Cisco IOS XE IP Routing Protocols Configuration Guide, Release 2 - OSPF Forwarding Address Suppression in Translated Type-5 LSAs [Cisco IOS XE Software]

Table Of Contents

OSPF Forwarding Address Suppression in Translated Type-5 LSAs

Finding Feature Information

Contents

Prerequisites for OSPF Forwarding Address Suppression in Translated Type-5 LSAs

Information About OSPF Forwarding Address Suppression in Translated Type-5 LSAs

Benefits of OSPF Forwarding Address Suppression in Translated Type-5 LSAs

When to Suppress OSPF Forwarding Address in Translated Type-5 LSAs

How to Suppress the OSPF Forwarding Address in Translated Type-5 LSAs

Suppressing the OSPF Forwarding Address in Translated Type-5 LSAs

Configuration Examples for OSPF Forwarding Address Suppression in Translated Type-5 LSAs

Suppressing OSPF Forwarding Address in Translated Type-5 LSAs: Example

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Feature Information for OSPF Forwarding Address Suppression in Translated Type-5 LSAs

OSPF Forwarding Address Suppression in Translated Type-5 LSAs

Last Updated: May 4, 2009

The OSPF Forwarding Address Suppression in Translated Type-5 LSAs feature causes a not-so-stubby area (NSSA) area border router (ABR) to translate Type-7 link state advertisements (LSAs) to Type-5 LSAs, but to use the address 0.0.0.0 for the forwarding address instead of that specified in the Type-7 LSA. This feature causes routers that are configured not to advertise forwarding addresses into the backbone to direct forwarded traffic to the translating NSSA ABRs.

Finding Feature Information

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 for OSPF Forwarding Address Suppression in Translated Type-5 LSAs" section.

Use Cisco Feature Navigator to find information about platform support and Cisco IOS XE 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 OSPF Forwarding Address Suppression in Translated Type-5 LSAs

•Information About OSPF Forwarding Address Suppression in Translated Type-5 LSAs

•How to Suppress the OSPF Forwarding Address in Translated Type-5 LSAs

•Configuration Examples for OSPF Forwarding Address Suppression in Translated Type-5 LSAs

•Additional References

•Feature Information for OSPF Forwarding Address Suppression in Translated Type-5 LSAs

Prerequisites for OSPF Forwarding Address Suppression in Translated Type-5 LSAs

This document presumes that you have OSPF configured on the networking device; it does not document other steps to configure OSPF.

Information About OSPF Forwarding Address Suppression in Translated Type-5 LSAs

Before you configure the OSPF Forwarding Address Suppression in Translated Type-5 LSAs feature, you should understand the following concepts:

•Benefits of OSPF Forwarding Address Suppression in Translated Type-5 LSAs

•When to Suppress OSPF Forwarding Address in Translated Type-5 LSAs

Benefits of OSPF Forwarding Address Suppression in Translated Type-5 LSAs

The OSPF Forwarding Address Suppression in Translated Type-5 LSAs feature causes an NSSA ABR to translate Type-7 LSAs to Type-5 LSAs, but use the 0.0.0.0 as the forwarding address instead of that specified in the Type-7 LSA. This feature causes routers that are configured not to advertise forwarding addresses into the backbone to direct forwarded traffic to the translating NSSA ASBRs.

When to Suppress OSPF Forwarding Address in Translated Type-5 LSAs

In Figure 1, it would be advantageous to filter Area 2 addresses from Area 0 to minimize the number of routes introduced into the backbone (Area 0). However, using the area range command to consolidate and summarize routes at the area boundary—filtering the Area 2 addresses—will not work because the Area 2 addresses include forwarding addresses for Type-7 LSAs that are generated by the ASBR. If these Type-7 LSA forwarding addresses have been filtered out of Area 0, the backbone routers cannot reach the prefixes advertised in the translated Type-5 LSAs (autonomous system external LSAs).

Figure 1 OSPF Forwarding Address Suppression in Translated Type-5 LSAs

This problem is solved by suppressing the forwarding address on the ABR so that the forwarding address is set to 0.0.0.0 in the Type-5 LSAs that were translated from Type-7 LSAs. A forwarding address set to 0.0.0.0 indicates that packets for the external destination should be forwarded to the advertising OSPF router, in this case, the translating NSSA ABR.

Before configuring this feature, consider the following caution.

