tricks of the internet gurus

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.Here's a basic telnet test to the SMTP port.The example is shown from a UNIX csh prompt, but it can just aseasily be done from any telnet client that lets you telnet to tcp ports other than 23, the one officially assigned tothe Telnet application.You would type what's in bold, and replace your own server name with the one in theexample:%telnet foo.any.net 25Trying 127.1.2.3.Connected to foo.any.net.Escape character is '^]'.http://docs.rinet.ru/ITricks/tig04.htm (5 of 23) [4/18/1999 12:37:59 AM]Tricks of the Internet Gurus tig04.htm220 foo.any.net SMTP ready at Mon, 1 Aug 94 10:41:43 CDT.noop200 OKquit221 foo.any.net closing connectionConnection closed by foreign host.%If your client uses POP, you can do an equivalent test with tcp port 109 of your POP server to establish similarconnectivity assumptions:%telnet pop.bogus.net 109Trying 127.1.2.3.Connected to pop.bogus.net.Escape character is '^]'.+ POP2 pop Server (Version 1.001 February, 1989)quit+ Bye POP2 pop Server (Version 1.001) shutdownConnection closed by foreign host.%As listed in RFC937, POP2 uses a default port of tcp/109; as listed in RFC1081, POP3 uses a default port oftcp/110.And finally, here's a test you can do to with port tcp/143 of your IMAP server to establish basic connectivity.Thepart you type may look a little strange to you, but IMAP requires that incoming commands be serialized; that'swhy there's an arbitrary code in front of each command you type.%telnet imap.bogus.net 143Trying 127.1.2.3.Connected to imap.bogus.net.Escape character is '^]'.* OK imap.bogus.net IMAP2bis Service 7.0(52) at Mon, 1 Aug 1994http://docs.rinet.ru/ITricks/tig04.htm (6 of 23) [4/18/1999 12:37:59 AM]Tricks of the Internet Gurus tig04.htmA1 noopA1 OK NOOP completedA2 logout* BYE imap.bogus.net IMAP2bis server terminating connectionA2 OK LOGOUT completedConnection closed by foreign host.%If all goes well, you will get replies from your SMTP, POP, or IMAP server similar to the preceding ones.If not,that's also good because it gives you information you can use to solve your problem.It's important to rememberthat there's no such thing as a failed experiment only one that didn't necessarily go as planned.Here are somethings that may have happened in the preceding tests and what they may indicate:%telnet server.bogus.net 25Trying 127.1.2.3.telnet: connect: Connection timed outtelnet>There are a variety of error messages that amount to "you can't get there from here." This may indicate loss ofend-to-end connectivity between the client and the server.More about that later.%telnet speigal.hou.tx.usspeigal.hou.tx.us: unknown hosttelnet>An unknown host message may indicate a couple of things:If it truly is an unknown host, you may just have the wrong name.One way to check is to use the IPaddress to connect to it.If that fails as well, and depending on just how it failed, you may have end-to-endconnectivity problems.If you know you have the correct name, and you are able to connect successfully to the IP address but notto the "Fully-Qualified Domain Name" or FQDN, you may have a problem with your Domain NameService.DNS is the system that associates FQDNs that are meaningful to people, and IP addresses that aremeaningful to computers.Before DNS, host managers had to keep local host files with a list of all hostsand all IP addresses on each host.With over 20 million users now on the Internet, the existence of DNS isgreat news for system managers probably lukewarm news for disk manufacturers.If your connection is refused:http://docs.rinet.ru/ITricks/tig04.htm (7 of 23) [4/18/1999 12:37:59 AM]Tricks of the Internet Gurus tig04.htm%telnet server.bogus.net 25Trying 127.5.4.3.telnet: connect: Connection refusedtelnet>it means that the machine you want to talk to is there, but it isn't accepting connections for the service you want.This can be caused by numerous things, including:You're trying to talk to the wrong machine another machine is actually the server you want.Double-check your information.The server software on the machine isn't working correctly.See if you can get whoever runs the machineto take a look at it.There's a security gotcha in place.Talk to the folks responsible for network security of whatever networkyou're using and see if the particular tcp service port you're trying to use has been blocked between yoursource machine and the destination server.This is appropriate as a last resort, in case nothing else pans out.If there is a security block in place, it's probably there for a good reason."The Check's in the Mail": Trace Your Mail on its TravelsIf you have established that you have basic e-mail connectivity, and you're using an e-mail program that lets youadd your own user-defined header lines, you can attempt to send mail with a return receipt.If you don't get a receipt, it doesn't mean you have a problem it may mean that one or more of the mail serversyour mail has to travel through to get to its destination doesn't support return receipts.Return receipts are great ifyou can get them, but they don't mean much if you don't unless you're previously confirmed that a given mailserver does support receipts.The method or possibility of adding a header line to a mail message varies from client-to-client, but essentially,you should add a line like this to your message, replacing the e-mail address with your own.Return-Receipt-To: cuss@blankety.blank.comAfter you send such a message, a mail server that supports return receipts on the e-mail route between you andyour addressee will send you a separate message informing you that it received your message.Usenet NewsMaking sure you're talking to the right Usenet news server isn't all that much different that confirming basice-mail connectivity.The transport protocol for most Usenet news, Network News Transport Protocol (NNTP), isa TCP-based service, as are SMTP, POP, and IMAP.As you may suspect, this means that there's a simple telnettest to make sure that there's end-to-end connectivity to the server to which you believe you're supposed toconnect to with your news reader.After you've ruled out obvious problems like a configuration file in the wrong subdirectory or lack of local diskspace, you may want to try the following test on your designated news server's NNTP port, tcp/119.http://docs.rinet.ru/ITricks/tig04.htm (8 of 23) [4/18/1999 12:37:59 AM]Tricks of the Internet Gurus tig04.htmNote: If you use UUCP, IP Multicasting, or another method to get your news, this method won't do youany good.%telnet news.clench.org 119Trying 127.1.5.5.Connected to news.clench.org.Escape character is '^]'.200 news NNTP server ENEWS 1.4 22-Dec-93 ready (posting ok).quit205Connection closed by foreign host.%Aside from the basic connectivity issues convered earlier, you can also determine if you are permitted tooriginate or "post" new Usenet articles through this server.On the greeting line that begins 200 news NNTPserver ENEWS 1.4, look at the end of the line.You'll see a statement of whether you can post or not.If an NNTPserver doesn't permit you to post, you may either be using the wrong server, or have essentially read-only accessto Usenet.GopherGopher is another TCP-based service, which means (as you may suspect) you can give it a cursory check bytelnetting to its service port.Although it's not a hard-and-fast rule, about half of all Gophers may be found onTCP port 70.If a Gopher doesn't respond on port 70, it's not necessarily down it may be installed on a differentTCP port [ Pobierz całość w formacie PDF ]

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