Bay Networks 5390, Administering, Page: 78 / 888

A2-18 893-741-B
Configuring the Model 5390 Server
Using the RWHO Protocol
Berkeley UNIX hosts use the RWHO protocol to pass information about themselves to other hosts.
This information includes the host’s name, who is logged in, up time, and load factor. The RWHO
daemon, rwhod, broadcasts this information and listens for RWHO messages from other hosts,
storing what it receives in a file. The information can be displayed with the rwho and ruptime
commands from a UNIX host.
The Model 5390 server uses the RWHO protocol as a name server.
The Model 5390 server runs an rwhod that listens for broadcasts from other hosts, but does not
broadcast information about itself. When the Model 5390 server receives an RWHO message, it
stores the host name, status information, and the source address from the IP header as the host’s
Internet address in its host table.
Using only RWHO messages to build the host table is satisfactory for a small network in which all
the hosts run rwhod. But, rwhod often is not used in networks primarily comprised of workstations
because of the load it imposes on hosts. In large or heavily loaded networks, RWHO broadcasts
can impose an excessive load on the network.
Some hosts send RWHO packets with incomplete source addresses in the IP header. The Model
5390 server is unable to store an Internet address for these hosts; causing the host table to display
the host’s Internet address as “_._._._”.
If an rwhod forwards packets from one network to another, the Internet address in the IP header is
that of the forwarding host, not of the host whose name is in the data packet. This results in the
Model 5390 server storing the wrong Internet address for that host.
Because the Model 5390 server does not broadcast RWHO messages, Model 5390 names never
appear in host tables built exclusively from these broadcasts. In which case, the only way to access
the Model 5390 server using the telnet command is with an Internet address.
The rwho parameter defines whether or not the Model 5390 server
listens for RWHO broadcasts. Setting the parameter to N disables the Model 5390 rwhod and
prevents the Model 5390 server from using RWHO messages for building the host table. The default
is Y.
Managing the Size of the Host Table
When the host table acquires a new entry after it is full, the Model 5390 server deletes the oldest,
least-used entry to make room for the new one. The Model 5390 server’s use of the host table is
erratic if the table size is too small. Increasing the size of the table reduces this problem.