How to ask about connectivity issues

So you're trying to connect one system to another using this newfangled TCP/IP stuff the kids are using these days. But what's this? It doesn't work? You need to ask someone to look into it. You even know who. But what should you ask and what information should you provide so that they can investigate quickly and effectively?

As well as a bit of background to the problem (applications involved, environments etc), you should provide at least the following:

• Has it ever worked?
• Have you changed anything recently?
• Source IP
• Destination IP
• Protocol (TCP or UDP etc) if it isn't obvious from the context
• Port if it isn't obvious from the context

Common causes are:

• Wrong information - are you connecting to the right host?
• Routing
• Firewalls
• Network or system outages

Have you tried the following?

• Doing a host, dig or nslookup if dealing with a domain
• Pinging the remote host
• Connecting using netcat or telnet
• Traceroute

It is probably worth providing the output to the above commands if possible.