EIGRP

I ) EIGRP Features

1. Fast convergence –It is using DUAL (Diffusing update algorithm). Router running Eigrp stores backup route (feasible successor).
2. Minimum Bandwidth usage- It does not make periodic updates (NON PERIODIC). It partial updates when the topology changes and Bounded.
3. Multiple Network layer protocol support- It supports IPX/SPX, Apple talk.
4. It supports VLSM, classless routing.
5. It supports load balancing of equal and unequal cost paths (up to 6 paths. Default is 4)
6. Use multicast (224.0.0.10) instead of broadcast
7. Summarization can do any router running in EIGRP. But in OSPF only in ABR and ASBR.
8. Combines best of distance vector and link state
9. hello packets from any EIGRP - 5 sec, hold-on time is 3 times to hello
10. Hello Packet on NBMA is - 60 sec and hold-on time is 3 times (180 sec)

II) Advertisement distance :
Cost between next hop router and destination router.
Feasible Distance : Cost between next hop router and destination router (AD) + Cost between local router and next hop router. Lowest FD is the best path (successor).
Successor: Best route stored in routing table and Topology table.
Feasible successor: Backup route stored in Topology table
To be considered A feasible successor, the AD must be less than the FD of the successor. Because of prevent the loop.
Passive Route: Passive state is a state when the router has identified the successor(s) for the destination.
Active Route: Active state when current successor no longer satisfies the Feasibility Condition.

Neighbor Table: List of directly connected routers.
Topology Table: List of routers learned from each neighbor.
Routing Table: List of best routes.
Neighbor table update the routing information in Topology table and routing table is created taking the best paths form the topology table

EIGRP Pockets:

Hello- Establish neighbor relationships ( multicast)
Update- send routing updates
Query-Ask neighbors about routing information.
Reply- Respond to query
Ack- Acknowledge all reliable pocket except Hello pocket.

No auto-summary command prevents to advertisement all interfaces in the router. Also it turns on Classless characteristics of EIGRP.

Metric: Bandwidth, Delay, Reliability ,Loading, MTU
Real (default) Metric : 256* (BW+Delay)
BW= 10^7/BW
Delay= Delay in Micro seconds.
If want to change the other metrics manually use this command
This command is not in Cisco website; Very rarely known and used.
#router eigrp 10
#metric weights (tos) k1 k2 k3 k4 k5
Tos- Type of service. It always 0.

Trouble shooting commands:
Show IP EIGRP topology, Show IP EIGRP neighbor, Show IP EIGRP traffic

Summarization:
#IP summary-address EIGRP 1 172.16.0.0 255.255.255.248

Unequal cost load balancing:

#Variance 2 (2 is multiplier)
#Variance 1 ( equal cost load balancing)

Stuck in Active:
A router sends query message for identify the backup route to other routers through its active interfaces. The router will wait for 3minits to get reply messages from all routers even though it gets a backup route from any of one routers.
Methods to Prevent STA : 1) Summary route 2) Stub configuration

NewYork#sh ip eigrp neighbor

IP-EIGRP neighbors for process 10
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
1 172.16.251.2 Se0/1 10 00:17:08 28 2604 0 7
0 172.16.250.2 Se0/0 13 00:24:43 12 2604 0 14.

Router# show ip eigrp topology
IP-EIGRP Topology Table for process 77
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply, r - Reply status
P 172.16.90.0 255.255.255.0, 2 successors, FD is 0
via 172.16.80.28 (46251776/46226176), Ethernet0
via 172.16.81.28 (46251776/46226176), Ethernet1
via 172.16.80.31 (46277376/46251776), Serial0
P 172.16.81.0 255.255.255.0, 1 successors, FD is 307200
via Connected, Ethernet1
via 172.16.81.28 (307200/281600), Ethernet1
via 172.16.80.28 (307200/281600), Ethernet0
via 172.16.80.31 (332800/307200), Serial0

ROUTING

COMMON

Default Administrative distance :
Connected Interface – 0
Static Route - 1
External BGP -20
Internal EIGRP -90
IGRP – 100
OSPF-110
IS-IS- 115
RIP V1, V2-120
External EIGRP-170
IBGP-200
Unknown-255
Distance vector Protocol:
It finds best path by using distance i.e Hops. Ex: RIP, IGRP
Link State Protocol:
Using 3 tables finds best path (Neighbor Table, Topology Table, and Routing Table).( OSPF,IS-IS).
Link state protocols using Area architecture.
The link state Protocol advertise its all routes to neighbor, even though the neighbors not using those routes.
Hybrid Protocol:
Mixing of Distance vector and Link state. (EIGRP).
EIGRP advertise only the best route about its neighbors, to its neighbor. So that only EIGRP is not coming under Link state routing protocol.
ROUTING Preference
1. Specific subnet Mask
2. Administrative difference
3. Metric