[Mageia-discuss] network balancing by default

[Maarten Vanraes]

Op dinsdag 26 oktober 2010 01:54:00 schreef P. Christeas:
> On Monday 25 October 2010, you wrote:
> > Op maandag 25 oktober 2010 00:56:32 schreef P. Christeas:
> > > On Sunday 24 October 2010, Maarten Vanraes wrote:
> > > > I would propose the following:
> > > > 
> > > > A.) by default, add for every interface, a little advanced routing
> > > > which makes packets return from the same way they came.
> > > > This usually is only useful with incoming packets, but can still be
> > > > useful if laptops have for example 2 gateways because the wifi is
> > > > still on and the cable is too. That would mean that from both
> > > > interfaces it'd be possible to use ssh or vnc or whatever.
> > > > 
> > > > B.) if we have multiple gateways (like in that case), have them use
> > > > both balancedly. ie: start a small daemon which checks which of the
> > > > gateways is up or down; and change the default gateway accordingly,
> > > > or even both in some kind of balanced mode. (with advanced routing.)
> > > > 
> > > > This would have the benefit, if you have really clueless users with a
> > > > laptop; that everything will still work well. and you're still able
> > > > to take over his laptop.
> > > 
> > > Will that do ? :
> > > http://git.hellug.gr/?p=xrg/ip-multipath;a=summary
> > > 
> > > (note to myself: I have to build a man^Hgeia rpm..)
> > 
> > This looks like something different than what i intended; isn't this more
> > of a configured thing?
> > 
> > I would propose some changes to the networkingscripts. when having
> > gateway addresses (through various means) to change the stuff.
> 
> Please excuse me for the lack of documentation.
> This script is an addon over the if-up scripts, which adds the support for
> multiple gateways to and from the internet.
> You only need to place this script in
> /etc/sysconfig/network-scripts/ifup.d/ and then some extra variables will
> help you configure the interfaces: MULTIPATH_TABLE=10  # needed, just a
> unique one per interface
> MULTI_GATEWAY_IN=1.2.3.4 # if this is a gateway route, but don't want to
> use # the interface by default
> MULTI_GATEWAY=1.2.3.4  # default route, along with other interfaces.
> 
> The functionality is provided by kernel itself. By using multiple kernel
> routing tables, the first thing you achieve is to have your server listen
> on all its internet-routing interfaces, so that you can connect *to* your
> server from any of them. This is _extremely_ useful, because it allows you
> to ssh to the server from /any/ interface that works, and then fix all the
> others. Saves the day.
> The second one, a little more tricky, is to have multiple routes to the
> internet. With TCP connections, this works /almost/ fine, because it may
> assign each connection to a different gateway, thus load-balancing. With
> UDP ones, well, this is not really working (AFAIK). However, if you also
> give different weights, it may activate the kernel's /slow/ transition
> mechanism (5-10 min responses), which will automatically pick the first
> working interface as its default gw (even if all interfaces are up and
> some of them respond with ICMP unreachable, it will work).


Ah, then i guess we are on the same page after all. the first part neatly 
conforms to my point A.

now the thing is, you can indeed configure that; but perhaps it would be better 
to let it autoconfigure; depending on the IP address at the time, when the 
gateways are being added as default routes. thus not needing any extra 
configuration.

i was under the impression that routes are being cached; so that even UDP will 
not have any problem here.

I have not heard about /slow/ transition mechanism though; i don't know what 
you mean by this.