EIGRP Tutorial

EIGRP Tutorial

Certiology’s free EIGRP tutorial and notes. Learn EIGRP ( Enhanced Interior Gateway Routing Protocol) for free.

EIGRP: Enhanced Interior Gateway Routing Protocol is a Cisco proprietary routing protocol. It is a Hybrid protocol as it uses features of Link state and Distance Vector also called an advanced Distance Vector routing protocol.

EIGRP has some features like:

–         Faster convergence

–         VLSM is supported in EIGRP

–         The Multicast address used

–         Authentication Support using MD5

–         Makes use of Reliable Transport protocol for reliable delivery

–         Hello Packets are sent and received to maintain neighbor relationship

–         Uses composite metric ( Bandwidth and Delay are default)

–         The max hop counted supported is 224 and the default is 100

Concept of Successor / Feasible Successor

EIGRP use the concept of Success and Feasible Successor, the best path to a destination is known as Successor and this is copied from Topology table to routing table.

Feasible Successor is the second best path or secondary path to a destination. 

EIGRP (Enhanced Interior Gateway Routing Protocol)

Description : EIGRP (Enhanced Interior gateway Routing Protocol) is Hybrid Dynamic Routing Protocol , it is most powerful routing protocol. EIGRP was Cisco proprietary now before one year it has become open standard means now available on all the routers. EIGRP uses the best features of both Distance Vector & Link state Routing Protocol That’s why it is called Hybrid Dynamic Routing protocol.

Notes :

    • EIGRP is Hybrid Dynamic Routing Protocol
      EIGRP uses the best features of both Distance Vector & Link state Routing Protocol That’s why it is called Hybrid Dynamic Routing protocol.
    • Event Trigger
      EIGRP does not send the routing table updates periodically to other routers like Distance Vector routing protocol, but it send the routing table updates when some changes occur in network, that ’s why it is Event Trigger.

    • Second Hand Update
      EIGRP uses second hand update as Distance Vector Routing Protocol.
    • Maximum Hop Count 255 Default 100
      EIGRP has maximum hop count 255 , it can pass the routing update to max. 255 routers in the network. We can set the Hop count by default it’s value is 100 respectively.
    • Administrative Distance is 90
      The Term Administrative Distance (AD) indicates the reliability of routing protocol , more the AD of Routing protocol less the reliability . EIGRP has AD 90 & it is more efficient & reliable routing protocol . The AD (Administrative Distance) value ranges from 0-255.
    • It was CISCO Proprietary before , now it’s open standard
      The EIGRP was CISCO proprietary (as it was developed by CISCO) before, it was only available on CISCO routers i.e., You can only configure this protocol on CISCO routers but Before 1 year CISCO has stated it Open Standard.
    • Support VLSM (Variable Length Subnet Mask)
      EIGRP support VLSM(Variable Length Subnet Mask) What does it mean? It means that EIGRP send the subnet mask information along with IP Address.
    • Multicast every 10 Sec & Dead Time is 40 Sec
      EIGRP is event trigger protocol. It Does not Broadcast (one to all) the update like RIP but it multicast (one to specific). It does not send Whole routing table update periodically but it send “HELLO” packets to neighbor router saying them that he is alive (Interface is up). The Dead Time of EIGRP is 40 sec, when some interface in the network has gone down it will wait until 40 sec after this the route in the routing table will be flushed. So the EIGRP is very fast than other protocols.
    • Metric COST
      EIGRP uses COST as metric . It finds the feasibility of protocol by COST (bandwidth & Hop).
    • Structure
      EIGRP has Hierarchical Structure using AS (Autonomous System).It has Topology Table & Neighbor Table along with the Routing Table.
    • Some Basic Commands
      EIGRP commands Are as follow
    • Router eigrp AS
    • Show ip route
    • Show ip protocol
    • Show ip eigrp topology
    •  Show ip eigrp neighbor