6.3. OSPF Commands

Command Purpose

To enable authentication for an Open Shortest Path First (OSPF) area, use the area authentication command in router configuration mode. To remove an authentication specification of an area or a specified area from the configuration, use the no form of this command.

Prerequisites

Command Syntax

area AREA-ID authentication ( message-digest | )

no area AREA-ID authentication

Command Mode

Router Configuration

Default

Type 0 authentication (no authentication)

Usage

Specifying authentication for an area sets the authentication to Type 1 (simple password) as specified in RFC 1247. If this command is not included in the configuration file, authentication of Type 0 (no authentication) is assumed.

The authentication type must be the same for all routers and access servers in an area. The authentication password for all OSPF routers on a network must be the same if they are to communicate with each other via OSPF. Use the ip ospf authentication-key interface command to specify this password.

If you enable MD5 authentication with the message-digest keyword, you must configure a password with the ip ospf message-digest-key interface command.

To remove the authentication specification for an area, use the no form of this command with the authentication keyword.

Examples

The following example mandates authentication for areas 0 and 10.0.0.0 of OSPF routing process 100. Authentication keys are also provided:

Switch# configure terminal
Switch(config)# interface eth-0-1
Switch(config-if)# no switchport
Switch(config-if)# ip address 192.168.251.201/24
Switch(config-if)# ip ospf authentication-key adcdefgh
Switch(config)# interface eth-0-2
Switch(config-if)# no switchport
Switch(config-if)# ip address 10.56.0.201/16
Switch(config-if)# ip ospf authentication-key ijklmnop
Switch(config)# router ospf 100
Switch(config-router)# network 10.0.0.0 0.255.255.255 area 10.0.0.0
Switch(config-router)# network 192.168.0.0/16 area 0
Switch(config-router)# area 10.0.0.0 authentication
Switch(config-router)# area 0 authentication

Related Commands

ip ospf authentication-key

Command Purpose

To specify a cost for the default summary route sent into a stub, use the area default-cost command in router configuration mode. To remove the assigned default route cost, use the no form of this command.

Prerequisites

Command Syntax

area AREA-ID default-cost COST

no area AREA-ID default-cost

Command Mode

Router Configuration

Default

COST: 1

Usage

The command is used only on an Area Border Router (ABR) attached to a stub.

There are two stub area router configuration commands: the stub and default-cost options of the area command. In all routers and access servers attached to the stub area, the area should be configured as a stub area using the stub option of the area command. Use the default-cost option only on an ABR attached to the stub area. The default-cost option provides the metric for the summary default route generated by the ABR into the stub area.

Examples

The following example shows how to configure a stub area and set its COST value:

Switch# configure terminal
Switch(config)# interface eth-0-1
Switch(config-if)# no switchport
Switch(config-if)# ip address 10.56.0.201/16
Switch(config)# router ospf 100
Switch(config-router)# network 10.0.0.0/8 area 10.0.0.0
Switch(config-router)# area 10.0.0.0 stub
Switch(config-router)# area 10.0.0.0 default-cost 20

Related Commands

None

Command Purpose

To filter prefixes advertised in type 3 link-state advertisements (LSAs) between Open Shortest Path First (OSPF) areas of an Area Border Router (ABR), use the area filter-list command in router configuration mode. To change or cancel the filter, use the no form of this command.

Prerequisites

Command Syntax

area AREA-ID filter-list ( access ACCESSS-LIST-NAME | prefix PREFIX-LIST-NAME ) ( in | out )

no area AREA-ID filter-list ( access ACCESSS-LIST-NAME | prefix PREFIX-LIST-NAME ) ( in | out )

Command Mode

Router Configuration

Default

This command has no default behavior.

Usage

With this feature enabled in the “in” direction, all type 3 LSAs originated by the ABR to this area, based on information from all other areas, are filtered by the prefix list. Type 3 LSAs that were originated as a result of the area range command in another area are treated like any other type 3 LSA that was originated individually. Any prefix that does not match an entry in the prefix list is implicitly denied.

With this feature enabled in the “out” direction, all type 3 LSAs advertised by the ABR, based on information from this area to all other areas, are filtered by the prefix list. If the area range command has been configured for this area, type 3 LSAs that correspond to the area range are sent to all other areas, only if at least one prefix in the area range matches an entry in the prefix list.

