Why use EIGRP

1) only routing protocol that uses Backup Routes (Fast Convergence and uses Dual Algorithm)
2) Simple Configuration
3) Flexibility and Summarisation
4) Unequal cost load balancing (unequal links and accurately balance bandwidth)
Hybrid/Advanced Distance Vector (Distance vector and Link-state)
6) Supports Multiple network Protocols
Support for VLSM

8) Support for all layer 2 (data link layer) protocols and topologies

9) Support for authentication

EIGRP Maintains three tables
– Neighbour Table (who are my neighbours)
– Topology Table (what do my neighbours know? Successor/FS)
– Routing Table (put best route here)

EIGRP Tables
– the AD and FD describes how far a route is:
–Feasible Distance (FD)
–Advertised Distance (AD)

The AD must be less than the FD of the successor to be considered a Feasible Successor (loop prevention mechanism)

Primary path

-Feasible Successor
backup path

-Active Route
Bad: Actively trying to find a path

-Passive Route
Good: traffic passing fine

Debugging Messages:
Hello: Forms relationship
Update: Sends Partial Updates
Query: asks for routes
Reply: Response to a Query
ACK: Acknowledges the update, Query and Reply
-After 16 unacknowledged retransmissions the neighbour is removed from the neighbour table

EIGRP debugs

Debug ip eigrp packets – debug’s all eigrp packets
Debug ip eigrp packets query reply –debugs query and reply packets
Debug ip eigrp –to see the update process
Debug ip eigrp neighbors –to see the neighbour table

Metric Calculation:

Metric: How good is that route (best path)

Sh int s0 (will show Bandwidth and Delay)
RTR#sh int fa0/0
FastEthernet0/0 is up, line protocol is up
Description: LAN
MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
reliability 255/255, txload 1/255, rxload 1/255


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