[c-nsp] What is VFM?

[Matyas Koszik]

Hi,

We have a 3550 acting as a gateway for a small subnet filtering
unwanted packets. Today we got a DoS, all evil packets died on the switch,
so I was happy, but:

sh proc cpu | i (CPU|VFM)
CPU utilization for five seconds: 20%/5%; one minute: 17%; five minutes: 16%
  65     2977272  19711175        151 14.82% 12.32% 11.34%   0 VFM Queue Proces
  66         132        51       2588  0.00%  0.00%  0.00%   0 VFM/VQM Merge Pr
  67          12        11       1090  0.00%  0.00%  0.00%   0 VFM Deferred Upd

There's still some DoS traffic, about 90 mbit/s of full sized udp (not
1500 but 65000, so a lot of fragments), I guess it is the reason of this
'high' cpu load, but I don't really see why, since all of this traffic
gets dropped on ingress.. Also a "vfm site:cisco.com" revelaed nothing
about it.

So, the question is, what is VFM and why does it need so many CPU?