RFC2740 - OSPF for IPv6

Network Working Group R. Coltun
Requests for Comments: 2740 Siara Systems
Category: Standards Track D. Ferguson
Juniper Networks
J. Moy
Sycamore Networks
December 1999
OSPF for IPv6
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (1999). All Rights Reserved.
Abstract
This document describes the modifications to OSPF to support version
6 of the Internet Protocol (IPv6). The fundamental mechanisms of
OSPF (flooding, DR election, area support, SPF calculations, etc.)
remain unchanged. However, some changes have been necessary, either
due to changes in protocol semantics between IPv4 and IPv6, or simply
to handle the increased address size of IPv6.
Changes between OSPF for IPv4 and this document include the
following. 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 and
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.
All of OSPF for IPv4"s optional capabilities, including on-demand
circuit support, NSSA areas, and the multicast extensions to OSPF
(MOSPF) are also supported in OSPF for IPv6.
Table of Contents
1 IntrodUCtion ........................................... 4
1.1 Terminology ............................................ 4
2 Differences from OSPF for IPv4 ......................... 4
2.1 Protocol processing per-link, not per-subnet ........... 5
2.2 Removal of addressing semantics ........................ 5
2.3 Addition of Flooding scope ............................. 5
2.4 EXPlicit support for multiple instances per link ....... 6
2.5 Use of link-local addresses ............................ 6
2.6 Authentication changes ................................. 7
2.7 Packet format changes .................................. 7
2.8 LSA format changes ..................................... 8
2.9 Handling unknown LSA types ............................ 10
2.10 Stub area support ..................................... 10
2.11 Identifying neighbors by Router ID .................... 11
3 Implementation details ................................ 11
3.1 Protocol data structures .............................. 12
3.1.1 The Area Data structure ............................... 13
3.1.2 The Interface Data structure .......................... 13
3.1.3 The Neighbor Data Structure ........................... 14
3.2 Protocol Packet Processing ............................ 15
3.2.1 Sending protocol packets .............................. 15
3.2.1.1 Sending Hello packets ................................. 16
3.2.1.2 Sending Database Description Packets .................. 17
3.2.2 Receiving protocol packets ............................ 17
3.2.2.1 Receiving Hello Packets ............................... 19
3.3 The Routing table Structure ........................... 19
3.3.1 Routing table lookup .................................. 20
3.4 Link State Advertisements ............................. 20
3.4.1 The LSA Header ........................................ 21
3.4.2 The link-state database ............................... 22
3.4.3 Originating LSAs ...................................... 22
3.4.3.1 Router-LSAs ........................................... 25
3.4.3.2 Network-LSAs .......................................... 27
3.4.3.3 Inter-Area-Prefix-LSAs ................................ 28
3.4.3.4 Inter-Area-Router-LSAs ................................ 29
3.4.3.5 AS-external-LSAs ...................................... 29
3.4.3.6 Link-LSAs ............................................. 31
3.4.3.7 Intra-Area-Prefix-LSAs ................................ 32
3.5 Flooding .............................................. 35
3.5.1 Receiving Link State Update packets ................... 36
3.5.2 Sending Link State Update packets ..................... 36
3.5.3 Installing LSAs in the database ....................... 38
3.6 Definition of self-originated LSAs .................... 39
3.7 Virtual links ......................................... 39
3.8 Routing table calculation ............................. 39
3.8.1 Calculating the shortest path tree for an area ........ 40
3.8.1.1 The next hop calculation .............................. 41
3.8.2 Calculating the inter-area routes ..................... 42
3.8.3 Examining transit areas" summary-LSAs ................. 42
3.8.4 Calculating AS external routes ........................ 42
3.9 Multiple interfaces to a single link .................. 43
References ............................................ 44
A OSPF data formats ..................................... 46
A.1 Encapsulation of OSPF packets ......................... 46
A.2 The Options field ..................................... 47
A.3 OSPF Packet Formats ................................... 48
A.3.1 The OSPF packet header ................................ 49
A.3.2 The Hello packet ...................................... 50
A.3.3 The Database Description packet ....................... 52
A.3.4 The Link State Request packet ......................... 54
A.3.5 The Link State Update packet .......................... 55
A.3.6 The Link State Acknowledgment packet .................. 56
A.4 LSA formats ........................................... 57
A.4.1 IPv6 Prefix Representation ............................ 58
A.4.1.1 Prefix Options ........................................ 58
A.4.2 The LSA header ........................................ 59
A.4.2.1 LS type ............................................... 60
A.4.3 Router-LSAs ........................................... 61
A.4.4 Network-LSAs .......................................... 64
A.4.5 Inter-Area-Prefix-LSAs ................................ 65
A.4.6 Inter-Area-Router-LSAs ................................ 66
A.4.7 AS-external-LSAs ...................................... 67
A.4.8 Link-LSAs ............................................. 69
A.4.9 Intra-Area-Prefix-LSAs ................................ 71
B Architectural Constants ............................... 73
C Configurable Constants ................................ 73
C.1 Global parameters ..................................... 73
C.2 Area parameters ....................................... 74
C.3 Router interface parameters ........................... 75
C.4 Virtual link parameters ............................... 77
C.5 NBMA network parameters ............................... 77
C.6 Point-to-MultiPoint network parameters ................ 78
C.7 Host route parameters ................................. 78
Security Considerations ............................... 79
Authors" Addresses .................................... 79
Full Copyright Statement .............................. 80
1. Introduction
This document describes the modifications to OSPF to support version
6 of the Internet Protocol (IPv6). The fundamental mechanisms of
OSPF (flooding, DR election, area support, SPF calculations, etc.)
remain unchanged. However, some changes have been necessary, either
due to changes in protocol semantics between IPv4 and IPv6, or simply
to handle the increased address size of IPv6.
This document is organized as follows. Section 2 describes the
differences between OSPF for IPv4 and OSPF for IPv6 in detail.
Section 3 provides implementation details for the changes. Appendix A
gives the OSPF for IPv6 packet and LSA formats. Appendix B lists the
OSPF architectural constants. Appendix C describes configuration
parameters.
1.1. Terminology
This document attempts to use terms from both the OSPF for IPv4
specification ([Ref1]) and the IPv6 protocol specifications
([Ref14]). This has produced a mixed result. Most of the terms used
both by OSPF and IPv6 have roughly the same meaning (e.g.,
interfaces). However, there are a few conflicts. IPv6 uses "link"
similarly to IPv4 OSPF"s "subnet" or "network". In this case, we have
chosen to use IPv6"s "link" terminology. "Link" replaces OSPF"s
"subnet" and "network" in most places in this document, although
OSPF"s Network-LSA remains unchanged (and possibly unfortunately, a
new Link-LSA has also been created).
