show cdp nei

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Sep 6th, 2005
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What could cause "show cdp nei" to no longer work after changing from switch access to trunking and vlans? I change my network from a single vlan (router with two secondary interfaces configured) with 3 subnets - -to 3 separate vlan interfaces and trunking. I have a combination of a 6513 wan router, 3550 lan router, Catalyst 3550 & 3524XL's. Before I made the change "sho cdp nei worked". After the change to trunks and vlans, "sh cdp nei" can not see any 3524XL's when they are by themselves. If there is a 3550 upstream or downstream from a 3524 XL then, "sh cdp nei" seems to work only on that link. I believe we are running the same version of CDP on all the lan switches. Everything is working as planned except "sh cdp nei".

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Overall Rating: 2 (1 ratings)
glen.grant Tue, 09/06/2005 - 17:40
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try doing a clear interface commnad on the connecting links , have seen this before and this seemed to fix it after doing a clear interface command on your connecting links.

stickhg Thu, 09/08/2005 - 18:03
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In the case where there are qty 4 3524XL's connected by gigastack, which is then connected by fiber SX GBIC, you are suggesting to execute a clear int G0/X on each 3524XL and the corresponding port on the 3550-12T lan routing switch? ie all the way from the end of the stack to the lan routing switch. Please confirm.

glen.grant Thu, 09/08/2005 - 18:20
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Corrext ,try the 3524 end first and then wait a couple minutes until cdp can run . If that doesn't work do the same on the 3550 end . If you have to you can run a debug cdp on each and see if you are getting reply's from each end . If you have cdp active on every port though you will get a lot of messages . I would do this as a last resort.

stickhg Sun, 09/11/2005 - 13:39
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Thanks for staying with me on this. I have gone thru my whole environment and cleared all the connecting interfaces, found a couple of interfaces run V2 cdp advert., changed everything to disable V2, cleared cdp counters. I noticed where "cdp nei" does not work, I do not see any cdp input - -but devices connected upstream and downstream are incrementing the cdp output counters. All the 3524XL are running the same version of IOS. It appears as tho there must be a 3550 in the connectivity stream to make cdp nei to work. I have another facility with 3534 and 3548 where the cdp nei works just fine. Any insight?

scottmac Sun, 09/11/2005 - 14:27
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Check that your Native VLANs are set up properly.

CDP will only work across the Native VLAN.

Good Luck


stickhg Sun, 09/11/2005 - 19:13
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I have all my native vlans identical. It is strange that doing a "sh cdp traffic" indicates these devices are advertising, because I see the output counters increment, but the input counters are on "zero" yet. I have verified all devices are running V1 of cdp, cdp is enabled, and the 3524XL's can not be seen with cdp unless there is a 3550 somewhere in the path of the Xl's.

sangvak Sun, 09/11/2005 - 21:29
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could u show the configurations of 7513 and 3550?

i wonder using trunking for "router on stick" configuration u had


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