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Chapter 34
Configuring IP Unicast Routing
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:
Command
Step 1
configure terminal
Step 2
interface interface-id
Step 3
no switchport
Step 4
ip address ip-address subnet-mask
Step 5
no shutdown
Step 6
end
Step 7
show interfaces [interface-id]
show ip interface [interface-id]
show running-config interface [interface-id]
Step 8
copy running-config startup-config
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:
Command
Step 1
configure terminal
Step 2
ip subnet-zero
Step 3
end
Step 4
show running-config
Step 5
copy running-config startup-config
Use the no ip subnet-zero global configuration command to restore the default and disable the use of
subnet zero.
OL-8915-03
Purpose
Enter global configuration mode.
Enter interface configuration mode, and specify the Layer 3
interface to configure.
Remove the interface from Layer 2 configuration mode (if it is a
physical interface).
Configure the IP address and IP subnet mask.
Enable the interface.
Return to privileged EXEC mode.
Verify your entries.
(Optional) Save your entries in the configuration file.
Purpose
Enter global configuration mode.
Enable the use of subnet zero for interface addresses and routing updates.
Return to privileged EXEC mode.
Verify your entry.
(Optional) Save your entry in the configuration file.
Cisco Catalyst Blade Switch 3020 for HP Software Configuration Guide
Configuring IP Addressing
34-5
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