The names of some of the OSPF LSAs have also changed. See Section 2.8
for details.
2. Differences from OSPF for IPv4
Most of the algorithms from OSPF for IPv4 [Ref1] have preserved in
OSPF for IPv6. However, some changes have been necessary, either due
to changes in protocol semantics between IPv4 and IPv6, or simply to
handle the increased address size of IPv6.
The following subsections describe the differences between this
document and [Ref1].
2.1. Protocol processing per-link, not per-subnet
IPv6 uses the term "link" to indicate "a communication facility or
medium over which nodes can communicate at the link layer" ([Ref14]).
"Interfaces" connect to links. Multiple IP subnets can be assigned to
a single link, and two nodes can talk directly over a single link,
even if they do not share a common IP subnet (IPv6 prefix).
For this reason, OSPF for IPv6 runs per-link instead of the IPv4
behavior of per-IP-subnet. The terms "network" and "subnet" used in
the IPv4 OSPF specification ([Ref1]) should generally be relaced by
link. Likewise, an OSPF interface now connects to a link instead of
an IP subnet, etc.
This change affects the receiving of OSPF protocol packets, and the
contents of Hello Packets and Network-LSAs.
2.2. Removal of addressing semantics
In OSPF for IPv6, addressing semantics have been removed from the
OSPF protocol packets and the main LSA types, leaving a network-
protocol-independent core. In particular:
o IPv6 Addresses are not present in OSPF packets, except in
LSA payloads carried by the Link State Update Packets. See
Section 2.7 for details.
o Router-LSAs and Network-LSAs no longer contain network
addresses, but simply express topology information. See
Section 2.8 for details.
o OSPF Router IDs, Area IDs and LSA Link State IDs remain at
the IPv4 size of 32-bits. They can no longer be assigned as
(IPv6) addresses.
o Neighboring routers are now always identified by Router ID,
where previously they had been identified by IP address on
broadcast and NBMA "networks".
2.3. Addition of Flooding scope
Flooding scope for LSAs has been generalized and is now explicitly
coded in the LSA"s LS type field. There are now three separate
flooding scopes for LSAs:
o Link-local scope. LSA is flooded only on the local link, and
no further. Used for the new Link-LSA (see Section A.4.8).
o Area scope. LSA is flooded throughout a single OSPF area
only. Used for Router-LSAs, Network-LSAs, Inter-Area-Prefix-
LSAs, Inter-Area-Router-LSAs and Intra-Area-Prefix-LSAs.
o AS scope. LSA is flooded throughout the routing domain. Used
for AS-external-LSAs.
2.4. Explicit support for multiple instances per link
OSPF now supports the ability to run multiple OSPF protocol instances
on a single link. For example, this may be required on a NAP segment
shared between several providers -- providers may be running separate
OSPF routing domains that want to remain separate even though they
have one or more physical network segments (i.e., links) in common.
In OSPF for IPv4 this was supported in a haphazard fashion using the
authentication fields in the OSPF for IPv4 header.
Another use for running multiple OSPF instances is if you want, for
one reason or another, to have a single link belong to two or more
OSPF areas.
Support for multiple protocol instances on a link is accomplished via
an "Instance ID" contained in the OSPF packet header and OSPF
interface structures. Instance ID solely affects the reception of
OSPF packets.
2.5. Use of link-local addresses
IPv6 link-local addresses are for use on a single link, for purposes
of neighbor discovery, auto-configuration, etc. IPv6 routers do not
forward IPv6 datagrams having link-local source addresses [Ref15].
Link-local unicast addresses are assigned from the IPv6 address range
FF80/10.
OSPF for IPv6 assumes that each router has been assigned link-local
unicast addresses on each of the router"s attached physical segments.
On all OSPF interfaces except virtual links, OSPF packets are sent
using the interface"s associated link-local unicast address as
source. A router learns the link-local addresses of all other
routers attached to its links, and uses these addresses as next hop
information during packet forwarding.
On virtual links, global scope or site-local IP addresses must be
used as the source for OSPF protocol packets.
Link-local addresses appear in OSPF Link-LSAs (see Section 3.4.3.6).
However, link-local addresses are not allowed in other OSPF LSA
types. In particular, link-local addresses must not be advertised in
inter-area-prefix-LSAs (Section 3.4.3.3), AS-external-LSAs (Section
3.4.3.5) or intra-area-prefix-LSAs (Section 3.4.3.7).
2.6. Authentication changes
In OSPF for IPv6, authentication has been removed from OSPF itself.
The "AuType" and "Authentication" fields have been removed from the
OSPF packet header, and all authentication related fields have been
removed from the OSPF area and interface structures.
When running over IPv6, OSPF relies on the IP Authentication Header
(see [Ref19]) and the IP Encapsulating Security Payload (see [Ref20])
to ensure integrity and authentication/confidentiality of routing
exchanges.
Protection of OSPF packet exchanges against accidental data
corruption is provided by the standard IPv6 16-bit one"s complement
checksum, covering the entire OSPF packet and prepended IPv6 pseudo-
header (see Section A.3.1).
2.7. Packet format changes
OSPF for IPv6 runs directly over IPv6. Aside from this, all
addressing semantics have been removed from the OSPF packet headers,
making it essentially "network-protocol-independent". All addressing
information is now contained in the various LSA types only.
In detail, changes in OSPF packet format consist of the following:
o The OSPF version number has been increased from 2 to 3.
o The Options field in Hello Packets and Database description Packet
has been expanded to 24-bits.
o The Authentication and AuType fields have been removed from the
OSPF packet header (see Section 2.6).
o The Hello packet now contains no address information at all, and
includes an Interface ID which the originating router has assigned
to uniquely identify (among its own interfaces) its interface to
the link. This Interface ID becomes the Netowrk-LSA"s Link State
ID, should the router become Designated-Router on the link.
o Two option bits, the "R-bit" and the "V6-bit", have been added to
the Options field for processing Router-LSAs during the SPF
calculation (see Section A.2). If the "R-bit" is clear an OSPF
speaker can participate in OSPF topology distribution without
being used to forward transit traffic; this can be used in multi-
homed hosts that want to participate in the routing protocol. The
V6-bit specializes the R-bit; if the V6-bit is clear an OSPF
speaker can participate in OSPF topology distribution without
being used to forward IPv6 datagrams. If the R-bit is set and the
V6-bit is clear, IPv6 datagrams are not forwarded but diagrams
belonging to another protocol family may be forwarded.
o TheOSPF packet header now includes an "Instance ID" which allows
multiple OSPF protocol instances to be run on a single link (see
Section 2.4).
