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what can block ARP?


We recently updated a site2site link to metro ethernet, ISP call it 100mbps LAN Extension, but to me it is just QinQ over fibre connection. Most went well, one thing (annoying to me) is we can not ping our switches on both ends anymore.

We have a 3750 in headend and another 2960 on the other end. I used to be able to ping/telnet to the management IP from one to the other. Now we can not. I think the ISP is applying some configuration on ports of their customer-premises equipments (both are Cisco switches) but agent in ISP told me no.

I thought there is some configuration on Cisco switch to block "MAC discovery" but i just can not remmenber what was that and google also failed me this time. So please let me know if you know what could be the possible configuration.


3 Replies 3

Hieu Cao
Level 4
Level 4

Thanks, VACL is a possible way however I asked that agent and he told me they do not filter traffic on that fibre link...So that makes me think about some interface configure.

Cisco Employee
Cisco Employee

As you mentioned ISP is perform QinQ, at times the following can also cause troubles:

Incorrect traffic switching can happen around the improper Native VLAN setup, however I would expect you to see more troubles than seen.

The following discussion outlines possible ways to block MAC's:

I can't think of any other way. Certainly ISP should perform more troubleshooting in their network to identify the cause behind this issue. To prove the same to them, you can perform SPAN of the edge ports at either ends for your switches facing ISP.

Best Regards,


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