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Show cdp neighbor displays loopback addresses for 3 of several 6500s

Sup720 running 12.2((17d)SXB8

We had a 6500 that experienced a partial failure. Every 6500 connected to this box with interfaces configured for UDLD placed their interfaces into err disabled state. This 6500 attempted to write a crash info file and also attempted to reboot. When we telneted into the devices that went error disabled and issued a no shut everything came back up. There were still a few problems occuring so the box that attempted to write the crash info file was rebooted. After doing a little poking around it was noticed the show cdp neig detail had 3 6500s that were reporting an IP address of,, etc... We know these are loopback addresses that point to slots however, I've never seen this being reported via CDP. Two of these switches are connected via 10gig links with no configuration yet. The other 6500 is connected via a gig port and is setup as a switchport. Has anyone seen the loopback addresses reported via CDP?


Re: Show cdp neighbor displays loopback addresses for 3 of sever

If you have an access port on a VLAN that does not have a corresponding L3 VLAN interface and IP

address, the switch advertises an internal loopback number as its address in CDP.I think that what you're seeing is normal behaviour. the workaround would be to configure a L3 interface for every VLAN coming to the box so that CDP will not use the internal address to advertise.

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