EIGRP Flapping through Subinterface

[Jason Wong]

Dear All Guy,

I get some EIGRP flapping on my CE router (c2921) 2 subinterface to another two site. The router IOS version "c2900-universalk9-mz.SPA.152-2.T1". I capture the debug log as attached. I know understand some log meaning from the debug, Can anybody help to explain the log detail who flapping will happen. Thank you so much.

[Dan-Ciprian Cicioiu]

Hi Jason,

Your phisical interface is flapping :

9 00:37:37.787: %LINK-3-UPDOWN: Interface GigabitEthernet0/1, changed state to down

00:37:39.787: %LINK-3-UPDOWN: Interface GigabitEthernet0/1, changed state to up

00:40:18.785: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/1, changed state to down

Dan

[Jason Wong]

Thank Dan,

But do you understand the EIGRP log, why flapping will happen?

[Giuseppe Larosa · Accepted solution]

Hello Jason,

as Dan has noted the link is not stable at OSI layer2 and layer1 as a result of this EIGRP flaps.

You need to fix the problems at physical layer and then also EIGRP will be stable

What is connected to gi0/1 of the device with IP 10.7.10.5 ?

show interface gi0/1

is your starting point

Hope to help

Giuseppe