If all specific prefixes are denied by the prefix list, type 3 LSAs that correspond to the area range command will not be sent to any other area. Prefixes that are not permitted by the prefix list are implicitly denied.

Examples

The following example filters prefixes that are sent from all other areas to area 1:

Switch# configure terminal
Switch(config)# router ospf 100
Switch(config-router)# area 1 filter-list prefix AREA_1 in

Related Commands

area range

Command Purpose

To consolidate and summarize routes at an area boundary, use the area range command in router configuration mode. To disable this function, use the no form of this command.

Prerequisites

Command Syntax

area AREA-ID range ( ADDRESS MASK | ADDRESS / PREFIX-LENGTH ) ( advertise | not-advertise | )

no area AREA-ID range ( ADDRESS MASK | ADDRESS / PREFIX-LENGTH }

Command Mode

Router Configuration

Default

This command is disabled by default.

Usage

The area range command is used only with Area Border Routers (ABRs). It is used to consolidate or summarize routes for an area. The result is that a single summary route is advertised to other areas by the ABR. Routing information is condensed at area boundaries. External to the area, a single route is advertised for each address range. This behavior is called route summarization.

Multiple area router configuration commands specifying the range option can be configured. Thus, OSPF can summarize addresses for many different sets of address ranges.

Examples

The following example specifies one summary route to be advertised by the ABR to other areas for all subnets on network 10.0.0.0 and for all hosts on network 192.168.110.0:

Switch# configure terminal
Switch(config)# interface eth-0-1
Switch(config-if)# no switchport
Switch(config-if)# ip address 192.168.110.201/24
Switch(config)# interface eth-0-2
Switch(config-if)# no switchport
Switch(config-if)# ip address 192.168.120.201/24
Switch(config)# interface eth-0-3
Switch(config-if)# no switchport
Switch(config-if)# ip address 10.0.0.0/8
Switch(config)# router ospf 100
Switch(config-router)# network 192.168.110.0/24 area 0
Switch(config-router)# area 10.0.0.0 range 10.0.0.0/8
Switch(config-router)# area 0 range 192.168.110.0 255.255.0.0

Related Commands

None

Command Purpose

To define an area as a stub area, use the area stub command in router configuration mode. To disable this function, use the no form of this command.

Prerequisites

Command Syntax

area AREA-ID stub ( no-summary | )

no area AREA-ID stub ( no-summary | )

Command Mode

Router Configuration

Default

No stub area is defined.

Usage

You must configure the area stub command on all routers and access servers in the stub area. Use the area router configuration command with the default-cost keyword to specify the cost of a default internal router sent into a stub area by an ABR.

There are two stub area router configuration commands: the stub and default-cost options of the area router configuration command. In all routers attached to the stub area, the area should be configured as a stub area using the stub keyword of the area command. Use the default-cost keyword only on an ABR attached to the stub area. The default-cost keyword provides the metric for the summary default route generated by the ABR into the stub area.

To further reduce the number of link-state advertisements (LSAs) sent into a stub area, you can configure the no-summary keyword on the ABR to prevent it from sending summary LSAs (LSA type 3) into the stub area.

Examples

The following example shows how to configure a stub area and set its COST value:

Switch# configure terminal
Switch(config)# interface eth-0-1
Switch(config-if)# no switchport
Switch(config-if)# ip address 10.56.0.201/16
Switch(config)# router ospf 100
Switch(config-router)# network 10.0.0.0/8 area 10.0.0.0
Switch(config-router)# area 10.0.0.0 stub
Switch(config-router)# area 10.0.0.0 default-cost 20

Related Commands

None

Command Purpose

To define an area as a NSSA area, use the area nssa command in router configuration mode. To disable this function, use the no form of this command.

Prerequisites

Command Syntax

area AREA-ID nssa ( translator-role ( candidate | never | always ) | ) ( no-summary | ) ( no-redistribution | ) ( default-information-originate { metric METRIC_VALUE | metric-type TYPE-VALUE | } | )

no area AREA-ID nssa ( translator-role | ) ( no-summary | ) ( no-redistribution | ) ( default-information-originate | )

Command Mode

Router Configuration

Default

No NSSA area is defined.

