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| 5.6 |  | Troubleshooting EIGRP |
| 5.6.5 |  | Stuck in active – the ultimate solution |

The ultimate solution for preventing the EIGRP stuck in active problem is to manually summarize the routes whenever possible and to have a hierarchical network design. The more networks EIGRP summarizes, the less work EIGRP has to do when a major convergence takes place. Therefore, this reduces the number of queries being sent out and ultimately reduces the occurrence of EIGRP stuck in active errors. An example of a poor network design that will not scale in a large EIGRP network is shown.

In the example, each core router represents a region of the entire network and shows that there is no hierarchy in the IP addressing scheme. The Core 1 router is injecting routes 1.1.1.0, 3.3.4.0, 1.1.2.0, and 2.2.3.0 into the core network. The addresses are so scattered that no manual summarization is possible.

The other core routers are experiencing the same problem. The Core 3 and Core 4 routers can not summarize any routes into the core network. As a result, of the FastEthernet link of 3.3.3.0 network keeps flapping, the query would travel to the Core 3 router and then the query also would be seen in the Core1 and Core 4 region. Ultimately, the query will traverse to all routers in the internetwork, this would dramatically increase the likelihood of an EIGRP stuck in active problem.

The best practice is to readdress the IP addressing scheme. One region should take only a block of IP addresses, this way, the core routers would be capable of summarizing the routes into the core, resulting in a reduced routing table in the core. The routers and the query would be contained only in one region. Figure shows an improved and more scalable EIGRP network design.

Comparing the example networks makes it evident that the network presented in the second example is much more structured. The Core 1 router region takes only the 1.0.0.0 block of IP addresses, the Core 4 region takes only the 2.0.0.0 block, and the Core 3 region takes only the 3.0.0.0 block of IP addresses. This enables the three core routers to summarize their routes into the core. If the Fast Ethernet network of 3.3.3.0 flaps in the Core 3 region, the query would be bounded only in the Core 3 region and would not travel the entire network to affect all of the routers in the network. Summarization and hierarchy are the best design practices for a large-scale network.