Resolver configuration files

Understanding the resolver search orders used in native MVS™ and z/OS® UNIX environments is key to setting up your system properly.

The resolver can use available name servers, local definitions, or a combination of both, to process API resolver requests. Figure 1 shows how local definitions can be specified and searched for when needed.

Use the trace resolver facility to determine what TCPIP.DATA values are being used by the resolver and where they were read from. For information about dynamically starting the trace, see z/OS Communications Server: IP Diagnosis Guide. After the trace is active, issue the Netstat HOME/-h command to display the values. You can issue a Ping of a host name from TSO and from the z/OS UNIX shell to show the activity to the resolver cache and to any DNS servers that might be configured.

Figure 1. Resolver related configuration files in z/OS UNIX and native MVS environments
Shows local defined configuration files and their relationship to socket APIs

Table 1 shows the complete set of local definition possibilities available to the resolver.

Table 1. Local definitions available to resolver
File type description APIs affected Candidate files
Base resolver configuration files All APIs
  1. GLOBALTCPIPDATA
  2. RESOLVER_CONFIG environment variable
  3. /etc/resolv.conf
  4. SYSTCPD DD-name
  5. userid.TCPIP.DATA
  6. jobname.TCPIP.DATA
  7. SYS1.TCPPARMS(TCPDATA)
  8. DEFAULTTCPIPDATA
  9. TCPIP.TCPIP.DATA
Translate tables All APIs
  1. X_XLATE environment variable
  2. userid.STANDARD.TCPXLBIN
  3. jobname.STANDARD.TCPXLBIN
  4. hlq.STANDARD.TCPXLBIN
  5. Resolver-provided translate table, member STANDARD in SEZATCPX
Local host tables

endhostent
endnetent
getaddrinfo
gethostbyaddr
gethostbyname
gethostent
GetHostNumber
GetHostResol
GetHostString
getnameinfo
getnetbyaddr
getnetbyname
getnetent
IsLocalHost
Resolve
sethostent
setnetent
  1. X_SITE environment variable
  2. X_ADDR environment variable
  3. /etc/hosts
  4. userid.HOSTS.xxxxINFO
  5. jobname.HOSTS.xxxxINFO
  6. hlq.HOSTS.xxxxINFO
  7. GLOBALIPNODES
  8. RESOLVER_IPNODES environment variable
  9. userid.ETC.IPNODES
  10. jobname.ETC.IPNODES
  11. hlq.ETC.IPNODES
  12. DEFAULTIPNODES
  13. /etc/ipnodes
Protocol information

endprotoent
getprotobyname
getprotobynumber
getprotoent
setprotoent
  1. /etc/protocol
  2. userid.ETC.PROTO
  3. jobname.ETC.PROTO
  4. hlq.ETC.PROTO
Services information

endservent
getaddrinfo
getnameinfo
getservbyname
getservbyport
getservent
setservent
  1. /etc/services
  2. SERVICES DD-name
  3. userid.ETC.SERVICES
  4. jobname.ETC.SERVICES
  5. hlq.ETC.SERVICES
Host alias table

getaddrinfo
gethostbyname

 HOSTALIASES environment variable

The actual search order of the candidate files varies depending on the type of API that is used and the resolver setup. The search orders are explained in more detail in Search orders used in the z/OS UNIX environment and Search orders used in the native MVS environment. Because the resolver runs in the address space of the application, the resolver accesses the candidate files from the application address space.

Information about an application's search order can be obtained by using the trace resolver facility. Trace resolver output provides a caller API value that determines which search order is used. For information on dynamically starting the trace, see z/OS Communications Server: IP Diagnosis Guide.

The following caller API values indicate the z/OS UNIX environment search order is used:

The following caller API values indicate the native MVS environment search order is used:

The following commands are some examples of Communications Server TSO commands that use the native MVS search order:

The following commands are some examples of Communications Server UNIX commands that use the z/OS UNIX search order:

The following applications are some examples of Communications Server applications that use the native MVS search order:

The following applications are some examples of Communications Server applications that use the z/OS UNIX search order:

Parent topic: The resolver