2.8. LSA format changes
All addressing semantics have been removed from the LSA header, and
from Router-LSAs and Network-LSAs. These two LSAs now describe the
routing domain"s topology in a network-protocol-independent manner.
New LSAs have been added to distribute IPv6 address information, and
data required for next hop resolution. The names of some of IPv4"s
LSAs have been changed to be more consistent with each other.
In detail, changes in LSA format consist of the following:
o The Options field has been removed from the LSA header, expanded
to 24 bits, and moved into the body of Router-LSAs, Network-LSAs,
Inter-Area-Router-LSAs and Link-LSAs. See Section A.2 for details.
o The LSA Type field has been expanded (into the former Options
space) to 16 bits, with the upper three bits encoding flooding
scope and the handling of unknown LSA types (see Section 2.9).
o Addresses in LSAs are now expressed as [prefix, prefix length]
instead of [address, mask] (see Section A.4.1). The default route
is expressed as a prefix with length 0.
o The Router and Network LSAs now have no address information, and
are network-protocol-independent.
o Router interface information may be spread across multiple Router
LSAs. Receivers must concatenate all the Router-LSAs originated by
a given router when running the SPF calculation.
o A new LSA called the Link-LSA has been introduced. The LSAs have
local-link flooding scope; they are never flooded beyond the link
that they are associated with. Link-LSAs have three purposes: 1)
they provide the router"s link-local address to all other routers
attached to the link, 2) they inform other routers attached to the
link of a list of IPv6 prefixes to associate with the link and 3)
they allow the router to assert a collection of Options bits to
associate with the Network-LSA that will be originated for the
link. See Section A.4.8 for details.
In IPv4, the router-LSA carries a router"s IPv4 interface
addresses, the IPv4 equivalent of link-local addresses. These are
only used when calculating next hops during the OSPF routing
calculation (see Section 16.1.1 of [Ref1]), so they do not need to
be flooded past the local link; hence using link-LSAs to
distribute these addresses is more efficient. Note that link-local
addresses cannot be learned through the reception of Hellos in all
cases: on NBMA links next hop routers do not necessarily exchange
hellos, but rather learn of each other"s existence by way of the
Designated Router.
o The Options field in the Network LSA is set to the logical OR of
the Options that each router on the link advertises in its Link-
LSA.
o Type-3 summary-LSAs have been renamed "Inter-Area-Prefix-LSAs".
Type-4 summary LSAs have been renamed "Inter-Area-Router-LSAs".
o The Link State ID in Inter-Area-Prefix-LSAs, Inter-Area-Router-
LSAs and AS-external-LSAs has lost its addressing semantics, and
now serves solely to identify individual pieces of the Link State
Database. All addresses or Router IDs that were formerly expressed
by the Link State ID are now carried in the LSA bodies.
o Network-LSAs and Link-LSAs are the only LSAs whose Link State ID
carries additional meaning. For these LSAs, the Link State ID is
always the Interface ID of the originating router on the link
being described. For this reason, Network-LSAs and Link-LSAs are
now the only LSAs whose size cannot be limited: a Network-LSA must
list all routers connected to the link, and a Link-LSA must list
all of a router"s addresses on the link.
o 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-LSAs and Network-LSAs. See Section A.4.9 for
details.
o Inclusion of a forwarding address in AS-external-LSAs is now
optional, as is the inclusion of an external route tag (see
[Ref5]). In addition, AS-external-LSAs can now reference another
LSA, for inclusion of additional route attributes that are outside
the scope of the OSPF protocol itself. For example, this can be
used to attach BGP path attributes to external routes as proposed
in [Ref10].
2.9. Handling unknown LSA types
Handling of unknown LSA types has been made more flexible so that,
based on LS type, unknown LSA types are either treated as having
link-local flooding scope, or are stored and flooded as if they were
understood (desirable for things like the proposed External-
Attributes-LSA in [Ref10]). This behavior is explicitly coded in the
LSA Handling bit of the link state header"s LS type field (see
Section A.4.2.1).
The IPv4 OSPF behavior of simply discarding unknown types is
unsupported due to the desire to mix router capabilities on a single
link. Discarding unknown types causes problems when the Designated
Router supports fewer options than the other routers on the link.
2.10. Stub area support
In OSPF for IPv4, stub areas were designed to minimize link-state
database and routing table sizes for the areas" internal routers.
This allows routers with minimal resources to participate in even
very large OSPF routing domains.
In OSPF for IPv6, the concept of stub areas is retained. In IPv6, of
the mandatory LSA types, stub areas carry only router-LSAs, network-
LSAs, Inter-Area-Prefix-LSAs, Link-LSAs, and Intra-Area-Prefix-LSAs.
This is the IPv6 equivalent of the LSA types carried in IPv4 stub
areas: router-LSAs, network-LSAs and type 3 summary-LSAs.
However, unlike in IPv4, IPv6 allows LSAs with unrecognized LS types
to be labeled "Store and flood the LSA, as if type understood" (see
the U-bit in Section A.4.2.1). Uncontrolled introduction of such LSAs
could cause a stub area"s link-state database to grow larger than its
component routers" capacities.
To guard against this, the following rule regarding stub areas has
been established: an LSA whose LS type is unrecognized may only be
flooded into/throughout a stub area if both a) the LSA has area or
link-local flooding scope and b) the LSA has U-bit set to 0. See
Section 3.5 for details.
2.11. Identifying neighbors by Router ID
In OSPF for IPv6, neighboring routers on a given link are always
identified by their OSPF Router ID. This contrasts with the IPv4
behavior where neighbors on point-to-point networks and virtual links
are identified by their Router IDs, and neighbors on broadcast, NBMA
and Point-to-MultiPoint links are identified by their IPv4 interface
addresses.
This change affects the reception of OSPF packets (see Section 8.2 of
[Ref1]), the lookup of neighbors (Section 10 of [Ref1]) and the
reception of Hello Packets (Section 10.5 of [Ref1]).
The Router ID of 0.0.0.0 is reserved, and should not be used.
3. Implementation details
When going from IPv4 to IPv6, the basic OSPF mechanisms remain
unchanged from those documented in [Ref1]. These mechanisms are
briefly outlined in Section 4 of [Ref1]. Both IPv6 and IPv4 have a
link-state database composed of LSAs and synchronized between
adjacent routers. Initial synchronization is performed through the
Database Exchange process, through the exchange of Database
Description, Link State Request and Link State Update packets.
Thereafter database synchronization is maintained via flooding,
utilizing Link State Update and Link State Acknowledgment packets.
Both IPv6 and IPv4 use OSPF Hello Packets to discover and maintain
neighbor relationships, and to elect Designated Routers and Backup
Designated Routers on broadcast and NBMA links. The decision as to
which neighbor relationships become adjacencies, along with the basic
ideas behind inter-area routing, importing external information in
AS-external-LSAs and the various routing calculations are also the
same.
