gawkinet: Troubleshooting
1
1 2.3 Troubleshooting Connection Problems
1 =======================================
1
1 It may well be that for some reason the program shown in the previous
1 example does not run on your machine. When looking at possible reasons
1 for this, you will learn much about typical problems that arise in
1 network programming. First of all, your implementation of 'gawk' may
1 not support network access because it is a pre-3.1 version or you do not
1 have a network interface in your machine. Perhaps your machine uses
1 some other protocol, such as DECnet or Novell's IPX. For the rest of
1 this major node, we will assume you work on a Unix machine that supports
1 TCP/IP. If the previous example program does not run on your machine, it
1 may help to replace the name 'localhost' with the name of your machine
1 or its IP address. If it does, you could replace 'localhost' with the
1 name of another machine in your vicinity--this way, the program connects
1 to another machine. Now you should see the date and time being printed
1 by the program, otherwise your machine may not support the 'daytime'
1 service. Try changing the service to 'chargen' or 'ftp'. This way, the
1 program connects to other services that should give you some response.
1 If you are curious, you should have a look at your '/etc/services' file.
1 It could look like this:
1
1 # /etc/services:
1 #
1 # Network services, Internet style
1 #
1 # Name Number/Protocol Alternate name # Comments
1
1 echo 7/tcp
1 echo 7/udp
1 discard 9/tcp sink null
1 discard 9/udp sink null
1 daytime 13/tcp
1 daytime 13/udp
1 chargen 19/tcp ttytst source
1 chargen 19/udp ttytst source
1 ftp 21/tcp
1 telnet 23/tcp
1 smtp 25/tcp mail
1 finger 79/tcp
1 www 80/tcp http # WorldWideWeb HTTP
1 www 80/udp # HyperText Transfer Protocol
1 pop-2 109/tcp postoffice # POP version 2
1 pop-2 109/udp
1 pop-3 110/tcp # POP version 3
1 pop-3 110/udp
1 nntp 119/tcp readnews untp # USENET News
1 irc 194/tcp # Internet Relay Chat
1 irc 194/udp
1 ...
1
1 Here, you find a list of services that traditional Unix machines
1 usually support. If your GNU/Linux machine does not do so, it may be
1 that these services are switched off in some startup script. Systems
1 running some flavor of Microsoft Windows usually do _not_ support these
1 services. Nevertheless, it _is_ possible to do networking with 'gawk'
1 on Microsoft Windows.(1) The first column of the file gives the name of
1 the service, and the second column gives a unique number and the
1 protocol that one can use to connect to this service. The rest of the
1 line is treated as a comment. You see that some services ('echo')
1 support TCP as well as UDP.
1
1 ---------- Footnotes ----------
1
1 (1) Microsoft preferred to ignore the TCP/IP family of protocols
1 until 1995. Then came the rise of the Netscape browser as a landmark
1 "killer application." Microsoft added TCP/IP support and their own
1 browser to Microsoft Windows 95 at the last minute. They even
1 back-ported their TCP/IP implementation to Microsoft Windows for
1 Workgroups 3.11, but it was a rather rudimentary and half-hearted
1 implementation. Nevertheless, the equivalent of '/etc/services' resides
1 under 'C:\WINNT\system32\drivers\etc\services' on Microsoft Windows 2000
1 and Microsoft Windows XP.
1