Any additional lines in the channel block specify additional hosts or aliases for hosts the channel can reach. These lines have the form:
host-namewill be queued on this channel, but To: addresses will be rewritten in the transport layer (envelope) to use
host-name. Addresses in the message header are not rewritten in this fashion. If
proper-nameis omitted the official host name for the channel will be used instead ---
host-nameis then just a synonym for
All of these additional
host-name strings are
stored in the same table in which official channel host names are
stored. No duplicates are allowed amongst all these names.
The functionality of these additional channel table lines may appear to duplicate some of the capabilities of rewrite rules, and this is in fact true. The ability to specify multiple hosts per channel is an older feature of PMDF that is not heavily used in more recent times. One particular usage remains, however --- the mapping and unmapping of domain names to DECnet node names for hosts associated with the d channel. It is customary to use rewrite rules to canonicalize DECnet node names into full domain names and match them to the d channel. Then the channel table is used to inverse-map the domain names back into the DECnet node names. This approach results in the use of domain names in all places but envelope To: addresses, which is exactly what such systems need.