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IP troubleshooting

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IP troubleshooting – Troubleshooting at IP level

02.12.2008, 15:45 Uhr

In order to determine the source of an acute fault, the following questions should be clarified:

1. Are your systems receiving the correct IP addresses from the DNS resolver?
2. Can your systems access the t-online.de mail servers at IP level?
3. Are the t-online.de servers accepting e-mails from your systems?

 These checks should be carried out in the order specified. Should an error occur, this must first be resolved before moving on to further checks.

1. Checking the IP addresses

 If you are using Windows, UNIX or Linux, when entering the command nslookup -type=mx t-online.de into your computer, as a response, receive the IP addresses of the mail servers (MX).

C:\WINDOWS>nslookup -type=mx t-online.de

Server:  qeo00303.de.t-online.corp

Address:  10.224.209.3

Non-authorative answer:

t-online.de     MX preference = 10, mail exchanger = mx02.t-online.de

t-online.de     MX preference = 10, mail exchanger = mx03.t-online.de

t-online.de     MX preference = 10, mail exchanger = mx00.t-online.de

t-online.de     MX preference = 10, mail exchanger = mx01.t-online.de

 

mx02.t-online.de        internet address = 194.25.134.9

mx03.t-online.de        internet address = 194.25.134.73

mx00.t-online.de        internet address = 194.25.134.8

mx01.t-online.de        internet address = 194.25.134.72

 

C:\WINDOWS>

The results should match those shown above, although the order may be entirely different. If you receive different results, you must check your DNS infrastructure since your systems and/or the systems of your Internet service provider may have been compromised.

2. Checking the IP connection

E-mails are generally sent over several hops (stations/network nodes on the Internet) and may under certain circumstances go beyond the area of responsibility of your own ISP (Internet Service Provider) to that of another. A fault at IP level can occur at any hop, which is why an error in delivering e-mails from your systems to the t-online.de domain may also occur under the responsibility of a 3rd party ISP.

Using the command tracert mx00.t-online.de, (if you are using Windows) you can trace the specific path of IP data packets from your computer and thus check the connection between your client and the t-online.de domain e-mail servers. Under UNIX or Linux, the command traceroute mx00.t-online.de is available for this purpose.

In our first example there is no fault and the IP data packets reach the target computer: 

C:\WINDOWS>tracert mx00.t-online.de

 

Tracing route to mx00.t-online.de [194.25.134.8]  über maximal 30 Abschnitte:

 

 

  1    <1 ms     1 ms    <1 ms  10.224.143.254

  2    51 ms    46 ms    40 ms  217.0.116.193

  3    41 ms    40 ms    41 ms  217.0.76.42

  4    47 ms    45 ms    46 ms  0113699-1-1-gw.ULM.DE.net.DTAG.DE [194.25.10.94]

  5    46 ms    48 ms    46 ms  217.6.25.154

  6    46 ms    48 ms    46 ms  mx00.t-online.de [194.25.134.8]

 

Trace complete.

 

C:\WINDOWS>

If the target IP address cannot be reached, there is an error at IP level and a result with failure due to timeouts, similar to in the following example occurs: 

C:\WINDOWS>tracert mx00.t-online.de

 

Tracing route to mx00.t-online.de [194.25.134.8]  über maximal 30 Abschnitte:

 

 

  1   <1 ms     1 ms   <1 ms  10.224.143.254

  2    51 ms    46 ms    40 ms  217.0.116.193

  3    46 ms    48 ms    46 ms  62.156.138.89

  4     *        *        *     Zeitüberschreitung der Anforderung.

  5     *        *        *     Zeitüberschreitung der Anforderung.

  .

  .

 

 29     *        *        *     Zeitüberschreitung der Anforderung.

 30     *        *        *     Zeitüberschreitung der Anforderung.

 

Trace complete.

 

C:\WINDOWS>

You can identify the last network node actually reached in the result of the tracert mx00.t-online.de command. Please note that this network node may under certain circumstances be in the area of responsibility of an 3rd party Internet service provider and that only the operator of the relevant network node is the correct contact for eliminating such an error at IP level. If you have problems clarifying responsibility, please consult your network specialist, your Internet service provider or your peering partner.

In the example shown above, the hop last reached is the IP address 62.156.138.89, a system in the Deutsche Telekom AG (DTAG) network. Only in cases such as these where the last network node which can be reached is actually Deutsche Telekom's responsibility can the Postmaster team responsible for t-online.de offer you support.

3. Checking the SMTP dialog

If, using the command tracert mx00.t-online.de, you can reach the t-online.de mail server (MX) from your cclient; there is no technical fault at IP level. The problem may be occuring at Simple Mail Transfer Protocol (SMTP) level during an attempt to transmit data. Such an error should be written intp the log of your e-mail system. Information on the Simple Mail Transfer Protocol can be found online under http://www.rfc-editor.org/rfc/rfc5321.txt.

