If you are running a multi-honed server, and your server occasionally drops out of the master server listing, or appears on the wrong public IP, then you may be interested in testing our some beta binaries that might fix the problem. The problem begins with a disruption while talking on UDP (often during the weekly prop of Steam). The Steam client layer then enters a fallback pattern of TCP, then UDP, etc. Eventually the disruption is resolved, and it can be random whether your server managed to connect to Steam on TCP or UDP, depending on where it was in the retry pattern. The problem with TCP for multi-honed servers is that it will always bind to the default interface, disregarding any request to bind to a particular interface. This can cause Steam to see your server as coming from the wrong public IP. Depending on your routing rules, NAT, etc, your server can drop off of the server browser because clients cannot get to you when they send packets to that IP.
Some server operators have worked around this bug with firewall rules preventing the server from connecting to Steam via TCP.
These binaries disable TCP fallback for dedicated servers.http://media.steampowered.com/apps/440/ ... 586041.ziphttp://media.steampowered.com/apps/440/ ... 586041.zip
Be warned that they have not been widely tested. You should only try out these binaries if you think you are having problems related to multi-honed machines.
Also, note that if you do use these binaries, and then update your server, they will probably be reverted.