OSPFv3 External Path Preference Option
The Open Shortest Path First version 3 (OSPFv3) external path preference option feature provides a way to calculate external path preferences per RFC 5340.
Information About OSPFv3 External Path Preference Option
OSPFv3 External Path Preference Option
Per RFC 5340, the following rules indicate which paths are preferred when multiple intra-AS paths are available to ASBRs or forwarding addresses:
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Intra-area paths using nonbackbone areas are always the most preferred.
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The other paths, intraarea backbone paths and interarea paths, are of equal preference.
These rules apply when the same ASBR is reachable through multiple areas, or when trying to decide which of several AS-external-LSAs should be preferred. In the former case the paths all terminate at the same ASBR, and in the latter the paths terminate at separate ASBRs or forwarding addresses. In either case, each path is represented by a separate routing table entry. This feature applies only when RFC 1583 compatibility is set to disabled using the no compatibility rfc1583 command (RFC 5340 provides an update to RFC 1583).
![]() Caution |
To minimize the chance of routing loops, set identical RFC compatibility for all OSPF routers in an OSPF routing domain. |
How to Calculate OSPFv3 External Path Preference Option
Calculating OSPFv3 External Path Preferences per RFC 5340
SUMMARY STEPS
- enable
- configure terminal
- router ospfv3 [process-id ]
- no compatible rfc1583
DETAILED STEPS
Command or Action | Purpose | |
---|---|---|
Step 1 |
enable Example:
|
Enables privileged EXEC mode.
|
Step 2 |
configure terminal Example:
|
Enters global configuration mode. |
Step 3 |
router ospfv3 [process-id ] Example:
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Enables OSPFv3 router configuration mode for the IPv4 or IPv6 address family. |
Step 4 |
no compatible rfc1583 Example:
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Changes the method used to calculate external path preferences per RFC 5340. |
Configuration Examples for OSPFv3 External Path Preference Option
Example: Calculating OSPFv3 External Path Preferences per RFC 5340
show ospfv3
Routing Process "ospfv3 1" with ID 10.1.1.1
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
LSA group pacing timer 240 secs
Interface flood pacing timer 33 msecs
Retransmission pacing timer 66 msecs
Number of external LSA 0. Checksum Sum 0x000000
Number of areas in this router is 1. 1 normal 0 stub 0 nssa
Reference bandwidth unit is 100 mbps
RFC 1583 compatibility disabled
Area BACKBONE(0) (Inactive)
Number of interfaces in this area is 1
SPF algorithm executed 1 times
Number of LSA 1. Checksum Sum 0x00D03D
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Flood list length 0
Additional References
Related Documents
Related Topic |
Document Title |
---|---|
IPv6 addressing and connectivity |
IPv6 Configuration Guide |
OSPFv3 External Path Preference Option |
Configuring OSPF module |
Standards and RFCs
Standard/RFC |
Title |
---|---|
RFCs for IPv6 |
IPv6 RFCs |
Feature Information for OSPFv3 External Path Preference Option
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.
Releases |
Feature Information |
---|---|
Cisco IOS XE Fuji 16.8.1a |
The feature was introduced. |