OSPF Forwarding Address Suppression in Translated Type-5 LSAs
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 devices that are configured not to advertise forwarding
addresses into the backbone to direct forwarded traffic to the translating NSSA ABRs.
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest caveats and feature information,
see Bug Search Tool and 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.
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 OSPF Forwarding Address Suppression
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
Benefits of OSPF Forwarding Address Suppression
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
devices 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 the figure below, 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 device, in this case, the translating NSSA ABR.
Before configuring this feature, consider the following caution.
Caution
Configuring this feature causes the device 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
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 device 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
enable
configure terminal
router ospf process-id
area area-idnssa translate type7 suppress-fa
end
DETAILED STEPS
Command or Action
Purpose
Step 1
enable
Example:
Device> enable
Enables higher privilege levels, such as privileged EXEC mode.
Enter your password if prompted.
Step 2
configure terminal
Example:
Device# configure terminal
Enters global configuration mode.
Step 3
router ospf process-id
Example:
Device(config)# router ospf 1
Enables OSPF routing and enters router configuration mode.
The
process-id argument identifies the OSPF process.
Step 4
area area-idnssa translate type7 suppress-fa
Example:
Device(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:
Device(config-router)# end
Exits configuration mode and returns to privileged EXEC mode.
Configuration Examples for OSPF Forwarding Address Suppression
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:
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
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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 OSPF Forwarding Address Suppression
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 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:
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