EIGRP is a Cisco proprietary protocol which means it will work only on Cisco routers.
EIGRP is also called advanced distance vector or Hybrid routing protocol.
Multicast or unicast is used for exchange of information.
Multiple network layer protocols are supported.
By default,EIGRP will limit itself to use no more than 50% of the interface bandwidth
Maximum Hop-Count is 255[ 100 by default]
EIGRP is classless protocol
EIGRP supports VLSM and authentication
EIGRP uses Diffusing Update Algorithm (DUAL) to determine the best path among all “feasible” paths. DUAL also helps ensure a loop-free routing environment.
EIGRP will form neighbor relationships with adjacent routers in the same Autonomous System (AS)
EIGRP uses RTP (Reliable Transport Protocol) and its function is to deliver EIGRP packets between neighbors in a reliable and ordered way.
All EIGRP routing information are exchanged between neighbors via multicast using the address 220.127.116.11
EIGRP routers do not send periodic, full-table routing updates. Updates are sent when a change occurs, and include only the change
K-Values are used for calculating metric. By default EIGRP consider k1 and k3 only
EIGRP having internal Administrative distance as 90 and external AD as 170
EIGRP summary route AD value is 5
In EIGRP Summarization is enabled by default.”No auto-summary” command is needed because by default EIGRP will behave like a classfull routing protocol which means it won’t advertise the subnet mask along the routing information. For example 18.104.22.168/24 and 22.214.171.124/24 will be advertised as 126.96.36.199/8 and 188.8.131.52/8. Disabling auto-summary will ensure EIGRP sends the subnet mask along.
EIGRP converges rapidly after link failure
EIGRP can load balance on both equal and unequal cost paths.”Variance”command is used to configure load balancing
EIGRP supports up to 6 loop-free paths with a metric lowers than the product of variance and the best metric
Manual summarization can be enabled at any interface
If a packet is not acknowledged,EIGRP re transmit the packet to the non responding neighbor as a unicast.No other traffic is sent to this neighbor until it responds.After 16 unacknowledged re-transmissions,the neighbor is removed from the neighbor table
The process of neighbor discovery and route exchange between two EIGRP router is as follows
Router A sends out a hello
Router B sends back a hello and an update.The update contains routing information
Router A acknowledges the update
Router A sends its update
Router B acknowledges
A neighbor is considered as lost if no hello is relieved within 3 hello periods