The statements in the configuration file control the DNS Resolver.
The statements consist of the keywords nameserver, domain, search, followed by the specific operands. The keywords start in the first column of the line and must be written in lowercase.
A semicolon (;) or hash character (#) in the first column means that the line in question is treated as a comment line.
The following statements are possible:
nameserver IPv4 or IPv6 address
A nameserver entry informs LWRESD of the IPv4 or IPv6 address of a DNS server. In other words, both IP and IPv6 addresses are permitted. You must specify a minimum of one and a maximum of three nameserver entries in the configuration file.
Even if the local LWRESD is not active, it makes sense to enter a valid DNS server. It is then not essential to specify a server address when using DIG and NSLOOKUP.
As the DNS server resides on a partner processor, it must either be made known to BCAM by means of CREATE commands or be entered in the processor file.
In order to maintain compatibility with the previous version, a nameserver entry with the IP address 127.0.0.1 is entered in the configuration file supplied. This serves only to enable LWRESD to be started if no DNS server is to be used. You must delete this entry as soon as a DNS server which is actually used is entered.
If more than one DNS server is specified, it is not possible to define the order in which they are used. An algorithm in the program defines the order according to the accessibility of the DNS servers.
It is therefore necessary that the other DNS servers are always redundant and can always process every query.
Example with nameserver entries
nameserver 15.32.16.4 nameserver 16.63.31.5 nameserver FEDC:BA98:7654:3210:FEDC:BA98:7654:3210
domain domain
The domain entry defines a default domain for queries by the DNS Resolver daemon to the DNS name server or servers. It should be noted that a maximum of one domain entry is valid; domain and search entries are mutually exclusive.
- If the configuration file contains multiple domain entries but no search entries, then the last domain entry applies.
- If both statements are used then the last specified statement is evaluated.
The mode of operation of the domain entry depends on whether or not the DNS name specified in a DNS query contains a period (.). The following description applies to the default setting of the LWRESD options
The specified DNS name contains a period:
If the DNS server is not able to reply successfully to a DNS query for a name name.domain then the DNS Resolver daemon sends a new DNS query with name to the DNS server.The specified DNS name does not contain a period:
If the DNS server is not able to reply successfully to a DNS query for a name name then the DNS Resolver daemon sends a new DNS query for name.domain to the DNS server.
The examples below illustrate the names generated by the DNS Resolver daemon in the case of queries to a DNS server.
Example for a DNS name with a period
Entry in the configuration file:
domain part.my-company.com
Name specified by the user
my.host
Name generated by the DNS Resolver daemon:
my.host my.host.part.my-company.com my.host.my-company.com
Example for a DNS name without a period
Entry in the configuration file:
domain part.my-company.com
Name specified by the user
myhost
Name generated by the DNS Resolver daemon:
myhost.part.my-company.com myhost.my-company.com myhost
search domain1[ domain2[ .... [ domain8]...]
The search entry defines multiple domain names for the DNS Resolver daemon in the event of queries to the DNS name server or servers. It should be noted that a maximum of one search entry is valid; domain and search entries are mutually exclusive.
- Up to eight search entries are valid.
- domain and search entries are mutually exclusive.
- If both statements are used then the last specified statement is evaluated.
The mode of operation of the search entry depends on whether or not the DNS name specified in a DNS query contains a period (.).
The specified DNS name contains a period:
A DNS query with name.domain1 is sent to the DNS server. If this is not responded to successfully then the DNS Resolver daemon repeats the DNS query with the next domain name domaini (i = 2 ... 8) defined in the search entry. This process is continued until either the DNS query has been successfully answered by the DNS server or until no further domain names are defined in the search entry.
If, after all the domain names defined in the search statement have been worked through, no DNS query has been successfully answered by the DNS server then a DNS query with name is sent.
The specified DNS name does not contain a period:
If the DNS server is not able to reply successfully to a DNS query for a name name then the DNS Resolver daemon sends a new query with name.domain1 to the DNS server. If this DNS query is also not successfully responded to by the DNS server then the DNS Resolver daemon repeats the DNS query with the next domain name domaini (i = 2 ... 8) defined in the search entry. This process is continued until either the DNS query has been successfully answered by the DNS server or until no further domain names are defined in the search entry.
The examples below indicate the names generated by the DNS Resolver daemon for queries to a DNS server:
Example for a DNS name with a period
Entry in the configuration file:
search part-1.my-company.com part-2.my-company.com
Name specified by user:
my.host
Name generated by the DNS Resolver daemon:
my.host my.host.part-1.my-company.com my.host.part-2.my-company.com
Example for a DNS name without a period
Entry in the configuration file:
search part-1.my-company.com part-2.my-company.com
Name specified by user:
myhost
Name generated by the DNS Resolver daemon:
myhost.part-1.my-company.com myhost.part-2.my-company.com myhost
lwserver : IPv4 or IPv6 address
The list socket of LWRESD is opened at this address so that is can be accessed by the LWRES client.
lwlport Port number
The list socket of LWRESD is opened at this port number.
destport Port number
A port which differs from the default port number 53 can be specified here for the name servers entered. This enables tests of name servers to be performed which were started for this purpose under a non-default port number.
Changes with the keywords lwserver, lwlport and destport only become effective when LWRESD is restarted, in other words the command sequence STOP-LWRESD/START-LWRESD or RESTART-LWRESD is required.
Note
The specifications relating to the accessibility of LWRESD should comply with the default information in BCAM (IPv4 loopback address and default port 921) or the addressing data changed by the BCAM command MODIFY-DNS-ACCESS (IPv4 or IPv6 addresses, port number) (see section "MODIFY-DNS-ACCESS / MDDNA: Modify DNS access in BCAM")!
Default name of the configuration file:
SYSDAT.LWRESD.nnn.RESOLV.CONF