In particular, the following IPv4 OSPF functionality described in
[Ref1] remains completely unchanged for IPv6:
o Both IPv4 and IPv6 use OSPF packet types described in Section 4.3
of [Ref1], namely: Hello, Database Description, Link State
Request, Link State Update and Link State Acknowledgment packets.
While in some cases (e.g., Hello packets) their format has changed
somewhat, the functions of the various packet types remains the
same.
o The system requirements for an OSPF implementation remain
unchanged, although OSPF for IPv6 requires an IPv6 protocol stack
(from the network layer on down) since it runs directly over the
IPv6 network layer.
o The discovery and maintenance of neighbor relationships, and the
selection and establishment of adjacencies remain the same. This
includes election of the Designated Router and Backup Designated
Router on broadcast and NBMA links. These mechanisms are described
in Sections 7, 7.1, 7.2, 7.3, 7.4 and 7.5 of [Ref1].
o The link types (or equivalently, interface types) supported by
OSPF remain unchanged, namely: point-to-point, broadcast, NBMA,
Point-to-MultiPoint and virtual links.
o The interface state machine, including the list of OSPF interface
states and events, and the Designated Router and Backup Designated
Router election algorithm, remain unchanged. These are described
in Sections 9.1, 9.2, 9.3 and 9.4 of [Ref1].
o The neighbor state machine, including the list of OSPF neighbor
states and events, remain unchanged. These are described in
Sections 10.1, 10.2, 10.3 and 10.4 of [Ref1].
o Aging of the link-state database, as well as flushing LSAs from
the routing domain through the premature aging process, remains
unchanged from the description in Sections 14 and 14.1 of [Ref1].
However, some OSPF protocol mechanisms have changed, as outlined in
Section 2 above. These changes are explained in detail in the
following subsections, making references to the appropriate sections
of [Ref1].
The following subsections provide a recipe for turning an IPv4 OSPF
implementation into an IPv6 OSPF implementation.
3.1. Protocol data structures
The major OSPF data structures are the same for both IPv4 and IPv6:
areas, interfaces, neighbors, the link-state database and the routing
table. The top-level data structures for IPv6 remain those listed in
Section 5 of [Ref1], with the following modifications:
o All LSAs with known LS type and AS flooding scope appear in the
top-level data structure, instead of belonging to a specific area
or link. AS-external-LSAs are the only LSAs defined by this
specification which have AS flooding scope. LSAs with unknown LS
type, U-bit set to 1 (flood even when unrecognized) and AS
flooding scope also appear in the top-level data structure.
3.1.1. The Area Data structure
The IPv6 area data structure contains all elements defined for IPv4
areas in Section 6 of [Ref1]. In addition, all LSAs of known type
which have area flooding scope are contained in the IPv6 area data
structure. This always includes the following LSA types: router-LSAs,
network-LSAs, inter-area-prefix-LSAs, inter-area-router-LSAs and
intra-area-prefix-LSAs. LSAs with unknown LS type, U-bit set to 1
(flood even when unrecognized) and area scope also appear in the area
data structure. IPv6 routers implementing MOSPF add group-
membership-LSAs to the area data structure. Type-7-LSAs belong to an
NSSA area"s data structure.
3.1.2. The Interface Data structure
In OSPF for IPv6, an interface connects a router to a link. The IPv6
interface structure modifies the IPv4 interface structure (as defined
in Section 9 of [Ref1]) as follows:
Interface ID
Every interface is assigned an Interface ID, which uniquely
identifies the interface with the router. For example, some
implementations may be able to use the MIB-II IfIndex ([Ref3]) as
Interface ID. The Interface ID appears in Hello packets sent out
the interface, the link-local-LSA originated by router for the
attached link, and the router-LSA originated by the router-LSA for
the associated area. It will also serve as the Link State ID for
the network-LSA that the router will originate for the link if the
router is elected Designated Router.
Instance ID
Every interface is assigned an Instance ID. This should default to
0, and is only necessary to assign differently on those links that
will contain multiple separate communities of OSPF Routers. For
example, suppose that there are two communities of routers on a
given ethernet segment that you wish to keep separate.
The first community is given an Instance ID of 0, by assigning 0
as the Instance ID of all its routers" interfaces to the ethernet.
An Instance ID of 1 is assigned to the other routers" interfaces
to the ethernet. The OSPF transmit and receive processing (see
Section 3.2) will then keep the two communities separate.
List of LSAs with link-local scope
All LSAs with link-local scope and which were originated/flooded
on the link belong to the interface structure which connects to
the link. This includes the collection of the link"s link-LSAs.
List of LSAs with unknown LS type
All LSAs with unknown LS type and U-bit set to 0 (if unrecognized,
treat the LSA as if it had link-local flooding scope) are kept in
the data structure for the interface that received the LSA.
IP interface address
For IPv6, the IPv6 address appearing in the source of OSPF packets
sent out the interface is almost always a link-local address. The
one exception is for virtual links, which must use one of the
router"s own site-local or global IPv6 addresses as IP interface
address.
List of link prefixes
A list of IPv6 prefixes can be configured for the attached link.
These will be advertised by the router in link-LSAs, so that they
can be advertised by the link"s Designated Router in intra-area-
prefix-LSAs.
In OSPF for IPv6, each router interface has a single metric,
representing the cost of sending packets out the interface. In
addition, OSPF for IPv6 relies on the IP Authentication Header (see
[Ref19]) and the IP Encapsulating Security Payload (see [Ref20]) to
ensure integrity and authentication/confidentiality of routing
exchanges. For that reason, AuType and Authentication key are not
associated with IPv6 OSPF interfaces.
Interface states, events, and the interface state machine remain
unchanged from IPv4, and are documented in Sections 9.1, 9.2 and 9.3
of [Ref1] respectively. The Designated Router and Backup Designated
Router election algorithm also remains unchanged from the IPv4
election in Section 9.4 of [Ref1].
3.1.3. The Neighbor Data Structure
The neighbor structure performs the same function in both IPv6 and
IPv4. Namely, it collects all information required to form an
adjacency between two routers, if an adjacency becomes necessary.
Each neighbor structure is bound to a single OSPF interface. The
differences between the IPv6 neighbor structure and the neighbor
structure defined for IPv4 in Section 10 of [Ref1] are:
Neighbor"s Interface ID
The Interface ID that the neighbor advertises in its Hello Packets
must be recorded in the neighbor structure. The router will
include the neighbor"s Interface ID in the router"s router-LSA
when either a) advertising a point-to-point link to the neighbor
or b) advertising a link to a network where the neighbor has
become Designated Router.
