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SH IP ARP Incomplete

We went through a massive rewiring of a massive campus.  99% of the cabling had to be ripped out, and replaced.  We also replaced all of the data closet cabling.  Their data closets looked like some bad spaghetti.  Wires were so twisted that we couldn't make heads or tails.  We removed all of the cables, and started patching back to the switch, from the patch panel, with new wiring.  In doing so, we knocked out quite a few surveillance systems due to the fact that they have a security VLAN.  I know that most of the issues have to do with the ports not being VLAN'd, after our cabling.  Here's my question;  When you do a sh int arp, you see the layer 3 IP address. You also see an "incomplete" next to the IP address, instead of the layer 2 MAC address.  Is there any way, using the switch commands, that I can tell which switchport these systems are plugged into?  The problem is that most of these systems are exterior cameras that sit very high, on the buildings.  The only other way to figure out where they're plugged in would be to take my Fluke and tone them out.  That would require bringing in a lift.  Before I go down that route, I was wondering if anyone had any other suggestions by using commands to take care of this.  Thanks for all of your help!

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Rising star

Hi Stavros

If You know the ip address of the systems You can do it this way.

For example a camera with ip address 10.1.1.1 that should be on vlan 10

Configure a static route pointing to another vlan

"ip route 10.1.1.1 255.255.255.255 vlan 20"

then ping 10.1.1.1, if You got an answer look at the arp table to find out the mac-address and follow it up.

if You don't get an answer remove the static route and put it in with next vlan.

"no ip route 10.1.1.1 255.255.255.255 vlan 20"

"ip route 10.1.1.1 255.255.255.255 vlan 30"

try and ping again, and so on until You get an answer.

It's a loot of work, but maybe it's easier than going out and trying to find the cable with the fluke.

/Mikael

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3 REPLIES 3
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Rising star

Hello,

before the IP Arp, you need to make sure all your wires are connected properly and there is connectivity between IP Cameras and the Switch ports.

you need to make sure the Switch port is recieving a valid host mac-addresses on these Switch ports, you can check this by issuing the below command:

show mac-address table dynamic interface x/y

If this is resolved, there should be an ARP entry on the layer-3 Switch.

Regards,

Mohamed

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Mohamed,  thank you for the quick response.  The problem that I have is that I do not know which switchport the device is plugged into.  That's what I'm looking to find.  These devices have static IP addresses.  Since they're plugged into a switchport that's in a different VLAN, I can't see the device, nor the port that it's plugged into.  If these devices were physially accessible, I'd just plug their ethernet cable into my Fluke and tone them out, or the Fluke would tell me which port they're on.  Unfortunately, these devices are anywhere from 50 to 70 ft, on the side of buildings.  Thanks!

Highlighted
Rising star

Hi Stavros

If You know the ip address of the systems You can do it this way.

For example a camera with ip address 10.1.1.1 that should be on vlan 10

Configure a static route pointing to another vlan

"ip route 10.1.1.1 255.255.255.255 vlan 20"

then ping 10.1.1.1, if You got an answer look at the arp table to find out the mac-address and follow it up.

if You don't get an answer remove the static route and put it in with next vlan.

"no ip route 10.1.1.1 255.255.255.255 vlan 20"

"ip route 10.1.1.1 255.255.255.255 vlan 30"

try and ping again, and so on until You get an answer.

It's a loot of work, but maybe it's easier than going out and trying to find the cable with the fluke.

/Mikael

View solution in original post

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