[c-nsp] CDP -- more than one neighbor on the same port?

Furnish, Trever G TGFurnish at herffjones.com
Wed Dec 12 13:58:07 EST 2007


Under what circumstances would CDP show more than one neighbor on the
same port?

We have a site where the local IT staff is claiming that a switch
interface (switch2 g0/2) is connected directly to exactly one other
cisco switch, but 'show cdp nei' on switch 2 shows three other switches
as neighbors on that interface.

LewSw2#show cdp nei g0/2
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
                  S - Switch, H - Host, I - IGMP, r - Repeater

Device ID        Local Intrfce     Holdtme    Capability  Platform  Port
ID
LewSw8.hj-int    Gig 0/2            145         T S       WS-C3508G-Gig
0/8
LewSw1.hj-int    Gig 0/2            126         T S       WS-C3548-XGig
0/1
LewSw12          Gig 0/2            156         S I       WS-C3550-1Gig
0/11

Am I correct in assuming that this should only happen if the g0/2 port
is connected to a hub?

I realize CDP's not supposed to traverse switches, although I'm not
quite sure *why*.  The destination's always 01000ccccccc, but I'm not
quite clear why such a frame wouldn't be flooded by a non-cdp-aware
switch.

--
Trever Furnish, tgfurnish at herffjones.com



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