network lockdown on mips build daemons

["Zack Weinberg" <zackw@panix.com>]

A package I maintain (monotone) fails to build on (some of?) the mips
build daemons, and I've been informed that this is because those
daemons restrict network access, causing spurious failures in the
package's testsuite.  (Bug #472480.) I would like to change the
testsuite to skip the problem tests when network access is restricted,
but I can find no information about *how* the network access is
restricted or how I might detect that from the build scripts.

Can anyone please tell me what is and is not allowed, as far as
network access, on the mips buildds, and how the failure appears to a
program that tries to do something forbidden, or best of all, suggest
either a shell command or a C function that will succeed on a machine
with normal network access and fail (instantly!) on a machine with
this kind of network lockdown?

zw