Date: Sat, 22 Aug 1998 14:27:24 -0600 From: Allen Campbell <allenc@verinet.com> To: "G.R. Gaudreau" <grgaud@sprint.ca> Cc: freebsd-newbies@FreeBSD.ORG Subject: Re: Ports (was: FreeBSD main platform & Linux) Message-ID: <35DF29AC.70062752@verinet.com> References: <3.0.1.32.19980821053638.0068ea4c@pop.netaddress.com> <3.0.5.32.19980822074143.007a1aa0@pop3.sprint.ca> <3.0.6.32.19980822142714.007a9a20@pop3.sprint.ca>
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G.R. Gaudreau wrote: > [ My previous, badly formatted message, snipped ] > > Something you mentioned brought up another question that's been on my > mind lately. I realize that the ports you mention above are ports to > FreeBSD, and that physical ports on my box are COM1 & 2 and the > printer port, etc.; but I've also read of other ports, such as > Internet ports and such. What are these last ports? Linux and FreeBSD > seem to work quite a lot with these things, and I get the feeling > that there are other "soft" ports, if I can put it that way, that > UNIX-like OSs use. Anyone know what I'm talking about, and could you > explain what they are and how they're used? Thanks For your input > Allen, 'preciate it. This is the classic case of a much too overloaded term. I'll share what I know. I'll start with the FreeBSD ports collection. To 'port' software is to make it compatible with another platform. A person doing this is may be called a porter, who is porting software. The result is sometimes called a port. FreeBSD maintains a large and growing collection of these ports. Using these ports, you may obtain the standard distribution of some piece of software and allow the ports system to automatically 'patch' and install the distribution. The handbook and the ports man page have more information on the FreeBSD ports collection. The ports you asked about are IP (internet protocol) ports. IP ports are specific to IP networks (such as the Internet.) Every hoston an IP network (including computers which dial into the Internet via an ISP) has a unique IP address. This address is a 32 bit number, usually represented by a four octet symbol: 201.134.160.12, for example. When an IP host needs to communicate with another IP host, it must establish a connection with that host. Because IP hosts can establish multiple connections with multiple remote hosts (including the same remote host,) it becomes necessary to distinguish connections. This is what IP port numbers do. Some port numbers are referred to as `Well Known' ports. These are ports which are reserved for specific types of communication. You will find the list of Well Known ports in the /etc/services file. You will probably recognize a few of these: ftp 21/tcp #File Transfer [Control] telnet 23/tcp http 80/tcp www www-http #World Wide Web HTTP When you use FTP, your host connects to port number 21 of the remote host. Meanwhile, other people are also likely use FTP to connect to port number 21 of the same remote host. For example, the server at ftp.cdrom.com is likely to have several thousand FTP connections established at any moment. You may also perform another FTP connection to the same remote host while your first FTP connection is still going. So how is the remote system supposed to distinguish between all of these different connections? Any one connection between two IP hosts is described by a tuple of five components: local IP address local port number Protocol remote IP address remote port number If you establish two FTP sessions with port 21 at ftp.cdrom.com, the only component that will change is the local port number. When some other host establishes a connection with port 21 of ftp.cdrom.com, their local IP address and port will be different. If you FTP to two different hosts, the remote IP addresses will be different. This is how IP hosts distinguish between multiple connections. The 'soft' ports you mentioned I don't recognize. -- Allen Campbell | Lurking at the bottom of the allenc@verinet.com | gravity well, getting old. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-newbies" in the body of the message
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