[Mageia-discuss] network balancing by default

[Maarten Vanraes]

Op maandag 25 oktober 2010 22:07:16 schreef Luca Berra:
> >> >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?
> >
> >more the other way around; in the event of dns failure; the dns of the
> >other gateway could be used. if it would be a routing issue to the DNS
> >(and others), then other rules could be triggered (C+D)
> 
> this has to be implemented very well, my comment was sarcastic, if you
> do it badly (i.e. pruning and not reinstating dns you will sooner or
> later end with none)

imo, this can be handled just like ifup and the like do it; but i'm not sure 
if i would have this option on by default.

> >> >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 choose that.
> >> >
> >> >Or we could try to have each retry of unreplied packet go through the
> >> >next default route.
> >> >
> >> >Or we could just not handle that (like it is now).
> >> 
> >> +1
> >> 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)
> >
> >I don't see what you mean by this. i list 4 options; knowing full well
> >that some of those options are not usefull by default. also, this is only
> >required if more than one default gateway is active; which is a small
> >percentage in itself. (my personal favourite is having it sent to the
> >other default gateway after failure; or seeing which has more unreplied
> >packets; and then check some public services)
> 
> i mean that if mageia is known for misbehaving wrt dhcp leases corporate
> policies will start including a ban on mageia.

right, i understand now.

> >> >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 cases.
> >> 
> >> 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.
> >
> >it could be worse, depending on the type of person.
> >
> >> 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
> >> worse.
> >
> >i meant on average in total, depending on what kind of balancing is used.
> 
> I believe you cannot change the ip load balancing method.

I mean there are several rules that can be used to decide what balancing is 
used; the most common one being the weighted one.

> I would prefer an option (not active by default) that would allow users
> to decide preferred default network connections and fail over to backup
> network connections if the active one fails (possibly allowing failback,
> but not by default).
> It could implement some smart way of finding wether a connection is
> actually working. But data to do this has to be user supplied, it is too
> difficult to find the right one with so diverse possible networking
> environments.
> I'd leave all load balancing out of the picture, it is very difficult to
> get right.
> Even interface bonding with tlb can be disruptive to network setups.
> 
> L.


i have seen lots of environments that have wifi direct out access and the 
cabled access being internal and having extra access to internal servers. 
(also some the other way around too.)

I think we should allow multiple configurable policies for this; but we should 
try to find one that will work well for everyone and use that one as default.


if one interface has all it's packets unreplied for X time (30sec with a 
minimum of 10 packets?) we could evaluate that interface to be temporarily 
down. i think this kind of setup would work for everyone.

just my thoughts,

Maarten