EIGRP Diffusing Update Algorithm (DUAL) and Reliable Transport Protocol (RTP)

Diffusing Update Algorithm (DUAL) is an algorithm used from EIGRP to select & maintains the best route to each remotes networks. DUAL is also used for following purposes:

·         discover the backup route if there are one available.

·         support for the variable length subnet masks ((VLSMs)).

·         perform dynamic the routes recoveries.

·         queries neighbours for unknown alternates routes.

·         send out the queries for alternate routes.

 

EIGRP stores all the routes advertised by all EIGRP neighbours. The metrics of these routes is used by DUAL to select efficient and the loop free paths. DUAL selects routes that will inserted into the routing tables. If a routes fails, & there is no feasible successor, DUAL chooses a replacement routes, which usually takes the couples of seconds.

The following requirements must have met in the order for DUAL to the work properly:

·         EIGRP neighbours must be discovered.

·         All transmitted EIGRP the messages should receive correctly.

·         All changes and the messages should be processed in order in which they are detected

 

EIGRP Reliable Transport Protocol (RTP)

EIGRP does not send the messages with UDP or TCP instead the Cisco’s protocol called Reliable Transport Protocol (RTP) is used for the communication between EIGRP-speaking routers. As name implies, reliability is key features of protocol, & it’s designed to the enable quick delivery of the updates and tracking of the data reception.

Five different packets types are used by (EIGRP):

·         Update – The contains routes information. When routing updates are the sent in response to metric or topology change, reliable multicasts are the used. In event that only one router needs an updates, for the example when a new neighbour is discovered, unicasts are the used.

·         Query – The request for specific routes that always are

·          Uses reliable multicast method. Routers sends queries when they are realizing they have lost the path to particular network & are looking for the alternative paths.

·         Reply – The sent in response to query via the unicasts methods. Replies can be including a specific route to queried destinations or the declare that there are no known routes.

·         Hello – The used to discover EIGRP neighbours. It is the sent via unreliable multicast & no acknowledgment required.

·         Acknowledgment (ACK) – The sent in response to an update and the always unicasts. ACKs are not the sent reliably.