Um, read up a little on TCP.

Back in the day when you got an address space when you
had multiple providers, we used routers, a fixed adress
space and a routing protocol.

The bump is that say you have a long lived session (more than
one packet).  It goes out your, hmm DSL.  As IP address:
128.0.1.2 (for example).  Oops, DSL dies.  Now you're going out
the cable as:  204.89.168.50.

The other end gets packets from an established connection from
a new, apparently arbitrary address.  And rejects it.

It fails.



Quoting Tomas Hlavacek (tomas.hlavacek@elfove.cz):
> Hi,
>    I am sorry if this question is not so suitable here.
> 
> I would like to ask if it is possible to set up snat, when I have got 
> two internet connections and I would like to reach that the traffic is 
> balanced between this connections.
> 
> reading manuals I have not found anything like that. so may I use 
> something like this?
> 
> map ne3 192.168.1.0/24 -> <1st connection IP>/32 proxy port ftp ftp/tcp
> map ne3 192.168.1.0/24 -> <1st connection IP>/32 portmap tcp/udp 40000:60000
> map ne3 192.168.1.0/24 -> <1st connection IP>/32
> 
> map ne4 192.168.1.0/24 -> <2nd connection IP>/32 proxy port ftp ftp/tcp
> map ne4 192.168.1.0/24 -> <2nd connection IP>/32 portmap tcp/udp 40000:60000
> map ne4 192.168.1.0/24 -> <2nd connection IP>/32
> 
> 
> and what if one of these connection fails?