DSL link aggregation?

[Bradley Hook]

If you were like a large corporation or university, you might have an
ISP setup to handle multipath routing for end-users. Multipath can route
to/from the same IP address over multiple paths. But this isn't the
scenario here, because it isnt' the same IP address on each connection.

In the setup described here, with 2 standard ADSL connections, you will
have two different IP addresses. Many ISPs are turning on source address
verification, which means you can't spoof the source address on one line
to match that of the other. Keep in mind it only takes ONE hop in the
entire route that has source address verification turned on to break
your spoofing setup (this isn't as much of an issue if you are using the
same ISP for both circuits, because they will both have all the same hops).

Even with separate IP addresses, you can still load balance between
them. However, you can't load balance a single TCP session over two IP
addresses (well, you can, but a lot of software will tear down the
connection if you try it). You can encapsulate your TCP connections into
a UDP VPN that is load balanced over the two circuits, but as I already
described you will end up getting only minimal gains due to the latency
and overhead of wrapping the packets. If he was uploading lots of small,
individual files, he could be simultaneously uploading different files
on each connection. However, he seems to be dealing with large
individual files, so load balancing over two public IP addresses wont
help in this case.

Jon Pruente wrote:
> On Tue, May 6, 2008 at 9:37 PM, Greg Brooks <gregb at west-third.com> wrote:
>> Anyone successfully used link aggregation to combine two ADSL lines for
>>  greater outbound bandwidth?
> 
> Wouldn't it be feasible to use a router machine between the home PC
> and the DSL lines?  Use two outbound NICs and set the router to load
> balance between them for the 3rd internal NIC.  I don't really see a
> technical reason why it's as complicated as people are making it out
> to be.  By the very nature of TCP/IP packets can take multiple paths.
> You just want to force half one way and half the other.  That's not a
> big deal to do, IMHO.
> 
> Jon.
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> 

-- 
~Bradley Hook
Education Systems Administrator
Kansas State School for the Blind
1100 State Avenue
Kansas City, KS 66102
Voice: (913) 281-3308 ext. 363
Mobile: (913) 645-9958
Facsimile: (913) 281-3104
http://www.kssb.net

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