Cisco IOS IP Routing Protocols Configuration Guide, Release 12.4 - Area Command in Interface Mode for OSPFv2 [Cisco IOS Software Releases 12.4 Mainline]

Table Of Contents

Area Command in Interface Mode for OSPFv2

Contents

Prerequisites for Area Command in Interface Mode for OSPFv2

Restrictions for Area Command in Interface Mode for OSPFv2

Information About Area Command in Interface Mode for OSPFv2

Benefits of Area Command in Interface Mode for OSPFv2 Feature

Configuration Guidelines for the Area Command in Interface Mode for OSPFv2 Feature

How to Enable the Area Command in Interface Mode for OSPFv2

Enabling OSPFv2 on an Interface

Configuration Examples for Area Command in Interface Mode for OSPFv2 Feature

Enabling OSPFv2 on an Interface: Example

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Command Reference

Feature Information for Area Command in Interface Mode for OSPFv2

Area Command in Interface Mode for OSPFv2

First Published: August 09, 2004

Last Updated: May 5, 2008

This document describes how to enable Open Shortest Path First version 2 (OSPFv2) on a per-interface basis to simplify the configuration of unnumbered interfaces. The ip ospf area command allows you to enable OSPFv2 explicitly on an interface. The ip ospf area command is an alternative to enabling OSPFv2 through the address of the interface that matches the address range specified by the network area command.

Finding Feature Information in This Module

Your Cisco IOS software release may not support all of the features documented in this module. To reach links to specific feature documentation in this module and to see a list of the releases in which each feature is supported, use the "Feature Information for Area Command in Interface Mode for OSPFv2" section.

Finding Support Information for Platforms and Cisco IOS and Catalyst OS Software Images

Use Cisco Feature Navigator to find information about platform support and Cisco IOS and Catalyst OS software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Contents

•Prerequisites for Area Command in Interface Mode for OSPFv2

•Restrictions for Area Command in Interface Mode for OSPFv2

•Information About Area Command in Interface Mode for OSPFv2

•How to Enable the Area Command in Interface Mode for OSPFv2

•Configuration Examples for Area Command in Interface Mode for OSPFv2 Feature

•Additional References

•Command Reference

•Feature Information for Area Command in Interface Mode for OSPFv2

Prerequisites for Area Command in Interface Mode for OSPFv2

OSPFv2 must be running on your network.

Restrictions for Area Command in Interface Mode for OSPFv2

The ip ospf area command is supported only for OSPFv2.

Information About Area Command in Interface Mode for OSPFv2

This section contains the following information:

•Benefits of Area Command in Interface Mode for OSPFv2 Feature

•Configuration Guidelines for the Area Command in Interface Mode for OSPFv2 Feature

Benefits of Area Command in Interface Mode for OSPFv2 Feature

OSPF is enabled on an interface when the network address for the interface matches the range of addresses that is specified by the network area command that is entered in router configuration mode. You can enable OSPFv2 explicitly on an interface with the ip ospf area command that is entered in interface configuration mode. This capability simplifies the configuration of unnumbered interfaces with different areas.

Because the ip ospf area command is configured explicitly for an interface, it will supersede the effects of the network area command that is entered at the network level to affect the interfaces whose addresses fall within the address range specified for the network area command.

If you later disable the ip ospf area command, the interface still will run OSPFv2 as long as its network address matches the range of addresses that is specified by the network area command.

Configuration Guidelines for the Area Command in Interface Mode for OSPFv2 Feature

When you use the ip ospf area command in interface configuration mode to enable OSPFv2 on an interface, we recommend that you be familiar with the following guidelines.

Interface Is Already OSPFv2-Enabled by network area Command with Same Area and Process

If you enter the ip ospf area command on an interface that is enabled in OSPFv2 by the network area command, the process ID or area ID of the interface does not change, and the interface status will not be changed. However, the interface will be flagged as being configured from interface configuration mode and the configuration data will be saved in the interface description block (IDB).

