[LARTC] Bridging two subnets selectively using routing

[joshk@triplehelix.org (Joshua Kwan)]

Hi LARTC,

I have two networks that I manage, A and B.  They both have their own
primary gateways for hosts on the network, let's call them AR and BR.
There is another box, A1, which lives on network A but also has a wire
connecting it to a switch on network B. My goal is to let hosts on B
access three particular hosts on A's subnet (192.168.4.0/24) and let
hosts on A access one particular host on B's subnet (10.3.0.0/24).

Suppose the IP addresses of the machines I wish to address on either
network are A2, A3, A4 and B1.

A1 has IP 10.3.0.13 on network B and 192.168.4.10 on network A. Is it
possible to just tell the gateways for each network:

on BR: ip route add {A2, A3, A4} via 10.3.0.13
on AR: ip route add B1 via 192.168.4.10

But when I do that, ping does something like:

PING A2 56(84) bytes of data.
From BR: Redirect Host (new nexthop: 10.3.0.13)

and doesn't actually report success on the ping.

What am I doing wrong? Is this a job for iptables? I feel like I can do
this with just routing table magic.

Thanks,

-- 
Joshua Kwan
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