38-7
Catalyst 3750 SwitchSoftware Configuration Guide
OL-8550-09
Chapter38 Configuring IP Unicast Routing
Configuring IP Addressing
Assigning IP Addresses to Network Interfaces
An IP address identifies a location to which IP packets can be sent. Some IP addresses are reserved for
special uses and cannot be used for host, subnet, or network addresses. RFC 1166, “Internet Numbers,”
contains the official description of IP addresses.
An interface can have one primary IP address. A mask identifies the bits that denote the network number
in an IP address. When you use the mask to subnet a network, the mask is referred to as a subnet mask.
To receive an assigned network number, contact your Internet service provider.
Beginning in privileged EXEC mode, follow these steps to assign an IP address and a network mask to
a Layer 3 interface:

Use of Subnet Zero

Subnetting with a subnet address of zero is strongly discouraged because of the problems that can arise
if a network and a subnet have the same addresses. For example, if network 131.108.0.0 is subnetted as
255.255.255.0, subnet zero would be written as 131.108.0.0, which is the same as the network address.
IRDP Disabled.
Defaults when enabled:
Broadcast IRDP advertisements.
Maximum interval between advertisements: 600 seconds.
Minimum interval between advertisements: 0.75 times max interval
Preference: 0.
IP proxy ARP Enabled.
IP routing Disabled.
IP subnet-zero Disabled.
Table38-1 Default Addressing Configuration (continued)
Feature Default Setting
Command Purpose
Step1 configure terminal Enter global configuration mode.
Step2 interface interface-id Enter interface configuration mode, and specify the Layer 3
interface to configure.
Step3 no switchport Remove the interface from Layer 2 configuration mode (if it is a
physical interface).
Step4 ip address ip-address subnet-mask Configure the IP address and IP subnet mask.
Step5 no shutdown Enable the interface.
Step6 end Return to privileged EXEC mode.
Step7 show interfaces [interface-id]
show ip interface [interface-id]
show running-config interface [interface-id]
Verify your entries.
Step8 copy running-config startup-config (Optional) Save your entries in the configuration file.