what's on the other side of the port?

[jimfixit]

I have been tasked by my client to identify and mark all the cabling in their server room. Seven years and no one marked a thing or put a desc in the switch port config.

I first thought it would not be so bad, using show mac address and show arp would give port-->Mac add-->IP address then all I would have to do is ping IP to get the name...simple.

BUT often the Mac address and IP tables are pretty sparse compared to the number of active ports that are tranmitting and receiving. Like one switch (3750) has 40 port actively transmitting but only 8 or 10 entries in the mac and even fewer in arp. I tried a ping sweep against the entire network range thinking that would force a transmit from the devices when they replied to the ping...only a few improvements in the number of entries. Extending the mac aging time out did not help with this issue.

Can't hand trace, the yahoo that ran them stuffed all the cables in and out of holes in the side of racks that are butted and BOLTED together. I can't get my hand in there. Some have so many cables that the ones on the bottom are showing signs of slicing into insulation. (yeah I told them about that. They were surprised but not willing to shut down and fix.) Toner requires me to disconnect whatever is on other end, and they don't want stuff to be down.

I can't figure out why the learning of mac addresses isn't taking place when, by looking at port stats, transmissions are happening. All on are the same vlan so I don't think I'm missing something there...

 

[lerdalt]

My first instinct was to point you towards this posting for the cammer script:

http://www.tek-tips.com/viewthread.cfm?qid=1041814&page=5

It works great, and will resolve to a DNS name even. But if your MAC tables aren't fully populating, I'd say you have a bigger problem.

Dumb thought...is there a timer set really low that keeps flushing the CAM table?

 

[zinkann]

I use the command, SHOW CDP NEIGHBORS and
SHOW CDP NEIGHBORS DETAIL religously. Most network devices support CDP. Its not going to give you everything, but it will help.

CCNA, Network+

 

[burtsbees]

How many traces are we talking here? Perhaps Angry IP scanner from a node, and then relate IP addresses to arp antries? If everything is in the same vlan, then maybe do an arp -a from a workstation to get more MAC addresses...

Burt

 

[vipergg]

If you have very few entries in the arp table then the 3750 probably isn't even setup to route anything and the routing is being done by another device and the 3750 is acting as layer 2 only . You would have to figure who is doing the routing . If there are 40 connections and it was doing the routing you would have at least that many entires in the arp table . See where the default gateway or default static route is pointing to and go to that device and see if that is doing the routing . "show ip route or a show ip default command should give you that.

 

[jimfixit]

The cam timeout is set to 14400 which is 4 hours. They are all on vlan 1 so there should not be any need for routing. But I think I will try the suggested tools to see what I can get, perhaps that will at least cut down the number i'm going to have to hand trace. Thanks all.

 

[lerdalt]

If you have to hand trace and can afford to take some downtime, you might want to look into a line toner. Wouldn't have to really trace the cable from end to end, but could find the tones.

 

[burtsbees]

lerdalt, he did indicate that they don't want anything unplugged though...
Burt

 

[brianinms]

Download a copy of trial copy of Solarwinds and use the switch mapper function.

 

[lerdalt]

that's why I added the comment about taking downtime. One of those times where I might fight for some downtime thinking it would take less time/effort and be more accurate than trying to chase each cable.