[nsp] Strange request

[Gert Doering]

Hi,

On Tue, Jan 20, 2004 at 08:31:10AM -0800, Aaron Howell wrote:
> diagram will help me explain:
> 
>     Site A <----T1----> Site B <----T1----> Site C
> 192.168.2.x/24	    192.168.1.x/24	192.168.0.x/24
> 
> Note that Site A is now in 192.168.2.x, but the host 192.168.0.97 will
> remain there. For reasons far too complicated to get into here, they
> cannot change the IP on this host, and they seem unwilling to change the
> addressing they've already worked out, (I suggested swapping Site A and
> Site C's IP space, but they are unwilling to do so). I'm drawing a blank
> on how they could accomplish what they want to do within the constraints
> of the design they've come up with, so if anyone has any ideas I would
> be most grateful.

The *correct* way to do that would be to fire the network admin in
question, and get proper addressing.


A workable-if-ugly pragmatic way would involve overlapping routes and
proxy ARP.

That is:

* The router in Site A will have a static route
      192.168.0.97 255.255.255.255 Ethernet0
  (A /32, pointing at the LAN interface on which the host in question
  is connected to).

  Further, it needs "ip proxy-arp" on that LAN (!).

* All routers between A and C need a /32 route towards "A" and a 
  /24 route towards "C".  Due to "most specific wins", this will work.

* The router connected to the LAN segment of C needs "ip proxy-arp"
  on its LAN interface.  That way, it will pick up queries from all
  stations on LAN C destined to the host 192.168.0.97.


Make it work, but make it EXPENSIVE.  Stupid design MUST hurt, otherwise
they will never learn.

gert

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Gert Doering - Munich, Germany                             gert at greenie.muc.de
fax: +49-89-35655025                        gert at net.informatik.tu-muenchen.de