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My laptop has got 2 IP addresses!

Discussion in 'Network+' started by Boycie, Jun 6, 2005.

  1. Boycie
    Honorary Member

    Boycie Senior Beer Tester

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    Hi,

    Making my way through the Sybex Network + book (what a great book :D )
    Got to the section on TCP/IP utilities. Starting playing around with ARP.
    Turns out my laptop has 2 IP addresses and therefore 2 MAC addresses :blink
    It also says they were assigned dynamically when I statically assigned the one listed.
    If I ping both of them they time out! Even though everthing on the network is fine.

    I only have the wireless enabled. Is it showing me the MAC address of the LAN port? If yes, how come the IP address is listed when it is disabled?
     
    Certifications: MCSA 2003, MCDST, A+, N+, CTT+, MCT
  2. Mitzs
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    Mitzs Ducktape Goddess

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    Why is the wireless giving you 2 IP?
     
    Certifications: Microcomputers and network specialist.
    WIP: Adobe DW, PS
  3. Boycie
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    Boycie Senior Beer Tester

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    See the edit Mitz, thanks
     
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  4. tripwire45
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    tripwire45 Zettabyte Poster

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    Boyce, are you saying that when you open a command prompt and type:

    ipconfig/all

    you get a listing for your wireless and LAN ports and each one lists a dynamically assigned IP? Just trying to find out the process that is giving you this information.

    Have you tried using the command

    ipconfig/release

    and then

    ipconfig/renew

    If your LAN interface is disabled, it shouldn't be picking up a DHCP addy and it shouldn't be available for a static assignment either. If possible, could you post the output of the ipconfig/all command so we can see what you're seeing? Thanks.
     
    Certifications: A+ and Network+
  5. Boycie
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    Boycie Senior Beer Tester

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    Trip,

    Thanks for your reply and sorry about the wait in responding. I posted last night as I was packing up to go to bed :sleeping

    I have woke up this morning and answered my own question :biggrin

    The first arp -a command I got was just my laptop addresses.
    Five minutes later my missus logged on the upstairs computer and because they are networked my laptop was showing me the addy's for that too!
    As you say ipconfig/all will only display the computer you are sat at whereas arp -a will show everyone on the subnet.

    As for saying dynamically assigned addresses when I statically assigned them via Network connections....properties....TCP/IP....use this address and dns
    I can only put this down to the fact that because they weren't assigned using the arp utility it treats them as dynamic. Please correct me if this isn't the case.
    edit- I have just used the arp utility to delete my address and re-create it using arp. It makes no difference to the network connection that has been created using TCP/IP properties and even when manually entered using the -s switch it still says dynamically assigned :blink

    As far as the ping test failing when everything is fine I can only put this down to my Linksys router blocking ping requests- I cannot ping my router when the whole set-up is working perfectly. I can administer my router wirelessly too :biggrin
     
    Certifications: MCSA 2003, MCDST, A+, N+, CTT+, MCT
  6. Phoenix
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    Phoenix 53656e696f7220 4d6f64

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    Boyce
    the output of the arp is saying that the ARP entry was dynamicly learned as opposed to static

    you can enter ARP entries statically, or you can let arp do its job and find them all out automatically :)

    arp is merly a service to handle address mapping from layer2 to layer3, and does not actually handle the addressing itself

    Code:
    C:\Documents and Settings\rcoates>arp -a
    
    Interface: 172.17.27.254 --- 0x3
      Internet Address	  Physical Address	  Type
      172.17.27.1		   00-a0-c5-42-8e-2a	 dynamic
      172.17.27.24		  00-0e-a6-2e-93-7e	 dynamic
      172.17.27.25		  00-09-5b-1f-eb-1c	 static
      172.17.27.55		  00-0e-a6-1a-27-3b	 dynamic
      172.17.27.253		00-09-5b-2c-ae-1a	 dynamic
    
    C:\Documents and Settings\rcoates>
    
    lets clear up some details above,
    Interface: 172.17.27.254 is the address of the interface arp is listening on, ie the address of the machine your looking at, this doesnt need to go onto the translation table, as it knows the answers already

    the below lines are any other machines picked up by arp, im guessing the two entries were your router and other machine

    I have added a static entry for my server to highlight the difference here, i dont usually do this, and it was done with the command
    arp -s 172.17.27.25 00-09-5b-1f-eb-1c
     
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  7. Boycie
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    Boycie Senior Beer Tester

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    Ryan,

    Thanks for a full explanation. :D
    Don't suppose you fancy taking a look at my post on subnetting
    :oops:
     
    Certifications: MCSA 2003, MCDST, A+, N+, CTT+, MCT
  8. tripwire45
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    tripwire45 Zettabyte Poster

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    Glad you got it sorted, Boyce. Ryan's explanations are usually dead on so once he's answered, there's usually nothing left for me to add. :)
     
    Certifications: A+ and Network+
  9. Boycie
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    Boycie Senior Beer Tester

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    Thanks trip. Yes, Ryan is always spot on. A credit to the forum :D
     
    Certifications: MCSA 2003, MCDST, A+, N+, CTT+, MCT

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