C4500 Trunk encap

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Dec 3rd, 2008
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I have a same IOS on Cisco4500 (cat4500-ENTSERVICESK9-M), Version 12.2(46)SG, RELEASE SOFTWARE (fc1)

MPC8245 CPU at 333Mhz, Supervisor 6 E

I am trying to configure:

switchport trunk encap

but looks lits its not supported on the device or the IOS.

Is thier a correct IOS which support the trunk encaplusation.

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Mark Yeates Wed, 12/03/2008 - 07:57
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In many cases especially with newer linecards they only support dot1q trunking. This means that the "switchport trunk encap" command is no longer used. the switchport mode trunk" command is all that is needed. You can verify this by issuing the "show int trunk" command.



patel.nishit Wed, 12/03/2008 - 08:08
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So, when I did "switchport mode trunk" we lost connect to the server

Mark Yeates Wed, 12/03/2008 - 08:16
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Is your sever configured for a dot1q trunk?

patel.nishit Wed, 12/03/2008 - 08:23
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Yes it is configures as dot1q trunk.

Is it when we change the port from access port to trunk port we will lose connectiovity until the switch and server sync to trunk mode.

Mark Yeates Wed, 12/03/2008 - 08:26
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There shouldn't be any sync required. what is the output of "show int trunk" of the interface connected to your server?

patel.nishit Wed, 12/03/2008 - 08:30
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I had to put it back to original config as it caused an outage. But it showed 802.1q trunking on.

Its strange as it lost connection then. If 802.1q is their as default why it would lose connection when I put the port in the trunk mode.

Mark Yeates Wed, 12/03/2008 - 08:34
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I would double check that the server NIC is configured correctly. If it works on an access port, but loses connection when the port is configured as a trunk means there is something not configured correctly. You might consider troubleshooting this after hours to prevent server downtime.


Jon Marshall Wed, 12/03/2008 - 07:58
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Not all modules on the 4500 support ISL trunking -


By default, the Catalyst 4500 series switch that runs Cisco IOS Software supports both ISL and 802.1Q trunking modes. The support is on all interfaces except blocking Gigabit ports on the WS-X4418-GB and WS-X4412-2GB-T modules. These ports do not support ISL and only support 802.1Q trunking. Ports 3 through 18 are blocking Gigabit ports on the WS-X4418-GB module. Ports 1 through 12 are blocking Gigabit ports on the WS-X4412-2GB-T module.




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