FD is 128256

via Connected, Loopback1

P

131.13

8.4.3/24,

1

successors, FD is 128256

via Connected, Loopback0

P

131.13

8.3.3/33,

1

successors, FD is 2169856

via Connected, Serial0/0

via 131.

13

8.10.2 (21024000/1761792), Serial0/1

P

131.13

8.2.3/24,

1

successors, FD is 2195456

via 131.

13

8.3.2 (10537472/281600), Serial0/0

via 131.

13

8.10.2 (20537600/281600), Serial0/1

P

131.13

8.1.3/24,

1

successors, FD is 281600

via Connected, Ethernet0/0

Example 2-17 shows that the remote network 131.108.2.0 is via two paths, and because the feasible distance is lower through Serial 0/0, that path is injected into the routing table. If, for some reason, the link with Serial 0/0 on R1 fails, the alternate path will be chosen and inserted into the routing table, increasing convergence times.

When EIGRP loses a path to a remote network, it sends requests to neighboring routers for alternative ways to reach the failed network. The neighboring router that returns the most favorable routes is called the feasible successor; in Figure 2-15, that router is R2.

NOTE The Cisco CD Documentation Codes State of this topology table entry are defined as follows:

• P (Passive)—No EIGRP computations are being performed for this destination.

• A (Active)—EIGRP computations are being performed for this destination.

• U (Update)—Indicates that an update packet was sent to this destination.

• Q (Query)—Indicates that a query packet was sent to this destination.

• R (Reply)—Indicates that a reply packet was sent to this destination.

• r (Reply status)-A flag that is set after the software has sent a query and is waiting for a reply.

*Cisco Connection online was the source for this material,

www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fiprrp_r/1rfeigrp.htm#1 025659.

OSPF

OSPF is a link-state routing protocol. Link-state protocols use Dijkstra's shortest path first (SPF) algorithm to populate the routing table. OSPF shares information with every router in the network. OSPF is a classless protocol and supports VLSM. Table 2-11 defines common OSPF terminology.

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