Interface Is Already Configured by network area Command with Different Area or Process

If you enter the ip ospf area command on an interface that is enabled in OSPFv2 by the network area command, but change the configuration by changing the process ID and area ID of the interface, after the new configuration information is stored in the IDB, the interface will be removed and reattached. Therefore, the interface will be removed from the original area and process and be added to the new ones. The state of the interface will also be reset.

Interface Is Not Configured by network area Command

If the interface is not enabled in OSPFv2 by the network area command, the area and OSPF router instance will be created if needed. When the router is reloaded, the OSPF process will not begin running until system initialization is complete. To remove an OSPF router instance, enter the no router ospf command. Removing the ip ospf area command in interface mode will not result in removing an OSPF router instance.

Removing an interface enable Command

When the interface enable command is removed, the interface will be detached from the area. The area will be removed if it has no other attached interfaces. If the interface address is covered by the network area command, the interface will be enabled once again in the area for the network that it is in.

New Processes

If an OSPF process does not already exist, and a router ID cannot be chosen when either the router ospf command or the interface command is configured, a Proximity Database (PDB) and a process will be created, but the process will be inactive. The process will become active when a router ID is chosen, either when it is explicitly configured using the router-id command or when an IP address becomes available. Note that the router ospf command will now be accepted even if a router ID cannot be chosen, putting the command-line interface (CLI) into the OSPF configuration context. Therefore, the router-id command is to be entered before an IP address is available. If the process is not active and the show ip ospf command is entered, the message "%OSPF: Router process X is not running, please provide a router-id" will be displayed.

Link-State Advertisements and Shortest Path First

If a state change occurs as a result of the interface enable command, new router link-state advertisements (LSAs) will be generated (also for the old area, if the interface is changing areas) and shortest path first (SPF) will be scheduled to run in both the old and new areas.

How to Enable the Area Command in Interface Mode for OSPFv2

This section contains the following procedure:

•Enabling OSPFv2 on an Interface (required)

Enabling OSPFv2 on an Interface

Perform this task to enable OSPFv2 on an interface.

SUMMARY STEPS

1. enable

2. configure terminal

3. interface type number

4. ip ospf process-id area area-id [secondaries none]

5. end

6. show ip ospf interface [interface-type interface-number]

DETAILED STEPS

Command or Action

Purpose

Step 1

enable
Example:

Router> enable

Enables privileged EXEC mode.

•Enter your password if prompted.

Step 2

configure terminal
Example:

Router# configure terminal

Enters global configuration mode.

Step 3

interface type number
Example:

Router(config)# interface FastEthernet 0/2

Configures an interface type and enters interface configuration mode.

Step 4

ip ospf process-id area area-id [secondaries none]
Example:

Router(config-if)# ip ospf 1 area 0 secondaries none

Enables OSPFv2 on an interface.

•To prevent secondary IP addresses on the interface from being advertised, you must enter the optional secondaries keyword followed by the none keyword.

Step 5

end
Example:

Router(config-if)# end

Exits interface configuration mode and returns to privileged EXEC mode.

Step 6

show ip ospf interface [interface-type interface-number]
Example:

Router# show ip ospf interface FastEthernet 0/2

Displays OSPF-related interface information.

•Once you have enabled OSPFv2 on the interface, you can enter the show ip ospf interface command to verify the configuration.

