|Front | Info | Lists | Newsfeeds | Study Guide | What is BSD?|
This is the BSDA Study Guide Book written via a wiki collaboration. This is a work in progress. You may contribute to or discuss this specific page at http://bsdwiki.reedmedia.net/wiki/Verify_the_availability_of_a_TCP--IP_service.html.
Verify the availability of a TCP/IP service
Be able to determine if a remote system is available via TCP/IP, and if so, telnet(1) to a particular TCP service to determine if it is responding to client requests.
Some times you need to check some network service on remote or local system. How can we do it? Firstly we must check the firewall rule, it's common error when someone check network service on remote host when your firewall block this type of request. And then you can start your test.
ping it's a most common tool for check availability host(remember some admins blocks ping). Instead of Windows system ping in BSD will ping host until you press Ctrl+C.
Now we ping freebsd.org and know that this server is up. Let's check service like www and ssh
www is work on freebsd.org and ssh is too. Also we can see that freebsd.org support only ssh 2(if server support 1 and 2 it will show 1.99). Not so hard but very usefull. You can use nc tool for this - check the manual.
Imagine that ping is filed but your system work fine and network work too. What's happen? May be some host in your route to destination service is down. We can check this via traceroute tool.
In this case all host in route to ya.ru is up.
ping(8), traceroute(8), telnet(1); nc(1) on FreeBSD and OpenBSD