Fast way to check if a server is accessible over the network in C#

Question

I\'ve got a project where I\'m hitting a bunch of custom Windows Performance Counters on multiple servers and aggregating them into a database. If a server is down, I want

Answer 1

Opening Socket to a specific port usually does the trick. If you really want it to be fast, be sure to set the NoDelay property on the new socket (Nagle algorithm) so there is no buffering.

Fast will largely depend on latency but this is probably the fastest way I know to connect to an endpoint. It's pretty simple to parallelize using the async methods. How fast you can check will largely depend on your network topology but in tests for 1000 servers (latency between 0-75ms) I've been able to get connectivity state in ~30 seconds. Not scientific data at all but should give you the idea.

Also, don't ever do this through UNC file shares because if the server no longer exists you will have a lot of dangling connections that take forever to timeout. So if you have a lot of servers with invalid DNS records and you try to poll them you will bring Windows down completely over time. Things like File.Exists and any file access will cause this.