Configuration Examples for Area Command in Interface Mode for OSPFv2 Feature

This section provides the following configuration example:

•Enabling OSPFv2 on an Interface: Example

Enabling OSPFv2 on an Interface: Example

In the following example, OSPFv2 is configured explicitly on Ethernet interface 0/0/0:
Router(config)# interface Ethernet 0/0/0
Router(config-if)# bandwidth 10000
Router(config-if)# ip address 172.16.1.1 255.255.255.0
Router(config-if)# ip ospf hello-interval 1
Router(config-if)# ip ospf 1 area 0
When the show ip ospf interface command is entered, the following output shows that Ethernet interface 0/0/0 was configured in interface configuration mode to run OSPFv2. The secondary IP addresses on the interface will also be advertised:
Router# show ip ospf interface Ethernet 0/0/0
Ethernet0/0/0 is up, line protocol is up 
  Internet Address 172.16.1.1/24, Area 0 
  Process ID 1, Router ID 172.16.11.11, Network Type BROADCAST, Cost: 10
  Enabled by interface config, including secondary ip addresses
  Transmit Delay is 1 sec, State DR, Priority 1 
  Designated Router (ID) 172.16.11.11, Interface address 172.16.1.1
  Backup Designated router (ID) 172.16.22.11, Interface address 172.16.1.2
  Timer intervals configured, Hello 1, Dead 4, Wait 4, Retransmit 5
    oob-resync timeout 40
    Hello due in 00:00:00
  Supports Link-local Signaling (LLS)
  Index 2/2, flood queue length 0
  Next 0x0(0)/0x0(0)
  Last flood scan length is 1, maximum is 1
  Last flood scan time is 0 msec, maximum is 0 msec
  Neighbor Count is 1, Adjacent neighbor count is 1 
    Adjacent with neighbor 172.26.22.11  (Backup Designated Router)
  Suppress hello for 0 neighbor(s)
Additional References

The following sections provide references related to the Area Command in Interface Mode for OSPFv2 feature.

Related Documents

Related Topic

Document Title

OSPF commands

"OSPF Commands" chapter in the Cisco IOS IP Routing Protocols Command Reference.

OSPF configuration tasks

"Configuring OSPF" chapter in the Cisco IOS IP Routing Protocols Configuration Guide.

Standards

Standard

Title

No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.

—

MIBs

MIB

MIBs Link

No new or modified MIBs are supported by this feature, and support for existing MIBs has not been modified by this feature.

To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:

http://www.cisco.com/go/mibs

RFCs

RFC

Title

RFC 2328

OSPF Version 2

Technical Assistance

Description

Link

The Cisco Support website provides extensive online resources, including documentation and tools for troubleshooting and resolving technical issues with Cisco products and technologies.

To receive security and technical information about your products, you can subscribe to various services, such as the Product Alert Tool (accessed from Field Notices), the Cisco Technical Services Newsletter, and Really Simple Syndication (RSS) Feeds.

Access to most tools on the Cisco Support website requires a Cisco.com user ID and password.

http://www.cisco.com/techsupport

Command Reference

The following commands are introduced or modified in the feature or features documented in this module. For information about these commands, see the Cisco IOS IP Routing Protocols Command Reference at http://www.cisco.com/en/US/docs/ios/iproute/command/reference/irp_book.html. For information about all Cisco IOS commands, go to the Command Lookup Tool at http://tools.cisco.com/Support/CLILookup or to the Cisco IOS Master Commands List.

•ip ospf area

Feature Information for Area Command in Interface Mode for OSPFv2

Table 1 lists the release history for this feature.

Not all commands may be available in your Cisco IOS software release. For release information about a specific command, see the command reference documentation.

Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS and Catalyst OS software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Note Table 1 lists only the Cisco IOS software release that introduced support for a given feature in a given Cisco IOS software release train. Unless noted otherwise, subsequent releases of that Cisco IOS software release train also support that feature.

Table 1 Feature Information for Area Command in Interface Mode for OSPFv2

Feature Name

Releases

Feature Information

Area Command in Interface Mode for OSPFv2

12.0(29)S
12.3(11)T
12.2(28)SB
12.2(33)SRB

This document describes how to enable Open Shortest Path First version 2 (OSPFv2) on a per-interface basis to simplify the configuration of unnumbered interfaces. The ip ospf area command allows you to enable OSPFv2 explicitly on an interface. The ip ospf area command is an alternative to enabling OSPFv2 through the address of the interface that matches the address range specified by the network area command.

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