Re: MultiPath Routing

Re: MultiPath Routing

[pravin b shelar]

>Christian Schmid <webmaster@rapidforum.com> wrote:
>> 
>> Since this seems to be an undocumented feature.... How is this equal-cost multipath supposed to 
>> work? I just want to send outgoing traffic over two gateways. I tried this:
>> 
>> ip route replace default scope global nexthop via 192.168.0.1 dev eth1 weight 100 nexthop via 
>> 192.168.0.100 dev eth1 weight 100
>> 
>> It it doesnt work. It always uses the last for all download-users (around a few hundreds)
>
>Did you enable IP_ROUTE_MULTIPATH_CACHED? If so please disable it
>since it breaks multipath routing for forwarded traffic.

Hi ,
	This was a bug reported by Christian Schmid long back. It is related to equal cost multipath caching on forwarded traffic. The solution suggested for this was 
to disable equal-cost multipath caching. But It does not look like a clean solution.

I investigated the problem further and observed that, If multipath caching is "on" then all route entries are added to the route cache. This leads to selection of same
NIC for all route going through this ( forwarding ) sever. This is because we don't have selection logic for forwarded traffic in multipath caching code.

On digging this list further, I found a patch posted by Herbert, which  disables multipath route cache entry addition for input case.
I tested this patch and everything works fine now.
for the patch ref: http://oss.sgi.com/projects/netdev/archive/2005-04/msg00232.html

So how about including this patch ?

Comments ?

Regards,
Pravin.

MultiPath Routing

[Christian Schmid]

Hello.

Since this seems to be an undocumented feature.... How is this equal-cost multipath supposed to 
work? I just want to send outgoing traffic over two gateways. I tried this:

ip route replace default scope global nexthop via 192.168.0.1 dev eth1 weight 100 nexthop via 
192.168.0.100 dev eth1 weight 100

It it doesnt work. It always uses the last for all download-users (around a few hundreds)

Or is this the wrong way? (2.6.12rc3)

Best regards,
Chris

Re: MultiPath Routing

[Herbert Xu]

Christian Schmid <webmaster@rapidforum.com> wrote:
> 
> Since this seems to be an undocumented feature.... How is this equal-cost multipath supposed to 
> work? I just want to send outgoing traffic over two gateways. I tried this:
> 
> ip route replace default scope global nexthop via 192.168.0.1 dev eth1 weight 100 nexthop via 
> 192.168.0.100 dev eth1 weight 100
> 
> It it doesnt work. It always uses the last for all download-users (around a few hundreds)

Did you enable IP_ROUTE_MULTIPATH_CACHED? If so please disable it
since it breaks multipath routing for forwarded traffic.
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

Re: MultiPath Routing

[Christian Schmid]

> Did you enable IP_ROUTE_MULTIPATH_CACHED? If so please disable it
> since it breaks multipath routing for forwarded traffic.

Yes I enabled it. But it shouldnt do anything because its no forwarded traffic here. I just used 
example-IPs. Or does the bug also break non-forwarded traffic?

Re: MultiPath Routing

[Herbert Xu]

Christian Schmid <webmaster@rapidforum.com> wrote:
> 
> Yes I enabled it. But it shouldnt do anything because its no forwarded traffic here. I just used 
> example-IPs. Or does the bug also break non-forwarded traffic?

Did you select one of the multipath algorithm options? If you selected
them as modules did you load them? If no algorithms are available it
will degenerate into deterministic routing.

It will also work properly if you disable IP_ROUTE_MULTIPATH_CACHED
completely.

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

Re: MultiPath Routing

[Christian Schmid]

I tried disabling MULTIPATH_CACHED and now it completely works :) Thank you for your help. I thought 
your hint only is for NATed traffic but it seems its for all traffic.

Herbert Xu wrote:
> Christian Schmid <webmaster@rapidforum.com> wrote:
> 
>>Yes I enabled it. But it shouldnt do anything because its no forwarded traffic here. I just used 
>>example-IPs. Or does the bug also break non-forwarded traffic?
> 
> 
> Did you select one of the multipath algorithm options? If you selected
> them as modules did you load them? If no algorithms are available it
> will degenerate into deterministic routing.
> 
> It will also work properly if you disable IP_ROUTE_MULTIPATH_CACHED
> completely.
> 
> Cheers,