Topology Services, CDP and VRF

Unanswered Question
Apr 6th, 2009


Situation: We've approx. 15 L3 switches running VRF Lite (3550-12G. 3750, 3560E, 6506), CDP enabled, Management addresses Loopback0 in global routing table. We've all devices are in Device Repository in LMS, all pass the Credential Test, but the devices are missing in topology View or cannot form adjacency.

From several documents I found in the past I assume, that the reason is in IP addresses: Both devices (e.g. access L2 switch "A" and backbone L3 switch with multi VRF "B") see each other as CDP neighbors, but the "A" see bad Management IP address of "B", which is unreachable from security reason (e.g. it is customers' VRF).

None of our devices supports "cdp source-interface" (which seems to be the best sollution for this kind of problems), so the questions are

- is there any other way how to solve this kind of problem ?

- how does CDP selects IP address, which is used as "Managemet Address"

Thanks for answer.

Jan Klicka, SITMP

I have this problem too.
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smahbub Mon, 04/13/2009 - 06:16

ensure verify that CDP is enabled on switch.

Cisco Discovery Protocol (CDP) is primarily used to obtain protocol addresses of neighboring devices and discover the platform of those devices. CDP can also be used to show information about the interfaces your router uses. CDP is media- and protocol-independent, and runs on all Cisco-manufactured equipment including routers, bridges, access servers, and switches.

Each device configured for CDP sends periodic messages, known as advertisements, to a multicast address. Each device advertises at least one address at which it can receive SNMP messages. The advertisements also contain time-to-live, or holdtime, information, which indicates the length of time a receiving device should hold CDP information before discarding it. Each device also listens to the periodic CDP messages sent by others in order to learn about neighboring devices and determine when their interfaces to the media go up or down.


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