Troubleshooting EIGRP

Chapter Description

Learn how to quickly identify and fix the most common causes of EIGRP problems with these debugs, configurations, and useful show commands.

Troubleshooting EIGRP Redistribution Problems

In many instances, a problem occurs when redistributing from another routing protocol into EIGRP. Figure 7-32 shows a flowchart for troubleshooting EIGRP redistribution problem.

Figure 7-32Figure 7-32 Flowchart for Troubleshooting EIGRP Redistribution Problem

Consider the network diagram in Figure 7-33, in which the router is the border router between three routing protocols, RIP, OSPF, and EIGRP.

Figure 7-33Figure 7-33 Network Susceptible to EIGRP Redistribution Problems

Example 7-57 shows the configuration for Router A.

Example 7-57 Configuration for Router A in Figure 7-33

Router A# interface ethernet 0
  ip address 172.16.1.1 255.255.255.0
interface ethernet 1
  ip address 172.16.2.1 255.255.255.0
interface serial 0
  ip address 172.16.3.1 255.255.255.0
router ospf 1
  network 172.16.0.0 0.0.255.255 area 0
router rip
  network 172.16.0.0
  passive-interface ethernet 1 
    
router eigrp 1
  network 172.16.0.0
  redistribute rip
  default-metric 10000 100 255 1 1500

Router A wants to redistribute all the routes in the RIP domain into the EIGRP domain. The problem is that the network 150.150.0.0/16 is not getting redistributed into the EIGRP domain.

Referring to Figure 7-33, you can see that the 150.150.0.0/16 network is present in the RIP domain and the OSPF domain. Before the route is getting redistributed into EIGRP, the route must be in the EIGRP topology table first. Look at the EIGRP topology table on Router A for the 150.150.0.0/16 network in Example 7-58.

Example 7-58 EIGRP Topology Table for 150.150.0.0/16

Router A# show ip eigrp topology 150.150.0.0 255.255.0.0

% Route not in topology table

As this output shows, the route 150.150.0.0/16 is not even in the EIGRP topology table. Example 7-59 shows the routing table for the 150.150.0.0/16 network.

Example 7-59 Routing Table for 150.150.0.0/16

Router A# show ip route 150.150.0.0 255.255.0.0

Routing entry for 150.150.0.0/16
 Known via "
OSPF 1
", distance 110, metric 186
 Redistributing via OSPF 1
 Last update from 172.16.2.2 on Ethernet 1
 Routing Descriptor Blocks:
 *  172.16.2.2, from 172.16.2.2, 00:10:23 ago, via Ethernet 1
 Route metric is 186, traffic share count is 1

The output in Example 7-59 shows that the 150.150.0.0/16 route is showing up as an OSPF route, not a RIP route. This is why the route is not getting redistributed into EIGRP. Before RIP routes are redistributed into EIGRP, the router looks at the routing table and redistributes all the RIP routes into EIGRP. As Example 7-59 shows, the router hears the update for the 150.150.0.0/16 route from both OSPF and RIP. The router installs the OSPF route because OSPF has a lower administrative distance than RIP. Therefore, if the route is showing up as an OSPF route, the router will not redistribute this route into EIGRP. In other words, the router will redistribute only RIP routes that are showing in the routing table into the EIGRP domain.

The resolve this problem, you must make Router A install the RIP route instead of the OSPF route. One way to do this is to configure a distribute list under OSPF to not install the 150.150.0.0/16 route, as demonstrated in Example 7-60.

Example 7-60 Configuring a Distribute List Under OSPF to Not Install the 150.150.0.0/16 Route

router OSPF 1
  network 172.16.0.0 0.0.255.255 area 0
distribute-list 1 out
access-list 1 deny 150.150.0.0 0.0.255.255
access-list 1 permit any

With the distribute list in place, Router A's routing table for the 150.150.0.0/16 will now show the results in Example 7-61.

