I have an 2960 switch connected to 3Com Hub, I don't know why the switch continuous to prompt
me duplex mismatch
Switch#sh run int FastEthernet0/5
Switch#sh int fastEthernet 0/5
FastEthernet0/5 is up, line protocol is up (connected)
Hardware is Fast Ethernet, address is 001a.6d95.4505 (bia 001a.6d95.4505)
MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Half-duplex, 100Mb/s, media type is 10/100BaseTX
input flow-control is off, output flow-control is unsupported
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:00, output 00:00:00, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 20000 bits/sec, 16 packets/sec
5 minute output rate 1000 bits/sec, 3 packets/sec
103093 packets input, 14393135 bytes, 0 no buffer
Received 93264 broadcasts (0 multicast)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 57009 multicast, 0 pause input
0 input packets with dribble condition detected
19782 packets output, 1315325 bytes, 0 underruns
0 output errors, 82 collisions, 1 interface resets
0 babbles, 0 late collision, 0 deferred
0 lost carrier, 0 no carrier, 0 PAUSE output
01:56:28: %CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on FastEthernet0/5 (not full duplex), with 069070588 6/18 (
01:57:28: %CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on FastEthernet0/5 (not full duplex), with 069070588 6/18 (
The message that you see comes from the Cisco Discovery Protocol. CDP contains info about speed/duplex settings of the sending interface. The basic issue is that the 3Com does not understand CDP. However, CDP packets from other IOS devices on the 3Com switch are forwarded (CDP uses multicast) and the receiving switch cannot determine wheter the message comes from a directly attached device or not.
So, in fact this message is probably false.
Normally I turn off cdp on the interfaces that are connected to non-Cisco switches. You should of course verify that the actual speed/duplex settings are correct.
It depends on what the 3com port was set to. By the sounds of it it was set to 100 full. So when you tried 100 half duplex you got a mismatch.
Setting it to auto also didn't work because the other end wasn't set to auto.