[CUWiN] circular route

[David Young]

On Fri, Jan 20, 2006 at 12:07:56AM -0500, simon-cuw at uc.org wrote:
> Hello,
> 
> I have the following setup:
> (internet)--(Router A)--<LAN A>--(Node A)~~~(Node Z)--<LAN Z>
> 
> - Router A provides DHCP for LAN A
> - Node Z provides DHCP for LAN Z
> - A computer on LAN A has a static route for LAN Z pointing to Node A'a
>   address on LAN A.
> 
> I can ping from computesr on LAN Z to LAN A, but trying to do the
> opposite, pinging form LAN A to LAN Z seems to reveal a circular route
> somewhere. Any ideas how I could start troubleshooting this?
> 
> 
> 
> i.e.:
> 
> Node A = 192.168.42.22, on 192.168.42.0/24, internet/dhcp from linksys rtr
> Node Z = 10.216.103.254, on 10.216.103.0/24, dhcp from cuw node
> 
> mylaptop_on_A$ sudo route add -net 10.216.103.0/24 gw 192.168.42.22
> 
> mylaptop_on_A$ ping 10.216.103.252
> PING 10.216.103.252 (10.216.103.252) 56(84) bytes of data.
> 64 bytes from 192.168.42.22: icmp_seq=1 ttl=62 time=7.12 ms
> 64 bytes from 192.168.42.22: icmp_seq=2 ttl=62 time=4.37 ms
> 64 bytes from 192.168.42.22: icmp_seq=2 ttl=62 time=4.37 ms

It's NAT bogosity: note the reply comes from 192.168.42.22 instead of
10.216.103.252.

When a node gets a lease on an RFC1918 address on its ethernet, maybe
it should map the RFC1918 subnet to its self-assigned ethernet subnet,
10.x.y/24.  E.g., add a NAT rule for each ethernet,

        map ath0 192.168.42/24 -> 10.x.y/24 portmap tcp/udp 10000:20000
        map ath0 192.168.42/24 -> 10.x.y/24 

They say "NAT is eeeevil" for a reason.

Dave

-- 
David Young             OJC Technologies
dyoung at ojctech.com      Urbana, IL * (217) 278-3933