Re: netmask of alias IP

[Dave Taira <bodhi_(_at_)_hagakure_(_dot_)_org>]

On Thu, 4 Jul 2002, RJ45 wrote:

> You seem to tell correct thing, but fi I SEt up 255.255.255.255
> as netmask of the 2 aliases IPs I cannot ping anymore hosts on the 2
> subnets 172.16.254.254 and 172.16.253.254. The configuration shown on the
> bottom works, if I change it with netmask 0xffffff it won;t work... how we
> can explain this ?
> thanks
>
>
> On Thu, 4 Jul 2002, Daniel Malament wrote:
>
> > > /etc/hostname.fxp0
> > > inet 192.84.x.y 255.255.255.0 NONE
> > > inet alias 172.16.254.254 255.255.255.0 NONE
> > > inet alias 172.16.253.254 255.255.255.0 NONE
> > >
> > > AND THIS WORKS
[snip]
> > Note the following in the FAQ:
> > >>>Assuming you are using multiple IP addresses which are in the same IP
> > subnet<<< with aliases, your netmask setting for each alias becomes
> > 255.255.255.255.

If you are using multiple IP addresses which are in *different* subnets,
you should not be using a 255.255.255.255 netmask. In your example
above, you are using three IP addresses in three separate subnets.
If, instead, you had:
inet       172.16.254.1 255.255.255.0 NONE
inet alias 172.16.254.253 255.255.255.255 NONE
inet alias 172.16.254.254 255.255.255.255 NONE
           ^^^^^^^^^^ note: all the same subnet
then, you'd use a 255.255.255.255 netmask, and it should all work.


[ Dave Taira <bodhi_(_at_)_hagakure_(_dot_)_org>                2002.07.04/00:08:46 PDT ]
[ Morlock for Hire                                                       ]
[ I'm licensing a new technology called "lying". I invented it.          ]
[                                                               --Andr00 ]