I read about CDP - which says its a cisco protocol. It lists devices that are connected to each other. But if i don't have all cisco vender, how can I see what connects where?

I have cisco router R1 connected to another vender router R2, and from there to another cisco R3. CDP can only show R1 connecting to R3? How can I see R2?


Actually even with CDP you cannot see R3 as being neighbors with R1. CDP, is link-local. Which basically means that CDP can only show devices directly connected as neighbors 1 hop away. In your example, R3 is two hops away. Unless it has another directly connected link to R1, it won't become a CDP neighbor.

What you are looking for is LLDP. Its can run on CISCO as well as most other vendor gear. And it functions similar to CDP - shows the immediate neighbor.

  • What is link-local mean?
    – ccnaQuest
    Sep 30 '15 at 1:27
  • 2
    See Ron's answer for an explanation of link-local. Its only valid on the connected link, and not beyond it. Hence with these protocols, you get a picture of only whats on the other end of the link, not whats another router away
    – ajaysdesk
    Sep 30 '15 at 1:29

As @ajaysdesk writes, CDP and LLDP are only valid on the link on which they are originated. These protocols use special layer-2 frames which are not switched or routed beyond the device on the other end of the link.

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