Automagical port allocation for tests

Ceri Storey wrote “It’s quite common to want to test a net­work ser­vice from the out­side, as if it was being ac­cessed from a cli­ent. Quite of­ten, people will pick a “well-­known” port to use, eg: port 8080 or 8888 for a HTTP ser­vice. But that means that if you leave a stray service process lying around, you’ll need to hunt it…”

Sturmfront auf Doppler-Radar-Schirm, public domain, von www.noaa.gov

Adventures in TCP latency measurement

Ceri Storey wrote “Re­cently, Google have pub­lished an art­icle on BRR, an al­gorithm that ex­pli­citly meas­ures the round-trip latency and band­width ca­pa­city of the link between two ma­chines (be it in a data­center, or a mo­bile phone) to avoid sending more traffic than is use­ful, causing queues to build up in the net­work that need­lessly in­crease latency. So…”

By User:Salimfadhley (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons

4-way TCP handshake and firewalls

Jarek Siembida wrote “This is one of those pieces that you keep in your head for ages but never get around to write up. Tcpdumping I was doing of late brought it back so here it is. We all know the 3-way handshake in TCP: SYN + SYN/ACK + ACK and voila! But this is not the end…”