Example 7-61 Routing Table for 150.150.0.0/16 After Configuring the Distribute List in Example 7-60

Router A# show ip route 150.150.0.0 255.255.0.0

Routing entry for 150.150.0.0/16
 Known via 
"RIP"
, distance 120, metric 4
 Redistributing via RIP
 Last update from 172.16.3.2 on Serial 0
 Routing Descriptor Blocks:
 *   172.16.3.2, from 172.16.3.2, 00:00:23 ago, via Serial 0
 Route metric is 4, traffic share count is 1

Because the routing table in Router A shows the 150.150.0.0/16 route as a RIP route, redistribution into EIGRP takes place and the EIGRP topology table in Router A now shows the results in Example 7-62.

Example 7-62 EIGRP Topology Table for 150.150.0.0/16 After Configuring the Distribute List in Example 7-60

Router A# show ip eigrp topology 150.150.0.0 255.255.0.0
IP-EIGRP topology entry for 150.150.0.0/16
State is Passive, Query origin flag is 1, 1 Successor(s), FD is 281600
Routing Descriptor Blocks:
0.0.0.0, from RIP, Send flag is 0x0
Composite metric is (281600/0), Route is External
  Vector metric:
  Minimum bandwidth is 10000 Kbit
  Total delay is 1000 microseconds
  Reliability is 255/255
  Load is 1/255
  Minimum MTU is 1500
  Hop count is 0
  External data:
  Originating router is 172.16.3.1 (this system)
  AS number of routes is 0
  External protocol is RIP, external metric is 4
  Administrator tag is 0

The topology table shows that route 150.150.0.0/16 is getting redistributed into EIGRP with the external routing protocol being RIP. The originating router is 172.16.3.1, which is Router A.

Consider another case in which the network setup is shown in Figure 7-34. The routes in the OSPF domain fails to be redistributed into the EIGRP domain.

Figure 7-34Figure 7-34 Network Setup of Case Study for OSPF to EIGRP Route Redistribution Problem

From the setup shown in Figure 7-34, Router B is redistributing from OSPF to EIGRP. The 10.0.0.0/8 network comes from the OSPF domain and is being redistributed into EIGRP domain by Router B. However, Router A never sees the 10.0.0.0/8 route in its routing table. Example 7-63 shows the configuration of Router A and Router B, and Example 7-64 shows the routing table of 10.0.0.0/8 route in Router A and Router B.

Example 7-63 Configurations for Routers A and B for Network Setup in Figure 7-34

Router A# interface ethernet 0
  ip address 172.16.3.1 255.255.255.0
interface serial 0
  ip address 172.16.1.1 255.255.255.0
router eigrp 1
  network 172.16.0.0

Router B# interface ethernet 0
  ip address 172.16.2.1 255.255.255.0
interface serial 0
  ip address 172.16.1.2 255.255.255.0
router ospf 1
  network 172.16.0.0 0.0.255.255 area 0
router eigrp 1
  network 172.16.0.0
  redistribute ospf 1

Example 7-64 Routing Table and EIGRP Topology Table for 10.0.0.0/8 Route in Routers A and B

Router_A#show ip route 10.0.0.0 255.0.0.0
% Network not in table

Router_A# show ip eigrp topology 10.0.0.0 255.0.0.0
% Route not in topology table
Router_B# show ip route 10.0.0.0 255.0.0.0
Routing entry for 10.0.0.0/8
 Known via "OSPF 1", distance 110, metric 206
 Redistributing via OSPF 1
 Last update from 172.16.2.2 on Ethernet 0
 Routing Descriptor Blocks:
 *  172.16.2.2, from 172.16.2.2, 00:18:13 ago, via Ethernet 0
 Route metric is 206, traffic share count is 1

Router_B# show ip eigrp topology 10.0.0.0 255.0.0.0
% Route not in topology table

From the output of Example 7-64, notice that Router B has the 10.0.0.0/24 route in its routing table as an OSPF route, but Router A doesn't have the routing entry for 10.0.0.0/8. Also, the EIGRP topology table on Router B doesn't even have the entry for the 10.0.0.0/8 route. You can conclude from this that the OSPF to EIGRP redistribution in Router B is not working.

