Advanced OSPF Design Concepts

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The Cisco IOS software will use the specified authentication key only when authentication is enabled for the backbone with the area area-id authentication router configuration command. The two authentication schemes, simple text and MD5 authentication, are mutually exclusive. You can specify one or the other or neither. Any keywords and arguments you specify after authentication-key key or message-digest-key keyid md5 key are ignored. Therefore, specify any optional arguments before such a keyword- argument combination.


Notes:  
Each virtual link neighbor must include the transit area ID and the corresponding virtual link neighbor’s router ID in order for a virtual link to be properly configured. Use the show ip ospf EXEC command to see the router ID.

Example 1: The following example establishes a virtual link with default values for all optional parameters:

    router ospf 201    network 36.0.0.0 0.255.255.255 area 36.0.0.0    area 36.0.0.0 virtual-link 36.3.4.5 

Example 2: The following example establishes a virtual link with MD5 authentication:

    router ospf 201    network 36.0.0.0 0.255.255.255 area 36.0.0.0    area 36.0.0.0 virtual-link 36.3.4.5 message-digest-key 3 md5 sa5721bk47 

Related Commands: area authentication, service password-encryption, show ip ospf

default-information originate

To generate a default route into an OSPF routing domain, use the default-information originate router configuration command. To disable this feature, use the no form of this command. The syntax for this command (and the no form) is as follows:

    default-information originate [always] [metric metric-value]    [metric-type type-value] {level-1 | level-1-2 | level-2}    [route-map map-name]    no default-information originate [always] [metric metric-value]    [metric-type type-value] {level-1 | level-1-2 | level-2}    [route-map map-name] 

Syntax Description:

originate. Causes the Cisco IOS software to generate a default external route into an OSPF domain if the software already has a default route and you want to propagate to other routers.
always (optional). Advertises the default route regardless of whether the software has a default route.
metric metric-value (optional). Metric used for generating the default route. If you omit a value and do not specify a value using the default metric router configuration command, the default metric value is 10. The value used is specific to the protocol.
metric-type type-value (optional). External link type associated with the default route advertised into the OSPF routing domain. The values can be either 1 (Type 1 external route) or 2 (Type 2 external route). The default is 2
level-1. Level 1 routes are redistributed into other IP routing protocols independently. It specifies if IS-IS advertises network 0.0.0.0 into the Level 1 area.
level-1-2. Both Level 1 and Level 2 routes are redistributed into other IP routing protocols. It specifies if IS-IS advertises network 0.0.0.0 into both levels in a single command.
level-2. Level 2 routes are redistributed into other IP routing protocols independently. It specifies if IS-IS advertises network 0.0.0.0 into the Level 2 subdomain.
route-map map-name (optional). Routing process will generate the default route if the route-map is satisfied.

Default: Disabled.

Command Mode: Router configuration.

Usage Guidelines: Whenever you use the redistribute or the default-information router configuration commands to redistribute routes into an OSPF routing domain, the Cisco IOS software automatically becomes an ASBR. However, an ASBR does not, by default, generate a default route into the OSPF routing domain. The software still needs to have a default route for itself before it generates one, except when you have specified the always keyword.

When you use this command for the OSPF process, the default network must reside in the routing table and you must satisfy the route-map map-name keyword. Use the default-information originate always route-map map-name form of the command when you do not want the dependency on the default network in the routing table.

Example: The following example specifies a metric of 100 for the default route redistributed into the OSPF routing domain and an external metric type of type 1:

    router ospf 109      redistribute igrp 108 metric 100 subnets      default-information originate metric 100 metric-type 1 

Related Commands: redistribute

default-metric

To set default metric values for the BGP, EGP, OSPF, and RIP routing protocols, use this form of the default-metric router configuration command. To return to the default state, use the no form of this command. The syntax for this command (and the no form) is as follows:

    default-metric number    no default-metric number 

Syntax Description:

number. Default metric value appropriate for the specified routing protocol.

distance

To define an administrative distance, use the distance router configuration command. To remove a distance definition, use the no form of this command. The syntax for this command (and the no form) is as follows:

    distance weight [address mask [access-list-number | name]] [ip]    no distance weight [address mask [access-list-number]] [ip] 


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OSPF Network Design Solutions
OSPF Network Design Solutions
ISBN: 1578700469
EAN: 2147483647
Year: 1998
Pages: 200
Authors: Tom Thomas

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