IGP Redistribution Examples

I. RIP Redistribution Principles

• 1. Doesn’t differentiate between internal and external routes.
• a. Administrative Distance of 120 for all routes.
• 2. No default seed metric.
• a. Command to redistribute is “redistribute [protocol] metric [hops]
• b. Command to set the default-metric is “default-metric [hops]

II. EIGRP Redistribution Principles

• 1. AD of 170 for external EIGRP
• a. Helps to automatically prevent route feedback
• 2. No default seed metric unless EIGRP to EIGRP, or connected to EIGRP
• a. Command is “redistribute [protocol] metric [bandwidth][delay][load][reliability][MTU]”
• b. Command for default metric is “default-metric [bandwidth][delay][load][reliability][MTU]
• 3. EIGRP uses router-id for loop prevention
• a. As of EIGRP release 5.0, router-id is also included in internal routes.
  • 1. Show eigrp plugins shows the versions of EIGRP
  • a. Example:

R8#sh eigrp plugins
EIGRP plugins installed:
igrp2 1.0.1
ipv4 1.0.1
ipv6 1.0.1
ipx 1.0.1
manet 1.0.1

• 4. The route will be dropped if the same router-id is present in internal/external routes.

Looking at R4:

R4#
R4#sh run | s r e
router eigrp 1
network 172.16.0.8 0.0.0.3
network 172.16.0.12 0.0.0.3
network 192.168.0.4 0.0.0.0
no auto-summary

Check route to router 3:

R4#sh ip route 192.168.0.3
Routing entry for 192.168.0.3/32
Known via “eigrp 1”, distance 170, metric 2560025856, type external
Redistributing via eigrp 1
Last update from 172.16.0.9 on FastEthernet0/0, 00:01:27 ago
Routing Descriptor Blocks:

• 172.16.0.9, from 172.16.0.9, 00:01:27 ago, via FastEthernet0/0
  Route metric is 2560025856, traffic share count is 1
  Total delay is 1010 microseconds, minimum bandwidth is 1 Kbit
  Reliability 1/255, minimum MTU 1 bytes
  Loading 1/255, Hops 1

F0/0 is through R1

R4#sh ip eigrp top 192.168.0.3/32
IP-EIGRP (AS 1): Topology entry for 192.168.0.3/32
State is Passive, Query origin flag is 1, 1 Successor(s), FD is 2560025856
Routing Descriptor Blocks:
172.16.0.9 (FastEthernet0/0), from 172.16.0.9, Send flag is 0x0
Composite metric is (2560025856/2560000256), Route is External
Vector metric:
Minimum bandwidth is 1 Kbit
Total delay is 1010 microseconds
Reliability is 1/255
Load is 1/255
Minimum MTU is 1
Hop count is 1
External data:
Originating router is 192.168.0.1——>this is the originating router, R1
AS number of route is 1
External protocol is OSPF, external metric is 11
Administrator tag is 0 (0x00000000)

If we make R4 router id same as R1:

R4#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R4(config)#router eigrp 1

R4(config-router)#eigrp router-id 192.168.0.1
R4(config-router)#end

Now we lost our route through R1 because EIGRP is using router id for loop prevention:

R4#sh ip route 192.168.0.3
Routing entry for 192.168.0.3/32
Known via “eigrp 1”, distance 170, metric 2560025856, type external
Redistributing via eigrp 1
Last update from 172.16.0.9 on FastEthernet0/0, 00:00:06 ago
Routing Descriptor Blocks:

• 172.16.0.9, from 172.16.0.9, 00:00:06 ago, via FastEthernet0/0
  Route metric is 2560025856, traffic share count is 1
  Total delay is 1010 microseconds, minimum bandwidth is 1 Kbit
  Reliability 1/255, minimum MTU 1 bytes
  Loading 1/255, Hops 1

R4#clear ip eigrp nei
R4#
*Mar 1 00:05:26.951: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.16.0.9 (FastEthernet0/0) is down: route configuration changed
*Mar 1 00:05:26.955: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.16.0.14 (FastEthernet0/1) is down: route configuration changed
R4#sh ip route 192.168.0.3
*Mar 1 00:05:30.215: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.16.0.9 (FastEthernet0/0) is up: new adjacency
*Mar 1 00:05:30.223: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.16.0.14 (FastEthernet0/1) is up: new adjacency

R4#sh ip route 192.168.0.3
Routing entry for 192.168.0.3/32
Known via “eigrp 1”, distance 170, metric 2560077056, type external
Redistributing via eigrp 1
Last update from 172.16.0.14 on FastEthernet0/1, 00:00:01 ago
Routing Descriptor Blocks:

• 172.16.0.14, from 172.16.0.14, 00:00:01 ago, via FastEthernet0/1<———this path is R6
  Route metric is 2560077056, traffic share count is 1
  Total delay is 3010 microseconds, minimum bandwidth is 1 Kbit
  Reliability 1/255, minimum MTU 1 bytes
  Loading 1/255, Hops 3

When we correct the router id, we have a route through R1 again:

R4(config)#router eigrp 1

R4(config-router)#eigrp router-id 192.168.0.4
R4(config-router)#do sh ip route 192.168.0.3
Routing entry for 192.168.0.3/32
Known via “eigrp 1”, distance 170, metric 2560077056, type external
Redistributing via eigrp 1
Last update from 172.16.0.14 on FastEthernet0/1, 00:00:05 ago
Routing Descriptor Blocks:

• 172.16.0.14, from 172.16.0.14, 00:00:05 ago, via FastEthernet0/1
  Route metric is 2560077056, traffic share count is 1
  Total delay is 3010 microseconds, minimum bandwidth is 1 Kbit
  Reliability 1/255, minimum MTU 1 bytes
  Loading 1/255, Hops 3

R4(config-router)#
*Mar 1 00:07:59.183: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.16.0.9 (FastEthernet0/0) is down: route configuration changed
*Mar 1 00:07:59.183: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.16.0.14 (FastEthernet0/1) is down: route configuration changed
R4(config-router)#
*Mar 1 00:08:00.619: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.16.0.9 (FastEthernet0/0) is up: new adjacency
R4(config-router)#
*Mar 1 00:08:02.779: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.16.0.14 (FastEthernet0/1) is up: new adjacency
R4(config-router)#do sh ip route 192.168.0.3
Routing entry for 192.168.0.3/32
Known via “eigrp 1”, distance 170, metric 2560025856, type external
Redistributing via eigrp 1
Last update from 172.16.0.9 on FastEthernet0/0, 00:00:01 ago
Routing Descriptor Blocks:

• 172.16.0.9, from 172.16.0.9, 00:00:01 ago, via FastEthernet0/0–——->routes through R1 again
  Route metric is 2560025856, traffic share count is 1
  Total delay is 1010 microseconds, minimum bandwidth is 1 Kbit
  Reliability 1/255, minimum MTU 1 bytes
  Loading 1/255, Hops 1

R4(config-router)#

Since EIGRP is distance vector, the router says if my router id is present in the update, I no longer install the route. They will form an adjacency, but the route is not in the route table, or RIB. With OSPF it’s the same, but it will be a “flood war”. The router will say I’m originating the route, then withdraw the route. EIGRP is only able to install routes that don’t have the duplicate router identifier. Therefore, one of the first things you should do when configuring your router is set the router id manually to a unique value.