CCNP EIGRP Fundamentals

Enhanced Interior Gateway Routing Protocol (EIGRP) is an advanced distance vector protocol. However, it also has a hybrid routing protocol capability since it combines the best of a distance vector protocol with link state algorithms by using partial updates and neighbor discovery. From other distance vector protocols it offers improvements such as reduction of bandwidth use, fast convergence, support for classless subnets which use CIDR and VLSM, and support for multiple routed protocols like Apple Talk, IP and IPX.


Among the key feature of EIGRP the following are included:
1)Fast Convergence
2)VLSM Subnetting
3)Partial Update
4)Multiple Network Layer Protocol Support

Fast Convergence: EIGRP stores its neighbours routing table so it can take alternatives routes if it original route is gone. Also, it has the ability to ask its neighbours for alternative routes if needed.

VLSM Support: EIGRP uses classless subnets within it routing network. For classful major networks it automatically summarizes routes on the attached interfaces. EIGRP also support manual summarization, and for this it uses VLSM to force a summary route from an interface.

Partial Updates: Partial Updates contain information about the change routes, and they are sent when route need a change in its metric or path. They are handled by multicast or unicast packet instead of broadcast packets since it reduces the use of bandwidth.

Multiple Network Layer Protocol: EIGRP can support IP, IPX, and AppleTalk routed protocols which enable EIGRP to have good stability and high performance networks.


EIGRP has four unique key components.

1. Protocol-dependent modules: Responsible for requirements within the network layer protocols.
2. Reliable Transport Protocol (RTP) : Support Unicast and Multicast transmission. RTP's main role is to guarantee a a timely, reliable and efficiently. EIGRP reliable transport protocol (RTP) guarantees timely, reliable, and efficient exchange of routing data between EIGRP neighbours.
3. Neighbor Discovery and Recovery: Discovery and Recovery allow routers about the other routers that are attached on the network neighbor discovery and recovery enables routers to dynamically learn about other routers on their directly attached network . It does this by allowing EIGRP to build a neighbor table which shows all neighbors adjacent to the router, to a topology table which discovers routes and routing table which choses the best path.
   

4. Diffusing Update Algorithm (DUAL): DUAL is the heart of EIGRP. It relies on
protocols and data structures to provide all the routers in a network to lead up to the final route.