[LARTC] Balancing multiple connections and NAT

[Markus Schulz]

Am Donnerstag, 23. Februar 2006 20:14 schrieb Raj Mathur:
> Hi,
>
> I have a client connected to the 'net through 3 ISP's.  Have set up a
> Linux box to do routing and load sharing for the 3 connections.  A
> fourth interface is connected to the LAN with private IP addresses.
> Am using iptables to SNAT traffic to the appropriate IP depending on
> the interface the packet gets routed onto.  The setup looks something
> like this:
>
> Interface       IP               Gateway	  Table	  Network
> ---------       --               -------          -----   -------
> intA            ipA              gwA		  tableA  netA
> intB            ipB              gwB		  tableB  netB
> intC            ipC              gwC		  tableC  netC
> [intD is the LAN interface]
> intD            ipD (private)    no gateway	  global  netD
>
> This works fine most of the time, except that once in a while (every
> 5-10 minutes or so) packets going out on (e.g.) intB suddenly start
> getting NAT'ed to source address ipA (i.e. the address of another
> interface).  Obviously this plays hell with the existing connections
> on that link!

you need a patch for NAT processing with multiple gateways. this will 
then save the routing information for each connection inside NAT 
structures, so that each packet of an established connection will be 
get routed over the same gateway. you can find the patches here:
http://www.ssi.bg/~ja/#routes
please read the guides (nano howto or dgd-usage) carefully.


-- 
Markus Schulz