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288 Chapter 5: Network Protocols
this command is preferred. If a different setting is desired for IP, the ip mtu command sets the
value used for IP.
A few nuances relate to the two MTU-setting commands. If both are configured on an interface,
then the IP MTU setting takes precedence on the interface. However, if the mtu command is
configured after the ip mtu is configured, the ip mtu value is reset to the same value as that of
the mtu command. So, care must be taken when changing these values.
IP Naming Commands and Telnet
Names are never important to the process of routing IP packets. However, most human users
prefer to use names instead of IP addresses, for obvious reasons. So, the process of using
names--and, most frequently, using a Domain Name System (DNS) to identify the IP address
that corresponds to a name--is important for end users.
Router and switch administrators like to use names in many cases, for the same reason that end
users like to use names. When the administrator uses a PC or workstation, that person can open
up a variety of windows and Telnet to various routers and switches. This short section is not
concerned with naming in that case.
When a router or switch administrator is logged in to the router or switch, a variety of
commands are available. Particularly for the trace, ping, and telnet commands, one key
parameter is the IP address or host name of that with which you want to trace, ping, or telnet.
This section describes the use of host names on an IOS-based device. Along the way, some
nuances of the use of Telnet are covered.
The IOS can use statically configured names as well as refer to one or more DNSs. Example
5-12 shows some names statically configured, with configuration pointing to two different
DNSs.
Example 5-12
IP Naming Configuration and show ip host Command
hostname Cooperstown
!
ip host Mays 10.1.1.1
ip host Aaron 10.2.2.2
ip host Mantle 10.3.3.3
!
ip domain-name lacidar.com
ip name-server 10.1.1.200 10.2.2.200
ip domain-lookup
Seville#show hosts
Default domain is lacidar.com
Name/address lookup uses static mappings
Host Flags Age Type Address(es)
Mays (perm, OK) 0 IP 10.1.1.1
Aaron (perm, OK) 0 IP 10.2.2.2
Mantle (perm, OK) 0 IP 10.3.3.3
Seville#
ch05.fm Page 288 Monday, March 20, 2000 5:06 PM