Bandwidth distribution per ip

Denys Fedoryshchenko denys at visp.net.lb
Wed Dec 20 17:04:46 CST 2017


On 2017-12-20 17:52, Saku Ytti wrote:
> On 20 December 2017 at 16:55, Denys Fedoryshchenko <denys at visp.net.lb> 
> wrote:
> 
>> And for me, it sounds like faulty aggregation + shaping setup, for 
>> example,
>> i heard once if i do policing on some models of Cisco switch, on an
>> aggregated interface, if it has 4 interfaces it will install 25% 
>> policer on
>> each interface and if hashing is done by dst ip only, i will face such
>> issue, but that is old and cheap model, as i recall.
> 
> One such old and cheap model is ASR9k trident, typhoon and tomahawk.
> 
> It's actually pretty demanding problem, as technically two linecards
> or even just ports sitting on two different NPU might as well be
> different routers, they don't have good way to communicate to each
> other on BW use. So N policer being installed as N/member_count per
> link is very typical.
> 
> ECMP is fact of life, and even thought none if any provider document
> that they have per-flow limitations which are lower than nominal rate
> of connection you purchases, these do exist almost universally
> everywhere. People who are most likely to see these limits are people
> who tunnel everything, so that everything from their say 10Gbps is
> single flow, from POV of the network.
> In IPv6 world at least tunnel encap end could write hash to IPv6 flow
> label, allowing core potentially to balance tunneled traffic, unless
> tunnel itself guarantees order.
> 
> I don't think it's fair for operator to demand equal bandwidth per IP,
> but you will expose yourself to more problems if you do not have
> sufficient entropy. We are slowly getting solutions to this, Juniper
> Trio and BRCM Tomahawk3 can detect elephant flows and dynamically
> unequally map hash results to physical ports to alleviate the problem.
As person who is in love with embedded systems development, i just 
watched
today beautiful 10s of meters long 199x machine, where multi kW VFDs 
manage
huge motors(not steppers), dragging synchronously and printing on thin 
paper
with crazy speed and all they have is long ~9600 link between a bunch of 
encoders
and PLC dinosaur managing all this beauty. If any of them will apply a 
bit wrong
torque, stretched paper will rip apart.
In fact nothing complex there, and technology is ancient these days.
Engineers who cannot synchronize and update few virtual "subinstances"
policing ratio based on feedback, in one tiny, expensive box, with 
reasonable
update ratio, having in hands modern technologies, maybe incompetent?

National operator doesn't provide IPv6, that's one of the problems.
In most of cases there is no tunnels, but imperfection still exist.
When ISP pays ~$150k/month (bandwidth very expensive here), and because
CDN has 3 units & 3 ingress ips, and carrier have bonding somewhere over
4 links, it just means ~$37.5k is lost in rough estimations,
no sane person will accept that.
Sometimes one CDN unit are in maintenance, and 2 existing can perfectly
serve demand, but because of this "balancing" issues - it just go down,
as half of capacity missing.

But, tunnels in rare cases true too, but what we can do, if they don't 
have
reasonable DDoS protection tools all world have (not even blackholing).
Many DDoS-protection operators charge extra for more tunnel endpoints 
with
balancing, and this balancing is not so equal as well (same src+dst ip 
at best).
And when i did round-robin on my own solution, i noticed except
this "bandwidth distribution" issue, latency on each ip is unequal,
so RR create for me "out of order" issues.
Another problem, most popular services in region (in matters of 
bandwidth)
is facebook, whatsapp, youtube. Most of them is big fat flows running 
over
few ips. I doubt i can convince them to balance over more.


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