- Configuring OSPF
- OSPF Stub Router Advertisement
- OSPF Update Packet-Pacing Configurable Timers
- OSPF Sham-Link Support for MPLS VPN
- OSPF Support for Multi-VRF on CE Routers
- OSPF Forwarding Address Suppression in Translated Type-5 LSAs
- OSPF Inbound Filtering Using Route Maps with a Distribute List
- OSPF Shortest Path First Throttling
- OSPF Support for Fast Hello Packets
- OSPF Incremental SPF
- OSPF Limit on Number of Redistributed Routes
- OSPF Link-State Advertisement Throttling
- OSPF Support for Unlimited Software VRFs per PE Router
- OSPF Area Transit Capability
- OSPF Per-Interface Link-Local Signaling
- OSPF Link-State Database Overload Protection
- OSPF MIB Support of RFC 1850 and Latest Extensions
- OSPF Enhanced Traffic Statistics
- Configuring OSPF TTL Security Check and OSPF Graceful Shutdown
- OSPF Sham-Link MIB Support
- OSPF SNMP ifIndex Value for Interface ID in Data Fields
- OSPFv2 Local RIB
- OSPF Support for Forwarding Adjacencies over MPLS TE Tunnels
- Enabling OSPFv2 on an Interface Basis
- OSPF NSR
- OSPFv2 Loop-Free Alternate Fast Reroute
- Finding Feature Information
- Prerequisites for Enabling OSPFv2 on an Interface Basis
- Restrictions on Enabling OSPFv2 on an Interface Basis
- Information About Enabling OSPFv2 on an Interface Basis
- How to Enable OSPFv2 on an Interface Basis
- Configuration Example for Enabling OSPFv2 on an Interface
- Additional References
- Feature Information for Enabling OSPFv2 on an Interface Basis
Enabling OSPFv2 on an Interface Basis
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
- Prerequisites for Enabling OSPFv2 on an Interface Basis
- Restrictions on Enabling OSPFv2 on an Interface Basis
- Information About Enabling OSPFv2 on an Interface Basis
- How to Enable OSPFv2 on an Interface Basis
- Configuration Example for Enabling OSPFv2 on an Interface
- Additional References
- Feature Information for Enabling OSPFv2 on an Interface Basis
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the Feature Information Table at the end of this document.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Prerequisites for Enabling OSPFv2 on an Interface Basis
OSPFv2 must be running on your network.
Restrictions on Enabling OSPFv2 on an Interface Basis
The ip ospf area command is supported only for OSPFv2.
Information About Enabling OSPFv2 on an Interface Basis
- Benefits of Enabling OSPFv2 on an Interface Basis
- Implications of Configuring OSPFv2 On a Router Basis or an Interface Basis
Benefits of Enabling OSPFv2 on an Interface Basis
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, which is entered in router configuration mode. Alternatively, you can enable OSPFv2 explicitly on an interface by using the ip ospf area command, which 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 supersedes the effects of the network areacommand, which 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 areacommand.
Implications of Configuring OSPFv2 On a Router Basis or an Interface Basis
Before you use the ip ospf area command to enable OSPFv2 on an interface, we recommend that you understand the following scenarios and command behavior. There are implications to using the network areacommand (configuring OSPFv2 in router configuration mode) versus using the ip ospf area command (configuring OSPFv2 in interface configuration mode).
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 areacommand, 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 areacommand, but you 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 ip ospf area Command
When the ip ospf areacommand 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 ospfcommand 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 ip ospf areacommand, 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 OSPFv2 on an Interface Basis
Enabling OSPFv2 on an Interface
DETAILED STEPS
Configuration Example for Enabling OSPFv2 on an Interface
Example Enabling OSPFv2 on an Interface
In the following example, OSPFv2 is configured explicitly on GigabitEthernet interface 0/0/0:
Router(config)# interface GigabitEthernet 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 GigabitEthernet 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 GigabitEthernet 0/0/0
GigabitEthernet0/0/0 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 enabling OSPFv2 on an interface.
Related Documents
| Related Topic |
Document Title |
|---|---|
| Configuring OSPF |
Configuring OSPF |
| OSPF commands |
Cisco IOS IP Routing: OSPF Command Reference |
| Cisco IOS master command list, all releases |
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 XE releases, and feature sets, use Cisco MIB Locator found at the following URL: |
RFCs
| RFC |
Title |
|---|---|
| RFC 2328 |
OSPF Version 2 |
Technical Assistance
| Description |
Link |
|---|---|
| The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password. |
Feature Information for Enabling OSPFv2 on an Interface Basis
The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
| Table 1 | Feature Information for Enabling OSPFv2 on an Interface Basis |
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Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.
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