I'm posting this primarily because my original searches on the matter turned
up a similar problem report on this list (Feb 26, 2002), but no solutions.
Here are my findings, for the record.
Problem: very poor network throughput on Linux masqueraded TCP connections. No
problem with performance when data is moved via an HTTP proxy on the
masquerading box, but data transfer drops to painfully slow levels (1 to 10
kB/s, as opposed to >500 kB/s) when a masqueraded HTTP connection is
attempted. (Effect is not exclusive to HTTP.) Closer analysis shows that
masqueraded links are operating in short bursts, punctuated by several
seconds of non-activity, for no obvious reason.
Configuration: VIA EPIA 1GHz 512MB in the router role. Has on-board "rhine"
ethernet, plus a "tulip" card in the PCI slot. The "tulip" card is connected
to a cable modem at 10Mb/s, the "rhine" to the local network switch at
100Mb/s. The system is loaded with Debian "Woody", and the problem persists
with both a Debian kernel package (2.4.18) and a locally configured and
compiled kernel 2.4.24. Two different clients on the local network were
tested (using "wget" to fetch a file directly, or through the non-caching
HTTP proxy on the router) with identical results: fast proxy operation, but
horribly slow masqueraded operation.
Work-around: replacing the "tulip" card with a "RTL8139" ("8139too" driver)
card eliminated the problem. This is suggestive of a bug in the "tulip"
driver code, although other explanations are possible. Replacing the NIC also
resulted in the "rhine" ethernet becoming eth0 (previously eth1), and I
attached the cable modem to the "rhine" ethernet instead of editing network
configurations.
Regards,
TFBW
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