Editing Open Shortest Path First (section)

==OSPF v3==
OSPF version 3 introduces modifications to the IPv4 implementation of the protocol.<ref name="rfc5340" /> 
Despite the expansion of addresses to 128 bits in IPv6, area and router identifications are still 32-bit numbers.

=== High-level changes ===
* Except for virtual links, all neighbor  exchanges use IPv6 link-local addressing exclusively. The IPv6 protocol runs per link, rather than based on the [[subnet]]. 
* All IP prefix information has been removed from the link-state advertisements and from the ''hello'' discovery packet, making OSPFv3 essentially protocol-independent. 
*  Three separate flooding scopes for LSAs:
** Link-local scope: LSA is flooded only on the local link and no further.
** Area scope: LSA is flooded throughout a single OSPF area. 
** AS scope: LSA is flooded throughout the routing domain.
* Use of IPv6 link-local addresses, for neighbor discovery, auto-configuration.
* Authentication has been moved to the [[IPsec|IP Authentication Header]]

=== Changes introduced in OSPF v3, then backported by vendors to v2 ===
* Explicit support for multiple instances per link<ref>{{cite web |title=secondary (Protocols OSPF) - TechLibrary - Juniper Networks |url=https://www.juniper.net/documentation/en_US/junos/topics/reference/configuration-statement/secondary-edit-protocols-ospf.html |website=www.juniper.net |access-date=7 November 2021 |archive-date=November 7, 2021 |archive-url=https://web.archive.org/web/20211107130418/https://www.juniper.net/documentation/en_US/junos/topics/reference/configuration-statement/secondary-edit-protocols-ospf.html |url-status=live }}</ref>

=== Packet format changes ===
* OSPF version number changed to 3
* From the LSA header, the options field has been removed.
* In hello packets and database description, the options field is changed from 16 to 24 bits.
* In hello packet, the address information has been removed. The interface ID has been added.
* In router-LSAs, two options bits, the ''R-bit'' and the ''V6-bit'', have been added.
** ''R-bit'': allows for multi-homed hosts to participate in the routing protocol.
** ''V6-bit'': specializes the R-bit. 
* Add ''instance ID'', which allows multiple OSPF protocol instances on the same logical interface.

=== LSA format changes ===
* The LSA type field is changed to 16 bits.
** Add support for handling unknown LSA types
** Three bits are used for encoding flooding scope.
* With IPv6, addresses in LSAs are expressed as [[IPv6#Addressing|prefix]] and prefix length.
* In router-LSAs and network-LSAs, the address information is removed.
* Router-LSAs and network-LSAs are made network-protocol independent.
* A new LSA type is added, link-LSA, which provides the router's link-local address to all other routers attached to the logical interface, provides a list of IPv6 prefixes to associate with the link, and can send information that reflect the router's capabilities.
* LSA Type-3 summary-LSAs have been renamed "inter-area-prefix-LSAs".
* LSA Type-4 summary LSAs have been renamed "inter-area-router-LSAs".
* Intra-area-prefix-LSA is added, an LSA that carries all IPv6 prefix information.