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OSPFv3 Overview

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Sun, 01/27/2013 - 15:06
Jun 12th, 2009
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Open Shortest Path First Version3 (OSPFv3)

Open Shortest Path First (OSPFv3) is a link state protocol that supports IPv6 and as well as IPv4.OSPF version 3 differs from OSPF version 2 for IPv4  as some changes have been incorporated to facilitate IPv6.

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OSPFv3 Features:


RFC 2740 discuss in detail about the modifcations made in OSPF to support IPv6. Some of them are highlighted here.

  • Addressing  semantics have been removed from OSPF packets and the basic LSAs. New  LSAs have been created to carry IPv6 addresses and prefixes.
  • OSPF now runs on a per-link basis, instead of on a per-IP-subnet basis. Flooding scope for LSAs has been generalized.
  • Authentication  has been removed from the OSPF protocol itself, instead relying on  IPv6's Authentication Header an Encapsulating Security Payload.
  • Most  packets in OSPF for IPv6 are almost as compact as those in OSPF for  IPv4, even with the larger IPv6 addresses. Most field-XSand packet-size  limitations present in OSPF for IPv4 have been relaxed.
  • In addition, option handling has been made more flexible
  • OSPFv3 forms neighbor adjacencies using IPv6 Link-local addresses
  • OSPFv3 is enabled per interface basis unlike using network command in case of OSPF for IPv4.


OSPFv3 Router Types:

The below figure shows OSPFv3 router types:



-> Internal router: Any router whose all interface belongs to the same area. These routers keep only one link-state database

-> ABR: Router that is connected to more than one area, in which one area is Area 0.These router maintain a link state database for each area they belong to. These router generate summary LSAs

-> Backbone Router: Router with at least one interface attached to Area 0

-> ASBR: Router that inject external LSAs into the OSPF database via redistributing other protocol into OSPF domain.

OSPFv3 LSA Types:

OSPFV3 has same structure and concept as OSPFv2.Nine LSAs that can be used in OSPFv3


LSA NAME
LS TYPE
DESCRIPTION
Router LSA0x2001Define state of router interface
Network LSA0x2002DR router generate this LSA in broadcast  network
Interarea-prefix LSA0x2003Routes to prefixes in other areas
Interarea-router LSA0x2004Routes to routers in other areas
AS external LSA0x2005Routes to networks external to the AS
Group Membership LSA0x2006Networks that contain multicast groups
NSSA Type 7 LSA0x2007Routes to networks external to the AS,injected in the NSSA
Link LSA0x2008Link-local addresses and list IPv6 prefixes associates with the link
Inter-area-prefix LSA0x2009IPv6 prefixes associated with a router,stub network or an associated transit network segment


Configuring OSPFv3:

To Configure OSPFv3 refer Sample Configuration for OSPFv3


OSPFv3 Vs OSPFv2

To know the differences between OSPFv3 and OSPFv2 refer Comparing OSPFv3 & OSPFv2 Routing Protocol

OSPFv3 Stub Routing

OSPFv3 supports the stub, totally stubby and not so stubby (NSSA) areas in the same way as OSPFV2. To configure OSPFv3 stub routing

refer IPv6 OSPF/v3: Case Study


OSPFv3 Route Summarization:

OSPF is link state routing protocol that works on the  concept of areas. All routers in area must have same LSDB (link state  database); hence OSPF summarization can do only on the border routers.  There are two types of summarization you can do in OSPFv3:


•Inter-area route summarization


•External route summarization:


You  configure inter-area route summarization on ABRs, summarizing routes  between areas in the autonomous system. To take advantage of  summarization, assign network numbers in areas in a contiguous way to be  able to lump these addresses into one range.


External  route summarization is specific to external routes that are injected  into OSPFv3 using route redistribution. You should make sure that  external ranges that are being summarized are contiguous. Summarizing  overlapping ranges from two different routers could cause packets to be  sent to the wrong destination. Configure external route summarization on  ASBRs that are redistributing routes into OSPF.

OSPFv3 Route Filtering:

The OSPF algorithm requires that every router in an area must see exactly the same list of link state advertisements. Otherwise there is a serious risk that routing within this area will become unstable and perhaps generate loops. So there is no way to prevent a router from distributing the LSA information that it has received from other routers in the same area.However, because OSPF keeps the LSA database separate from the routing table, you can use a "distribute-list" command to prevent the router from installing particular routes in its own routing table.


Implementing OSPFv3

OSPFv3 Support for Address Families

Troubleshooting OSPFv3 Neighbor Adjacencies

                                   

Base Initial configuration:

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