DNS and DHCP
DNS — Domain Name Service
DNS is the network service that maps Internet domain names to numerical IP addresses. For example, a machine looking for forsythe.stanford.edu would request forsythe's IP address. One of the DNS servers would return this address associated with the NetDB name for that domain.
Stanford has multiple domains, including .sunet and .NoDomain. Names in the .sunet domain are only resolved for Stanford hosts. This is useful for hosts on private address spaces (not reachable from the Internet). Names in the .NoDomain domain are never resolved by DNS servers — they're typically used as placeholders.
If a node has multiple IP addresses, DNS will return those IP addresses in random order. If the DNS request comes from the same network as one of the IP addresses, that address will return first in the list.
For reverse lookup — that is, using an IP addresses to lookup a domain name — the name closest to the address will be returned first. In other words, the order is IP address name, interface name, node name. In the case of multiple node names, names are returned in random order.
For information about DNS update times, please see DNS Update Information.
DHCP — Dynamic Host Configuration Protocol
DHCP is the network service that maps hardware addresses to network configuration information. If a machine is configured for DHCP or BOOTP, it sends its hardware address and makes a request for information called "DHCP options" during network startup. The information returned is based on the NetDB entry for the node associated with that hardware address. For more information, see DHCP and BootP.
DHCP information is updated from NetDB approximately every 10 minutes.