When you are contacting a host that has multiple network interfaces, using a particular interface may give you better performance. If the multihomed host is local and shares a network (or subnet) with your host, one of the multihomed host’s addresses is “closer.”
Suppose you have an FTP server on two networks, cleverly called network A and network B, and hosts on both networks access the server often. Hosts on network A will experience better performance if they use the host’s interface to network A. Likewise, hosts on network B would benefit from using the host’s interface to network B as the address for their FTP client.
In Chapter 4, we mentioned that the Microsoft DNS Server returns all the addresses for a multihomed host. There was no guarantee of the order in which the DNS server would return the addresses, so we assigned aliases (wh249 and wh253 for wormhole) to the individual interfaces. If one interface is preferable, you (or more realistically, a DNS client) can use an appropriate alias to get the correct address. You can use aliases to choose the “closer” interface but, because of address sorting, they are not always necessary.
The Microsoft DNS Server sorts addresses by default. The server compares the IP address of the querier with the IP addresses of A records in a pending response. It moves those records with the same network as the querier to the top of the list in the response. This comparison is based on the class of network from ...