Neighbor IP address
Except on virtual links, the neighbor"s IP address will be an IPv6
link-local address.
Neighbor"s Designated Router
The neighbor"s choice of Designated Router is now encoded as a
Router ID, instead of as an IP address.
Neighbor"s Backup Designated Router
The neighbor"s choice of Designated Router is now encoded as a
Router ID, instead of as an IP address.
Neighbor states, events, and the neighbor state machine remain
unchanged from IPv4, and are documented in Sections 10.1, 10.2 and
10.3 of [Ref1] respectively. The decision as to which adjacencies to
form also remains unchanged from the IPv4 logic documented in Section
10.4 of [Ref1].
3.2. Protocol Packet Processing
OSPF for IPv6 runs directly over IPv6"s network layer. As such, it is
encapsulated in one or more IPv6 headers, with the Next Header field
of the immediately encapsulating IPv6 header set to the value 89.
As for IPv4, in IPv6 OSPF routing protocol packets are sent along
adjacencies only (with the exception of Hello packets, which are used
to discover the adjacencies). OSPF packet types and functions are the
same in both IPv4 and IPv4, encoded by the
Type field of the standard OSPF packet header.
3.2.1. Sending protocol packets
When an IPv6 router sends an OSPF routing protocol packet, it fills
in the fields of the standard OSPF for IPv6 packet header (see
Section A.3.1) as follows:
Version #
Set to 3, the version number of the protocol as documented in this
specification.
Type
The type of OSPF packet, such as Link state Update or Hello
Packet.
Packet length
The length of the entire OSPF packet in bytes, including the
standard OSPF packet header.
Router ID
The identity of the router itself (who is originating the packet).
Area ID
The OSPF area that the packet is being sent into.
Instance ID
The OSPF Instance ID associated with the interface that the packet
is being sent out of.
Checksum
The standard IPv6 16-bit one"s complement checksum, covering the
entire OSPF packet and prepended IPv6 pseudo-header (see Section
A.3.1).
Selection of OSPF routing protocol packets" IPv6 source and
destination addresses is performed identically to the IPv4 logic in
Section 8.1 of [Ref1]. The IPv6 destination address is chosen from
among the addresses AllSPFRouters, AllDRouters and the Neighbor IP
address associated with the other end of the adjacency (which in
IPv6, for all links except virtual links, is an IPv6 link-local
address).
The sending of Link State Request Packets and Link State
Acknowledgment Packets remains unchanged from the IPv4 procedures
documented in Sections 10.9 and 13.5 of [Ref1] respectively. Sending
Hello Packets is documented in Section 3.2.1.1, and the sending of
Database Description Packets in Section 3.2.1.2. The sending of Link
State Update Packets is documented in Section 3.5.2.
3.2.1.1. Sending Hello packets
IPv6 changes the way OSPF Hello packets are sent in the following
ways (compare to Section 9.5 of [Ref1]):
o Before the Hello Packet is sent out an interface, the interface"s
Interface ID must be copied into the Hello Packet.
o The Hello Packet no longer contains an IP network mask, as OSPF
for IPv6 runs per-link instead of per-subnet.
o The choice of Designated Router and Backup Designated Router are
now indicated within Hellos by their Router IDs, instead of by
their IP interface addresses. Advertising the Designated
Router (or Backup Designated Router) as 0.0.0.0 indicates that the
Designated Router (or Backup Designated Router) has not yet been
chosen.
o The Options field within Hello packets has moved around, getting
larger in the process. More options bits are now possible. Those
that must be set correctly in Hello packets are: The E-bit is set
if and only if the interface attaches to a non-stub area, the N-
bit is set if and only if the interface attaches to an NSSA area
(see [Ref9]), and the DC- bit is set if and only if the router
wishes to suppress the sending of future Hellos over the interface
(see [Ref11]). Unrecognized bits in the Hello Packet"s Options
field should be cleared.
Sending Hello packets on NBMA networks proceeds for IPv6 in exactly
the same way as for IPv4, as documented in Section 9.5.1 of [Ref1].
3.2.1.2. Sending Database Description Packets
The sending of Database Description packets differs from Section 10.8
of [Ref1] in the following ways:
o The Options field within Database Description packets has moved
around, getting larger in the process. More options bits are now
possible. Those that must be set correctly in Database Description
packets are: The MC-bit is set if and only if the router is
forwarding multicast datagrams according to the MOSPF
specification in [Ref7], and the DC-bit is set if and only if the
router wishes to suppress the sending of Hellos over the interface
(see [Ref11]). Unrecognized bits in the Database Description
Packet"s Options field should be cleared.
3.2.2. Receiving protocol packets
Whenever an OSPF protocol packet is received by the router it is
marked with the interface it was received on. For routers that have
virtual links configured, it may not be immediately obvious which
interface to associate the packet with. For example, consider the
Router RT11 depicted in Figure 6 of [Ref1]. If RT11 receives an OSPF
protocol packet on its interface to Network N8, it may want to
associate the packet with the interface to Area 2, or with the
virtual link to Router RT10 (which is part of the backbone). In
the following, we assume that the packet is initially associated with
the non-virtual link.
In order for the packet to be passed to OSPF for processing, the
following tests must be performed on the encapsulating IPv6 headers:
o The packet"s IP destination address must be one of the IPv6
unicast addresses associated with the receiving interface (this
includes link-local addresses), or one of the IP multicast
addresses AllSPFRouters or AllDRouters.
o The Next Header field of the immediately encapsulating IPv6 header
must specify the OSPF protocol (89).
o Any encapsulating IP Authentication Headers (see [Ref19]) and the
IP Encapsulating Security Payloads (see [Ref20]) must be processed
and/or verified to ensure integrity and
authentication/confidentiality of OSPF routing exchanges.
o Locally originated packets should not be passed on to OSPF. That
is, the source IPv6 address should be examined to make sure this
is not a multicast packet that the router itself generated.
After processing the encapsulating IPv6 headers, the OSPF packet
header is processed. The fields specified in the header must match
those configured for the receiving interface. If they do not, the
packet should be discarded:
o The version number field must specify protocol version 3.
o The standard IPv6 16-bit one"s complement checksum, covering the
entire OSPF packet and prepended IPv6 pseudo-header, must be
verified (see Section A.3.1).
o The Area ID found in the OSPF header must be verified. If both of
the following cases fail, the packet should be discarded. The
Area ID specified in the header must either:
(1) Match the Area ID of the receiving interface. In
this case, unlike for IPv4, the IPv6 source
address is not restricted to lie on the same IP
subnet as the receiving interface. IPv6 OSPF runs
per-link, instead of per-IP-subnet.
