Lantronix ETS Reference Manual - 2.7.4   Local Host Table

TCP/IP

Concepts

2-10

Text names make it unnecessary to remember long strings of address numbers. For example, suppose user 

Bob wishes to log into a host named “alex.weasel.ctcorp.com.” The other hosts on the network have no 

knowledge of which piece of hardware is associated with this name, so the ETS must translate the name into 

a numeric address, such as 199.25.172.6. After the name is translated (or resolved), the connection can be 

attempted.

See Set/Define Server Domain on page 12-65 for more information.If there is no local host table or name 

server to provide text name translation, or if the name server(s) cannot translate the name, the host’s numeric 

IP address would have to be used for the connection. Also, if the ETS has not been told which local host is 

acting as the name server (see the Set/Define Server Nameserver command), it assumes that none is 

available and the connect request will likely fail. 

The ETS also allows the setting of a default domain name to be appended to any host name for which name 

resolution is performed. In the example above, if Bob’s server had a default domain name of 

weasel.ctcorp.com, then Bob could type telnet alex and the ETS would attempt to resolve 

alex.weasel.ctcorp.com. This name checking occurs for all ETS commands that require text name 

resolution, such as Telnet, Rlogin, and Ping. If the connect destination name ends with a period, the domain 

name is not added to the hostname for resolution. 

2.7.4   Local Host Table

The ETS enhances name resolution by providing a simple host table, which is a list of node names and 

corresponding IP addresses. Using the Set/Define Telnet Hosts command, the server manager can add 

hosts to this table. This allows the user to enter a text name described in the table in place of an IP address, 

which in turn eliminates the need to remember IP addresses. The local host table is especially useful for 

sites that do not have a domain name server, or in cases where a few hosts are accessed frequently. 

The Show Hosts command displays all currently-known IP nodes and how they were learned: via the local 

host table, a local name server, rwho broadcasts, or name resolution during a connection attempt.

If name serving is enabled, the name server will be asked for the node’s IP address only if the local host 

table does not contain the information. This means that incorrect information in the local host table will be 

used, even if it is contrary to what a nameserver might report. The local host table does not have to be 

consistent with the name server, but consistency will avoid confusion. To maintain consistency, remove the 

old hosts from the host table with the Clear/Purge Telnet Hosts command.

Host table aliases should be easy to type, remember, and recognize. They are limited to 64 characters, with 

a maximum length of 16 characters per segment. For example, alex.weasel.ctcorp is legal, while 

alex.communicationsserver.ctcorp is not.

The ETS can also get host names and IP addresses from node rwho broadcasts and attempt to add entries to 

the host table based on this information. If the rwho addresses are cleared from the table, they will reappear 

the next time the host sends out an rwho message. Addresses will also reappear if a user attempts to connect 

to one of them.

2.7.5   Dynamic Host Control Protocol (DHCP)

DHCP, an extension to BOOTP, allows network administrators to lease IP addresses to network nodes as 

needed. ETS servers offer two levels of DHCP support: boot and runtime.