Link LSA (LSA Type 8) and Intra-Area-Prefix (LSA Type 9)

Introduction

This document describes the two new Link State Advertisement (LSA) types used for Open Shortest Path First (OSPF) v3 with the use of a Cisco router with a simple Designated Router (DR) and Backup Designated Router (BDR) on a FastEthernet segment directly connected in area 1.

Prerequisites

Requirements

Cisco recommends that you have knowledge of these topics:

• OSPFv2
• IPv6

Components Used

The information in this document is based on these software and hardware versions:

• Cisco IOS®
• IOS-XE

The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, ensure that you understand the potential impact of any command.

Background Information

OSPFv3 brings a few changes in the LSA types. How packet OSPFv2 exchanges LSA in order to exchange self originated routes is discussed here. OSPFv2 exchanges IPv4 routes with the help of LSA 1 (Router LSA). This helps to propagate the route. In a broadcast segment it exchanges LSA 2 (Network LSA). 

LSAs that are responsible to carry IPv6 Routes:

• LSA Type 8: Link LSA
• Link Local scope: LSA is only flooded on the local link and is further used for the LINK-LSA
• LSA Type 9: Intra-Area LSA
• Area Scope: LSA is only flooded throughout a single OSPF area. Used for router-LSA, Network-LSA, inter-area-prefix-LSA, inter-area-router-LSA and intra-area-prefix-LSA

For example:

Type-3 summary LSA have been renamed inter-area-prefix-LSA

Type-4 summary LSA have been renamed inter-area-router-LSA

A new LSA called the intra-area-prefix-LSA has been introduced. This LSA carries all IPv6 prefix information that in IPv4 is included in router LSA and network LSA.

Configure

Network Diagram

Configurations

R1#sh running-config | s r o

router ospfv3 1

router-id 1.1.1.1

!

address-family ipv6 unicast

  passive-interface Loopback0

exit-address-family

R1#

interface GigabitEthernet0/0

no ip address

duplex auto

speed auto

media-type rj45

ipv6 address 2001:ABCD::1/64

ospfv3 1 ipv6 area 1

end

Verify

Use this section in order to confirm that your configuration works properly.

LSA Type 8 - Link LSA

Why do you need Link-LSA?

This advertises the self originating Link Local address to all other routers attached to those links that are similar to Router LSA. It informs the other router in the domain to the link of a list IPv6 prefixes to associate with the link.

Note: Virtual Link should not be able to originate Link-LSA.

How it looks like when in the router:

Wireshark Capture:

The LSA type of a link-LSA is set to the value 0x0008. Link-LSAs have link local flooding scope. A router originates a separate Link-LSA for each attached link that support two or more routers.

Note: OSPFv3 sends hello and takes the source address as the Link Local Address.

LSA Type 9 - intra-area-prefix LSA

The LS Type of an intra-area-prefix-LSA is set to the value of 0x2009. Intra-area-prefix-LSA have area flooding scope.

What does intra-area-prefix-LSA do?

Before you dig further into this, lets analyze what it is:

It carries the Address Prefix 2001:abcd::/64. It either associates to a list of IPv6 address prefixes with a transit network link by referencing a network LSA or associates a list of IPv6 address with a router by referencinga router LSA. A stub link prefixes is associated with its attached router.

Basically it is a LSA Type 1 and LSA Type 2 as used in IPv4 OSPF in order to advertise the prefixes inside the areas.

Troubleshoot

There is currently no specific troubleshooting information available for this configuration.

Related Information

• https://tools.ietf.org/html/rfc5340
• Technical Support & Documentation - Cisco Systems