Kenneth Kalmer wrote:
Guys
Hi,
First the case study. An untrusted network with over-subscribed users
(and abusers). Common at universities and bigger enterprises. People
want good speed at any time, but abusers should be detected and
clamped down automatically. This system needs intelligence. Let's say
a good combo between HTB & WRR, through in a pacemaker and the
configurability of XML files.
I have a lot of experience in networks like this, so I'll post some
comments:
My thinking is Python (I only code interpreted) doing the
configurations and "live" htb manipulation to simulate wrr, but still
offer the gaurentees of htb.
I have heard that HTB doesn't scale well when you have it arranged in
this way (search "Ostrochovsky" in the archives, or perhaps it was
another list => use google). This would have to be analysed. Usually I
avoid it by creating more levels (think binary tree), but I don't have
any measurements on high load.
WRR on the other hand has many advantages: it scales very well,
automatically penalizes abusers, and behaves predictably (I performed a
statistical-mathematical analysis of one such case last week, got great
results). There is one problem though: what it distributes is actually
sending frequency, not bandwidth. Therefore, you can't set limits to
traffic of individuals, you can't give anyone "guaranteed" bandwith, or
give someone "twice as much bandwidth as the others". You can set it up
so that certain IPs are penalized less or more, but there is no way to
give them specific bandwidth.
In my experience (my customers) sometimes want to set specific
bandwidths, but after using WRR for some time, due to its fairness
characteristics they decide it's not necessary. A commercial ISP may
have different requirements though, so that they can sell different
bandwidths for different prices.
Although I don't have a mathematical proof :-), I think that these two
approaches are mutually exclusive. If you want predictable behaviour (no
latency peaks), you can either give individual people specific
bandwidth, or you can utilize the bandwidth fully. You can't utilize the
whole bandwidth while giving people specific amounts of it.
Nevertheless, I have some ideas how to bring certain advantages of HTB
to WRR:
- if you want to cap someone, you may be able to use a htb inside one
wrr-subclass
- if you want to guarantee someone's bandwidth, give him a permanently
higher weight (cap others to a lower weight), put htb there and set its rate
(For comparison, I use ESFQ inside the wrr-subclasses).
I'd like to stress however that you lose a lot of WRR's predictability
if you manually fiddle with the settings. This would have to be tested
extensively.
Extra things should be the ability to handle multiple subnets, not
just a single one,
WRR handles multiple subnets without problems and without the need to
set anything (classes are assigned dynamically as the IPs appear).
> and while doing Python we might as well have
options to produce rrd's to make sure that everything is running
perfectly.
Sorry for advertisement (again). Shurdix already does this, most of it
automatically (and uses perl, but the scripts are very simple). I use
ipt_ACCOUNT for accounting because I want it to be independent from
traffic control, but WRR has it's own accounting method (look on their
website, it is also more precise, because iptables-based accounting
doesn't know about packets that are dropped while doing egress).
Any advice, tips or suggestions? I know it won't be an easy feat, but
it is worth a shot...
As I said, the first thing you should do is to set your priorities:
- if you want to utilise the bandwidth fully, go WRR
- if you want to set specific parameters, go HTB
And you have to test, test, test, because if you lose predictability
you're screwed :-).
Best
Kenneth Kalmer
Yours sincerely,
Peter
--
http://www.shurdix.org - Linux distribution for routers and firewalls
_______________________________________________
LARTC mailing list
LARTC@xxxxxxxxxxxxxxx
http://mailman.ds9a.nl/cgi-bin/mailman/listinfo/lartc