(2) Indicate the backbone. In this case, the packet
has been sent over a virtual link. The receiving
router must be an area border router, and the
Router ID specified in the packet (the source
router) must be the other end of a configured
virtual link. The receiving interface must also
attach to the virtual link"s configured Transit
area. If all of these checks succeed, the packet
is accepted and is from now on associated with
the virtual link (and the backbone area).
o The Instance ID specified in the OSPF header must match the
receiving interface"s Instance ID.
o Packets whose IP destination is AllDRouters should only be
accepted if the state of the receiving interface is DR or Backup
(see Section 9.1).
After header processing, the packet is further processed according to
its OSPF packet type. OSPF packet types and functions are the same
for both IPv4 and IPv6.
If the packet type is Hello, it should then be further processed by
the Hello Protocol. All other packet types are sent/received only on
adjacencies. This means that the packet must have been sent by one
of the router"s active neighbors. The neighbor is identified by the
Router ID appearing the the received packet"s OSPF header. Packets
not matching any active neighbor are discarded.
The receive processing of Database Description Packets, Link State
Request Packets and Link State Acknowledgment Packets remains
unchanged from the IPv4 procedures documented in Sections 10.6, 10.7
and 13.7 of [Ref1] respectively. The receiving of Hello Packets is
documented in Section 3.2.2.1, and the receiving of Link State Update
Packets is documented in Section 3.5.1.
3.2.2.1. Receiving Hello Packets
The receive processing of Hello Packets differs from Section 10.5 of
[Ref1] in the following ways:
o On all link types (e.g., broadcast, NBMA, point-to- point, etc),
neighbors are identified solely by their OSPF Router ID. For all
link types except virtual links, the Neighbor IP address is set to
the IPv6 source address in the IPv6 header of the received OSPF
Hello packet.
o There is no longer a Network Mask field in the Hello Packet.
o The neighbor"s choice of Designated Router and Backup Designated
Router is now encoded as an OSPF Router ID instead of an IP
interface address.
3.3. The Routing table Structure
The routing table used by OSPF for IPv4 is defined in Section 11 of
[Ref1]. For IPv6 there are analogous routing table entries: there are
routing table entries for IPv6 address prefixes, and also for AS
boundary routers. The latter routing table entries are only used to
hold intermediate results during the routing table build process (see
Section 3.8).
Also, to hold the intermediate results during the shortest-path
calculation for each area, there is a separate routing table for each
area holding the following entries:
o An entry for each router in the area. Routers are identified by
their OSPF router ID. These routing table entries hold the set of
shortest paths through a given area to a given router, which in
turn allows calculation of paths to the IPv6 prefixes advertised
by that router in Intra-area-prefix-LSAs. If the router is also an
area-border router, these entries are also used to calculate paths
for inter-area address prefixes. If in addition the router is the
other endpoint of a virtual link, the routing table entry
describes the cost and viability of the virtual link.
o An entry for each transit link in the area. Transit links have
associated network-LSAs. Both the transit link and the network-LSA
are identified by a combination of the Designated Router"s
Interface ID on the link and the Designated Router"s OSPF Router
ID. These routing table entries allow later calculation of paths
to IP prefixes advertised for the transit link in intra-area-
prefix-LSAs.
The fields in the IPv4 OSPF routing table (see Section 11 of [Ref1])
remain valid for IPv6: Optional capabilities (routers only), path
type, cost, type 2 cost, link state origin, and for each of the equal
cost paths to the destination, the next hop and advertising router.
For IPv6, the link-state origin field in the routing table entry is
the router-LSA or network-LSA that has directly or indirectly
produced the routing table entry. For example, if the routing table
entry describes a route to an IPv6 prefix, the link state origin is
the router-LSA or network-LSA that is listed in the body of the
intra-area-prefix-LSA that has produced the route (see Section
A.4.9).
3.3.1. Routing table lookup
Routing table lookup (i.e., determining the best matching routing
table entry during IP forwarding) is the same for IPv6 as for IPv4.
3.4. Link State Advertisements
For IPv6, the OSPF LSA header has changed slightly, with the LS type
field expanding and the Options field being moved into the body of
appropriate LSAs. Also, the formats of some LSAs have changed
somewhat (namely router-LSAs, network-LSAs and AS-external-LSAs),
while the names of other LSAs have been changed (type 3 and 4
summary-LSAs are now inter-area-prefix-LSAs and inter-area-router-
LSAs respectively) and additional LSAs have been added (Link-LSAs and
Intra-Area-Prefix-LSAs). Type of Service (TOS) has been removed from
the OSPFv2 specification [Ref1], and is not encoded within OSPF for
IPv6"s LSAs.
These changes will be described in detail in the following
subsections.
3.4.1. The LSA Header
In both IPv4 and IPv6, all OSPF LSAs begin with a standard 20 byte
LSA header. However, the contents of this 20 byte header have changed
in IPv6. The LS age, Advertising Router, LS Sequence Number, LS
checksum and length fields within the LSA header remain unchanged, as
documented in Sections 12.1.1, 12.1.5, 12.1.6, 12.1.7 and A.4.1 of
[Ref1] respectively. However, the following fields have changed for
IPv6:
Options
The Options field has been removed from the standard 20 byte LSA
header, and into the body of router-LSAs, network-LSAs, inter-
area-router-LSAs and link-LSAs. The size of the Options field has
increased from 8 to 24 bits, and some of the bit definitions have
changed (see Section A.2). In addition a separate PrefixOptions
field, 8 bits in length, is attached to each prefix advertised
within the body of an LSA.
LS type
The size of the LS type field has increased from 8 to 16 bits,
with the top two bits encoding flooding scope and the next bit
encoding the handling of unknown LS types. See Section A.4.2.1
for the current coding of the LS type field.
Link State ID
Link State ID remains at 32 bits in length, but except for
network-LSAs and link-LSAs, Link State ID has shed any addressing
semantics. For example, an IPv6 router originating multiple AS-
external-LSAs could start by assigning the first a Link State ID
of 0.0.0.1, the second a Link State ID of 0.0.0.2, and so on.
Instead of the IPv4 behavior of encoding the network number within
the AS-external-LSA"s Link State ID, the IPv6 Link State ID simply
serves as a way to differentiate multiple LSAs originated by the
same router.
For network-LSAs, the Link State ID is set to the Designated
Router"s Interface ID on the link. When a router originates a
Link-LSA for a given link, its Link State ID is set equal to the
router"s Interface ID on the link.
