Sockets: code works locally but fails over LAN

[n00m]

I was trying to test the send() vs sendall() like this:

x=send(data)
print len(data)-x > 0 ? (when the code fails)

but I could not reproduce the failures anymore.
As if the lan got "refreshed" after the first
using of sendall() instead of send().

Btw, why we need send() if there is sendall()?