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  1. #1
    Join Date
    Aug 2002
    Location
    Denver, CO
    Posts
    331

    Subnet Masks and Multiple IP Addresses

    I've just got a new server. In Local Area Network properties I see:

    IP Address: 1.2.3.244
    Subnet Mask: 255.255.255.240

    I was trying to bind additional IPs to this machine. After playing with it for a few minutes I realized I could successfully add:

    IP Address: 1.2.3.245
    Subnet Mask: 255.255.255.0

    OR I could add:

    IP Address: 1.2.3.245
    Subnet Mask: 255.255.255.240

    Can someone please explain to me why the above two work? I somewhat understand subnet masks, but am not totally sure what is going on here.

    Andrew

  2. #2
    Join Date
    Aug 2002
    Location
    Denver, CO
    Posts
    331
    This is a windows machine by the way. Not that I think it matters, as this should be a numbers game, and nothing to do with Microsoft I don't think.

  3. #3
    Join Date
    Jul 2002
    Location
    Manchester, UK
    Posts
    774
    When you say successfully exactly what do you mean? Do you mean it simply let you put them in, or did they both respond successfully?

    As far as I know, only one should work and that is the one with the same netmask as the default gateway unless you have specified additional gateways.

  4. #4
    Join Date
    Aug 2002
    Location
    Denver, CO
    Posts
    331
    I mean I was able to put those two subnet masks in, and I was able to ping that IP address and do web hosting off of them. I agree, that it seems odd that both 255.255.255.0 and 255.255.255.240 work. And no, I only have one default gateway set up as 1.2.3.241, but I don't know what it's subnet mask is.

    Andrew

  5. #5
    Join Date
    Feb 2005
    Posts
    334
    They would both work because ideally as long as you only used IPs within your assigned subnet it 'should' be switched/routed properly (ymmv there). If you tried to use IP'd below your own assigned subnet (as it looks like you have the tail end of the /24 in question) then you would start seeing things begin to break.

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