10 EIGRP Design Best Practices

EIGRP is a popular routing protocol used in many enterprise networks. It is a hybrid protocol that combines the features of both distance vector and link-state protocols. EIGRP is a Cisco proprietary protocol, but it can be used in multi-vendor networks.

Designing an EIGRP network is not a trivial task. It requires careful planning and implementation of best practices. In this article, we will discuss 10 EIGRP design best practices that will help you design a robust and reliable EIGRP network.

1. Use EIGRP for internal routes only

EIGRP is a proprietary protocol, meaning it’s not supported by other vendors. This means that if you use EIGRP for external routes, you won’t be able to communicate with devices from other vendors.

Additionally, using EIGRP for internal routes only allows you to keep your network more secure. Since EIGRP is a closed protocol, it’s much harder for malicious actors to gain access to the routing information and manipulate it.

Finally, using EIGRP for internal routes only helps simplify your network design. By keeping all of your internal routes on one protocol, you can easily manage them without having to worry about different protocols or configurations.

2. Enable authentication on all interfaces

Authentication ensures that only authorized routers can join the EIGRP network. Without authentication, any router could join the network and potentially cause disruption or even malicious activity. By enabling authentication on all interfaces, you are ensuring that only trusted devices can join the network.

Additionally, authentication helps protect against man-in-the-middle attacks by verifying the identity of each device in the network. This is especially important if your network spans multiple locations or has a large number of users.

3. Configure a single process per autonomous system

Having multiple EIGRP processes running on the same autonomous system can lead to routing loops, instability, and other issues. It also makes it difficult to troubleshoot problems because you have to keep track of multiple processes.

By configuring a single process per autonomous system, you ensure that all routers in the network are using the same parameters and settings. This simplifies configuration and management, as well as reduces the risk of errors or misconfigurations.

4. Set the hello and hold timers to match

The hello timer is the interval at which EIGRP routers send out hello packets to their neighbors. The hold timer is the amount of time a router will wait for a response from its neighbor before declaring it dead. If these two timers are not set to match, then one router may declare the other as dead while the other still considers them alive. This can lead to routing loops and instability in your network.

To avoid this issue, make sure that you always configure the hello and hold timers to be the same on all routers in an EIGRP domain.

5. Tune the default bandwidth metric

By default, EIGRP uses the bandwidth of an interface as its metric for determining the best path to a destination. This means that if you have two paths with different bandwidths, EIGRP will always choose the one with the higher bandwidth.

However, this isn’t always the most efficient route. For example, if one path has a higher latency than the other, it may be more beneficial to use the lower-bandwidth path. To ensure that EIGRP takes into account both bandwidth and latency when calculating the best path, you can tune the default bandwidth metric. This allows you to assign weights to each factor so that EIGRP can make the most optimal routing decisions.

6. Adjust the variance multiplier

The variance multiplier is a setting that determines how many paths EIGRP will use to reach the same destination. By default, it’s set to 1, meaning only one path will be used.

However, if you increase the variance multiplier, more paths can be used for load balancing and redundancy purposes. This helps ensure that traffic is evenly distributed across multiple links, which improves performance and reliability. It also allows for faster failover in case of link failure.

When adjusting the variance multiplier, make sure to consider your network topology and available bandwidth. You don’t want to overload any single link with too much traffic, so adjust the multiplier accordingly.

7. Use passive interfaces

Passive interfaces are used to prevent EIGRP from sending and receiving hello packets on a particular interface. This is important because it helps reduce the amount of unnecessary traffic that can be generated by EIGRP, which in turn reduces the load on your network. It also prevents EIGRP from forming neighbor relationships with other routers on the same segment, which can help improve security. Finally, using passive interfaces can help you troubleshoot issues more quickly since you know exactly which interfaces are participating in EIGRP.

8. Summarize at major network boundaries

Summarizing at major network boundaries helps reduce the size of the EIGRP topology table, which in turn reduces the amount of bandwidth used for routing updates. It also helps to prevent route flapping and instability due to changes in the underlying network.

When summarizing routes, it’s important to ensure that all subnets within a summary are contiguous. This will help avoid any potential issues with packet fragmentation or incorrect routing. Additionally, make sure to use the same mask length when summarizing routes as this will help keep the routing tables consistent across different routers.

9. Use manual summarization where possible

Manual summarization allows you to control the size of your EIGRP topology table, which is important for scalability. It also helps reduce the amount of routing traffic on your network by reducing the number of routes that need to be advertised. Finally, manual summarization can help improve convergence times in large networks because it reduces the amount of time needed to propagate updates throughout the network.

When using manual summarization, make sure to use a consistent subnet mask across all routers in the same area. This will ensure that all routers have the same view of the network and will prevent any unnecessary route flapping or instability.

10. Disable auto-summary

Auto-summary is a feature that allows EIGRP to automatically summarize routes at major network boundaries. This can cause problems if the networks on either side of the boundary have different subnet masks, as it will result in incorrect routing information being sent out.

By disabling auto-summary, you ensure that all routes are advertised with their full prefixes and no summarization takes place. This ensures that all routers within the EIGRP domain receive accurate route information and can make informed decisions about how to reach destinations.