EIGRP

EIRGP Protocol (Enhanced Interior Gateway Routing Protocol)

·         Its advance distance vector & Cisco Proprietary protocol.

·         Its working like Link state Routing Protocol & Distance Vector Routing Protocol.

·         Fast convergence, 100% loop free & Classless routing protocol.

·         Reduced bandwidth usage. EIGRP does not send periodic updates as with Distance Vector Routing protocols. Additionally, the update is propagated only to routers that require it, instead of all routers within an area as with LS routing protocols. 

·         EIGRP works on network layer Protocol of osi model and uses the protocol number 88.

·         EIGRP does not require special configuration across any L2 protocols. EIGRP was designed to operate effectively in both LAN and WAN environments. EIGRP supports all multi-access networks, eg: Ethernet, Token Ring, FDDI, and all WAN topologies – leased lines, point-to-point links, and non-broadcast multi-access (NBMA) topologies, eg: X.25, SMDS, ATM, and Frame Relay.

·         EIGRP uses Diffusing Update Algorithm (DUAL) to find out the best path available to a network.

      EIGRP speaking routers maintains a topology table in which all the routes to the network are maintained. If the best path (successor) goes down, then second best path (feasible successor) is used from the topology table. If there is no path available in topology table then it sends a query message to resolve the query.

·         EIGRP maintains a neighbor table, a topology table, and a routing table for each running routed protocols.

·         Neighbor table: It contains information about the routers with which neighbourship has been formed. It also contains queue count value for the hello messages that are not being acknowledged.

·         Topology table: It contains all the routes available to a network (both feasible successor and successor).

·         Routing table: It contains all the routes which are being used to make current routing decisions. The routes in this table are considered as successor (best path) route.

·         Support Variable Length Subnet Mask (VLSM), IPv4 and IPv6.

·         EIGRP has 3 AD value-

·         1^st priority given to AD-5 use in within summary EIGRP

·         2^nd  priority given to AD-90 use in Internal EIGRP

·         3^rd  priority given to AD-170 use in External EIGRP

·         EIGRP uses below mentioned metrics to determine the best route to a destination.

·         Bandwidth (K1) – Slowest link in the route path, measured in Kbps. Value K1=1

·         Load (K2) – Cumulative load of all outgoing interfaces in the path, given as a fraction of 255. Value K2=0

·         Delay of the Line (K3) – Cumulative delay of all outgoing interfaces in the path in tens of microseconds. Value K3=1

·         Reliability (K4) – Average reliability of all outgoing interfaces in the path, given as a fraction of 255. Value K4=0

·         MTU (K5) – The smallest Maximum Transmission Unit in the path. The MTU value is actually never used to calculate the metric. Value K5=0

·         EIGRP metric is called Composite metric, EIGRP metric = [Bandwidth + Delay]*256

·         Unequal metric value can do load-balancing.

·         EIGRP scalability is 100 Hops by default, but it can be go upto 255.

·         EIGRP will form neighbor relationships with adjacent routers in the same Autonomous System (AS).

·         EIGRP traffic is either sent as unicasts, or as multicasts on address 224.0.0.10, depending on the EIGRP packet type.

·         Reliable Transport Protocol (RTP) is used to ensure delivery of most EIGRP packets.