Problem: Redistributed Routes Are Not Getting Installed in the Routing Table-Cause: Metric Is Not Defined During Redistribution into IGRP

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Problem: Redistributed Routes Are Not Getting Installed in the Routing Table ‚ Cause: Metric Is Not Defined During Redistribution into IGRP

IGRP has a composite metric made up of bandwidth, delay, reliability, load, and MTU; however, by default, it utilizes only bandwidth and delay. OSPF's metric is based on interface cost. Cost is derived from the bandwidth of the link. Cisco uses 100,000,000/bandwidth to get the cost. IGRP does not understand the metrics of other protocols (except EIGRP) so it is necessary to input a default metric when doing redistribution.

Figure 5-32 shows the network setup susceptible to the problem in which redistributed routes do not get installed in the routing table.

Figure 5-32. Network Setup Conducive to Redistributed Routes Not Being Installed in the Routing Table

OSPF is redistributed into IGRP at R1, but R2 is not receiving IGRP routes that are OSPF routes in R1.

Figure 5-33 shows the flowchart to follow to solve this problem.

Figure 5-33. Problem-Resolution Flowchart

Debugs and Verification

Example 5-81 shows that R3 is advertising 131.108.6.0/24 through OSPF to R1.

Example 5-81 R1's Routing Table Shows That R3 Is Advertising 131.108.6.0/24 Through OSPF
 R1#  show ip route 131.108.6.0    Routing entry for 131.108.6.0/24   Known via "ospf 1", distance 110, metric 20, type intra area 

Example 5-82 shows that R1 is redistributing OSPF in IGRP.

Example 5-82 R1 Configuration to Redistribute OSPF into IGRP
 R1#  router igrp    redistribute ospf 1    network 131.108.0.0  

Example 5-83 shows that in R2, 131.108.6.0/24 is not present in the IGRP routing table.

Example 5-83 R2's Routing Table Is Missing the Redistributed Route
 R2#  show ip route 131.108.6.0  % Subnet not in table 

Solution

To solve this problem, R1 needs to put a metric command under the router igrp statement so that it can calculate the OSPF metric properly.

Example 5-84 shows the new configuration for R1. OSPF is redistributed into IGRP with metric values of bandwidth, delay, load, reliability, and MTU. Setting low bandwidth and high delay yields to a high metric for redistributed routes.

Example 5-84 Configuring R1 to Calculate OSPF Metrics
 R1#  router igrp 1    redistribute ospf 1 metric 1 10000 255 1 1500    network 131.108.0.0  

Another way to fix this problem is to define a default metric under the router igrp statement. The difference between using a default metric and defining a metric as shown in Example 5-84 is that a default metric will be used for all the redistribution. For example, if the router igrp statement has multiple redistribution commands, all the redistributed routes will have a default metric value defined under the router igrp command.

Example 5-85 shows the syntax for default-metric command under the router igrp state-ment when redistributing into IGRP. The metric values are based on bandwidth, delay, load, reliability, and MTU. So, in this case, all the static and OSPF routes will be redistributed with the default metric configured here.

Example 5-85 Configuring a Default Metric
 R1#  router igrp 1    redistribute ospf 1     redistribute static     default-metric 1 10000 255 1 1500    network 131.108.0.0  

Example 5-86 shows that the route gets installed in the routing table.

Example 5-86 R2's Routing Table Verifies That the New Configuration for R1 Has Corrected the Problem
 R2#  show ip route 131.108.6.0   Routing entry for 131.108.6.0/24   Known via "igrp", distance 100, metric 8976  
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Troubleshooting IP Routing Protocols
Troubleshooting IP Routing Protocols (CCIE Professional Development Series)
ISBN: 1587050196
EAN: 2147483647
Year: 2002
Pages: 260

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