Loadbalance outgoing traffic over two cable modems in same network

[Craig Butler]

On 22/12/2009 00:46, Mel Flynn wrote:
> On Monday 21 December 2009 09:56:11 Nikos Vassiliadis wrote:
>    
>> On 12/21/2009 6:03 AM, Mel Flynn wrote:
>>      
>>> Hi,
>>>
>>> I've looked over http://www.openbsd.org/faq/pf/pools.html but this
>>> assumes two different gateways for the two interfaces.
>>> I'm faced with two cable modems from the same ISP, with the same gateway.
>>> I can't lagg(4) the interfaces, since specific IP's are bound to specific
>>> modems.
>>>        
>> This can probably be fixed from the ISP side. It should probably be some
>> antispoofing rule that drops the packets you are sending via the "wrong"
>> interface. You could try communicating the problem to the ISP and hope for
>> the best...
>>      
> I'd rather not go that route. However, I might ask the ISP to move swap two
> IP's, so that I have two consecutive IPs on two modems and can use /31
> notation for the pool. Source hash should then work better.
>
>    
>>> So I'm wondering if using stick-address with a round-robin nat pool is
>>> really sufficient to do load balancing of outgoing traffic and not get
>>> into session problems with various protocols. Has anybody had similar
>>> experiences?
>>>        
>> I have no experience on this, but theoretically a state can expire while
>>   the upper layers are still active... so, I *think* you may have
>>   problems... Of course, you could increase the lifetime of states
>>      
> True, I'm mostly worried about DNS queries and other UDP protocols. TCP should
> theoretically be fine.
> Thanks for your feedback.
>    

Would ECMP (aka RADIX_MPATH) not be suitable for your requirements ?? 2 
default routes, one to each of the modems IP's ... that should start 
bunting traffic down both pipes.

Works for me here...

=================================================
Equal cost multipath routing

Status: Committed to 8-CURRENT
Will appear in 8.0: sure
Authors: Qing Li
Web: commit message

ECMP routing allows for multiple routes to be handled by the kernel, 
including default routes. It potentially offers substantial increases in 
bandwidth by load-balancing traffic over multiple paths.
=================================================
http://en.wikipedia.org/wiki/Equal-cost_multi-path_routing
http://lists.freebsd.org/pipermail/cvs-src/2008-April/089956.html

/Craig B