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| 5.1 |  | EIGRP Fundamentals |
| 5.1.2 |  | EIGRP design |

Even though EIGRP is compatible with IGRP, it operates quite differently than its predecessor. As an advanced distance vector routing protocol, EIGRP acts like a link-state protocol when updating neighbors and maintaining routing information. The advantages of EIGRP over simple distance vector protocols include the following:

- Rapid convergence – EIGRP routers converge quickly because they rely on a state-of-the-art routing algorithm called the Diffusing Update Algorithm (DUAL). DUAL guarantees loop-free operation at every instant during route computation and allows all routers involved in a topology change to synchronize at the same time.
- Efficient use of bandwidth – EIGRP makes efficient use of bandwidth by sending partial, bounded updates and it consumes minimal bandwidth when the network is stable.

> - Partial, bounded updates – EIGRP routers make partial, incremental updates rather than sending their complete tables. This is similar to OSPF operation. However, unlike OSPF routers, EIGRP routers send these partial updates only to the routers that need the information. They do not send to all routers in an area. For this reason, they are called bounded updates.
> - Minimal consumption of bandwidth when the network is stable – EIGRP does not use timed routing updates. Instead, EIGRP routers keep in touch with each other using small hello packets. Though exchanged regularly, hello packets do not use a significant amount of bandwidth.

- Support for VLSM and CIDR – Unlike IGRP, EIGRP offers full support for classless IP addressing by exchanging subnet masks in routing updates.
- Multiple network-layer support – EIGRP supports IP, IPX, and AppleTalk through protocol-dependent modules (PDMs).
- Independence from routed protocols – PDMs protect EIGRP from painstaking revision. Evolution of a routed protocol, such as IP, may require a new protocol module, but not necessarily a reworking of EIGRP itself.