Usage

No NSSA area is configured as default. You must configure the area nssa command on all routers and access servers in the NSSA area.

There are many similarities between NSSA and stub area, neither of which propagates external routes from other area. The difference is that NSSA area can introduce and propagate external routes to the OSPF autonomous domain, while STUB area can not introduce external routes.

Examples

The following example shows how to configure a NSSA area :

Switch# configure terminal
Switch(config)# interface eth-0-1
Switch(config-if)# no switchport
Switch(config-if)# ip address 10.56.0.201/16
Switch(config)# router ospf 100
Switch(config-router)# network 10.0.0.0/8 area 10.0.0.0
Switch(config-router)# area 10.0.0.0 nssa

Related Commands

None

Command Purpose

To control how Open Shortest Path First (OSPF) calculates default metrics for the interface, use the auto-cost command in router configuration mode. To assign cost based only on the interface type, use the no form of this command.

Prerequisites

Command Syntax

auto-cost reference-bandwidth RATE

no auto-cost reference-bandwidth

Command Mode

Router Configuration

Default

100 Mbps

Usage

The value set by the ip ospf cost command overrides the cost resulting from the auto-cost command.Bandwidth dividing port rate is cost.

Examples

The following example changes the cost of the cost link to 1GBps:

Switch# configure terminal
Switch(config)# router ospf 100
Switch(config-router)# auto-cost reference-bandwidth 1000

Related Commands

ip ospf cost

Command Purpose

To clear redistribution based on the Open Shortest Path First (OSPF) routing process ID, use the clear ip ospf command in privileged EXEC mode.

Prerequisites

Command Syntax

clear ip ospf ( PID | ) process

Command Mode

Privileged EXEC

Default

None

Usage

Use the PID argument to clear only one OSPF process. If the PID argument is not specified, all OSPF processes are cleared.

Examples

The following example clears all OSPF processes:

Switch# clear ip ospf process

Related Commands

None

Command Purpose

To restore the method used to calculate summary route costs per RFC 1583, use the compatible rfc1583 command in router configuration mode. To disable RFC 1583 compatibility, use the no form of this command.

Prerequisites

Command Syntax

compatible rfc1583

no compatible rfc1583

Command Mode

Router Configuration

Default

Not compatible with RFC 1583.

Usage

To minimize the chance of routing loops, all Open Shortest Path First (OSPF) routers in an OSPF routing domain should have RFC compatibility set identically.

Because of the introduction of RFC 2328, OSPF Version 2, the method used to calculate summary route costs has changed. Use the no compatible rfc1583 command to enable the calculation method used per RFC 2328.

Examples

The following example specifies that the router process is compatible with RFC 1583:

Switch# configure terminal
Switch(config)# router ospf 100
Switch(config-router)# compatible rfc1583

Related Commands

None

Command Purpose

To generate a default external route into an Open Shortest Path First (OSPF) routing domain, use the default-information originate command in router configuration mode. To disable this feature, use the no form of this command.

Prerequisites

Command Syntax

default-information originate ( route-map WORD | always | metric METRIC-VALUE | metric-type TYPE-VALUE | )

no default-information originate ( route-map WORD | always | metric | metric-type | )

Command Mode

Router Configuration

Default

This command is disabled by default.

Usage

Whenever you use the redistribute or the default-information router configuration command to redistribute routes into an OSPF routing domain, the switch automatically becomes an autonomous System Boundary Router (ASBR). However, an ASBR does not, by default, generate a default route into the OSPF routing domain. The system still must have a default route for itself before it generates one, except when you have specified the always keyword.

Examples

The following example specifies a metric for the default route redistributed into the OSPF routing domain and an external metric type:

Switch# configure terminal
Switch(config)# router ospf 100
Switch(config-router)# redistribute rip metric 100
Switch(config-router)# default-information originate metric 100 metric-type 1

Related Commands

redistribute (OSPF)

Command Purpose

To set default metric values for the Open Shortest Path First (OSPF) routing protocol, use the default-metric command in router configuration mode. To return to the default state, use the no form of this command.

