35-5
Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
OL-9639-07
Chapter 35 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. 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.
You can use the all ones subnet (131.108.255.0) and even though it is discouraged, you can enable the
use of subnet zero if you need the entire subnet space for your IP address.
Beginning in privileged EXEC mode, follow these steps to enable subnet zero:
Use the no ip subnet-zero global configuration command to restore the default and disable the use of
subnet zero.
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
interface interface-id Enter interface configuration mode, and specify the Layer 3
interface to configure.
Step 3
no shutdown Enable the interface if necessary. User network interfaces
(UNIs) and enhanced network interfaces (ENIs) are disabled by
default; network node interfaces (NNIs) are enabled by default.
Step 4
no switchport Remove the interface from Layer 2 configuration mode (if it is a
physical interface).
Step 5
ip address ip-address subnet-mask Configure the IP address and IP subnet mask.
Step 6
end Return to privileged EXEC mode.
Step 7
show interfaces [interface-id]
show ip interface [interface-id]
show running-config interface [interface-id]
Verify your entries.
Step 8
copy running-config startup-config (Optional) Save your entries in the configuration file.
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
ip subnet-zero Enable the use of subnet zero for interface addresses and routing updates.
Step 3
end Return to privileged EXEC mode.
Step 4
show running-config Verify your entry.
Step 5
copy running-config startup-config (Optional) Save your entry in the configuration file.
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