CDP - seeing CDP from one side only....

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Oct 21st, 2009
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Hello,

I have a 3845 enabled for CDP connected to a stack of 3750 switches. From the router, i dont see any CDP neighbors. From the switch, i can see the router as neighbor. Why isn't the switch showing as a neighbor from the router side?


san-rt-rogers-01#sh cdp traffic

CDP counters :

Total packets output: 8349, Input: 0

Hdr syntax: 0, Chksum error: 0, Encaps failed: 0

No memory: 0, Invalid packet: 0, Fragmented: 0

CDP version 1 advertisements output: 90, Input: 0

CDP version 2 advertisements output: 8259, Input: 0

san-rt-rogers-01#sh cdp in

san-rt-rogers-01#sh cdp interface

GigabitEthernet0/0 is up, line protocol is up

Encapsulation ARPA

Sending CDP packets every 60 seconds

Holdtime is 180 seconds

GigabitEthernet0/1 is administratively down, line protocol is down

Encapsulation ARPA

Sending CDP packets every 60 seconds

Holdtime is 180 seconds

Serial4/0 is up, line protocol is up

Encapsulation HDLC

Sending CDP packets every 60 seconds

Holdtime is 180 seconds

san-rt-rogers-01#

san-rt-rogers-01#sh cdp neighbors

Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge

S - Switch, H - Host, I - IGMP, r - Repeater


Device ID Local Intrfce Holdtme Capability Platform Port ID

san-rt-rogers-01#


san-sw-lr-02#sh cdp neighbors

Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge

S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone


Device ID Local Intrfce Holdtme Capability Platform Port ID

san-sw-lr-01.nucomm.net

Gig 1/0/1 157 R S I WS-C3750- Gig 1/0/1

san-rt-rogers-01.yourdomain.com

Fas 1/0/1 142 R S I 3845 Gig 0/0

SAN-CORE-SW-02 Fas 3/0/47 124 S I WS-C3750E Fas 0

san-sw-lr-02#



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Joe Clarke Wed, 10/21/2009 - 18:31
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Perhaps the switch stack is configured not to send CDP. Post a show run and show ver from the 3750 stack.

George Stefanick Wed, 10/21/2009 - 19:02
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Is the router local or going over a WAN. I have seen ISPs not support CDP before...

yeshwenth Mon, 07/16/2012 - 08:27
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I know this post was from 2009 and i am answering now, I had the same issue as stated above.I was seeiing packets with CDP-EV. It happened that the particular switchport which was connected the to the router was configured for an ip-phone. So no wonder the neighbour was only forming on one side. Once i corrected the configuration on the switch, everything was back to normal.


Hope it helps some1 out there.


Yesh

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