Prerequisites

Command Syntax

default-metric METRIC-VALUE

no default-metric

Command Mode

Router Configuration

Default

1 for BGP routes

20 for others

Usage

The default-metric command is used in conjunction with the redistribute router configuration command to cause the current routing protocol to use the same metric value for all redistributed routes.

Examples

The example advertises OSPF-derived routes using RIP and assigns the Internal Gateway Protocol (IGP)-derived routes a RIP metric of 10.:

Switch# configure terminal
Switch(config)# router ospf 100
Switch(config-router)# default-metric 10
Switch(config-router)# redistribute rip

Related Commands

redistribute (OSPF)

Command Purpose

To define Open Shortest Path First (OSPF) route administrative distances based on route type, use the distance command in router configuration mode. To restore the default value, use the no form of this command.

Prerequisites

Command Syntax

distance { DISTANCE | ospf [ external DIST1 ] [ inter-area DIST2 ] | [ intra-area DIST3 ] }

no distance { DISTANCE | ospf }

Command Mode

Router Configuration

Default

DIST1: 110

DIST2: 110

DIST3: 110

Usage

You may specify one of the keywords or use distance only to apply to all types of routes.

The distance command allows you to set a distance for an entire group of routes, rather than a specific route that passes an access list.

A common reason to use the distance command is when you have multiple OSPF processes with mutual redistribution, and you want to prefer internal routes from one over external routes from the other.

Examples

The example advertises OSPF-derived routes using RIP and assigns the Internal Gateway Protocol (IGP)-derived routes a RIP distance of 90:

Switch# configure terminal
Switch(config)# router ospf 100
Switch(config-router)# distance 90
Switch(config-router)# redistribute rip

Related Commands

None

Command Purpose

To filter networks received in updates or suppress networks from being advertised in updates, use the distribute-list command in router configuration mode. To cancel this function, use the no form of this command.

Prerequisites

Command Syntax

distribute-list prefix PREIFX-LIST-NAME ( in | out )

Command Mode

Router Configuration

Default

None

Usage

This command must specify an access list.

Examples

In the following example, OSPF process 1 is configured to accept network 20.0.0.0/8.:

Switch# configure terminal
Switch(config)# ip prefix-list plist permit 20.0.0.0/8
Switch(config)# router ospf 100
Switch(config-router)# network 20.0.0.0/8 area 0
Switch(config-router)# distribute-list prefix plist in

Related Commands

None

Command Purpose

To filter networks received in updates or suppress networks from being advertised in updates, use the distribute-list command in router configuration mode. To cancel this function, use the no form of this command.

Prerequisites

Command Syntax

distribute-list ACCESSS-LIST-NAME ( in | out )

no distribute-list ACCESSS-LIST-NAME ( in | out )

Command Mode

Router Configuration

Default

None

Usage

This command must specify an access list.

Examples

In the following example, OSPF process 1 is configured to accept two networks, network 20.0.0.0 and network 10.108.0.0:

Switch# configure terminal
Switch(config)# ip access-list acl1
Switch(config-ip-acl)# permit any 20.0.0.0 0.0.255.255 any
Switch(config-ip-acl)# permit any 10.108.0.0 0.0.255.255 any
Switch(config-ip-acl)# deny any any any
Switch(config)# router ospf 100
Switch(config-router)# network 10.108.0.0/16 area 1
Switch(config-router)# distribute-list acl1 in

Related Commands

ip access-list

Command Purpose

To specify the authentication type for an interface, use the ip ospf authentication command in interface configuration mode. To remove the authentication type for an interface, use the no form of this command.

Prerequisites

Command Syntax

ip ospf authentication ( message-digest | null | )

no ip ospf authentication

Command Mode

Interface Configuration

Default

The area default is no authentication (null authentication).

Usage

Before using the ip ospf authentication command, configure a password for the interface using the ip ospf authentication-key command. If you use the ip ospf authentication message-digest command, configure the message-digest key for the interface with the ip ospf message-digest-key command.

