packet pass through vs ftp -- performance weirdity

[Gary Aitken]

I'm seeing some weird network performance I don't understand.

If I sit at an NT box and using a web browser, go through my fbsd 4.10
firewall to someplace out in the world through a slow dsl connection,
I get download speeds of 20KB - 45KB/sec, pretty much the max my DSL
connection can deliver.

The nt box is connected to the fbsd box over a 10Mb/sec full duplex
crossover cable for test purposes.

If I ftp (shell window) or use a browser to ftp from the fbsd box
itself, I see a max speed of something like 8KB/sec.

This makes absolutely no sense to me, given the relative speeds of the
network connections, which I would have thought was the limiting
factor.

The fbsd box is a p200, 128M, single 7200rpm 9.4ms seagate ultra scsi
drive, 10MB/sec negotiated xfr rate.  Data used for testing was ~8MB
file in /var partition, don't know how badly fragmented.

Is passing packets through the firewall and ipfw rules that much
faster than an ftp access?

Ideas for where to look for what's slowing things down?

Thanks,

Gary