IP alias Networking Errors.

Malcolm Kay malcolm.kay at internode.on.net
Sat May 24 19:30:59 PDT 2003


On Sun, 25 May 2003 11:51, Andy Farkas wrote:
> On Sat, 24 May 2003, Grant Peel wrote:
> > fxp0: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> mtu 1500
> >         inet 65.39.193.154 netmask 0xfffffff0 broadcast 65.39.193.159
> >         inet 65.39.193.155 netmask 0xffffffff broadcast 65.39.193.155
> >         inet 65.39.193.156 netmask 0xffffffff broadcast 65.39.193.156
> >         inet 65.39.193.157 netmask 0xffffffff broadcast 65.39.193.157
> >         inet 216.187.107.125 netmask 0xffffffff broadcast 216.187.107.125
> >         inet 216.187.107.126 netmask 0xffffffff broadcast 216.187.107.126     
> >         inet 216.187.107.123 netmask 0xffffffff broadcast 216.187.107.123
> >         inet 216.187.107.124 netmask 0xffffffff broadcast 216.187.107.124
> >         ether 00:06:5b:ee:40:32
> >         media: Ethernet autoselect (100baseTX <full-duplex>)
> >         status: active
>
> ...
>
> > When the next group of IP were assigned to me, and I set them as aliases
> > on this machine, thats when I started getting the errors.
>
> When you add aliases for a different subnet, the netmask should be the
> proper one for the subnet ie. netmask 0xfffffff0.

From the man pages (ifconfig(8)):
alias   Establish an additional network address for this interface.  This
             is sometimes useful when changing network numbers, and one wishes
             to accept packets addressed to the old interface.  If the address
             is on the same subnet as the first network address for this
             interface, a non-conflicting netmask must be given.  Usually
             0xffffffff is most appropriate.

Malcolm


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