[LARTC] SNAT based on MAC before routing

["Eduard Calvo (B-teljpa) EXP JAN 03" <ecalvo@mat.upc.es>]

 
  Hi gurus, 
 
  I need a way to do SNAT based on source mac before routing. This is because 
hosts attached to my gateway can have duplicate IP addresses, and I have to 
distinguish over them.  
 
  I tried to use the nat tool that comes with iproute2, but this force to make 
a mapping only address to address, and I wanted to do it by mark (I also use 
iptables to do that). For example, I tried to do that: 
  
  iptables -t mangle -A PREROUTING -m mac --mac-source XX:XX:XX:XX:XX:XX -j 
MARK --set-mark 1 
  ip rule add fwmark 1 nat to a.b.c.d lookup table <table> 
 
  And so I also did: 
 
  ip route add nat a.b.c.d via e.f.g.h 
  (where e.f.g.h. is the IP associated with mac XX:XX:XX:XX:XX:XX) 
 
  This doesn't work. 
 
  I also tried to do a loop with the packets, forwarding them for the first 
time through the loopback interface (doing SNAT in POSTROUTING with iptables) 
and routing correctly for the next time they come (having passed through lo). 
I do this marking the packets coming from lo interface, and having an 
according ip rule that force them to go through the correct output interface 
(let be eth1). This way, I would want to be able to make a diferent routing 
policy for each host (because de nat'ed address is different from each other). 
The only thing I observe is a funny looping that makes packets go round my box 
until they die (TTL=0). 
 
  Can someone help me, please? 
  Thanks in advance, and excuse my long mail. 
 
                                               Eduard. 
  

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