[Mageia-discuss] network balancing by default
bluca at vodka.it
Mon Oct 25 08:41:01 CEST 2010
On Mon, Oct 25, 2010 at 12:00:46AM +0200, Maarten Vanraes wrote:
>Op zondag 24 oktober 2010 22:39:29 schreef Luca Berra:
>> On Sun, Oct 24, 2010 at 11:43:28AM +0200, Maarten Vanraes wrote:
>> >I would propose the following:
>First off, the timing of this proposal is probably too soon, i just wanted to
>get it out there, in case i forgot later.
open an enhancement on initscripts :P
>> >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.
>> this is possible with incoming packets, but, how do you select the
>> source of a new one?
>this step is only for the replies of incoming packets and never has any effect
>on new outgoing packets; this step doesn't change anything for new outgoing
>packets. and this can even be used on interfaces that aren't used as default
i did not understood the second and third sentence in A.), then.
anyways i believe A is useful and can be implemented without any issue
>A) interface down
>B) DHCP expired
>C) gateway down
>D) further routing down
>E) DNS down
>A is trivial, so we'll just skip that one.
>B seems easy to do too; however, reusing the last DHCP lease could still be
>usefull, it might well be only a dhcp failure; we should try with the current
>lease if possible.
if it is expired you should not. doing this will result in duplicate
>E is a bit of an extra (it's not really routing, but a DNS that's down (does
>not answer) could well be eliminated (not sure if this should be done
>separately or not)) OTOH, failure of the recursive DNS of the ISP seems to be
>somewhat frequent in my experience.
so a connectivity issue will leave users without dns?
>C+D are tricky: D is even a bit of a grey area; my ISP frequently has a few
>routes broken. icmp can definately not be relied on in all cases. and even if
>you ping your gateway, you don't know if it goes any further.
>This could be circumvented by putting known servers that actually echo icmp in
>a list and ping those. but for that matter, it doesn't have to be icmp; we
>could easily have a list of public services that can be connected to. but is
>this really what we want?
>We could even just monitor how much packets are unreplied to per interface and
>Or we could try to have each retry of unreplied packet go through the next
>Or we could just not handle that (like it is now).
you are considering the only scenario of a home user. doing some things
you propose above would prevent using mageia in any medium sized
network. (i.e. i could not use my mageia laptop at work)
>remember that right now only A(+B) is used; and having balanced default routes
>would probably mean that there is 50% packet loss, instead of 100% in most
which may be worse.
if nothing works the user will try switching to a different connection
if stuff do not work at random the user will not know what to do.
btw, the assumption about 50% is flawed, i don't know if it is an
oversimplification or a failure to understand how load balancing over
multiple network links work in practice.
it is not round-robin, it is route-based (on ip hash)
the result of a failure upstream will result in the user being able to,
say, watch some videos on youtube, but not update her fb profile, or
>also remember that if the metrics are the same for some reason, you will get
>much stranger things when both are working perfectly.
btw, there is no need to cc me on discussions, in fact it breaks my
Luca Berra -- bluca at vodka.it
More information about the Mageia-discuss