The communication between your client and the t-online.de mail server may also be tested manually. To do this, a connection to the t-online.de mail server must first be established via the command telnet 194.25.134.8 25. Via this Telnet connection you can then manually transfer a message in accordance with SMTP and trace each individual step. For a reliable check you should use your original helo and transfer the exact e-mail which failed to be delivered before.

Example of an error-free e-mail transfer

C:\WINDOWS>telnet 194.25.134.8 25

Trying 194.25.134.8...

Connected to 194.25.134.8.

Escape character is '^]'.

220-mailin06.aul.t-online.de T-Online ESMTP receiver fssmtpd2025 ready.

220 T-Online ESMTP receiver ready.

helo lalal

250 Ok.

mail from: <geek@congster.de>

250 2.1.0 Sender accepted.

rcpt to: <bob@t-online.de>

250 2.1.5 Recipient accepted.

data

354 Ok, start with data.

Subject: ein test

 

und hier der body

 

viele Gruesse

posthamster


.

250 2.0.0 Message accepted.

quit

221-2.0.0 mailin06.aul.t-online.de closing.

221 2.0.0 Closing.

Connection closed by foreign host.

C:\WINDOWS>

Errors which occur during the SMTP dialog are displayed with an appropriate message. In the event of exceptional e-mail volumes on the client-side, one of the two error messages are returnd as shown below.

Error message 554 (IP-Blocking)

C:\WINDOWS>telnet 194.25.134.8 25

Trying 194.25.134.8...

Connected to 194.25.134.8.

Escape character is '^]'.

554 IP:87.167.75.190 - A problem occurred. (Ask your postmaster for help or to contact tosa@rx.t-online.de to clarify.)

Connection closed by foreign host.

C:\WINDOWS>

Should an error message be received as shown above with the ID 554, t-online.de systems are not currently accepting e-mails from the IP address used by your clients. This IP blocking may be due to a previously observed unusual volume of e-mails at the IP address concerned.

If IP-Adresses are being rejected by the t-online systems by mistake, we ask that you use our online form and notify us of the IP concerned. We can then look into cause of the IP blocking and where necessary amend our system settings.

Error message 550 (suspected spam)

C:\WINDOWS>telnet 194.25.134.8 25

Trying 194.25.134.8...

Connected to 194.25.134.8.

Escape character is '^]'.

220-mailin16.aul.t-online.de T-Online ESMTP receiver fssmtpd2025 ready.

220 T-Online ESMTP receiver ready.

helo lala

250 Ok.

mail from: <geek@congster.de>

250 2.1.0 Sender accepted.

rcpt to: <bob@t-online.de>

250 2.1.5 Recipient accepted.

data

354 Ok, start with data.

Date: Mon, 6 Oct 2003 12:08:47 +0200

Subject: get it for FREE !

... some SPAM here ...

.

550-5.7.0 Message considered as spam or virus, rejected
550-5.7.0 Message rejected because it was considered as spam. If you feel this
550-5.7.0 to be an error, please forward the wrong classified e-mail to our
550-5.7.0 abuse department at FPR@RX.T-ONLINE.DE with all the header lines!
550-5.7.0 We will analyse the problem and solve it. We are sorry for any
550-5.7.0 inconvenience and thank you very much in advance for your support!
550-5.7.0
550-5.7.0 Die Annahme Ihrer Nachricht wurde abgelehnt, da sie als Spam
550-5.7.0 eingestuft wurde. Sollten Sie dies als Fehler ansehen, bitten wir
550-5.7.0 Sie darum, die E-Mail mit allen Kopfzeilen an FPR@RX.T-ONLINE.DE
550-5.7.0 weiterzuleiten. Das Problem wird dann untersucht und geloest.
550-5.7.0 Wir bedauern, Ihnen Unbequemlichkeiten bereitet zu haben, und
550 5.7.0 bedanken uns vorab fuer Ihre freundliche Unterstuetzung!

quit

221-2.0.0 mailin16.aul.t-online.de closing.

221 2.0.0 Closing.

Connection closed by foreign host.

C:\WINDOWS>

If a specific e-mail is classified as spam, acceptance is rejected in compliance with the RFC.

Should an e-mail have been mistakingly classified as spam, please use our online form and forward the e-mail to us with all the header lines. We can then check the cause of the assessment.

Special case: timeout

C:\WINDOWS>telnet 194.25.134.8 25

Trying 194.25.134.8...

Connected to 194.25.134.8.

Escape character is '^]'.

220-mailin18.aul.t-online.de T-Online ESMTP receiver fssmtpd2025 ready.

220 T-Online ESMTP receiver ready.

heloConnection closed by foreign host.

C:\WINDOWS>

If the delivering client does not respond within 3 seconds after connect, an immediate disconnection takes place. In the case of manual transmission, it is therfore imperitive write quickly or use cut & paste.

This kind of error may also be caused by your client, for example if an outdated software version is used.

You will find more information on possible error messages here


Fault reports
Further informations

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