FreeBSD network stack is quite stable but lacks some of the improvements/features available in other OSes.
A bunch of us have started an effort to try and identify current problems to improve transport layer (TCP, UDP, SCTP and others) for FreeBSD:
Traditionally, freebsd-net has been the mailing list where networking problems get discussed but some have complained it to be too spammy and too focused on NIC drivers related issues. So a new mailing list has been created to specifically talk about transport level protocols: transport@
We’ve also started creating a list of TCP related RFCs and their support for FreeBSD to have a single point of reference.
Plan is to have a coordinated effort to improve TCP, UDP, etc.. so if you are interested in any of those protocols, please join the mailing list and help FreeBSD. :)