DSL "aggregation".... NO

Mark Smith nanog at 85d5b20a518b8f6864949bd940457dc124746ddc.nosense.org
Thu Apr 15 17:09:39 CDT 2010

On Thu, 15 Apr 2010 17:39:54 -0400
Jack Carrozzo <jack at crepinc.com> wrote:

> You can balance over DSL by putting different L2TPv3 tunnels over each
> physical device and agg it at someplace with real connections and
> such. It's possible to do it with GRE or OpenVPN too, but much less
> classy.

Depends a bit on the tunnel overhead you're willing to pay. I've done
this, and I'd have preferred to use pure IP in IP, however Cisco's have
GRE keep alives to monitor tunnel state, so I used that, at the cost of
extra 4 bytes.

As the tunnel creates a dumbbell path MTU (1500 Inet, <1500, 1500 LAN),
you need to pay attention to PMTU issues, such as destination
unreachable rate limitting, MSS hacks, and copying the DF bit from the
tunnelled packet to the outer encapsulating tunnel packet.

Depending on your traffic profile, and the latency of the paths the
tunnels take (i.e. if they're very similar), per packet rather than the
default per src/destination CEF load balancing is worth considering.

> Clearly the downside of this is that you need an agg machine on your
> end somewhere, but it gives you lots of control for sure.
> -Jack Carrozzo
> On Thu, Apr 15, 2010 at 5:05 PM, Bill Lewis <blewis at hottopic.com> wrote:
> > Group,
> >
> > Since I'm told that DSL aggregation / mux is currently not possible, we
> > are looking at doing stream splitting via a technology like FatPipe
> > uses. Anyone have this in production usage? Or something similar?
> >
> > Cisco has offered some ways to split via CEF, but most DSL carriers do
> > not have this turned on / available.
> >
> >
> >
> > Thank you,
> >
> > Bill
> >
> > Network dude
> >
> >

More information about the NANOG mailing list