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
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.