CRC errors when I turn on vlan trunking

[justinmk99]

I have a cisco 2600 with a c2600-is-mz.122-23a.bin system file. This router has several sub-interfaces set up for the different vlans. Each vlan is encapsulated with ISL.

The 2600 router connects to a C2912MF-XL switch with IOS version 12.0(5.2)XU.

This switch connects to a C2950C-24 with IOS version 12.1(22)EA4. This is where the device is for the vlan specified on the router.

Whenever we enable trunking on the 2912 for the port that connects to the 2950, we get numerous CRC errors.

Ideas? What else can I look for? What other info do you want?

[ankurbhasin]

Hi Justin,

I do not think trunking relates to CRC but still just check the speed and duplex settings on both the connections and try to make it manual settings then auto auto and also check if the vlans allowed are same on both the sides including the Native vlan and lastly but not the least check you cable because I think the CRC is mostly related to layer 1 and layer 2 problem. So cable or duplex and speed settings can be a major concern.

HTH

Ankur

[justinmk99]

The cable connecting the two switches is a brand new multi-mode fiber. We took out the fiber and tried trunking over a copper line and it gave us the same problems.

We tried setting it to half-duplex & 100Mbps manually but that did not stop the CRC errors on the 2912.

[ankurbhasin]

Have you also tried with full-duplex. If full duplex is also giving you CRC errors can you give a shot with auto auto settings. And I hope the config for the trunk is same for both the ends and there is no native vlan mismatch.

If everythig is ok and still we are experiencing the CRC errors check in "sh version" if you IOS version is Maintainence Entrim software that can be the last option.

HTH

Ankur

[justinmk99]

I have not tried locking both to full-duplex.

I know that the IOS version of the 2912 is a Maintainence entrim version. What's are the chances that this is the problem?

[ankurbhasin]

In my experience Maint Entrim code gives you such problem which your switches are experiencing as these codes are mainly used for testing purposes and gives you lot of pain in your genaral network routine.

Just give a shot with full duplex settings and if that does not work try upgrading the code to the latest version.

If you want to consult TAC you may go ahead with it but if cable and dupplex and speed settings does not resolve the issue it is code problem especially when you have main entrim code.

HTH

Ankur

[bbaillie]

The 2912MF-XL can support ISL trunks and dot1q trunks but the 2950C-24 only supports dot1q for trunks. The problem can be rectified by configuring the port on the 2924MF-XL for dot1q encapsulation "switchport trunk encapsulation dot1q". Also the 2950C-24 supports dynamic trunking protocol, many issues noted with this protocol when it faces a 2924 switch, so on the 2950C-24 switch port that faces the 2924MF-XL use the command "switchport nonegotiate" to disable DTP. Upgrading to the latest firmware is always a good idea but the trunking encapsulation type is most likely your root cause.