3.4.2. The link-state database
In IPv6, as in IPv4, individual LSAs are identified by a combination
of their LS type, Link State ID and Advertising Router fields. Given
two instances of an LSA, the most recent instance is determined by
examining the LSAs" LS Sequence Number, using LS checksum and LS age
as tiebreakers (see Section 13.1 of [Ref1]).
In IPv6, the link-state database is split across three separate data
structures. LSAs with AS flooding scope are contained within the
top-level OSPF data structure (see Section 3.1) as long as either
their LS type is known or their U-bit is 1 (flood even when
unrecognized); this includes the AS-external-LSAs. LSAs with area
flooding scope are contained within the appropriate area structure
(see Section 3.1.1) as long as either their LS type is known or their
U-bit is 1 (flood even when unrecognized); this includes router-LSAs,
network-LSAs, inter-area-prefix-LSAs, inter-area-router-LSAs, and
intra-area-prefix-LSAs. LSAs with unknown LS type and U-bit set to 0
and/or link-local flooding scope are contained within the appropriate
interface structure (see Section 3.1.2); this includes link-LSAs.
To lookup or install an LSA in the database, you first examine the LS
type and the LSA"s context (i.e., to which area or link does the LSA
belong). This information allows you to find the correct list of
LSAs, all of the same LS type, where you then search based on the
LSA"s Link State ID and Advertising Router.
3.4.3. Originating LSAs
The process of reoriginating an LSA in IPv6 is the same as in IPv4:
the LSA"s LS sequence number is incremented, its LS age is set to 0,
its LS checksum is calculated, and the LSA is added to the link state
database and flooded out the appropriate interfaces.
To the list of events causing LSAs to be reoriginated, which for IPv4
is given in Section 12.4 of [Ref1], the following events and/or
actions are added for IPv6:
o The state of one of the router"s interfaces changes. The router
may need to (re)originate or flush its Link-LSA and one or more
router-LSAs and/or intra-area-prefix-LSAs.
o The identity of a link"s Designated Router changes. The router may
need to (re)originate or flush the link"s network-LSA and one or
more router-LSAs and/or intra-area-prefix-LSAs.
o A neighbor transitions to/from "Full" state. The router may need
to (re)originate or flush the link"s network-LSA and one or more
router-LSAs and/or intra-area-prefix-LSAs.
o The Interface ID of a neighbor changes. This may cause a new
instance of a router-LSA to be originated for the associated area,
and the reorigination of one or more intra-area-prefix-LSAs.
o A new prefix is added to an attached link, or a prefix is deleted
(both through configuration). This causes the router to
reoriginate its link-LSA for the link, or, if it is the only
router attached to the link, causes the router to reoriginate an
intra-area-prefix-LSA.
o A new link-LSA is received, causing the link"s collection of
prefixes to change. If the router is Designated Router for the
link, it originates a new intra-area-prefix-LSA.
Detailed construction of the seven required IPv6 LSA types is
supplied by the following subsections. In order to display example
LSAs, the network map in Figure 15 of [Ref1] has been reworked to
show IPv6 addressing, resulting in Figure 1. The OSPF cost of each
interface is has been displayed in Figure 1. The assignment of IPv6
prefixes to network links is shown in Table 1. A single area address
range has been configured for Area 1, so that outside of Area 1 all
of its prefixes are covered by a single route to 5f00:0000:c001::/48.
The OSPF interface IDs and the link-local addresses for the router
interfaces in Figure 1 are given in Table 2.
..........................................
. Area 1.
. + .
. .
. 3+---+1 .
. N1 --RT1-----+ .
. +---+ .
. ______ .
. + / 1+---+
. * N3 *------RT4------
. + /_______/ +---+
. / .
. 3+---+1 / .
. N2 --RT2-----+ 1 .
. +---+ +---+ .
. RT3----------------
. + +---+ .
. 2 .
. .
. +------------+ .
. N4 .
..........................................
Figure 1: Area 1 with IP addresses shown
Network IPv6 prefix
-----------------------------------
N1 5f00:0000:c001:0200::/56
N2 5f00:0000:c001:0300::/56
N3 5f00:0000:c001:0100::/56
N4 5f00:0000:c001:0400::/56
Table 1: IPv6 link prefixes for sample network
Router interface Interface ID link-local address
-------------------------------------------------------
RT1 to N1 1 fe80:0001::RT1
to N3 2 fe80:0002::RT1
RT2 to N2 1 fe80:0001::RT2
to N3 2 fe80:0002::RT2
RT3 to N3 1 fe80:0001::RT3
to N4 2 fe80:0002::RT3
RT4 to N3 1 fe80:0001::RT4
Table 2: OSPF Interface IDs and link-local addresses
3.4.3.1. Router-LSAs
The LS type of a router-LSA is set to the value 0x2001. Router-LSAs
have area flooding scope. A router may originate one or more router-
LSAs for a given area. Each router-LSA contains an integral number of
interface descriptions; taken together, the collection of router-LSAs
originated by the router for an area describes the collected states
of all the router"s interfaces to the area. When multiple router-LSAs
are used, they are distinguished by their Link State ID fields.
The Options field in the router-LSA should be coded as follows. The
V6-bit should be set. The E-bit should be clear if and only if the
attached area is an OSPF stub area. The MC-bit should be set if and
only if the router is running MOSPF (see [Ref8]). The N-bit should be
set if and only if the attached area is an OSPF NSSA area. The R-bit
should be set. The DC-bit should be set if and only if the router can
correctly process the DoNotAge bit when it appears in the LS age
field of LSAs (see [Ref11]). All unrecognized bits in the Options
field should be cleared
To the left of the Options field, the router capability bits V, E and
B should be coded according to Section 12.4.1 of [Ref1]. Bit W should
be coded according to [Ref8].
Each of the router"s interfaces to the area are then described by
appending "link descriptions" to the router-LSA. Each link
description is 16 bytes long, consisting of 5 fields: (link) Type,
Metric, Interface ID, Neighbor Interface ID and Neighbor Router ID
(see Section A.4.3). Interfaces in state "Down" or "Loopback" are not
described (although looped back interfaces can contribute prefixes to
Intra-Area-Prefix-LSAs). Nor are interfaces without any full
adjacencies described. All other interfaces to the area add zero, one
or more link descriptions, the number and content of which depend on
the interface type. Within each link description, the Metric field is
always set the interface"s output cost and the Interface ID field is
set to the interface"s OSPF Interface ID.
Point-to-point interfaces
If the neighboring router is fully adjacent, add a Type 1 link
description (point-to-point). The Neighbor Interface ID field is
set to the Interface ID advertised by the neighbor in its Hello
packets, and the Neighbor Router ID field is set to the neighbor"s
Router ID.
