Re: [LARTC] multipath device round robin not working?

[Grant Taylor <gtaylor@riverviewtech.net>]

On 01/13/07 05:54, zutph3n@gmail.com wrote:
> Both links have their own ip but have the same gateway. The problem is I 
> can't seem to get egress traffic load balanced over the 2 nics.

I don't know if it is still a problem or not, but I ran in to something 
very similar a LONG time ago (mid 2.4).

Basically what I found was the problem was that (I believe) multi-path 
routing really is multi gateway routing.  I.e. load balancing across two 
(or more) different gateways.  In your case, and the case that I had, 
all the IPs in the world did not make any difference b/c each path had 
the same default gateway.

My solution at the time was to use UML routers to provide different 
subnets to the box doing ECMP routing.  Each UML basically NATed from 
the one upstream network to a small downstream private subnet that was 
unique for each link.  This allowed the box doing ECMP to see different 
gateways.  This worked great until I hit a memory limit on connection state.

I should probably say that the problem I ran in to was not a problem 
with ECMP but the number of hosts that I was trying to NAT with the 
amount of RAM that was on the box.  I was able to resolve this by adding 
RAM to the box to provide a larger Connection State Table.  For the 
record, the box was running a mid 2.4 kernel with a subnet that was the 
size of 4 class C networks (2048 IPs) on a box that had 256 MB of RAM. 
I ended up taking the box up to 2 GB of RAM and things have been working 
GREAT ever sense.  I do believe this memory / connection state problem 
has been resolved long ago.  However the system is working and payed for 
and the client is perfectly happy with what is in place and sees no 
reason to do any thing with it.  (If any one would like more details, 
just ask.)



Grant. . . .
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