When configuring large-scale networks, mistakes are bound to happen given the sheer amount of work involved. This article provides an in-depth summary of common router configuration errors, so you can avoid wasting unnecessary time during setup.
1. Ignoring Filtering When Redistributing Routes. When redistributing routes for a router, you need to enable route filtering to remove paths that might cause routing loops. Therefore, failing to apply route filtering policies often leads to errors.
However, applying filtering on a very large network without complete global information is a complex task for administrators; it is easy to miss paths here or there.
Thus, the best way to avoid this issue is simply to avoid redistributing routes whenever possible. In fact, route redistribution is usually a last resort. There is often a correct method to solve the problem without needing to redistribute routes.
2. Mismatched Neighbor Parameters in OSPF. To establish adjacencies with neighboring nodes, OSPF-based routers typically need to maintain several shared parameters. These parameters include authentication, area ID, network mask, Hello interval, and router dead interval. In actual network deployments, non-standard configurations, incorrect passwords, and other erroneous neighbor parameters can cause neighbor adjacency failures.
For such errors, network administrators can fairly easily use OSPF adjacency-related debug commands to discover whether the fault stems from mismatched neighbor parameters, identify which parameters are wrong, and then correct them.
3. Forgetting to Append the Subnet Mask Keyword When Redistributing Routes. When redistributing routes into an OSPF-based network, another common error is finding several routes missing. The cause is usually that the administrator forgot to append the subnet keyword at the end of the redistribution command. For example, on Cisco routers, the subnet keyword is critical when OSPF redistributes subnet routes. Without this subnet mask keyword, OSPF will only redistribute network routes outside of the subnets.
4. Forgetting to Configure Metrics. When redistributing routes in an EIGRP-based network, if you find that all path information is lost, it is highly likely because the administrator forgot to configure routing metrics. The default behavior requires the administrator to manually set the metric values.
Therefore, if the administrator does not set the metrics, the route redistribution will not succeed. This also shows that when using an EIGRP network, route redistribution is not a very reasonable choice.
5. Improperly Set EIGRP Metrics. It is often difficult to rationally adjust EIGRP metrics so that network traffic is distributed reasonably. Generally speaking, sending business traffic over an Internet VPN might be more sensible than sending it over a low-bandwidth Frame Relay link, so the former should be assigned more traffic.
Bandwidth and delay metrics seem relatively easy to set. However, it is much harder for administrators to plug all the metrics they set into a weighted objective function formula