IPv4

Link LSA (LSA TYPE 8) & Intra-Area-Prefix (LSA TYPE 9)

This post will take a look at the two new LSA types in OSPFv3 using a Cisco router with a simple DR <-> BDR on a FastEthernet segment directly connected in area 1. Cisco with the Cisco as DR and then Cisco to Cisco with the Cisco as DR viewing the results of the OSPFv3 database on the BDR.

OSPFv3 bring few change in the LSA types. Before we start with the details. Lets think about how packet OSPFv2 exchange LSA in order to exchange self originated routes.

OSPFv2 exchange IPv4 routes with the help of LSA 1 (Router LSA). Which will help to propagate the route. In a broadcast segment it exchange LSA 2 (Network LSA).

 What it will send when OSPF need to exchange IPv6 routes. This adds two new LSA which helps to exchange IPv6 routes. Which is defined in RFC 5340.

 https://tools.ietf.org/html/rfc5340

Let us take a look, which all LSA are responsible to carry IPv6 Routes.

 LSA TYPE 8 : LINK LSA

Link Local scope : LSA is only flooded on the local link and on 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.

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.

Lets Dig Deep Into NEW LSA TYPE 8 & 9

Lets originated and do a analysis for LSA 8 and LSA 9.

Network Diagram

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Configure

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

LSA TYPE 8 – LINK LSA

Why we need Link-LSA ?

  • This advertise the self originating Link Local address to all other routers attached to that links. Similar to Router LSA.
  • This inform 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 look like when in the router :
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Wireshark Capture :
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  • The LSA type of a link-LSA is set to the value 0x0008. Link-LSA have link local flooding scope.
  • A router originate a separate Link-LSA for each attached link that support two or more routers.

 Note : OSPFv3 sends hello taking 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 we dig further into this lets analyze, what it is :
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  • It carried the Address Prefix 2001:abcd::/64
  • It either associate 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 referencing  a router LSA. A stub links prefixes are associated with its attached router.
  • Basically it is a LSA Type 1 and LSA Type 2 as they were used in IPv4 OSPF to advertise the prefixes inside the areas.

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Refrence Link : 

 https://tools.ietf.org/html/rfc5340

https://www.cisco.com/c/en/us/support/docs/ip/ip-version-6-ipv6/212828-link-lsa-lsa-type-8-and-intra-area-pr.html

 

 

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Categories: IPv4, OSPF

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