During ongoing operation BCAM attempts to get DNS information for the known hosts and processors. The DNS names are obtained either from the Domain Name System (DNS) or from the internal FQDN file.
The FQDN file always has priority for BCAM, i.e. BCAM always checks in the first step whether there is a suitable entry in the FQDN file. Only if this is not the case BCAM does attempt to obtain the DNS information from the DNS.
Obtaining the FQDN name from the FQDN file
FQDNs can be assigned internally to processors via the FQDN file. In addition, an IP/IPv6 address can be specified, whereby the corresponding IP/IPv6 address is also assigned to the processor (see section "FQDN file"). While the association of processors and IP/IPv6 addresses is important for automatic end-system inclusion (see the section Automatic End-System Inclusion), it is not relevant for managing DNS names in BCAM.
If a processor in the FQDN file has an assigned DNS name, that processor can be identified in BCAM using this FQDN.
Note:
By adding additional lines with identical BCAM processor names in the FQDN file, DNS alias names can be defined.
Obtaining the FQDN name from DNS
The requests for resolving DNS names into IP/IPv6 addresses and vice versa, which user programs send to DNS servers, are usually handled by a central DNS resolver instance. The DNS resolver for BCAM and SOCKETS(BS2000) (and therefore also indirectly for POSIX-SOCKETS) is implemented through the BIND-based program LWRESD (Light Weight Resolver Daemon). Therefore a prerequisite for the use of DNS in BCAM is that LWRESD is running and a DNS server is accessible for BCAM. More detailed information on setting up DNS usage via LWRESD can be found in the section "Settings for DNS usage via LWRESD".
Note:
An FQDN can be associated with multiple IP/IPv6 addresses, and conversely, an IP/IPv6 address can be associated with multiple FQDNs. When a name resolution request is made, the DNS server provides a list of all corresponding names or IP/IPv6 addresses. The specific FQDN or IP/IPv6 address used depends on the application.