Welcome to the SolarWinds Blog Series, ‘Basics of Routing Protocols’. This is the last of a four part series where you can learn the fundamentals of routing protocols, types, and their everyday applications in network troubleshooting.

In the previous blog, we discussed Open Shortest Path First (OSPF), OSPF message types, and the protocol’s advantages and disadvantages. In this blog, we’ll shed some light on another popular routing protocol: EIGRP (Enhanced Interior Gateway Routing Protocol).

 

What is EIGRP (Enhanced Interior Gateway Routing Protocol)?

EIGRP, a distance vector routing protocol, exchanges routing table information with neighboring routers in an autonomous system. Unlike RIP, EIGRP shares routing table information that is not available in the neighboring routers, thereby reducing unwanted traffic transmitted through routers. EIGRP is an enhanced version of IGRP and uses Diffusing Update Algorithm (DUAL), which reduces time taken for network convergence and improves operational efficiency. EIGRP was a proprietary protocol from Cisco®, which was later made an Open Standard in 2013.

 

EIGRP Packet Types

Different message types in EIGRP include:

  • Hello Packet – The first message type sent when EIGRP process is initiated on the router. Hello packet identifies neighbors and forms adjacencies while being multicast every 5 seconds by default (60 seconds on low bandwidth network).
  • Update Packet – Contains route information that is only forwarded when there is a change. They are only sent to the routes that have partial updates. If there’s a new neighbor discovered, the packet is sent to the router as a unicast.
  • Acknowledgement – This is unicast as a response to Update packet by acknowledging when they receive an update.
  • Query – This packet is sent to query routes from neighbors. When a router loses a route while sending the multicast, Query packet is sent to all neighboring routers to find alternate paths for the router.
  • Reply – These are unicast by routers that know alternate routes for the neighboring routers queried on a network.


EIGRP – Pros and Cons

Speedy network convergence, low CPU utilization, and ease of configuration are some of the advantages of EIGRP. The EIGRP routers store everything as routing table information so they can quickly adapt to alternate routes. The variable length subnet mask reduces time to network convergence and increases scalability. EIGRP also includes MD5 route authentication. Compared to RIP and OSPF, EIGRP has more adaptability and versatility in complex networks. EIGRP combines many features of both link-state and distance-vector. Since EIGRP is mostly deployed in large networks, routers tend to delay sending information during allotted time, which can cause neighboring routers to query the information again, thus increasing traffic.


Monitor Routers Using EIGRP in Your Network

Advanced network monitoring tools have the ability to monitor network route information and provide real-time views on issues that might affect the network. Using monitoring tools in small networks, you can view router topology, routing tables, and changes in default routes. You can also check out overview blogs on RIP and OSPF routing protocols.