Hi all,
We are experiencing performance problems with CBWFQ and I think I might be
running into what is either a CBWFQ scaling limitation, or I might have
misconfigured our routers.
The situation is that we have 12 x 2mb lines between 2 of our sites, 6 lines
to each 7xxx router (one 7206, 3 7576), 2 routers per pop:
SiteA: SiteB:
|-7576==6 x 2Mb lines==7576-|
GigEthernet-| |-FastEthernet
|-7576==6 x 2Mb lines==7206-|
Across all 12 lines on both directions I have a CBWFQ policy to reserve
256Kb/s of bandwith per line, i.e. 3Mb/s for traffic of a higher precedence
- This is more than adequate for the volumes of such traffic in our network,
and it is seen via a "show policy s1/2/3" for any and all such interfaces to
never actually have any discards or tail drops on this "priority policy",
whereas there are drops on the interfaces themselves, as the lines do run to
congestion during the day.
The problem is that, when there is congestion, two "side-by-side" tests,
comparing priority traffic to non-priority, the priority traffic latencies
are often worse than those of the non-priority traffic (using ping) and are
highly variable. Application (http/ftp) throughput is also lower than
expected and virtually the same (some would say worse!) as the non-priority
traffic. Some packet loss also occurs on both classes of traffic.
All routers are running CEF/dCEF and have "ip load-sharing per-packet" on
all serial interfaces, as well as "ip route-cache flow".
I would like to know if I am perhaps hitting a scaling issue on CBWFQ /
load-balancing or if I might have misconfigured something?
Thanks
Paul
Paul van der Zel
The Internet Solution
Tel: +27 (21) 425-3060
Fax: +27 (21) 425-3061
Mobile: +27 (82) 391-9410
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