[kwlug-disc] Bandwidth aggregation

Bob Jonkman bjonkman at sobac.com
Wed Feb 11 11:50:34 EST 2009

And after teasing us like that, now we want to see pretty network 
diagrams, sample config files, scripts, and maybe even a demo.

Yes, it's esoteric, and No, we promise not to try this at home, but 
it's still interesting and presentation-worthy.

+1 for a presentation by Andrew!


-- -- -- --
Bob Jonkman <bjonkman at sobac.com>         http://sobac.com/sobac/
SOBAC Microcomputer Services              Voice: +1-519-669-0388
6 James Street, Elmira ON  Canada  N3B 1L5  Cel: +1-519-635-9413
Software   ---   Office & Business Automation   ---   Consulting

On 11 Feb 2009 at 9:59 Andrew Kohlsmith (lists) <kwlug-disc at kwlug.org> 
about "Re: [kwlug-disc] Bandwidth aggregat[...]"

>On February 10, 2009 03:52:44 pm L.D. Paniak wrote:
>> I think it would be a great topic.  WAN connections are easily the most
>> unreliable part of a modern computer system.  For things like VOIP,
>> failover capability is essentially a requirement.
>> Is it really that esoteric?  Don't most homes/businesses have access to
>> cable and DSL or two channels of DSL?
>Yes it is.  I said "multihomed IP space" -- that is not the same thing as two 
>DSL or cable connections at all.
>Multihomed IP space means an IP address which is reachable through two or more 
>providers. I'm not aware of any DSL, Cable, Cell or Wifi providers which give 
>you this kind of address.
>If you get from your DSL provider and through your cable 
>provider, both of those addresses are single-homed from your perspective.  If 
>someone on the internet sends a packet to, it will ONLY come from 
>your DSL line, and never from your cable.  If you send a request out your DSL 
>connection, the response will come back through your DSL connection.  It 
>won't balance between the DSL and cable connections.  You can try to fake 
>your source address to have a request go out one and back the other, but any 
>ISP worth their salt will be dropping packets not sourced from their own IP 
>What I am doing is "extruding" multihomed IP space through a number of 
>single-homed connections.  Through SCS Internet, I have access to multihomed 
>IP space.  (e.g.  Traffic to any of these addresses can come 
>from one of (I think) three or four different providers into his rack.
>Using a server in that rack (with IP, for example), I "extrude" an 
>IP, say  I use proxy-arp to as a means to capture traffic for that 
>IP.  Basically that means that whenever someone asks for the ethernet address 
>of, the server responds with its own MAC.
>Your router at the office has a DSL and cable connection, with IP and 
> from your respective providers.  What I do now is to set up two GRE 
>tunnels, one from to and one from to  So 
>now your home router actually has four routes: DSL-to-world, cable-to-world, 
>DSL-to-server-via-tunnel0, cable-to-server-via-tunnel1.
>What I do now is to use iproute2 and iptables to set up a packet marking and 
>load balancing system.  I say that traffic for the world (i.e. default route) 
>is via DSL-to-server-via-tunnel1 *AND* to cable-to-server-via-tunnel1, with 
>equal weighting (neither route is preferred). I also to disable route 
>caching, which works against us in this scenario.  Now any traffic that the 
>router wants to send out to the world will go through either tunnel and "pop 
>out" as traffic from
>It may have taken the path through the cable or DSL IP, but it was 
>encapsulated in the tunnel at that point.  The traffic exits from 151 Front 
>with a source IP of and heads out through any of the providers that 
>he has available.  It reaches the destination, and a response comes back to 
>  The server receives that traffic, sends it back through one of the 
>two tunnels, and your router gets it and does what it would normally do with 
>it.  All the tunnels are brought up and torn down with your standard ip-up 
>style scripts that PPPoE gives, but you could also do it with the normal 
>networking post-route scripts (for cable or wifi connections, for example).
>If a tunnel fails, the other tunnel's there, and traffic still flows.  If you 
>add more tunnels, the bandwidth is load-balanced over them.  Since the 
> address is multihomed, you don't lose connectivity when one of the 
>providers that SCS Internet uses has troubles, since that IP is reachable 
>through several other paths.  You can play with route metrics to favour one 
>tunnel over the other, and of course you can play with the routing table 
>selections on the router so that you do NOT use the multihomed space for 
>regular web traffic, windows updates or whatever other nonessential traffic 
>you may have.
>You can *also* use IPSec to encrypt everything over the tunnel.
>The only real downsides are
>1) bandwidth considerations at the colo
>2) slightly increased latency due to tunnelling and encryption
>I've used this method to provide highly-available bandwidth for the auto 
>industry, where they were willing to pay for the colocated server at 151 
>Front -- multihomed IP space was simply not available at some of their 
>plants, and simply too expensive at others. They decided to get more bang for 
>their buck by using the colocated server as an IPSec endpoint, FTP server for 
>*huge* CAD drawings and a conferencing bridge instead of bringing absolutely 
>all that traffic back to their home network.
>Anyway -- that's why I feel it's an esoteric topic.  You can bring two DSL or 
>cable connections together for home/office use, but that's not the same thing 
>as what I described.
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