With today's connectivity stretching over the internet via VPN and firewalls it is often necessary to put sniffers on Lans to diagnose issues with filtering, ports etc. There are a number of tools such as PING, CWBPING NBTSTAT etc and we generally use these tools in certain areas depending on the problem. One of the techniques I use to determine if base connectivity on a port level is functioning is to use TELNET SYSTENAME PORTNUMBER from a DOS prompt on a PC. Normally we just use TELNET SERVERNAME and expect to get a signon screen. By specifying a port number we can determine if a connection at a socketlevel can be made. Things like firewalls can restrict ports. TELNET SERVERNAME 449 will bring up a blank telnet screen with the cursor in the top left. This tells us that we have established a connection to the servermapper. On the AS/400 NETSTAT option 3 will show the connection established. TELNET SERVERNAME 139 creates a socket connection to as400 NETSERVER netbios over TCP. If the connection cannot be established we get "could not open a connection to servername. By specifying servername we can also determine if name resolution is taking place via HOSTS file or DNS server.