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Enhanced Interior Gateway Routing Protocol (EIGRP) is a Cisco proprietary routing protocol based on their original IGRP. EIGRP is a balanced hybrid IP routing protocol, with optimizations to minimize both the routing instability incurred after topology changes, as well as the use of bandwidth and processing power in the router. Cisco Systems, Inc. ...
In computer networking the term routing refers to selecting paths in a computer network along which to send data. ...
Interior Gateway Routing Protocol (IGRP) is a proprietary distance-vector routing protocol invented by Cisco, used by routers to exchange routing data within an autonomous system. ...
Some of the routing optimizations are based on the Diffusing Update Algorithm (DUAL) work from SRI, which guarantees loop-free operation. In particular, DUAL avoids the "count to infinity" behaviour of RIP when a destination becomes completely unreachable. The maximum hop count of EIGRP-routed packets is 224. DUAL stands for Diffusing Update Algorithm in full and it is the algorithm used to calculate and create routing tables based on certain criteria. ...
This article needs to be cleaned up to conform to a higher standard of quality. ...
This article is chiefly about the Routing Information Protocol for IPv4 and IPv6. ...
Basic operation
The data EIGRP collects is stored in three tables: - Neighbour Table: Stores data about the neighbouring routers, i.e. those directly accessible through directly connected interfaces.
- Topology Table: Confusingly named, this table does not store an overview of the complete network topology; rather, it effectively contains the aggregation of the routing tables gathered from all the neighbours. This table actually contains only those routes which are considered not to potentially be part of routing loops (part of the DUAL algorithm); in EIGRP terminology, they are considered "Feasible Successors".
- Routing table: Stores the actual routes to all destinations; routes may be marked either as "Passive", which is the normal state when the routing has stabilized, or "Active" when the topology has changed, and the router is in the process of updating its route to that destination.
A topology table is used by routers that are routing traffic in a network. ...
Multiple metrics EIGRP associates five different metrics with each route: - Delay
- Bandwidth
- Reliability
- Load
- MTU (though not actually used in the calculation)
For the purposes of comparing routes, these are combined together in a weighted formula to produce a single metric: - [(K1*Bandwidth) + ((K2*Bandwidth)/(256-Load)) + (K3*Delay)] * [(K5/(Reliability + K4))]
where the various constants (K1 through K5) can be set by the user to produce varying behaviours. If K5 is set to zero, the K4/K5 term is not used (i.e. taken as 1). The default is for K1 and K3 to be set to 1, and the rest to zero, effectively reducing the above formula to: - Bandwidth + Delay
Obviously, these constants must be set to the same value on all routers in an EIGRP system, or permanent routing loops will probably result.
EIGRP scales Bandwidth and Delay metrics with following calculations:
- Bandwidth for EIGRP = (10000000/Bandwidth)*256
- Delay for EIGRP = Delay/10*256
That calculations are done because EIGRP unlike IGRP uses 32-bit metric, not 24-bit as in IGRP. Interior Gateway Routing Protocol (IGRP) is a proprietary distance-vector routing protocol invented by Cisco, used by routers to exchange routing data within an autonomous system. ...
Other details EIGRP is able to deal with classless interdomain routing allowing the use of VLSM which is its main advantage over its predecessor. Its main disadvantage is that it runs only on Cisco equipment which may lead to an organization being locked in to this vendor. Classless Inter-Domain Routing (CIDR), introduced starting in 1993, is the latest refinement to the way IP addresses are interpreted. ...
Classless Inter-Domain Routing (CIDR), introduced starting in 1993, is the latest refinement to the way IP addresses are interpreted. ...
In economics, vendor lock-in, also known as proprietary lock-in, lock-in, or the Pottersville pattern, is a situation in which a customer is dependent on a vendor for products and services and cannot move to another vendor without substantial switching costs, real and/or perceived. ...
EIGRP can run separate routing processes for IP, IPX and AppleTalk. However, this does not facilitate translation between protocols. The Internet Protocol (IP) is a data-oriented protocol used for communicating data across a packet-switched internetwork. ...
Internetwork Packet Exchange (IPX) is at the Network layer of the OSI model and is part of the IPX/SPX protocol stack. ...
AppleTalk is a suite of protocols developed by Apple Computer for computer networking. ...
Further reading
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