Examples

The following example enables message-digest authentication:

Switch# configure terminal
Switch(config)# interface eth-0-1
Switch(config-if)# ip ospf authentication message-digest

Related Commands

area authentication

ip ospf authentication-key

ip ospf message-digest-key

Command Purpose

To assign a password to be used by neighboring routers that are using the Open Shortest Path First (OSPF) simple password authentication, use the ip ospf authentication-key command in interface configuration mode. To remove a previously assigned OSPF password, use the no form of this command.

Prerequisites

Command Syntax

ip ospf authentication-key ( 8 | ) PASSWORD

no ip ospf authentication-key

Command Mode

Interface Configuration

Default

No password is specified.

Usage

The password created by this command is used as a “key” that is inserted directly into the OSPF header when the switch originates routing protocol packets. A separate password can be assigned to each network on a per-interface basis. All neighboring routers on the same network must have the same password to be able to exchange OSPF information.

Examples

The following example enables the authentication key with the string yourpass:

Switch# configure terminal
Switch(config)# interface eth-0-1
Switch(config-if)# no switchport
Switch(config-if)# ip ospf authentication-key yourpass

The following example enables the authentication key with the encrypt password 91c38996a1aa5699:

Switch# configure terminal
Switch(config)# interface eth-0-2
Switch(config-if)# no switchport
Switch(config-if)# ip ospf authentication-key 8 91c38996a1aa5699

Related Commands

area authentication

ip ospf authentication

Command Purpose

To explicitly specify the cost of sending a packet on an interface, use the ip ospf cost command in interface configuration mode. To reset the path cost to the default value, use the no form of this command.

Prerequisites

Command Syntax

ip ospf cost INTERFACE-COST

no ip ospf cost

Command Mode

Interface Configuration

Default

Different port rate has different default cost.

Usage

You can set the metric manually using this command, if you need to change the default. Using the bandwidth command changes the link cost as long as this command is not used.

Examples

The following example sets the interface cost value to 65:

Switch# configure terminal
Switch(config)# interface eth-0-1
Switch(config-if)# no switchport
Switch(config-if)# ip ospf cost 65

Related Commands

auto-cost reference bandwidth

Command Purpose

To filter outgoing link-state advertisements (LSAs) to an Open Shortest Path First (OSPF) interface, use the ip ospf database-filter all out command in interface configuration mode. To restore the forwarding of LSAs to the interface, use the no form of this command.

Prerequisites

Command Syntax

ip ospf database-filter all out

no ip ospf database-filter

Command Mode

Interface Configuration

Default

This command is disabled by default. All outgoing LSAs are flooded to the interface.

Usage

OSPF floods new LSAs over all interfaces in an area, except the interface on which the LSA arrives. This redundancy ensures robust flooding. However, too much redundancy can waste bandwidth and might lead to excessive link and CPU usage in certain topologies, resulting in destabilizing the network. To avoid this, use the database-filter command to block flooding of LSAs over specified interfaces.

Examples

The following example prevents flooding of OSPF LSAs to broadcast, nonbroadcast, or point-to-point networks reachable through the interface eth-0-1:

Switch# configure terminal
Switch(config)# interface eth-0-1
Switch(config-if)# no switchport
Switch(config-if)# ip ospf database-filter all out

Related Commands

None

Command Purpose

To set the interval during which at least one hello packet must be received from a neighbor before the router declares that neighbor down, use the ip ospf dead-interval command in interface configuration mode. To restore the default value, use the no form of this command.

Prerequisites

Command Syntax

ip ospf dead-interval SECONDS

no ip ospf dead-interval

Command Mode

Interface Configuration

Default

SECONDS: The neighbor is been considered as dead in 40s by default.

Usage

The dead interval is advertised in OSPF hello packets. This value must be the same for all networking devices on a specific network.

Specifying a smaller dead interval (seconds) will give faster detection of a neighbor being down and improve convergence, but might cause more routing instability.

Examples

The following example sets the OSPF dead interval to 20 seconds:

Switch# configure terminal
Switch(config)# interface eth-0-1
Switch(config-if)# no switchport
Switch(config-if)# ip ospf dead-interval 20

Related Commands

ip ospf hello-interval

show ip ospf interface

Command Purpose

To specify the interval between hello packets that the switch sends on the interface, use the ip ospf hello-interval command in interface configuration mode. To return to the default time, use the no form of this command.

