How two bridge two DSL lines

Hello

SHDSL not being available in our area we've been offered by our ISP to 
use two 512/512 SDSL lines to make a 1mbit symmetrical link.

They recommend the use of a cisco router that will combine the two links 
into one by balancing the packets between the two connections (e.g. 1 
packet goes on DSL1, the next one on DSL2 etc...).

On the ISP side they would also do the same thing by sending IP packets 
across the two DSL link.

Now the question is, would FreeBSD allow me to do this? I found some 
references using the Balance program ( http://www.**--****.com/ ) or 
using IPFW rules and probablity match.
I don't really like any of those solutions; balance only works with TCP 
traffic and IPFW rules means that should one link goes down I'll be 
stuck with a 512/512 link losing 50% of the packets.

Also FreeBSD not being RFC1122 compliant I'm not sure how it's possible 
to set up two default gateway.

Any help or link will be appreciated. The ultimate goal is really to 
have a 1mbit link only 1 mbit/s transfer over a single connection ; not 
2x512kbit/s max.

Thank you in advance
Jean-Yves

See my Whirlpool response ;-) 
 http://www.**--****.com/ #r2

Matt.

Begin  < XXXX@XXXXX.COM >



You could indeed just use a cisco. If you can get one cheapish, and
it helps keep your ISP happy, why not?



Use netgraph(4) to spread the load, maybe? Take a look at it and its
ng_one2many(4) node type. For an introduction, see

   http://www.**--****.com/ 


-- 
  j p d (at) d s b (dot) t u d e l f t (dot) n l .

In article < XXXX@XXXXX.COM > jpd
< XXXX@XXXXX.COM > writes:


Yes, I think netgraph is the "right" way to do this on FreeBSD. Even
"better" than ng_one2many(4) could be ng_fec(4) (only on 5.x it seems) -
does just what a Cisco does!:-) However it will probably not achieve the
desired goal of having a single session be able to use the full 1 Mbit,
since it should try to keep all packets for a given session on the same
link - round-robin (which ng_one2many does) can in general be pretty bad
as it may make packets arrive out of order, but is probably the only way
to achieve that goal. (It's certainly not guaranteed to do it though -
TCP may be very unhappy with out-of-order packets, resulting in unneeded
retransmits and other throughput-reducing things.)

--Per Hedeland
 XXXX@XXXXX.COM 

Begin  <cu0tj4$1nhv$ XXXX@XXXXX.COM >




There's some patches floating around for 4.*, but I can't be arsed to
look them up ATM. And for a new setup it may be better to go 5.3.



Does cisco support the use of fec with a couple of xDSL devices in
between? *google* feh, cisco supports a myriad of ways to effect the
load balancing, not all of which preserve order. OTOH, while reading
cisco's explanation, it occurred to me that if one has cisco (or
generally, fec- and PAgP-capable) switches, one could vlan out three
ports, two of which aggregated to the xDSL modems. After that comes
the FreeBSD box do to sundry routing stuff. The modems requiring PPPoE
convolutes this idea.



I'm inclined to tell tcp to shut up and deal with it--it's one of
it's features after all. As it happens, there's been some work on the
reassembly of tcp streams on FreeBSD recently, with rather positive
results. It might even be MFCed somewhere soonish. That probably
won't help much if the hosts aren't running FreeBSD -- routers don't
reassemble. One could circumvent this with a (caching?) proxy.


-- 
  j p d (at) d s b (dot) t u d e l f t (dot) n l .

Hello




Thank you all for this help and references. Always good to know those stuff.


It is my understanding that the two DSL lines will be bridged either in 
the DSLAM or at the ISP concentrator. Therefore out-of-order packets 
shouldn't be an issue and no fragmented packets will ever reach the 
internet. It's purely between me and my ISP.

I guess for the time-being I will have to find some pricing on the cisco 
router.

Cheers
Jean-Yves

Begin  < XXXX@XXXXX.COM >


                                      ^^^^^^^^^
<pedant> I keep on saying this too, much to my own chagrin: DSL already
stands for Digital Subscriber Line. </pedant>



Err, unless the link between you and ``the other side of the DSLs''
has another layer of ppp (eg, PPPoE), fragments _will_ get out to the
'net. Intermediate routers don't reassemble fragments.

Packets arriving out of order is something that can happen anytime, but
as some implementations are clearly worse at handling the phenomenon
than others, it pays to keep the percentage of packets that do arrive
out of order low, insofar that is possible.



Have to, no. But it is an option. The great thing about cisco is that you
can buy the same for years on end. The downside to that is that you'll be
paying the same inflated price for the entire span, if you buy from cisco.


-- 
  j p d (at) d s b (dot) t u d e l f t (dot) n l .