Which information is carried in an OSPFv3 intra-area-prefix LSA?
A.
IPv6 prefixes
B.
Link-local addresses
C.
Solicited node multicast addresses
D.
IPv6 prefixes and topology information
Explanation:
The OSPFv3 s new LSA, the Intra-area Prefix LSA (type 9), handles intra-area network
information that was previously included in OSPFv2 type 2 LSAs. It is used in order to advertise
one or more IPv6 prefixes. The prefixes are associated with router segment, stub network
segment or transit network segment. Intra-area prefix LSAs (type 9) & Inter-Area-Prefix-LSA (type
3) carry all IPv6 prefix information, which, in IPv4, is included in router LSAs and network LSAs.
Note: An address prefix is represented by three fields: prefix length, prefix options, and address
prefix. In OSPFv3, addresses for these LSAs are expressed as prefix, prefix length instead of
address, mask. The LSA types defined in OSPF are as follows:
Type 1 – Router LSA – the router announces its presence and lists the links to other routers or
networks in the same area, together with the metrics to them. Type 1 LSAs are flooded across
their own area only. The linkstate
ID of the type 1 LSA is the originating router ID.
Type 2 – Network LSA – the designated router on a broadcast segment (e.g. Ethernet) lists which
routers are joined together by the segment. Type 2 LSAs are flooded across their own area only.
The link-state ID of the type 2 LSA is the IP interface address of the DR.
Type 3 – Summary LSA – an Area Border Router (ABR) takes information it has learned on one of
its attached areas and it can summarize it (but not by default) before sending it out on other areas
it is connected to. This summarization helps provide scalability by removing detailed topology
information for other areas, because their routing information is summarized into just an address
prefix and metric. The summarization process can also be configured to remove a lot of detailed
address prefixes and replace them with a single summary prefix, also helping scalability. The linkstate ID is the destination network number for type 3 LSAs. Type 4 – ASBR-Summary LSA – this is
needed because Type 5 External LSAs are flooded to all areas and the detailed next-hop
information may not be available in those other areas. This is solved by an Area Border Router
flooding the information for the router (i.e. the Autonomous System Boundary Router) where the
type 5 originated. The link-state ID is the router ID of the described ASBR for type 4 LSAs. Type 5
– External LSA – these LSAs contain information imported into OSPF from other routing processes.
They are flooded to all areas (except stub areas). For “External Type 1” LSAs routing decisions
are made by adding the OSPF metric to get to the ASBR and the external metric from there on,
while for “External Type 2” LSAs only the external metric is used. The link-state ID of the type 5
LSA is the external network number.
Type 6 – Group Membership LSA – this was defined for Multicast extensions to OSPF (MOSPF)[1],
a multicast OSPF routing protocol which was not in general use. MOSPF has been deprecated
since OSPFv3[2] and is not currently used. It may be reassigned in the future.
Type 7 – Routers in a Not-so-stubby-area (NSSA) do not receive external LSAs from Area BorderRouters, but are allowed to send external routing information for redistribution. They use type 7
LSAs to tell the ABRs about these external routes, which the Area Border Router then translates
to type 5 external LSAs and floods as normal to the rest of the OSPF network.
Type 8 – A link-local only LSA for OSPFv3. A Type 8 LSA is used to give information about linklocal addresses and a list of IPv6 addresses on the link. In OSPFv2, however, the Type 8 was
originally intended to be used as a so-called External-Attributes-LSA for transit autonomous
systems where OSPFv2 could replace the internal Border Gateway Protocol (iBGP). In these
networks, the BGP destinations would be carried in LSA Type 5 while their BGP attributes would
be inserted into LSA Type 8. Most OSPFv2 implementations never supported this feature.
Type 9 – a link-local “opaque” LSA (defined by RFC2370) in OSPFv2 and the Intra-Area-Prefix
LSA in OSPFv3. It is the OSPFv3 LSA that contains prefixes for stub and transit networks in the
link-state ID.
Type 10 – an area-local “opaque” LSA as defined by RFC2370. Opaque LSAs contain information
which should be flooded by other routers even if the router is not able to understand the extended
information itself. Typically type 10 LSAs are used for traffic engineering extensions to OSPF,
flooding extra information about links beyond just their metric, such as link bandwidth and color.
Type 11 – an AS “opaque” LSA defined by RFC 5250, which is flooded everywhere except stub
areas. This is the opaque equivalent of the type 5 external LSA
OSPFv3 LSA Types
