Is there anyway to detect if the two ends of an 802.1q trunk have the same allowed VLAN list ? Does CDP doe anything here ? What will a switch report if it receives a packet that is tagged with a VLAN id that is not on it's allowed list from its partner on the other end of the trunk ? I am assuming here that evrything else about the trunk is OK so native VLANs match etc.
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I am afraid there is no such feature to inform you that the neighbor's allowed VLAN list is different from yours. CDP does not carry this information. No logging messages will be logged for frames arriving in unallowed VLANs. You could see side effects from this mismatch (such as inappropriate STP port roles) but nothing conclusive.
It is best to verify that setting manually from both sides of a trunk if possible
That was my thinking. A large customer asked me if it was possible to get an automaitic indication of such a misconfiguration, I thought not but said I would check.
Thank you !! I just checked the CiscoWorks diocumentation and this does indeed get reported as a "Trunk Logical Discrepency". Perfect.