[LARTC] HTB not working quite the way I'd expect?

[Jason Tackaberry <tack@auc.ca>]

I have a 2Mbit connection, and I would like to distribute that 250k/s
(upstream bandwidth, of course, because I am adding the qdisc on our
internet interface) as follows:
        * From our residence students (199.212.55.128/25), min 50k/s,
          ceil 200k/s
        * From our DMZ network (where our webserver is located,
          199.212.53.0/24), min 200k/s, ceil 250k/s

This is the configuration I _think_ should work:

    tc qdisc add dev eth8 root handle 1: htb default 11
    tc class add dev eth8 parent 1: classid 1:1 htb rate 250kbps
    tc class add dev eth8 parent 1:1 classid 1:10 htb rate 200kbps\
     ceil 250kbps burst 10k
    tc qdisc add dev eth8 parent 1:10 sfq perturb 5
    tc filter add dev eth8 protocol ip parent 1: prio 1 u32 match ip\
     src 199.212.53.0/24 flowid 1:10
    
    tc class add dev eth8 parent 1:1 classid 1:11 htb rate 50kbps \
     ceil 200kbps burst 2k
    tc qdisc add dev eth8 parent 1:11 sfq perturb 10
    
    tc filter add dev eth8 protocol ip parent 1: prio 4 u32 match \
     ip src 199.212.55.128/25 flowid 1:11
    
So, our residence students are assigned to classid 1:11.  Notice that
1:10, our DMZ, is given prio 1, because I want it to get any extra
bandwidth before our residence.  Indeed, residence users are happily
throttled at 200k/s (sustaining it, thanks to the proliferation of p2p
file sharing programs).  However, when I hit our webserver (from 3
outside sites with lots of bandwidth), I am only able to transfer at
about 65k/s (peak 85k/s), while the residence students only drop down to
about 160k-180k/s.  What I would expect to happen is residence dropping
to 50k/s, and our webserver serving up at 200k/s.  (Incidentally I am
monitoring the input/output on the interfaces using iptraf to measure
bandwidth usage.)  I am sustaining the transfer for 20-30 seconds before
measuring bandwidth usage.

If I drop the ceil on 1:11 to 150kbps, I am able to get about 100-120k/s
from the web server.  And if I again drop the ceil to 100kbps, I get
around 175k/s from the webserver.  So clearly my remote sites are able
to pull down the full 200k/s, which is my goal.

So knowing what I want, and my current configuration, can anyone see
what I'm doing wrong?

Thanks,
Jason.

-- 
Academic Computing Support Specialist
Algoma University College
Sault Ste. Marie, Ontario
705-949-2301 x330                                   Personal Home Page
http://www.auc.ca                                     http://sault.org

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