Re: arp magic

[Blars Blarson <blarson@blars.org>]

In article <[🔎] 20021026101853.GA1070@valiant.sbg.palfrader.org> 
weasel@debian.org writes:

>I've the following setup:
>
>                 10.200.118.0/24 (internal)
>                     |
>                     |
>                     | eth0:10.200.118.1
>                 +--------+
>                 | marvin |
>                 +--------+
>                     | eth1: 10.2.2.20
>                     |
>                     |
>                  10.0.0.0/8 (external)
>
>Now if a host on the external network sends an 'arp who-has
>10.200.118.1' request marvin answers on eth1.
>Is there any way to _stop_ that behaviour?

I assume what you realy want is eth1 to have all of 10.0.0.0/8 except
10.200.118.0/24.  This is possible but ugly.  Better solutions in most
cases involve either renumbering one of the networks (the
172.16.0.0/12 range is available in most cases) or putting a more
restrictive netmask on eth1.

To do the selective routing, set the netmask on eth1 to 10.0.0.0/9 and
add something like the following to your if-up script:

ip route add 10.128.0.0/10 dev eth1 src 10.2.2.20
ip route add 10.192.0.0/13 dev eth1 src 10.2.2.20
# stuff to split up 10.200 goes here
ip route add 10.201.0.0/16 dev eth1 src 10.2.2.20
ip route add 10.202.0.0/15 dev eth1 src 10.2.2.20
ip route add 10.204.0.0/14 dev eth1 src 10.2.2.20
ip route add 10.208.0.0/13 dev eth1 src 10.2.2.20
ip route add 10.216.0.0/11 dev eth1 src 10.2.2.20

The useful ip command is in the iproute package.

(Double check my netmasks...)


-- 
Blars Blarson			blarson@blars.org
				http://www.blars.org/blars.html
"Text is a way we cheat time." -- Patrick Nielsen Hayden