Prerequisites

Command Syntax

ip ospf hello-interval SECONDS

no ip ospf hello-interval

Command Mode

Interface Configuration

Default

10 seconds (Ethernet)

30 seconds (non-broadcast)

Usage

This value is advertised in the hello packets. The smaller the hello interval, the faster topological changes will be detected, but more routing traffic will ensue. This value must be the same for all routers and access servers on a specific network.

Examples

The following example sets the interval between hello packets to 15 seconds:

Switch# configure terminal
Switch(config)# interface eth-0-1
Switch(config-if)# no switchport
Switch(config-if)# ip ospf hello-interval 15

Related Commands

ip ospf dead-interval

Command Purpose

To enable Open Shortest Path First (OSPF) Message Digest 5 (MD5) authentication, use the ip ospf message-digest-key command in interface configuration mode. To remove an old MD5 key, use the no form of this command.

Prerequisites

Command Syntax

ip ospf message-digest-key KEY-ID md5 ( 8 | ) KEY

no ip ospf message-digest-key KEY-ID

Command Mode

Interface Configuration

Default

OSPF MD5 authentication is disabled.

Usage

All routers access the same network/sub network share the same password when using this type of authentication. For every OSPF packet, the password is used for generating/examining the “message digest” which is at the tail of the OSPF packet. This “message digest” is processed by OSPF packet and password. There may multiple password be activated on the same interface, this command line always used to transit smoothly to the new password from the old one.

Examples

The following example sets a new key 19 with the password 8ry4222:

Switch# configure terminal
Switch(config)# interface eth-0-1
Switch(config-if)# no switchport
Switch(config-if)# ip ospf message-digest-key 10 md5 xvv560qle
Switch(config-if)# ip ospf message-digest-key 19 md5 8ry4222

The following example sets a new key 2 with the encrypt password 91c38996a1aa5699:

Switch# configure terminal
Switch(config)# interface eth-0-1
Switch(config-if)# no switchport
Switch(config-if)# ip ospf message-digest-key 2 md5 8 91c38996a1aa5699

Related Commands

area authentication

service password-encryption

ip ospf authentication

Command Purpose

To set the MTU value when sending Database Descriptor (DD) packets, use the ip ospf mtu command in interface configuration mode. To restore a default value, use the no form of this command.

Prerequisites

Command Syntax

ip ospf mtu MTU-VALUE

no ip ospf mtu

Command Mode

Interface Configuration

Default

Decided by interface mtu

Usage

Whenever OSPF constructs packets, it uses interface MTU size as Maximum IP packet size. This command forces OSPF to use the specified value overriding the actual interface MTU size.

This command allows an administrator to configure the MTU size recognized by the OSPF protocol. It does not configure the MTU settings on the kernel. OSPF will not recognize MTU size configuration changes made to the kernel until the MTU size is updated through the CLI.

Examples

The following example sets a new MTU value when sending OSPF DD packets:

Switch# configure terminal
Switch(config)# interface eth-0-1
Switch(config-if)# no switchport
Switch(config-if)# ip ospf mtu 1280

Related Commands

ip ospf mtu-ignore

Command Purpose

To disable Open Shortest Path First (OSPF) maximum transmission unit (MTU) mismatch detection on receiving Database Descriptor (DD) packets, use the ip ospf mtu-ignore command in interface configuration mode. To reset to default, use the no form of this command.

Prerequisites

Command Syntax

ip ospf mtu-ignore

no ip ospf mtu-ignore

Command Mode

Interface Configuration

Default

OSPF MTU mismatch detection is enabled.

Usage

OSPF checks whether neighbors are using the same MTU on a common interface. This check is performed when neighbors exchange DD packets. If the receiving MTU in the DD packet is higher than the IP MTU configured on the incoming interface, OSPF adjacency will not be established.

Examples

The following example disables MTU mismatch detection on receiving DD packets:

Switch# configure terminal
Switch(config)# interface eth-0-1
Switch(config-if)# no switchport
Switch(config-if)# ip ospf mtu-ignore

Related Commands

ip ospf mtu

Command Purpose

To set the router priority, which helps determine the designated router for this network, use the ip ospf priority command in interface configuration mode. To return to the default value, use the no form of this command.

Prerequisites