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  • Find IP addresses from Switch

    Hey guys,

    Other than managing my small consulting business, I have a part time job as a technician for a small company.

    One of my projects is to find the IP addresses for all the ethernet cables plugged into their switches (which is a mess)! There's a switch in the server room on the second floor, and another on the first floor.

    I already found all the client IP addresses manually, going from PC to PC, but my question is if there's a tool I can use that I can plug into the switch, and it'll read out a report of the IP addresses connected, numbered by which # jack it's plugged into? Ex. IP address, 192.168.42.250 is plugged into jack #4 on the switch, or something like that.

    Otherwise, I gotta unplug one at a time and narrow it down 1 by 1 on 100 PC's!!

    Thanks!!

    Sam

  • #2
    Re: Find IP addresses from Switch

    with show arp, you can see all the cached ip adresses.
    AFAIK there is no such command line present.
    Marcel
    Technical Consultant
    Netherlands
    http://www.phetios.com
    http://blog.nessus.nl

    MCITP(EA, SA), MCSA/E 2003:Security, CCNA, SNAF, DCUCI, CCSA/E/E+ (R60), VCP4/5, NCDA, NCIE - SAN, NCIE - BR, EMCPE
    "No matter how secure, there is always the human factor."

    "Enjoy life today, tomorrow may never come."
    "If you're going through hell, keep going. ~Winston Churchill"

    Comment


    • #3
      Re: Find IP addresses from Switch

      As a matter of interest... why ???

      Why don't you use DHCP? And who cares what IP is plugged into which port? It seems a bit of "Documentation overkill" to me. Of course, there may be a very good reason, I am curious.

      But having 100 PCs really does lend itself to having a DHCP environment. Also, once you document the fact that port 2 has IP a.b.c.d attached, you cannot move anything without updating the document. What a chore!
      Best wishes,
      PaulH.
      MCP:Server 2003; MCITP:Server 2008; MCTS: SBS2008

      Comment


      • #4
        Re: Find IP addresses from Switch

        Thanks guys,
        Unfortunately... there isn't really a good reason. I agree with you guys...when my boss told me this, I was saying to myself "Are you kidding me? This will take a month, maybe even longer!" We have run cables all over the place, but for the most part, not even sure which cable goes to what PC, and that's what my boss wants to find out, by port. He's just a jerk haha. It really is documentation overkill...all I care is that if it works, who cares ?

        Thanks for your help anyways...I'll try show arp, but otherwise, looks like I'm gonna have to unplug 1 at a time .

        Comment


        • #5
          Re: Find IP addresses from Switch

          Just document which port is connected to which wall outlet.
          This can be importent, the rest is completely useless.
          Marcel
          Technical Consultant
          Netherlands
          http://www.phetios.com
          http://blog.nessus.nl

          MCITP(EA, SA), MCSA/E 2003:Security, CCNA, SNAF, DCUCI, CCSA/E/E+ (R60), VCP4/5, NCDA, NCIE - SAN, NCIE - BR, EMCPE
          "No matter how secure, there is always the human factor."

          "Enjoy life today, tomorrow may never come."
          "If you're going through hell, keep going. ~Winston Churchill"

          Comment


          • #6
            Re: Find IP addresses from Switch

            I will do that for the first floor (office) because all of those lead into a switch into a closet, so that will be easier. The second floor and the rest of the building are just the ethernet cables leading back to the server room switch, so that I'm narrowing down now...and it's not as bad as I thought it was. It's just a lot of walking, but that's ok .

            Comment


            • #7
              Re: Find IP addresses from Switch

              You might find this free "LAN Scan" software useful: http://www.radmin.com/radmin/utility/lscan.php

              All it does is scan the LAN and tell you what IP addresses are up (as well as other info) so you can do a scan, unplug one, do another scan and see which one fell off. Just an idea.
              Best wishes,
              PaulH.
              MCP:Server 2003; MCITP:Server 2008; MCTS: SBS2008

              Comment


              • #8
                Re: Find IP addresses from Switch

                Originally posted by Dumber View Post
                Just document which port is connected to which wall outlet.
                This can be importent, the rest is completely useless.
                Totally agree. Documenting jack to patch panel mappings is a good idea. This is especially useful if you have multiple subnets that need to be isolated from each other... but documenting what port on a switch a computer is connected to???

                But having said that, we have some 3com switches and I've used 3NS (3com Network Supervisor) to scan the network. It gives a lot of info, especially if you use 3com devices. For the 3com switches it lists all the configuration, all the connected MACs and what port and IP addresses and what port it's on.
                Regards,
                Jeremy

                Network Consultant/Engineer
                Baltimore - Washington area and beyond
                www.gma-cpa.com

                Comment


                • #9
                  Re: Find IP addresses from Switch

                  Guys, guys, guys, Stommy has a very important job that his boss asked him to do. This is an overtime bonanza so let's help him make that extra $$$$$$. What the boss wants, the boss should get. Cost is not an issue.

