RFC 1918 reserved three blocks of IP addresses for private internets. These come in handy when you create an internal IP network. Range RFC 1918 Name Description 10.0.0.0 - 10.255.255.255 24-bit block A single class A network number 172.16.0.0 - 172.31.255.255 20-bit block 16 contiguous class B network numbers 192.168.0.0 - 192.168.255.255 16-bit block 256 contiguous class C network numbers

Some ways to refresh DHCP on Linux: To release IP address lease: $ sudo dhclient -r then, to get fresh IP: $ sudo dhclient Use ifdown and ifup : $ sudo ifdown eth0 $ sudo ifup eth0 Restart network: $ sudo /etc/init.d/network restart or, $ sudo /etc/init.d/networking restart

In below examples, the default gateway is 105.52.84.1 . Use " netstat -rn ": $ netstat -rn Kernel IP routing table Destin... Use " route -n ": $ route -n Kernel IP routing table Destinati... Use " ip route show ": $ ip route show 105.52.84.0/24 dev eth0 proto ...

The command " ifconfig -a " does not list the DNS servers. Use " cat /etc/resolv.conf " to look at the DNS server configuration. It works for DHCP configured network interfaces also. $ cat /etc/resolv.conf # Generated by NetworkMa... If no DNS server is configured: $ cat /etc/resolv.conf # Generated by NetworkMa...

This works for OpenSSH . Steps: Start SSH tunnel: ssh -D 8088 user@remote.host.running.sshd Set socks proxy to "localhost:8088" in your browser. Result: Communication link between your computer and the remote host running sshd is encrypted. Why? You might want to do this when you are on a untrusted network, e.g., accessing your Yahoo! mail via wifi at Starbucks or a hotel.

cURL is a command line tool for transferring files with URL syntax. The main purpose and use for cURL is to automate unattended file transfers or sequences of operations. It's really easy to see HTTP headers with curl: C:\>curl --head http://www.google.com HTTP/1.0 ... or, headers and page together (dump headers to stdout): $ curl --dump-header - http://www.google.com HTTP/... Download openssl from openssl.org: curl http://www.openssl.org/source/openssl-0.9.6m.... C:\>curl --help Usage: curl [options...] <url> ...

Cygwin comes with openssh and X Windows. You need to select these packages from the cygwin installation screen: openssh (Net) X-start-menu-icons (X11, optional) xinit (X11) xorg-server (X11 server) To start an X-enabled remote SSH session, you need to start the X server on the cygwin side first: startxwin then enter: ssh -Y user@network-address This allows you run X apps on cygwin, but you won't see your normal Linux desktop (gnome, KDE etc.). In order to see remote desktop, you need to run XDMCP (Display Manager Control Protocol, which isn't secure). It's a bit tricky to set up XDMCP over ssh.

I installed vncserver on my Fedora box and tried to connect to it with vncviewer from Windows XP. I got this error: What could be the problem? These were the steps I took to diagnose it. I just list them here as a reminder. Is Windows firewall blocking the connection? No. It turned out that, unlike ZoneAlarm , the Windows firewall does not block outgoing traffic. It only blocks incoming requests. Is vncserver listening on the right IP address? Yes. netstat showed it's listening on all NICs. netstat -a | grep 5901 tcp 0 0 *:59... Is VNC port open on the local Fedora box on that IP address? Yes, telnet successfully connected: [jim@fedora ~] telnet 172.30.33.9 5901 Trying 1... What does telnet say from...

If no packets are dropped, TCP throughput can be calculated from the TCP window size and network latency: throughput = TCP window size / RTT (roud trip time... Assume that the TCP window size is 64KB and the RTT is 40ms, the throughput is: 65936 Bytes / 40 ms = 1.6 MBytes/s = 13 Mbits/s Note that the throughput has nothing to do with the bandwidth, which is the result of assuming that no packets are dropped, basically assuming that the bandwidth is infinite. Therefore, the bandwidth shown above is the maximum possible bandwidth given TCP window size and latency. But in reality the bandwidth is limited and throughput won't grow infinitely with the TCP window size - it can only grow to as big...