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  1. Senior Member boxerboy1168's Avatar
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    #1

    Default Question in regards to discovering what ports have a connection

    Hello all,

    Building myself a pretty big lab and trying to do this off the top of my head without looking up commands.

    So I have a bunch of switches with ip phones and hosts connected to them and I'm connecting them to ports based on which vlan they are in. The phone are in ports 10-15 and so on and so forth. So I logged into my lab to continue messing with the configuration and I had totally forgotten which ports needed configuration in order to continue with port security and all that.

    So what I'm trying to figure out is what is the best show commands to figure out what ports are connected and what they are connected to?
    Currently enrolling into WGU's IT - Security Program. Working on LPIC (1,2,3) and CCNA (and S) as long term goals and preparing for the Security+ and A+ as short term goals.
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  3. Senior Member
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    #2
    1) look at your networking diagram.
    2) there is a "description" field for each port
    3) label your wires
    there is a reason that network documentation is required
    4) there is the mac address table. but, your host device needs to be on and sending packets
    5) use cdp or lldp. but not all equipment support these
    6) start tracing back your wires.
    7) start over and document your network this time

    mine isn't documented either. You might remember it this week, maybe next month, but no way next year. I'm just guessing at it.

    you can see which ports show activity when pinging.
    see which port light come on/off when you plug the cable in/out.
    Last edited by clarson; 12-30-2017 at 04:26 PM.
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  4. Senior Member
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    #3
    clarson is spot on. Network documentation is important. I always add a description to the ports.


    My go to commands are

    show ip arp
    show mac address table address <mac address>
    show cdp neighbor (when using cisco IP Phones)
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  5. Senior Member boxerboy1168's Avatar
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    #4
    those commands are good if I have traffic on the network but if I'm setting up my network and handling original configurations technically there shouldn't be any access or traffic over the network

    if network documentation is the best way to go then I don't need to worry about it I can reference my diagram on packet tracer rather than try to problem solve through the CLI

    thanks
    Currently enrolling into WGU's IT - Security Program. Working on LPIC (1,2,3) and CCNA (and S) as long term goals and preparing for the Security+ and A+ as short term goals.
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  6. Senior Member cshkuru's Avatar
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    #5
    Maybe I am misunderstanding your question, but why wouldn't you start with the basic show commands? show run and show ip int br are the two most useful commands I can think of.
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  7. Network Engineer Hondabuff's Avatar
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    #6
    1) "show interfaces status" Shows you what ports are up and on
    2) "show arp" Gives you connected IP addresses and MAC's
    3) Ping the IP address in the arp table to verify it is working
    4) "show mac address-table address xxx.xxxx.xxxx" from the arp table, Shows you what port the mac address is on
    5) "show interfaces trunk" verify your trunk ports
    “The problem with quotes on the Internet is that you can’t always be sure of their authenticity.” ~Abraham Lincoln
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  8. Junior Member Registered Member
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    #7
    I typically use:
    sh vlan
    sh ip int bri
    sh int x/x/x

    If it involves IP phones then this could also be another:
    sh cdp neighbor

    To check what ports need configuring you can also use:
    sh run int gi x/x/x
    Last edited by networker050184; 01-05-2018 at 02:23 PM.
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  9. Senior Member boxerboy1168's Avatar
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    #8
    ahhh ok, the last 2 post really helped
    Currently enrolling into WGU's IT - Security Program. Working on LPIC (1,2,3) and CCNA (and S) as long term goals and preparing for the Security+ and A+ as short term goals.
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