Multipul ppp connections to different isp's

Richard Smith rdls at
Mon May 1 00:40:37 BST 2000

Ian MacDonald wrote:
> Is it possible to "load balance" across 2 or more modems to different isp's
> (e.g. freeserve, freenetname etc). I have had a look pack trough past FBSD
> mailing lists but the only things I could find were use ospf (not likely) or
> use mpd (which does not support multiple peers).
> What I can do is dial up both isp's and change the default route by hand and
> it will change the route the packets take. The only problem is that if the
> packets go out on one connection (quite rightly) they must come pack in on
> that connection. This is fine for ping and stateless connections but will
> not ahndle ftp etc.
> Has anyone got any ideas on this.

The problem is that the source IP address of packets passing over each
ISP is different. So a given TCP connection *must* use the same ISP
thoughout the entire session. If you want to load balance across
multiple ISPs you either need to add static routes or have a hoopy NAT
layer that handles multiple routes.


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