Solved: CDP Help

frikkiedupreez · ‎09-19-2007

Router1: 168.206.8.1

Router2: 168.206.8.65

Router3: 168.206.8.202

Router 1 and 2 exchange CDP info.

Router3 show cdp traf: Total packets output: 1036, Input: 0

All the router can ping each other. Any ideas why router3 doesn't show any neigh

paul.matthews · ‎09-20-2007

You need to look at your switches - I would put money on them not forwarding multicast traffic correctly. Am I right in an assumption (given use of plural and behaviour of CDP) that R1&R2 are in the same switch, with R3 in another? If so the first place to look is the inter switch link.

I am also a ittle concerned that R2 appears ro be showing itself in CDP (again assumption yyy=r2)

You really need to be looking at the switches.

View solution in original post

ankbhasi · ‎09-19-2007

Hi Friend,

Can you check if cdp is not disabled on interface of router 2 which is connected to router 3?

Regards,

Ankur

frikkiedupreez · ‎09-19-2007

Hi Ankur

CDP is enabled on all the routers

R1/R2/R3: show cdp

Global CDP information:

Sending CDP packets every 60 seconds

Sending a holdtime value of 180 seconds

Sending CDPv2 advertisements is enabled

ankbhasi · ‎09-19-2007

Hi Friend,

CDP can be enabled globally and also on interface level. It may be enabled globally on router 2 but can be disabled on per interface on which router 3 is connected?

run a command "sh run int " on router interface and check to confirm.

Regards,

Ankur

paul.matthews · ‎09-19-2007

How are these connected? Superficially the appear to be in the same subnet, but that is not necessarily the case, as the use of .1 and .65 suggests those may be on /26 subnets.

*assuming* they are on one subnets, then the chances are they are all on a switch. Can 1&2 see 3? If 1&2 can see each other but R3 neither sees nor is seen, then there is potentially an issue with L2 multicast traffic to/from R3.

We need to know more about the interconnections between the routers, and the configs of any switches - are they Cisco switches? I have seen other switches cause problems with CDP.

frikkiedupreez · ‎09-20-2007

Hi P

R1: 168.206.8.1/21 Eth0 (1605)

R2: 168.206.8.65/21 FA0 (1721)

R3: 168.206.8.201/1 FA0/1 (1841)

R1/2 & 3 is connected via ethernet cable and 3Com 4400 switches

Router 1: show cdp neighb

yyy Eth 1 159 R 1721 Fas 0

Router 2: show cdp neighb

yyy Ser 0 120 R 1721 Ser 0

zzz Fas 0 158 R 1605 Eth 1

Router 3: show cdp neigh: no output

3: show cdp traf

Total packets output: 1258, Input: 0

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

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

CDP version 1 advertisements output: 0, Input: 0

CDP version 2 advertisements output: 1258, Input: 0

paul.matthews · ‎09-20-2007

You need to look at your switches - I would put money on them not forwarding multicast traffic correctly. Am I right in an assumption (given use of plural and behaviour of CDP) that R1&R2 are in the same switch, with R3 in another? If so the first place to look is the inter switch link.

I am also a ittle concerned that R2 appears ro be showing itself in CDP (again assumption yyy=r2)

You really need to be looking at the switches.

frikkiedupreez · ‎09-20-2007

thanks Pall

Will do so.

sriggslev · ‎10-16-2007

Side note... wont cdp only show directly connected cisco devices??? if the routers are all connected to a L2 switch why would any be cdp neighbors... wouldnt they be neighbors of the L2 switch, which in this case is a 3COM...

paul.matthews · ‎10-16-2007

CDP can be fun. CDP will go one Cisco hop, and would normally traverse other vendors at L2.

Take a 3com switch that will forward multicast and plug six cisco switches into it. All Cisco switches will see five neighbours as the 3com has no interest in CDP, to the 3Com it is simply L2 multicast to be forwarded out all ports.

P.