Caution Configuring this feature causes the router to be noncompliant with RFC 1587. Also, suboptimal routing might result because there might be better paths to reach the destination's forwarding address. This feature should not be configured without careful consideration and not until the network topology is understood.

How to Suppress the OSPF Forwarding Address in Translated Type-5 LSAs

This section contains the following procedure:

•Suppressing the OSPF Forwarding Address in Translated Type-5 LSAs

Suppressing the OSPF Forwarding Address in Translated Type-5 LSAs

This task describes how to suppress the OSPF forwarding address in translated Type-5 LSAs. Before configuring this feature, consider the following caution.

Caution Configuring this feature causes the router to be noncompliant with RFC 1587. Also, suboptimal routing might result because there might be better paths to reach the destination's forwarding address. This feature should not be configured without careful consideration and not until the network topology is understood.

SUMMARY STEPS

1. enable

2. configure terminal

3. router ospf process-id

4. area area-id nssa translate type7 suppress-fa

5. end

DETAILED STEPS

Command or Action

Purpose

Step 1

enable
Example:

Router> enable

Enables higher privilege levels, such as privileged EXEC mode.

•Enter your password if prompted.

Step 2

configure terminal
Example:

Router# configure terminal

Enters global configuration mode.

Step 3

router ospf process-id
Example:

Router(config)# router ospf 1

Enables OSPF routing and enters router configuration mode.

•The process-id argument identifies the OSPF process.

Step 4

area area-id nssa translate type7 suppress-fa
Example:

Router(config-router)# area 10 nssa translate type7 suppress-fa

Configures an area as a not-so-stubby-area (NSSA) and suppresses the forwarding address in translated Type-7 LSAs.

Step 5

end
Example:

Router(config-router)# end

Exits configuration mode and returns to privileged EXEC mode.

Configuration Examples for OSPF Forwarding Address Suppression in Translated Type-5 LSAs

This section provides the following configuration example:

•Suppressing OSPF Forwarding Address in Translated Type-5 LSAs: Example

Suppressing OSPF Forwarding Address in Translated Type-5 LSAs: Example

This example suppresses the forwarding address in translated Type-5 LSAs:
interface gigabitethernet 0/0/0
 ip address 10.93.1.1 255.255.255.0
 ip ospf cost 1
!
interface gigabitethernet 0/01
 ip address 10.94.1.1 255.255.255.0
!
router ospf 1
 network 10.93.0.0 0.0.255.255 area 0.0.0.0
 network 10.94.0.0 0.0.255.255 area 10
 area 10 nssa translate type7 suppress-fa
Additional References

The following sections provide references related to OSPF Forwarding Address Suppression in Translated Type-5 LSAs:

Related Documents

Related Topic

Document Title

OSPF commands

Cisco IOS IP Routing Protocols Command Reference

Configuring OSPF

"Configuring OSPF" chapter in the Cisco IOS XE IP Routing Protocols Configuration Guide, Release 2

Cisco IOS master command list, all releases

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 releases, and feature sets, use Cisco MIB Locator found at the following URL:

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

RFCs

RFC

Title

RFC 1587

The OSPF NSSA Option

Note Configuring the OSPF Forwarding Address Suppression in Translated Type-5 LSAs feature causes the router to be noncompliant with RFC 1587, The OSPF NSSA Option.

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

Feature Information for OSPF Forwarding Address Suppression in Translated Type-5 LSAs

Table 1 lists the release history for this feature.

Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS XE 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 XE software release that introduced support for a given feature in a given Cisco IOS XE software release train. Unless noted otherwise, subsequent releases of that Cisco IOS XE software release train also support that feature.

Table 1 Feature Information for OSPF Forwarding Address Suppression in Translated Type-5 LSAs

Feature Name

Releases

Feature Information

OSPF Forwarding Address Suppression in Translated Type-5 LSAs

Cisco IOS XE
Release 2.1

The OSPF Forwarding Address Suppression in Translated Type-5 LSAs feature causes a not-so-stubby area (NSSA) area border router (ABR) to translate Type-7 link state advertisements (LSAs) to Type-5 LSAs, but to use the address 0.0.0.0 for the forwarding address instead of that specified in the Type-7 LSA. This feature causes routers that are configured not to advertise forwarding addresses into the backbone to direct forwarded traffic to the translating NSSA ABRs.

The following commands are introduced or modified in the feature documented in this module:

•area nssa translate

•show ip ospf

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