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New Member

lots of collisions

i have a cisco 3560G that has a 3 com switch connected to one of the ports. it is causing a lot of collisions. what can i do to prevent this?

here is the the port config.

interface GigabitEthernet0/3

switchport access vlan 24

switchport mode access

Hall of Fame Super Silver

Re: lots of collisions

If one of the switches is reporting collisions then it must be operating in half duplex mode. If one device is operating in half duplex mode and the connected device is operating in full duplex mode, one of the symptoms frequently is collisions on the device in half duplex mode.

I suggest that you do show port or show inteface on both switches and check the setting of duplex and speed. The 3560G should be using auto to negotiate speed and duplex. I suspect that the negotiation is failing on speed or duuplex and that the 3560G is operating in half duplex. If you do find a duplex mismatch and correct it then the issue with collisions should be resolved.



New Member

Re: lots of collisions

the only problem is i do not have access to get into the other switch (no password), my cisco switch is on AUTO like you said.

Thanks for ur help

Re: lots of collisions

If you do a 'show interface status' it will show you what it negotiated at. Here's an example.

Fa0/27 connected 11 a-full a-100 10/100BaseTX

Fa0/28 notconnect 11 auto auto 10/100BaseTX

Fa0/29 notconnect 12 auto auto 10/100BaseTX

Fa0/30 connected 11 a-half a-10 10/100BaseTX

Since you are receiving collisions, you could try changing the duplex. It would be best to get into the 3COM and hard set it too, but of can't this might be a temorary workaround.

Hall of Fame Super Silver

Re: lots of collisions


If you have access to your switch but not to the other switch it becomes more complicated to troubleshoot but not impossible. I would suggest that you post the output of show interface for the interface that connects to the other switch. I suspect that it will show that it is operating in half duplex mode. Half duplex is the resulting mode when the switch attempts to negotiate duplex but can not successfully negotiate duplex and I suspect that this is the case. I would probably suggest that if you can not get someone to access the other switch and check its interface that you hard code duplex full on your switch and see what happens.



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