EIGRP neighbors

Answered Question
Dec 12th, 2008
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Is it possible to configure eigrp neighbor list with neighbor's loopback interface?

Correct Answer by Giuseppe Larosa about 8 years 3 months ago

Hello Fuad,

the answer is no because to build EIGRP adjacency you need to use physical interfaces to communicate with somebody else and the two devices have to share a common IP subnet.

on a multilayer switch you could use an SVI ip address as neighbor but there is a L2 link between the two devices


even if you use overlapping ip addresses


r1

int loop1

ip address 10.10.1.1 255.255.255.0


r2

int loop 2

ip address 10.10.1.2 255.255.255.0


the two ip addresses cannot communicate for each router other router's ip address is out its loopback and this defeats a successful communication between them.


if you use /32 ip addresses then the hellos should go trough another L3 link but:

they have TTL 1


The only exception is if there is a physical link and the interface has ip unnumbered loop1 this could be used


Hope to help

Giuseppe


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Correct Answer
Giuseppe Larosa Fri, 12/12/2008 - 02:48
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Hello Fuad,

the answer is no because to build EIGRP adjacency you need to use physical interfaces to communicate with somebody else and the two devices have to share a common IP subnet.

on a multilayer switch you could use an SVI ip address as neighbor but there is a L2 link between the two devices


even if you use overlapping ip addresses


r1

int loop1

ip address 10.10.1.1 255.255.255.0


r2

int loop 2

ip address 10.10.1.2 255.255.255.0


the two ip addresses cannot communicate for each router other router's ip address is out its loopback and this defeats a successful communication between them.


if you use /32 ip addresses then the hellos should go trough another L3 link but:

they have TTL 1


The only exception is if there is a physical link and the interface has ip unnumbered loop1 this could be used


Hope to help

Giuseppe


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