Is there a Layer 2 analog implementation of "hop count"??

jjinno · 12-10-2009, 08:19 PM

I realize "hops" are Layer3, but is it possible to make a Layer2 version of "hop count"? AKA: "the number of switches between endpoints"

So basically I have 2 scenarios, and I want to identify the difference automatically. Seems like a L2 hop-count would be perfect, no?

Scenario 1:
[Box 1]-----[Switch 1]-----[Box 2]

Scenario 2:
[Box 3]-----[Switch 2]-- ... --[Switch N]-----[Box 4]

One (non-hopcount) idea is that if you start at the endpoints, checking the MACs of the connection out of the switch, then share that information between endpoints, you should have enough information to identify, in either case, the fact that you cant see the other end node MAC = Scenario 2. But is there a Layer2 protocol out there that keeps ALL the MACs handy like that?

jjinno · 12-14-2009, 12:01 PM

Ok, from a different point of view... Spanning Tree Protocol (STP) uses the MAC addresses of the switches in cases when priorities are the same.

From Wikipedia on The Spanning Tree Protocol:

Quote:

To compare two bridge IDs, the priority is compared first. If two bridges have equal priority, then the MAC addresses are compared. For example, if switches A (MAC=0200.0000.1111) and B (MAC=0200.0000.2222) both have a priority of 10, then switch A will be selected as the root bridge.

So if an algorithm for network loop avoidance can grab switch MAC addresses, how do I do it from an end node?