PM65776: USS NSLOOKUP AND DIG COMMANDS WITH UNQUALIFIED HOST NAME FAIL WITH "** SERVER CAN'T FIND XXX: NXDOMAIN" IN UDP MODE FROM DNS

APAR status

• Closed as fixed if next.

Error description

• When the z/OS UNIX nslookup or dig command is issued with an
  unqualified host name in UDP mode, it fails with the
  following messages:
  
  Allocated socket 5, type udp
  ;; Truncated, retrying in TCP mode.
  Allocated socket 5, type tcp
  
  Server:
  x.x.x.x
  Address:        x.x.x.x#53
  ** server can't find xxx: NXDOMAIN
  
  Because both nslookup and dig commands fail to append the
  unqualified host names to their configured domain names, DNS
  responds with NXDOMAIN to indicate that the name doesn't exist.
  If the unqualified name appended with its domain name had been
  specified on the command line or if the protocol mode is
  forced to be TCP, then DNS might be able to respond to the
  query. The packet truncation occurred for UDP because the
  reply containing the answer and authority records is larger
  than 512 bytes. This might not be an issue if DNS supports
  EDNSS0 to circumvent the UDP packet size restriction.
  

Local fix

• Do the following for circumvention where xxx is the
  unqualified host name:
  
  * nslookup:
  
    z/OS UNIX: nslookup -vc xxx
    TSO: nslookup xxx
  
    Note: The -vc option forces TCP mode
  
  * dig:
  
    z/OS UNIX: dig +sea +vc xxx
    TSO: dig xxx
  
    Note: The +sea (or +search) option tells dig to use the
          search list in TCPIP.DATA and the +vc option tells
          dig to override the default UDP mode with TCP mode.
  
  KEYWORDS:
  USS OMVS nslookup dig B9LOOK B9DIG DNS UNQUALIFIED HOST NAME
  UDP TCP TRUNCATED TRUNCATION BIND9 BINDV9
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of the IBM Communications Server   *
  *                 for z/OS Version 1 Release(s) 11, 12,        *
  *                 and 13 IP: z/OS UNIX nslookup and dig        *
  ****************************************************************
  * PROBLEM DESCRIPTION: If the z/OS UNIX nslookup or dig        *
  *                      command received a UDP truncated reply  *
  *                      from the queried DNS the command did    *
  *                      not correctly use TCP to query the DNS. *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  If the z/OS UNIX nslookup or dig command was issued without a
  Fully Qualified Domain Name(FQDN) specified the command will
  use the SEARCH or DomainOrigin TCPIP.DATA statement to form the
  FQDN for its DNS query. If the reply from the DNS was a UDP
  truncated reply the command switches to use TCP for its query
  but the query sent did not specify the FQDN. This would cause
  the DNS to return an NXDOMAIN reply which would cause the
  command to fail. For nslookup the failure message will be:
    ** server can't find "name": NXDOMAIN
  +-------------------------------------------------------------+
  + Please check our Communications Server for OS/390 homepages +
  + for common networking tips and fixes.  The URL for these    +
  + homepages can be found in Informational APAR II11334.       +
  +-------------------------------------------------------------+
  

Problem conclusion

Temporary fix

Comments

• This APAR is being closed FIN (Fixed If Next) with concurrence
  from the submitting customer. This means that a fix to this
  APAR is expected to be delivered from IBM in a release (if any)
  to be available within the next 24 months.
  
  This problem will be tracked as Feature F155781
  by Communications Server for z/OS Development.
  
  The solution for this APAR is included in
  CS for zOS Version 2 Release 1.
  

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

Fix information

Applicable component levels

• R1B0 PSN

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