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Author Topic: CDP link discovering with VRF-Lite configured C6509  (Read 3511 times)

steffen1

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CDP link discovering with VRF-Lite configured C6509
« on: December 08, 2010, 09:57:09 AM »
Hello,

Get some trouble with VRF-Lite (synonyme to multi-VRF) configured C6509, v12.2(18SXF9) in
CDP link discovering by nedi. A "show cdp neigh" from CLI is working but the SNMP represention seams not to be the same as with none VRF configured devices. In oposite direction all neighbor devices will show this C6500 in nedi as expected.

Does anybody knows this problem and maybe has a solution for this, thx in advance.

I did a verbose nedi call to this device already, but cant catch the cause.

Steffen

rufer

  • Guest
Re: CDP link discovering with VRF-Lite configured C6509
« Reply #1 on: December 09, 2010, 09:12:31 AM »
I recently added a VRF to my c6500 with 12.2(33)SXI3 but it didn't change anything in Nedi. When I was testing, I remarked that not everything is VRF aware, well most things aren't. Example: The routing table (by SNMP) is, the ARP table (by SNMP) isn't.
OK, it seems all my CDP links are on one VRF (at least the native VLAN are), that could help.

Greetings
Rufer

steffen1

  • Guest
Re: CDP link discovering with VRF-Lite configured C6509
« Reply #2 on: December 13, 2010, 10:35:56 AM »
thx rufer for your feedback with VRF.

I found the time for deeper troubleshooting and found out that the SNMP representation of CDP is exactly the same as with none VRF configured ones. The problem is that this Cat6509 contains a very large CDP table (45KB)  and you have to increase the max_msg_size to 64K in libsnmp.pl in thta function.

So the cause is one of this:
1. The C6509x cant handle fragmentation of SNMP packets
2. OR the Checkpoint in between drops fragmented SNMP packets
3. AND Perls Net::SNMP implementation is poor regarding snmwalk not beeing fault-tolerant:
Why you need a try-and-error parameter max_msg_size in Perl for a very basic function and why you dont need this using the CLI binary "snmpwalk" - this works allways?

Steffen