Re: IP aliasing

["Steven M. Bellovin" <smb%cs.columbia.edu@localhost>]

On Wed, 18 Jun 2008 16:57:01 +0100
Patrick Welche <prlw1%cam.ac.uk@localhost> wrote:

> On Wed, Jun 18, 2008 at 10:00:10AM -0400, DAve wrote:
> > Good morning,
> >
> > I have been told by my Network Administrator that we will be
> > changing IP blocks for several key services very soon. I have three
> > new DNS servers running NetBSD on the new IP block already. I also
> > have two legacy DNS servers (also on NetBSD) that I need to drag
> > along behind me for a few more months.
> >
> > My new IP block is 65.124.104.X and my old IP block is
> > 65.196.224.X. Is it possible to have a single machine answer for
> > both IPs on a single interface? The network Gods claim they can
> > route the traffic to me no problem, but I am unsure how to
> > configure the alias for the interface.
> >
> > Old address: 65.196.224.2
> > Netmask: 255.255.255.0
> > Gateway: 65.196.224.1
> >
> > New address: 65.124.104.25
> > Netmask: 255.255.255.224
> > Gateway: 65.124.104.1
> >
> > Is it even possible to alias the old address with the new gateway?
> 
>       ifconfig if0 inet 65.124.104.25 netmask 255.255.255.224
>       ifconfig if0 inet 65.196.224.2 netmask 255.255.255.0 alias
> 
> should do the trick? (replacing if0 with bge0 wm0 nfe0 or whatever
> you have)
> 
> Your gateway is a specific router, so what is its ip number?
> 65.124.104.1?
> 
>       route change default 65.124.104.1
> 
> for the outbound traffic?
> 
Right, but that can't coexist with the old setting; you can only have
one default route, I believe. 



                --Steve Bellovin, http://www.cs.columbia.edu/~smb