TELECOM Digest OnLine - Sorted: Re: Using Two ADSL Internet Connections Simultaneously

Re: Using Two ADSL Internet Connections Simultaneously

James Carlson (
09 Dec 2005 17:35:20 -0500 (Robert Bonomi) writes:

> "Incoming" traffic is an entirely different problem. And
> load-balancing _that_ traffic cannot be done in anything approaching a
> satisfactory manner without 'help' from the 'upstream' end.


> And it requires that both DSL circuits terminate at the same
> 'upstream' provider.

Not necessarily. There are at least two other possibilities here,
both of which allow for connections to multiple providers:

- NAT in use, and load balancing on a per-connection basis. This
automatically balances the return traffic as well, as everyone on
the net thinks you're actually two separate independent IP nodes.

- You're a big company and you can afford to arrange BGP peering
with the ISPs and inject routes into the backbone.

There are others as well that involve just living with the fact that
you'll appear to be separate nodes on the net, and remaining
multihomed -- this is what you'd probably do if you were doing this
for (say) a web server with multiple A records.

> *BUT* the 'standard' routing code _in_the_kernel_ of most operating
> systems does =not= support multiple equal-priority routes to the same
> destination, *with* rotating use of those routes on a per-packet
> basis.

Doing it on a per-packet basis ("round robin") is a mistake. It
causes poor performance by reordering packets and often causes trouble
with various middleboxes. Instead, you want to hash based on flow
identification, which some systems can do.

James Carlson, KISS Network <>
Sun Microsystems / 1 Network Drive 71.232W Vox +1 781 442 2084
MS UBUR02-212 / Burlington MA 01803-2757 42.496N Fax +1 781 442 1677

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