i wrote the line and that is the answer

still i dont know whats the device

#show cdp n fastEthernet 0/1
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
BDCHSS10         Fas 0/1            126        R S I      WS-C3750-4Fas 1/0/19
London-TT#
*Mar  2 13:49:09.151: %CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on Fast
Ethernet0/1 (not half duplex), with BDCHSS10 FastEthernet1/0/19 (half duplex).

Golan,

You need the keyword detail on the end of that command: show cdp n Fa0/1 detail.

That way it will give you a lot more information, including the IP address of the 3750 switch.

You could probably get rid of the error by forcing your side of the link to be half-duplex, but that would not be the best solution.

It is also possible that you have tried to hard-code full duplex, but the other side is in auto.  If that is the case, then making your side auto would not only get rid of the error message, but would also make the link full duplex.

Kevin Dorrell

Luxembourg

thank you vety much