                  If the PCs are names and assigned IPs using DHCP, then finding out which cable plugs into the switch is going to indicate which IP and switch port match. You may need to re-cable the cabinet so Patch Panel socket 1 goes into switch port 1. Patch Panel socket 2 goes into switch port 2. Patch Panel socket 3 goes into switch port 3, etc etc or at least in an order that is logical (Sorin can help you there )

                  If you recable the cabinet, make sure any uplinks, crossover cables etc are NOT moved. This would also be a weekend job when there is no one online so you cause no or at least minimal disruption. Use cable ties to group the cables so it looks nice and tidy AND different so it can be seen that you actually did something. A nice little project to get the boss to sign off on.
                  1 1 was a racehorse.
                  2 2 was 1 2.
                  1 1 1 1 race 1 day,
                  2 2 1 1 2

                  Comment


                  • #10
                    Re: Find IP addresses from Switch

                    With cisco use the sh mac-address-table to find out all mac-addresses on the switches
                    if i'm right, you can see somethinh like the following output:
                    Code:
                    ------------------------------------------
                    Vlan    Mac Address       Type       Ports
                    ----    -----------       ----       -----
                       1    000C.1258.1064    DYNAMIC    Fa0/2
                       1    000C.4006.4286    DYNAMIC    Fa0/1
                       1    000C.5299.1241    DYNAMIC    Fa0/3
                    now you need to know which ip is connected per mac address.
                    maybe you can get that from the DHCP leases.
                    However, if the client renews his address and he gets a new one, you need to start over again.

                    Personally i would talk to the boss and point him to this tread to let him read that it is completely useless.
                    Let him explain over here why he really really want to know each ipaddress which is connected to which accessport.
                    Marcel
                    Technical Consultant
                    Netherlands
                    http://www.phetios.com
                    http://blog.nessus.nl

                    MCITP(EA, SA), MCSA/E 2003:Security, CCNA, SNAF, DCUCI, CCSA/E/E+ (R60), VCP4/5, NCDA, NCIE - SAN, NCIE - BR, EMCPE
                    "No matter how secure, there is always the human factor."

                    "Enjoy life today, tomorrow may never come."
                    "If you're going through hell, keep going. ~Winston Churchill"

                    Comment


                    • #11
                      Re: Find IP addresses from Switch

                      Surely the better way is to map MAC addresses to switch ports? That way you can set switch config to "disable" a port which has the "wrong" MAC address. We did this at one of my former employers; most computers were desktops and therefore didn't move around. They required "secure" access to the network; they didn't want people bringing in their home PCs and using the LAN. So - they "opened" network switch ports in "learn MAC" mode. First device plugged in, and BANG, the port was in "Fixed MAC" mode. If any device with the wrong MAC address plugged into that port, the port would disable itself and require resetting on the NMS. Not only far simpler to manage than documenting IP addresses, it also adds a layer of security.


                      Tom
                      For my own and your protection, I do not provide support by private message under any circumstances. All such messages will be deleted and ignored.

                      Anything you say will be misquoted and used against you

                      Comment


                      • #12
                        Re: Find IP addresses from Switch

                        Thanks for all your help guys, I agree with all of your advise on why this is almost pointless, as this can keep changing constantly if cables are connected, disconnected, hire new employees, etc. However, I think biggles said it best... "What the boss wants, the boss should get. Cost is not an issue."

                        I've already banged out 1/2 of the computers this weekend and made an Excel spreadsheet of the port #, IP address and user. It was a little time consuming, as I expected, but I definitely got my exercise going back and forth from the server room to the PC's to find out which one went out, and it's one heck of a bonus!

                        Thanks guys!

                        Comment


                        • #13
                          Re: Find IP addresses from Switch

                          Hi Stommy,

                          There is a product that will do this for you called Solarwinds Engineers toolkit. It is expensive but there is a 30 day eval. I am sure in 30 days you could get the job done. The piece of the software is called "switch port mapper". It maps switch ports to MAC, IP, and hostname. Here is the URL-

                          http://www.solarwinds.net/products/t...ineer.aspx#NDT

                          Best of luck to you and thanks for posting!
                          David Davis - Petri Forums Moderator & Video Training Author
                          Train Signal - The Global Leader in IT Video Training
                          TrainSignalTraining.com - Free IT Training Products
                          Personal Websites: HappyRouter.com & VMwareVideos.com

                          Comment


                          • #14
                            Re: Find IP addresses from Switch

                            Apparently i came to this party a little late. I could have saved you maybe a little bit of time. I have used SolarWinds Switch Port Mapper. I am pretty sure that they have a trial version available. If you have SNMP configured on the router, you should be able to tell it to map your switch, and it will tell you the port, the speed, the MAC address, the IP, and the DNS name of the item plugged into each port.

                            It sounds like you are mostly completed with this project, but i figured i would post in case anyone else's boss wants them to do a similar project, and they end up at this thread.

                            talk to you later

                            app

                            EDIT: Apparently David and i were thinking along the same lines at the same time. It is a great product, i use it regularly to map my server connections to my switches in the NOC.
                            Last edited by apperrault; 5th March 2007, 16:48. Reason: forgot some information. Duplicated answer

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