Question about MAC and internet IP as assigned by the provider

Discussion in 'other security issues & news' started by Fly, Jul 25, 2009.

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  1. Fly

    Fly Registered Member

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    My ISP (cable, broadband) seems to assign me different IPs (external IPs), depending on whether I connect my computer to my modem by wire, or whether I use a wireless router between my modem and computer Configuration: modem, wire between modem and router, wireless connection between router and my USB adapter (using firmware). No other devices in the network.

    I've tested this a couple of times.

    It seems that even the specific router in question can make a difference regarding the IP assigned. (Difference between my obsolete router, and my new one). I suspect this has something to do with a MAC address of the router in question, but what do I know.

    Would each type/model of router have the same MAC address ? Or do all routers (not just a model) have a unique MAC address ? Is there unlimited space for a unique MAC address for every single router ? :doubt:
     
    Last edited: Jul 26, 2009
  2. Cudni

    Cudni Global Moderator

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    i think they will all have unique mac addresses
     
  3. Seer

    Seer Registered Member

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    The address space is certainly not unlimited (we're not talking quantum physics here ;) ) but a 48-bit. So a number of possible combinations is 2^48 (which is a pretty big number). No matter how small, a possibility of two same numbers exist, so most devices allow this address to be changed.
     
  4. Fly

    Fly Registered Member

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    Thanks.

    I think it's odd that my ISP assigns me an IP based ont the MAC address of my computer. They certainly won't give me a new IP address if I were to ask for one. (From what I understand, IP addresses are scarce). But they do if you buy a new router ?
     
  5. lotuseclat79

    lotuseclat79 Registered Member

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    Hi Fly,

    It is likely that your computer is setup to acquire addresses with DHCP which will get you a new IP address each time for the router you use - either that or the router is setup to acquire new IP addresses with DHCP whenever you power it up. The router only knows about your computer with an internal IP address, but the router's IP address is the one seen on the Internet.

    I somehow doubt that the IP address is dependent on your MAC address in the router unless you have a static IP address assigned by your ISP.

    -- Tom
     
  6. Fly

    Fly Registered Member

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    I'm just not quite sure about that DHCP thing.
    DHCP in the router is 'enabled'.

    When I connect my computer to the modem by wire (no wireless at all), the IP is assigned by the ethernet card (I think).
    In that case, DHCP is also enabled.
    I can switch between the wired and the wireless connection, and each time they give a separate IP and host name. Meaning, when I use a wired connection I get IP 82.X and host name X, when I switch back to wireless I get the IP 82.Y and host name Y.

    Technically I have a dynamic IP address (and configured as such), but it rarely changes. It just seems odd that the IP address changes when I switch from wireless to wired and vice versa.

    Again, configuration: Windows XP Home Edition service pack 2.
    Wireless setup: modem connected by wire to router, router sends a wireless signal to the USB adapter on my computer, no other devices in the network.
    Wired setup: connection by wire/cable between my computer and my modem, no other devices in the setup.

    Does it really have nothing to do with the MAC ? :doubt:
     
  7. lotuseclat79

    lotuseclat79 Registered Member

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    Hi Fly,

    I am noticing that I pick up the same IP address with my router when I shutdown and login the same day, and next day it is different.

    I get FiOS delivered via Coax, but have Coax disabled, and get the IP address assigned via Ethernet. I'll have to experiment with different configurations.

    -- Tom
     
  8. lotuseclat79

    lotuseclat79 Registered Member

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    Hi Fly,

    The reason my ip address is the same on a daily basis is that there is a timed lease on it, so unless I release the lease, it stays for the lease period defined by: option dhcp-lease-time 86400 (which is the number of seconds in a day).

    Since I use Linux, the pump command can be issued to change the lease and get a new ip address for the router.

    -- Tom
     
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