Re: [LARTC] Load Balance and SNAT problem.

[Grant Taylor <gtaylor@riverviewtech.net>]

On 6/27/2007 12:54 AM, Peter Rabbitson wrote:
> I am actually simply jealous that some people apparently get it to 
> work in-kernel, and I can't seem to.

Ah, so the truth comes out.  ;)

> My requirements are pretty simple:
> o As transparrent as possible DGD, that can detect 2nd and 3rd hop 
> failures

Think about what you just asked for.  "Dead Gateway Detection" is used 
to detect dead (upstream) (default) gateway(s).  Rather it is not meant 
to detect dead routes beyond your gateway(s).  To do this you will need 
some sort of utility to monitor things for you.  I.e. you will not be 
able to get the kernel to detect that a gateway is good for some things 
but not for others.  Actually if you stop to think about it, this is 
beyond the scope of what the kernel should do.  This is more the scope 
of a routing protocol and / or a route management daemon.

In short, use something to test reachability to destinations and use ip 
rules to choose routing tables accordingly.  I.e. have a default routing 
table that will try to use any / all interfaces routes and have 
alternative routing tables that will try fewer interfaces / routes.

> o Robust load balancing - connections are distributed over all 
> available links, regardless of source and destination, with the 
> possibility of assigning relative channel priorities

I think this is close to being possible depending on your scenario (NAT 
or not) and a few other things.

It was my understanding that equal cost multi path routing was suppose 
to accomplish this very thing.  I.e. if you had globally routable IP 
addresses behind the router, you could send traffic out either link, 
hopefully in such a fashion as to (hopefully) fully utilize all links. 
ECMP does include weight options to assign ratios to routes.

However, after discussion in this thread, I question if ECMP will do 
this or not.

> o NAT compatible - link hopping is not an option, traffic with a 
> specific SRC/DST must stay where it started.

I think this is the simpler of the above "robust load balancing" as you 
say.  In my opinion, this should be the first of the things to be 
achieved and then try to extend this to be the above.

What you have proposed with load balancing via Netfilter should be able 
to achieve this with out any problems.  Or at least I would think such.



Grant. . . .
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