I want to identify the clients connecting through my Cisco Catalyst ports on my network

Hello - I have a stack of Catalyst 3850's and a stack of older 3750 switches, comprising the backbone of my network.  I would like to be able to see what IP addresses or computer names (or some form of identification) from the switch ports.  How can this be done?  The LAN is on a single class C subnet, 192.168.1.1 / 255.255.255.0.
Damian_GardnerAsked:
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JohnBusiness Consultant (Owner)Commented:
I am not sure about your switch, but most switches (all that I have seen and used) do not identify the IP address of a device on a port. That is not the role of a switch.
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Damian_GardnerAuthor Commented:
Ok.  well..I found something while hunting that gave me the feeling that it was possible, but I wasn't able to get anywhere with it.  Take a look and let me know what you think:

COPIED FROM:  http://serverfault.com/questions/39345/identify-machines-connected-to-switch

From your first hop router(s), do a broadcast ping on each subnet that is trunked to a switch supporting the office space (as opposed to any data centre space you may have). Note, this should be the directed broadcast address of each subnet, rather than the 'all devices' broadcast IP of 255.255.255.255 In Cisco IOS, this can only be done from privileged exec mode. For example, to ping all machines on the subnet 192.168.100.0/25, use:
ping ip 192.168.100.127


This will populate the ARP cache of the router with entries for all machines on each subnet responding to ping.

Again on the first hop routers, extract the list of ARP entries for each subnet:
show ip arp interface vlan 100


This will give you all the IPs and MAC addresses of every device that responded to the ping. You can check the list of IPs against DNS (or another naming service) to identify the names of specific devices. Any IP address that you can't match a name to should be flagged for further investigation.
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JohnBusiness Consultant (Owner)Commented:
I read the article and I have not tried that (never any need to). All I can suggest is try the broadcast to see if you can make it work.
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Damian_GardnerAuthor Commented:
ok.  well the reason I'm wanting to do it is to identify some unmarked data jacks in an area of the building.  I have a couple users who are plugged into some of the jacks and on the network.  there is another user who's wall jack is dead.  I just can't seem to tone it out to a port in the MDF room.  So I figure - If I could identify a port on the switch by user somehow, I could possibly find the other jacks near it that need to be connected.  So that's my reasoning.

thanks
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JohnBusiness Consultant (Owner)Commented:
I am sitting here looking a the port diagram of my Cisco VPN router (two machines and a printer). It does not tell me the IP address of the end device, even in the details.

I am looking at my packet sniffer and it tells me what the IP addresses are doing but not what ports they are on.

I can only suggest trying the ideas in the article you linked to, although I did not find all the possibilities to be conclusive.
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Damian_GardnerAuthor Commented:
Ok - well I appreciate your efforts, John.  Thanks and I'll try it.
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JohnBusiness Consultant (Owner)Commented:
I think it is a complicated task because what you want is not a feature of a switch or router (the ones I have seen of my own and various clients). Good luck.
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arnoldCommented:
Take a look at the switch and the options available on it, are you currently using snmp to poll your switch and is the port, Mac address and IP part of the data being returned?
A port that feeds a switch might have multiple Mac addresses associated with that switch.
Try it on one.  Not sure cisco has an RMON report which lists the switch ports, Mac addresses the switch knows about.
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Netman66Commented:
From each workstation, open a CMD prompt and run ipconfig /all.
This command will show you all the network adapters, their MAC and IP addresses.
Find the ethernet entry and copy down the MAC and IP to take with you and also onto a sticky note to put on the monitor for easy identification.

From the console of your switch, ping each IP address, then run a show arp to find out what MAC is attached to each port.  This will give you your port map.
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Damian_GardnerAuthor Commented:
Ok - thanks Netman.  I'll definitely try that tomorrow.
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arnoldCommented:
before going to each system, check a switch to get the ARP table it has.
Then see whether the information you get from the switch either via snmp poll, or other means like RMON it it provides

Multiple arp entries on one switch port means that feeds another switch.
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Bryant SchaperCommented:
you can do it manually with arp, ip addresses and such, but download a switchport mapper, the benefit is it will pull the same info, but also query dns to get machine names. I think solarwinds offers a free tool.  You could export the list of mac addresses to port, and use DNS as well.  Just remember that uplink ports to other switches will show all macs on the downstream devices.
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Damian_GardnerAuthor Commented:
I tried using the ARP commands and it didn't seem to work.  I ended up resolving it with a telecom engineer who came in for another job on site here.  But I do want to try the other suggestions, so I will do this in the next week.  I wanted to thank everyone for their suggestions.
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JohnBusiness Consultant (Owner)Commented:
@Damian_Gardner  - Thanks for the good update. If any issues, keep us posted.
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