A tutorial.
I recently received the following message, and decided to investigate
why a perfectly-valid subscriber was automatically removed by LISTSERV.
+----
| Date: Thu, 5 Jan 1995 19:30:24 -0500
| From: BITNET list server at TEMPLEVM (1.8a) <[log in to unmask]>
| Subject: HELP-NET: [log in to unmask] auto-deleted
|
| The following users have been removed ("auto-deleted", in list owner jargon)
| from the HELP-NET list as a result of the nondelivery error report enclosed
| below. No action is required from you; this message is only for your
| information.
| List of deleted users:
| [log in to unmask]
| ------------------------ Nondelivery report (56 lines)
| Date: Thu, 05 Jan 95 19:30:29 EST
| From: <[log in to unmask]>
| To: <[log in to unmask]>
| Subject: Undeliverable Mail
| X-Report-Type: Nondelivery; boundary="> Error description:"
|
| This delivery error is in a special format that allows software like
| LISTSERV to automatically take action on incorrect addresses; you can
| safely ignore the numeric codes.
|
| Note: delivery error converted to LMail format at VM.TEMPLE.EDU.
|
| --> Error description:
| Error-For: [log in to unmask]
| Error-Code: 1
| Error-Text: 550 Host 'DPSSO.DGSC.DLA.MIL' Unknown
|
| Error-End: One error reported
|
| ----------------- Original delivery error (before conversion)
| pucc.Princeton.EDU unable to deliver following mail to recipient(s):
| <[log in to unmask]>
| 550 Host 'DPSSO.DGSC.DLA.MIL' Unknown
|
| ** Text of Mail follows **
| Date: Thu, 5 Jan 1995 19:25:39 EST
| Sender: Bitnet/Internet Help Resource
| <[log in to unmask]>
| From: <censored by KLASSEN>
| Subject: <censored by KLASSEN>
| To: Multiple recipients of list HELP-NET
| <[log in to unmask]>
|
| <censored by KLASSEN>
+----
The IP-address for 'DPSSO.DGSC.DLA.MIL' is '131.81.70.45',
but I had a "difficult" time finding that answer.
This "difficulty" explains why the SMTP-server gave the "host unknown"
message, which triggered LISTSERV into performing the "auto-delete".
I used the NSLOOKUP utility to find the top-level DNS (domain name-servers)
for the 'MIL' domain, i.e.,
$ nslookup
> set type=ns
> mil.
Non-authoritative answer:
mil nameserver = AOS.ARL.ARMY.mil
mil nameserver = NIC.NORDU.NET
mil nameserver = NS.ISC.ORG
mil nameserver = NS.INTERNIC.NET
mil nameserver = NS.NIC.DDN.mil
mil nameserver = C.PSI.NET
mil nameserver = TERP.UMD.EDU
mil nameserver = NS.NASA.GOV
Authoritative answers can be found from:
AOS.ARL.ARMY.mil inet address = 128.63.4.82
AOS.ARL.ARMY.mil inet address = 192.5.25.82
NIC.NORDU.NET inet address = 192.36.148.17
NS.ISC.ORG inet address = 192.5.5.241
NS.INTERNIC.NET inet address = 198.41.0.4
NS.NIC.DDN.mil inet address = 192.112.36.4
C.PSI.NET inet address = 192.33.4.12
TERP.UMD.EDU inet address = 128.8.10.90
NS.NASA.GOV inet address = 192.52.195.10
NS.NASA.GOV inet address = 128.102.16.10
Note that some of these "top-level" nameservers didn't respond. (See below).
This certainly is not "optimal", but it is "typical" of life on the Internet.
Then, I used NSLOOKUP, pointing to some of the above nameservers,
and asked for the IP-address, i.e.,
$ NSLOOKUP
> dpsso.dgsc.dla.mil. 192.5.5.241
*** Request to 192.5.5.241 timed-out
> dpsso.dgsc.dla.mil. 192.112.36.4
*** Request to 192.112.36.4 timed-out
> dpsso.dgsc.dla.mil. 198.41.0.4
Server: [198.41.0.4]
Address: 198.41.0.4
Name: dpsso.dgsc.dla.mil
Served by:
- DSACG1.DSAC.DLA.MIL
131.78.1.1
DLA.MIL
- DSACHG1.DSAC.DLA.MIL
131.77.1.2
DLA.MIL
- DSACNG1.DSAC.DLA.MIL
131.87.1.2
DLA.MIL
Note that the "top-level" nameservers generally don't give the answer; they
just point to lower-level nameservers which are delegated to give the answer.
I asked these name-servers for the IP-address of the problematic host:
$ NSLOOKUP
> dpsso.dgsc.dla.mil. 131.78.1.1
Server: [131.78.1.1]
Address: 131.78.1.1
Name: dpsso.dgsc.dla.mil
Address: 131.81.70.45
> dpsso.dgsc.dla.mil. 131.77.1.2
Server: [131.77.1.2]
Address: 131.77.1.2
*** 131.77.1.2 can't find dpsso.dgsc.dla.mil.: Non-existent domain
> dpsso.dgsc.dla.mil. 131.87.1.2
Server: [131.87.1.2]
Address: 131.87.1.2
*** 131.87.1.2 can't find dpsso.dgsc.dla.mil.: Non-existent domain
Note the "inconsistency" in the answers.
If all of these DNS servers were working correctly,
then each of them should have returned the same result.
The different answers, all of which are marked as "authoritative",
and which are delivered to the SMTP-server in a "random" order,
can cause the "unknown host" message to be generated.
Trusting this "mis-information", LISTSERV deletes the innocent user.
Sigh!
Question: what's the list-owner to do?
Answer:
1. contact the administrator of any name-server which is *not* functioning.
2. reinstate the user, if possible.
3. don't blame LISTSERV's "auto-delete" function for something
which is totally beyond its control.
|
