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Comparing OSPFv3 & OSPFv2 Routing Protocol

     

    Introduction

    This document outlines few comparisons of OSPFv3 and OSPFv2 Routing Protocol. OSPFv3 has few similarities with that of IPv4 version i.e. OSPFv2 in some ways, like Packet Type, Interface Type, Neighbor Discovery Pattern, LSA flooding & aging.

     

    OSPFv3 and v2 Differences:

     

    >Protocol processing per-link, not per-subnet

    >Removal of addressing semantics

    >Addition of Flooding scope

    >Explicit support for multiple instances per link

    >Use of IPv6 link-local addresses

    >Authentication method changes

    >Packet format, LSA’s header format changes

    >Handling of unknown LSA types

     

    Protocol processing per-link, not per-subnet:

    IPv6 uses the term "link" instead of "subnet" or "network" to define a medium used to communicate between nodes at the link layer. Multiple IP subnets can be assigned to a single link, and two nodes can communicate with each other even if they do not share a common IP subnet.

    OSPfv3 Packet/Interface Type

     

    OSPFv3 Packet TypeOSPFv3 Interface Type

    Type 1 - HelloP2P
    Type 2 - Database DescriptionP2MP
    Type 3 - Link State RequestBroadcast
    Type 4 - Link State UpdateNBMA
    Type 5 - Link State AcknowledgementVirtual

     

    OSPFv3 Header Comparison

     

    FieldOSPFv3OSPFv2

    Header Size16 Bytes24 Bytes
    Router & Area ID32 Bit32 Bit
    Instance IDYes

    No

    AuthenticationIP SecInterface Specific and Entire Area

     

    Note: In OSPFv3, Instance ID is a new field that is used to have multiple OSPF process’ instance per link. By default it is 0 and for any additional instance it is increased, instance ID has local link significance only. OSPFv3 routers will only become neighbors if the instanceIDs match. It is thus possible to have multiple routers on a broadcast domain and all run Ospfv3 but not all of them becoming neighbours.

     

    OSPFv3 Hello Packet and Functioning

     

    V3 Hello Packet.bmp

     

    Note: Interface ID is a 32-bit number uniquely identify an interface, virtual link gets its own interface ID.

     

    • As compared, OSPFv3 does not require a Network mask to form an adjacency formation. Adjacency is formed on the link local as v6 runs on per link instead of per subnet.
    • OSPFv3 Option field is 24-bit as that of V2 8-bits
    • Dead intervals field reduced to 16 bits from 32.
    • Multicast Address

     

    Multicast AddressOSPFv3OSPFv2

    All-SPF RoutersFF02::5224.0.0.5
    All-DR RoutersFF02::6224.0.0.6

     

    OSPFv3 LSA Types

    OSPF LSA Types.bmp

    • LSA Type or the function code matches the same  LSA type as in OSPFv2
    • Type 3 is now called inter-area-prefix-LSA
    • Type 4 is now called inter-area-router-LSA
    • Two new LSA type have been added (Link LSA and Intra-Area Prefix LSA)

     

    Note: Intra-Area Prefix LSA is a new LSA in OSPFv3 and used in order to advertise one or more IPv6 prefixes. In OSPFv2 the intera-area prefix information was carried in the router and network LSA's (Type 1 & 2).

     

    Support for Multiple Instances Per Link:

    Instance ID is a new field that is used to have multiple OSPF process instance per link. In order for 2 instances talk to each other they need to have the same instance ID. By default it is 0 and for any additionalinstance it is increased, Instance ID has local link significance only.

     

    Authentication method changes:

    OSPFv2 authentication is achieved by implementing a shared secret and MD5 HMAC supported as part of the OSPFv2 protocol. OSPFv3 does away its own support for authentication entirely, instead relying on the more flexible IPsec framework offered by IPv6.

     

    Reference

    Implementing OSPFv3

    OSPF For IPv6

    OSPF Version 2

    Cisco IPv6 Knowledge Base Portal

    OSPFv3 Address Families At-A-Glance

    Comments
    New Member

    Nice document. From the top of my head. Hope I don't do mistake since I did not verified what I am writing as it comes to my mind...

    1) Instances.

    Now you can have 16 instances of separate OSPFv3 processes on the same link which do not see each other. Like EIGRP with different AS numbers

    2) Authentification.

    Since IPv6 relies on IPSec, Authentication has been removed from OSPFv2 and is now performed by IPSec. Encryption is also possible then as it is IPSec.

    IPSec when used with IKE is better than plain MD5 as it is able to change the key when Lifetime expires which is good as we know that if we can snifff enough packet (4 Giga) we can break a key!

    3) LSAs

    2 new LSAs and 2 renamed LSAs

    New LSAs

    - Link-Local LSA (type 8) which have link flooding scope (new) to advertize the link-local addresses

    - Intra Area LSA. Since now the Router and Network LSAs do not carry prefixes but only topological information. So this new type advertize the prefixes which have an Area Flooding scope.

    Renamed LSA

    - Summary LSA (type 3) is now Inter-Area Prefix LSA The LSAs generated by the ABR to annnouce the routes to the neighbor Area as a Distance-Vector would do... They have a domain flooding scope

    - ASBR LSA (type 4) is now Inter-Area Router LSA. The LSA which are advertized by ASBR for the routers to compute the path to External Routes advertized in External LSA type 5  (E1 or E2 depending if the router only consider the external cost E2 or add the cost to reach the ASBR + the cost of the external route which is E1)

    Multicast Addresses are just transposed as FF02::x is equivalent to 224.0.0.x !

    This is not really a difference. 224.0.0.5 becomes FF02::5 and 224.0.0.6 becomre FF02::6!

    Cheers,

    Fred

    Silver

    Frederic,

    Thanks for all the inputs. Please feel free to update as and when required.

    Regards,

    Sunil.

    Bronze

    Good overview!

    But:

    Note: Intra-Area Prefix LSA is a new LSA in OSPFv3 and used in order to advertise one or more IPv6 prefixes. In OSPFv2 the intera-area prefix information was carried in the router and network LSA's (Type 1 & 2).

    I suppose you wanted to say 'intra-area' there?

    New Member

     

    Hi Sunil,

    Is it possible if you can share the above mentioned doc as PDF file.

    It will be very helpful  for me ..

    Appreciate response.

    New Member

    Hi Sunil,

     

    The Soft copy of the above provided documnet will be very helpful.

    Kindly provide if its avialable with you.

     

    Thanks and Regards

    Chirantan P. Chaudhary

    New Member

    thanks sir,

    it is very useful.

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