EIGRP Summary

EIGRP is similar to IGRP only in the sense that it uses the same metrics;

Delay
Bandwidth
Reliability
Load

passive-interface default to block all EIGRP adjacencies

no passive-interface default
!
router eigrp 80
passive-interface interface fastethernet 0/1 – no hello send but still advertise network.
passive-interface default – turns on passive-interface globally on all interfaces.
no passive-interface seial 0/1 – turns off passive-interface on these interfaces.
!
summary 172.16.0.0/16 to 172.16.7.255.
int serial 0/1
ip summary-address eigrp 90 172.16.0.0 255.255.248.0

Use specific wildcard mask
router eigrp 80
network 10.1.2.2 0.0.0.0 (host address only)

no auto-summary – Disables Auto Subnet Summarization.

default route pointing to 192.168.1.0/24
router eigrp 80
network 192.168.1.0
exit
ip default-network 192.168.1.0

in show ip route
will see “s* static route.

Unequal load cost balancing.
eigrp by default uses equal load cost balancing a variance of 1 meaning it will load balance
over 1 equal cost link of the same bandwidth.

configuring variance of 2 will load balance across 2 links as bad as the primary.

router eigrp 80
variance 2

you will see in routing-table 2 routes being used over 2 unequal cost bandwidth links

Frame Relay – locally significant
EIGRP Uses 224.0.0.10 mulicast

EIGRP packet delivery is handled using Reliable Transport Protocol (RTP).
EIGRP uses IP protocol number 88.

EIGRP uses the Neighbor Table to list adjacent routers.
Topology Table lists all the learned routes to a destination.
Routing Table contains the best route to a destination, which is known as the Successor.
The Feasible Successor is a backup route to a destination which is kept in the Topology Table.

Broadcast on router by default are denied.
EIGRP came up with “PSEUDO-BROADCASTS” or Manual Neighbors.

int s0/0
ip address 172.16.124.1 255.255.255.248 multipoint
frame-relay map ip 172.16.124.2 102 broadcast
frame-relay map ip 172.16.124.3 103 broadcast
!
show frame-relay map

Multipoint = everyone is on 1 subnet.
Point-to-Point = everyone is on its own subnet.

Advantage is multipoint it saves ip addresses.

Eigrp manual neighbors disables multicast and uses unicast.

router eigrp 25
neighbors 172.16.124.102
neighbors 172.16.124.103

In frame-relay networks :
Split Horizon is disabled on Physical Interfaces
Split Horizon is enabled on Sub-interfaces
!
Enable split horizon on a sub-interface :
This will allow routing updates to leave interface rather than just receive them :

On a multipoint set-up split-horizon will need to be disabled : Spoke and Hub Topology.

int s0/0.1
no ip split-horizon eigrp 25
!

Supports variable length subnet masks (VLSM).
Automatic Route Summarization.
3 Networks Summarization :

HQ
10.1.1.0/24
10.1.2.0/24
10.1.3.0/24
!
EAST
10.2.1.0/24
10.2.2.0/24
10.2.3.0/24
!
WEST
10.3.1.0/24
10.3.2.0/24
10.3.3.0/24
!
Summary Addresses :
in interface mode :

On HQ
ip summary-address eigrp 25 10.1.0.0 255.255.252.0/
!
On EAST
ip summary-address eigrp 25 10.2.0.0 255.255.252.0
!
On WEST
ip summary-address eigrp 25 10.3.0.0 255.255.252.0

Configure HQ router to utilise up to 30% more of the allocated interface bandwidth
than eigrp’s default configuration.

EIGRP’s default limits of 50% bandwith of the link bandwidth configured .

e.g
interface bandwidth configured :

int s0/0
bandwith 200
!
HQ router has 2 neighbors peering.

ip bandwidth-percent eigrp 25 80
equal 30% more bandwidth given.

Optionally, you can configure the amount of WAN link bandwidth that an
EIGRP router will use with this command:

Router(config-if)# ip bandwidth-percent eigrp XX

Once EIGRP is configured, you can check the status using the show ip route and
show ip eigrp commands.

!

R1(config)#router eigrp 100
R1(config-router)#eigrp stub ?
!
connected Do advertise connected routes
receive-only Set IP-EIGRP as receive only neighbor
static Do advertise static routes
summary Do advertise summary routes

They will then advertise their directly connected networks and summary
routes back to the hub and will receive only a default route back from the hub.

If R5 loses a successor and has no feasible successor, it will not send a
DUAL query packet to any of the stub routers, since it knows they are indeed
stub routers and cannot possibly have or acquire a replacement for the lost
successor route.

Logging EIGRP Neighbor State Changes

You want to log EIGRP neighbor state changes.

Solution

To enable the logging of EIGRP neighbor state changes, use the  eigrp log-neighbor-changes
configuration command:

Router1#configure terminal 
Enter configuration commands, one per line.  End with CNTL/Z.
Router1(config)#router eigrp 55
Router1(config-router)#eigrp log-neighbor-changes
Router1(config-router)#exit
Router1(config)#end
Router1#

Another closely related feature is the eigrp log-neighbor-warnings configuration command:

Router1#configure terminal 
Enter configuration commands, one per line.  End with CNTL/Z.
Router1(config)#router eigrp 55
Router1(config-router)#eigrp log-neighbor-warnings 300
Router1(config-router)#exit
Router1(config)#end
Router1#

When a neighbor relationship is lost, you also lose all of the routing entries for that neighbor.
And the effects of this lost routing information are often felt throughout the network. Therefore,
it can be extremely useful to have a good log of neighbor change events for troubleshooting strange
intermittent network problems.
However, this feature also gives you a good way of looking for faults on links that don’t have a way of
telling you about loss of connectivity. This command is enabled by default.

Troubleshooting EIGRP And Disabling Split Horizon

EIGRP has been correctly configured on each interface, 
but something odd occurs when we check the EIGRP tables - neither of the
spoke routers can see the other spoke router's loopback network.
!
Because EIGRP runs split horizon by default, R1 cannot send a
route advertisement out the same interface the advertisement was
received upon to begin with.

R1 is learning about R2's loopback and R3's loopback on Serial0,
so R1 cannot advertise those routes right back out the same interface.
We've got two choices - we can set up subinterfaces on R1 or we can
disable split horizon on R1's Serial0 interface

Let's disable SH with EIGRP, since the command is a little different than
what you may have seen in your studies.
!
R1(config)#int serial0
R1(config-if)#no ip split-horizon eigrp 100

Passive-Interface

The passive interface feature is used to make a routing protocol accept
routing information from neighbors, but prevent information from being
advertised to neighbors.

EIGRP discovers neighbors using hello messages before accepting routes and
installing them in the routing table. Hello messages are normally sent and
received on an interface configured for EIGRP.

However, the passive interface feature in EIGRP makes an interface stop sending
and receiving hello messages. This tears down any existing neighbor relationships
and stops learning routes from any EIGRP neighbors available on the interface and
configured as passive.

To enable Passive interface globally on all interfaces :
config t
router eigrp 10
passive-interface default 
then you will disable passive-interface on specified neighbor interfaces :


config t
router eigrp 10
no passive-interface loopback 0



To verify rather or not an interface is in passive-mode you can use :  
show ip protocols. 
Best Practices is to enable "Passive-Interface Default" on all interfaces
and to disable run the "no passive-interface fa0/0" on individual interfaces
to allow hello messages to communicate between neighbors to advertise their
networks.