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APIPA question

Discussion in 'A+' started by robbo1962, Apr 29, 2007.

  1. robbo1962

    robbo1962 Byte Poster

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    Hi all, i am having problems understanding this part, if i understand this correctly in Windows 2000 and XP if you cannot access a DHCP to obtain an IP Address your computer generates its own one in the range 169,254,0,0 to 169,254,255,254 and is class B and can only communicate with computers on the same subnet, IF i have this right (please correct me if not so) doesn't that provide a great restriction on what you have access to? Also what would happen in a Windows 9x situation where there was no access to a DHCP ? Thanks Gary
     
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  2. Sparky
    Highly Decorated Member Award

    Sparky Zettabyte Poster Moderator

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    Yes, it is restrictive as APIPA does not define a default gateway therefore the traffic cannot be routed to other subnets or the internet. The whole point of APIPA is if you wanted a small LAN to communicate with hosts on the same LAN but there is no DHCP source.

    As for Windows 9x as long as the NIC is configured to obtain an IP address automatically you will get a 169 IP. :biggrin
     
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  3. zebulebu

    zebulebu Terabyte Poster

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    Hi Robbo

    Basically, an APIPA will not provide you with much connectivity at all!

    It is a way of assigning basic network connectivity in lieu of either a statically assigned address or one provided by DHCP. In practice, you will see this when the NIC has been assigned to obtain an IP address automatically, but no DHCP server is present. As such it usually indicates a network connectivity issue - which is why one of the first things you need to do when troubleshooting a network problem is to run IPCONFIG and see what address the NIC is using. If its a 169.254.x.x address, then pound to a penny you have a problem getting an address via DHCP
     
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  4. robbo1962

    robbo1962 Byte Poster

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    Thanks for the replies, good point about being useful on a LAN Sparky, did'nt think of that. Thanks again. Gary
     
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  5. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    In fact Win9x also produces an APIPA address in the same circumstances as Win2k. i.e. when the machine is set to get an address automaticaly and no DHCP server can be found.

    Don't forget that if you have a network on a routable IP network, and no DHCP, then you would manualy allocate and set the IP address and it will work just fine.

    Harry.
     
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  6. Tinus1959

    Tinus1959 Gigabyte Poster

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    The windows 9x has to be 98. Windows 95 does not support APIPA.
    [from technet]
    When you connect to the host, the guest computer uses an address from the pool and the host computer uses the fixed IP address assigned to it. A fixed, assigned IP address is useful when a computer cannot handle automatic address assignment. This might occur when a computer is still running Windows 95, for example.
    [/technet]
     
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  7. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    Oops! Thanks for the correction. In mitigation I plead that it has been a *very* long time since I used Win95!
    :biggrin

    Harry.
     
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