EIGRP Flapping - Secondary Scope

[s.kanth]

Hi All,

I see these error messages on CR1 router
--------
Mar 13 01:05:28: %DUAL-5-NBRCHANGE: EIGRP-IPv4 1: Neighbor 10.1.1.2 (GigabitEthernet0/0.1) is down: retry limit exceeded
-----

COnfiguration:
--------------
on my CR1 router

int gi0/0.1
encapsulation dot1Q 1 native
ip address 10.56.52.12 255.255.255.192
ip address 10.1.1.4 255.255.255.0 secondary

on CR2 router

int gi0/0.1
encapsulation dot1Q 1 native
ip address 10.1.1.2 255.255.255.0

10.1.1.*/24 IP address configured on CR1 as secondary scope. is it causing the issue (EIGRP flaping continuously) ?

Thanks in Advance

Sri

[acampbell · Accepted solution]

Hi,

Looking at this link

http://www.cisco.com/en/US/tech/tk365/technologies_q_and_a_item09186a008012dac4.shtml#three

Q. Does EIGRP support secondary addresses?

A. EIGRP does support secondary addresses. Since EIGRP always sources data packets from the primary address, Cisco recommends that you configure all routers on a particular subnet with primary addresses that belong to the same subnet. Routers do not form EIGRP neighbors over secondary networks. Therefore, if all of the primary IP addresses of routers do not agree, problems can arise with neighbor adjacencies.

So router CR1 CANNOT form an adjacency using its secondary address

Regards,
Alex.
Please rate useful posts.

[s.kanth]

Thanks Alex,

One more doubt.. then why neighbour is forming and teared off again and again? (or is it expected behaviour ?)

--------------

Mar 13 01:45:12: %DUAL-5-NBRCHANGE: EIGRP-IPv4 1: Neighbor 10.1.1.2 (GigabitEthernet0/0.1) is down: retry limit exceeded

Mar 13 01:45:15: %DUAL-5-NBRCHANGE: EIGRP-IPv4 1: Neighbor 10.1.1.2 (GigabitEthernet0/0.1) is up: new adjacency

Mar 13 01:46:35: %DUAL-5-NBRCHANGE: EIGRP-IPv4 1: Neighbor 10.1.1.2 (GigabitEthernet0/0.1) is down: retry limit exceeded

Mar 13 01:46:39: %DUAL-5-NBRCHANGE: EIGRP-IPv4 1: Neighbor 10.1.1.2 (GigabitEthernet0/0.1) is up: new adjacency

[acampbell]

Hi,

CR2 - Sends EIGRP HELLO to 224.0.0.10 Multicast ( Every 5 secs)

CR1 - Hears this packet and responds with the IP address from
its primary IP address

CR2 - Hears this respons BUT the Ip address from CR1 is not
in the correct Ip subnet

This process will keep repating till 16 attempts have
been tried

At this time CR2 will alert
with
Mar 13 01:46:35: %DUAL-5-NBRCHANGE: EIGRP-IPv4 1: Neighbor 10.1.1.2 (GigabitEthernet0/0.1) is down: retry limit exceeded

Then the whole process starts again until you resolve the
fact that EIGRP neighbours CANNOT form on
IP secondary addresses.

Hope this helps

Regards,
Alex.
Please rate useful posts.

[Julio Carvajal]

Hello Alex,

I do understand the retry limit exceeded but why is the router showing this:

Mar 13 01:46:39: %DUAL-5-NBRCHANGE: EIGRP-IPv4 1: Neighbor 10.1.1.2 (GigabitEthernet0/0.1) is up: new adjacency

For me the router should see that the neighbor is on a different subnet that him and never say up.

I was wondering if you could clarify that to me,

Regards,

Julio Carvajal