By looking over the configuration in Router B, you notice that although the redistribute ospf 1 command is configured under EIGRP, there is no configuration of the default-metric command. When redistributing between different routing protocols, the default-metric com-mand must be configured. When one routing protocol is being redistributed into another, the router doesn't have a way to translate the routing metric from one routing protocol into another. The default-metric command is used so that the network administrator can manually initialize the routing metric during route redistribution. The fix for this problem: Configure a default metric under EIGRP in Router B. Example 7-65 shows the corrected configuration of Router B.

Example 7-65Å@Corrected Configurations of Router B to Fix the Redistribution Problem Shown in Figure 7-34

Router B# interface ethernet 0
  ip address 172.16.2.1 255.255.255.0
interface serial 0
  ip address 172.16.1.2 255.255.255.0
router ospf 1
  network 172.16.0.0 0.0.255.255 area 0
router eigrp 1
  network 172.16.0.0
  redistribute ospf 1
  default-metric 10000 100 255 1 1500

From Example 7-65, the default metric configured is default-metric 10000 100 255 1 1500. 10000 is the bandwidth in kilobits per second. 100 is the interface delay in unit of 10 micro-seconds. 255 is interface reliability, where 255 represents 100 percent reliable. 1 is interface load, where 255 represents 100 percent load. The last number, 1500, is the MTU of the inter-face. Because the 10.0.0.0/8 route comes from the Ethernet interface of Router B, we are setting the default metrics that matches the Ethernet interface—namely, bandwidth of 10,000 kbps, delay of 1000 ms, 100 percent reliability, 1/255 of interface load, and an MTU of 1500 bytes. Keep in mind that the router will accept any values for the default metric setting. The router will even accept default metric value of 1 1 1 1 1. However, using the default metric value that best matches the network topology will allow the router to make a better routing decision. Now with the correct configuration in place in Router B, Example 7-66 shows the routing table in Router A for the 10.0.0.0/8 route.

Example 7-66 Routing Table on Router A and EIGRP Topology Table in Router B for the 10.0.0.0/8 Route to Verify the Fix

Router_A#show ip route 10.0.0.0
Routing entry for 10.0.0.0/8
 
Known via "eigrp 1", distance 170, metric 2195456, 
type external
 Redistributing via eigrp 1
Last update from 172.16.1.2 on Serial0, 00:16:37 ago
 Routing Descriptor Blocks:
*172.16.1.2, from 172.16.1.2, 00:16:37 ago, via Serial0
   Route metric is 2195456, traffic share count is 1
   Total delay is 21000 microseconds, minimum bandwidth is 1544 Kbit
   Reliability 255/255, minimum MTU 1500 bytes
   Loading 1/255, Hops 1
Router B# show ip eigrp topology 10.0.0.0 255.0.0.0
IP-EIGRP topology entry for 10.0.0.0/8
State is Passive, Query origin flag is 1, 1 Successor(s), FD is 281600
Routing Descriptor Blocks:
0.0.0.0, from Redistributed, Send flag is 0x0
Composite metric is (281600/0), Route is External
  Vector metric:
  Minimum bandwidth is 10000 Kbit
  Total delay is 1000 microseconds
  Reliability is 255/255
  Load is 1/255
  Minimum MTU is 1500
  Hop count is 0
  External data:
  Originating router is 172.16.2.1 (this system)
  AS number of routes is 1
  External protocol is OSPF, external metric is 206
  Administrator tag is 0

From Example 7-66, you can see that Router A has the 10.0.0.0/8 route as EIGRP external route, whereas Router B has the EIGRP topology entry for the 10.0.0.0/8 route. The 10.0.0.0/8 route now has been successfully being redistributed from OSPF into EIGRP.

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