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New Member

L2 connectivity issue

Hi Guys,

I have the following topology:


             Cisco ASR1 _ _ _ _ _ _ _ _ _ _ _ _ X Device that support L2 connectivity_ ___ _ (Internal Network for X Device)


             Cisco ASR2


So basically we have:

1)  2 Cisco ASRs with L2 Trunk between them for HSRP keepalives connectivity.. 

2) ASR1 is connected to X device with multiple trunks each trunk running specific Vlans (vlans are not duplicated over different trunks)

3) no connectivity between ASR2 and X Device. However, the Vlans are replicated between ASR1 and ASR2

4) if the link between ASR1 and X device goes down the link will be changed manually to ASR2.

5) no spanning tree is running on the ASRs 


Now behind X device there is an internal network, we had a case where this internal network has :L2 loops (spanning tree) where the X device was looping with some device in its internal network. 

This scenario affected ASR1 and brought the whole link between X device and ASR1 down and the whole router just hanged, and it also affected ASR2.


What is the explanation for this scenario since even though spanning tree is not enabled on the ASRs, there is no way to create loops, since ASR1 is connected to X device with multiple trunks each trunk use unique vlans, also there is no connectivity between ASR2 and X device.


is it possible for the loop created between the X device and its internal network to bring down the ASRs since the vlans are configured on them ? if so, how such scenario can be prevented ?



New Member

appreciate any thoughts on

appreciate any thoughts on this issue

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