09-19-2007 10:45 PM - edited 03-05-2019 06:35 PM
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
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09-20-2007 12:47 AM
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.
09-19-2007 10:54 PM
Hi Friend,
Can you check if cdp is not disabled on interface of router 2 which is connected to router 3?
Regards,
Ankur
09-19-2007 11:00 PM
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
09-19-2007 11:07 PM
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
Regards,
Ankur
09-19-2007 11:42 PM
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.
09-20-2007 12:38 AM
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
09-20-2007 12:47 AM
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.
09-20-2007 01:11 AM
thanks Pall
Will do so.
10-16-2007 12:48 PM
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...
10-16-2007 01:08 PM
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.
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