| IPv6 Network - Old School: FTP, Telnet, and SSH |
IPv6 Network - Old School: FTP, Telnet, and SSH - FTP and Telnet are the oldest applications found on the Internet. They even date back to before the introduction of IPv4 in the early 1980s. It’s only fitting that these applications are the first to gain IPv6 support. Linux, FreeBSD, MacOS, and Windows all have command line ftp and telnet programs, and they all support IPv6. Except for the Windows incarnation, they all try all addresses for a host, so they should fall back to IPv4 if IPv6 connectivity is broken. The telnet and ftp programs aren’t the workhorses they used to be. The Telnet protocol has been largely replaced by SSH because SSH supports encryption.
Even though a lot of downloading happens over HTTP these days, the FTP protocol is still going strong, but users prefer more user-friendly graphical FTP clients. However, the original telnet and ftp are great for debugging. With telnet, it’s possible to connect to arbitrary TCP services to see if the service in question is running, and ftp is very useful for measuring available bandwidth, because it displays an accurate kilobyte per second value after transferring a file. Under FreeBSD and MacOS, ftp accepts HTTP and FTP URLs as arguments, which is great for downloading files from within a script.
The FTP server daemons on FreeBSD and MacOS both support IPv6. The Telnet daemon does as well, but it’s disabled on both systems. Under Red Hat Linux, there is no FTP or Telnet daemon installed by default. The SSH client and server programs that come with Linux, FreeBSD, and MacOS all support IPv6. Like most IPv6-enabled applications, the ssh program prefers IPv6 addresses over IPv4 ones if there is IPv6 connectivity. On all three systems, ssh will fall back on additional (IPv4 or IPv6) addresses when it can’t connect to the first address.
VanDyke Software has a commercial SecureCRT SSH (and more) client for Windows that supports IPv6 in version 5. SecureCRT 5 can be downloaded for a free 30-day trial from http://www.vandyke.com/. There is also Putty, a free multi-OS SSH client that is popular under Windows and supports IPv6. Putty is available at http://www.chiark.greenend.org.uk/~sgtatham/putty/.
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