Broadcast and NBMA interfaces
If the router is fully adjacent to the link"s Designated Router,
or if the router itself is Designated Router and is fully adjacent
to at least one other router, add a single Type 2 link description
(transit network). The Neighbor Interface ID field is set to the
Interface ID advertised by the Designated Router in its Hello
packets, and the Neighbor Router ID field is set to the Designated
Router"s Router ID.
Virtual links
If the neighboring router is fully adjacent, add a Type 4 link
description (virtual). The Neighbor Interface ID field is set to
the Interface ID advertised by the neighbor in its Hello packets,
and the Neighbor Router ID field is set to the neighbor"s Router
ID. Note that the output cost of a virtual link is calculated
during the routing table calculation (see Section 3.7).
Point-to-MultiPoint interfaces
For each fully adjacent neighbor associated with the interface,
add a separate Type 1 link description (point-to-point) with
Neighbor Interface ID field set to the Interface ID advertised by
the neighbor in its Hello packets, and Neighbor Router ID field
set to the neighbor"s Router ID.
As an example, consider the router-LSA that router RT3 would
originate for Area 1 in Figure 1. Only a single interface must be
described, namely that which connects to the transit network N3. It
assumes that RT4 has been elected Designated Router of Network N3.
; RT3"s router-LSA for Area 1
LS age = 0 ;newly (re)originated
LS type = 0x2001 ;router-LSA
Link State ID = 0 ;first fragment
Advertising Router = 192.1.1.3 ;RT3"s Router ID
bit E = 0 ;not an AS boundary router
bit B = 1 ;area border router
Options = (V6-bitE-bitR-bit)
Type = 2 ;connects to N3
Metric = 1 ;cost to N3
Interface ID = 1 ;RT3"s Interface ID on N3
Neighbor Interface ID = 1 ;RT4"s Interface ID on N3
Neighbor Router ID = 192.1.1.4 ; RT4"s Router ID
If for example another router was added to Network N4, RT3 would have
to advertise a second link description for its connection to (the now
transit) network N4. This could be accomplished by reoriginating the
above router-LSA, this time with two link descriptions. Or, a
separate router-LSA could be originated with a separate Link State ID
(e.g., using a Link State ID of 1) to describe the connection to N4.
Host routes no longer appear in the router-LSA, but are instead
included in intra-area-prefix-LSAs.
3.4.3.2. Network-LSAs
The LS type of a network-LSA is set to the value 0x2002. Network-
LSAs have area flooding scope. A network-LSA is originated for every
broadcast or NBMA link having two or more attached routers, by the
link"s Designated Router. The network-LSA lists all routers attached
to the link.
The procedure for originating network-LSAs in IPv6 is the same as the
IPv4 procedure documented in Section 12.4.2 of [Ref1], with the
following exceptions:
o An IPv6 network-LSA"s Link State ID is set to the Interface ID of
the Designated Router on the link.
o IPv6 network-LSAs do not contain a Network Mask. All addressing
information formerly contained in the IPv4 network-LSA has now
been consigned to intra-Area-Prefix-LSAs.
o The Options field in the network-LSA is set to the logical OR of
the Options fields contained within the link"s associated link-
LSAs. In this way, the network link exhibits a capability when at
least one of the link"s routers requests that the capability be
asserted.
As an example, assuming that Router RT4 has been elected Designated
Router of Network N3 in Figure 1, the following network-LSA is
originated:
; Network-LSA for Network N3
LS age = 0 ;newly (re)originated
LS type = 0x2002 ;network-LSA
Link State ID = 1 ;RT4"s Interface ID on N3
Advertising Router = 192.1.1.4 ;RT4"s Router ID
Options = (V6-bitE-bitR-bit)
Attached Router = 192.1.1.4 ;Router ID
Attached Router = 192.1.1.1 ;Router ID
Attached Router = 192.1.1.2 ;Router ID
Attached Router = 192.1.1.3 ;Router ID
3.4.3.3. Inter-Area-Prefix-LSAs
The LS type of an inter-area-prefix-LSA is set to the value 0x2003.
Inter-area-prefix-LSAs have area flooding scope. In IPv4, inter-
area-prefix-LSAs were called type 3 summary-LSAs. Each inter-area-
prefix-LSA describes a prefix external to the area, yet internal to
the Autonomous System.
The procedure for originating inter-area-prefix-LSAs in IPv6 is the
same as the IPv4 procedure documented in Sections 12.4.3 and 12.4.3.1
of [Ref1], with the following exceptions:
o The Link State ID of an inter-area-prefix-LSA has lost all of its
addressing semantics, and instead simply serves to distinguish
multiple inter-area-prefix-LSAs that are originated by the same
router.
o The prefix is described by the PrefixLength, PrefixOptions and
Address Prefix fields embedded within the LSA body. Network Mask
is no longer specified.
o The NU-bit in the PrefixOptions field should be clear. The coding
of the MC-bit depends upon whether, and if so how, MOSPF is
operating in the routing domain (see [Ref8]).
o Link-local addresses must never be advertised in inter-area-
prefix-LSAs.
As an example, the following shows the inter-area-prefix-LSA that
Router RT4 originates into the OSPF backbone area, condensing all
of Area 1"s prefixes into the single prefix 5f00:0000:c001::/48.
The cost is set to 4, which is the maximum cost to all of the
prefix" individual components. The prefix is padded out to an even
number of 32-bit Words, so that it consumes 64-bits of space
instead of 48 bits.
; Inter-area-prefix-LSA for Area 1 addresses
; originated by Router RT4 into the backbone
LS age = 0 ;newly (re)originated
LS type = 0x2003 ;inter-area-prefix-LSA
Advertising Router = 192.1.1.4 ;RT4"s ID
Metric = 4 ;maximum to components
PrefixLength = 48
PrefixOptions = 0
Address Prefix = 5f00:0000:c001 ;padded to 64-bits
3.4.3.4. Inter-Area-Router-LSAs
The LS type of an inter-area-router-LSA is set to the value
0x2004. Inter-area-router-LSAs have area flooding scope. In IPv4,
inter-area-router-LSAs were called type 4 summary-LSAs. Each
inter-area-router-LSA describes a path to a destination OSPF
router (an ASBR) that is external to the area, yet internal to the
Autonomous System.
The procedure for originating inter-area-router-LSAs in IPv6 is
the same as the IPv4 procedure documented in Section 12.4.3 of
[Ref1], with the following exceptions:
o The Link State ID of an inter-area-router-LSA is no longer the
destination router"s OSPF Router ID, but instead simply serves to
distinguish multiple inter-area-router-LSAs that are originated by
the same router. The destination router"s Router ID is now found
in the body of the LSA.
o The Options field in an inter-area-router-LSA should be set equal
to the Options field contained in the destination router"s own
router-LSA. The Options