[RndTbl] aggregating dsl lines

Theodore Baschak theodore at ciscodude.net
Tue Sep 29 11:28:26 CDT 2015

To get a single TCP connection/thread going over two or more equal bandwidth connections you just need equal cost routing to use all paths. 
An actual router (not firewall, or nat gateway) with two equal cost routes will load balance packets over both connections as long as you're not firewalling. If you're trying to do this multi-connection extension at layer2 though instead of at layer3, you'll probably have a lot more hair-pulling fun, and less success.


> On Sep 29, 2015, at 8:09 AM, Adam Thompson <athompso at athompso.net> wrote:
> This is an active area of research, particularly with the advent of multi-path TCP.
> Presently, however, you have to hide the two-link-ness from the TCP layer, and essentially from the IP layer as well.
> ECMP would work, as long as both lines are the same (this does not hold true as a dynamic assertion with DSL technology, *ever*).
> LACP will *not* work.
> If you have Linux boxes at both ends, you can use mod_bonding in its round-robin mode... I've done that in the past and it does work.
> Far more effective, however, would be to upgrade to a symmetric VDSL2 setup that supports DSL bonded pairs.
> That'll set you back around $600+ per end, IIRC, replaces both the DSLAM and the DSLR, but makes your problems go away by turning all the copper into a single Ethernet link.
> I just worked with someone else on this kind of setup, I'll see if I can find the links...
> -Adam
> On September 29, 2015 4:18:54 AM CDT, Trevor Cordes <trevor at tecnopolis.ca> wrote:
> Is it possible to aggregate DSL lines, to combine them to get X-times the 
> bandwidth on a single link?  In this situation, I control both ends, the 
> DSLAM and the DSL modem side on the other end of some POTS runs (CAT3-ish 
> I assume, or worse).
> Note, I don't want load balancing or fancy routing/sharing.  I need double 
> (or more) the bandwidth for a single application (single TCP connection).
> If required, we can have linux/bsd boxes we control at either end of the 
> links.
> If it's not possible, does anyone have any other ideas for somehow getting 
> better bandwidth out of 500m POTS wires (quantity 4)?
> Thanks!
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