Link-State Advertisement Types For Ospfv3 - Cisco ASR 9000 Series Configuration Manual

Link-State Advertisement Types for OSPFv3

Link-State Advertisement Types for OSPFv3
Each of the following LSA types has a different purpose:
• Router LSA (Type 1)—Describes the link state and costs of a the router link to the area. These LSAs
• Network LSA (Type 2)—Describes the link state and cost information for all routers attached to a
• Interarea-prefix LSA for ABRs (Type 3)—Advertises internal networks to routers in other areas (interarea
• Interarea-router LSA for ASBRs (Type 4)—Advertises an ASBR and the cost to reach it. Routers that
• Autonomous system external LSA (Type 5)—Redistributes routes from another autonomous system,
• Autonomous system external LSA (Type 7)—Provides for carrying external route information within
• Link LSA (Type 8)—Has link-local flooding scope and is never flooded beyond the link with which it
• Intra-area-prefix LSAs (Type 9)—A router can originate multiple intra-area-prefix LSAs for every router
An address prefix occurs in almost all newly defined LSAs. The prefix is represented by three fields: Prefix
Length, Prefix Options, and Address Prefix. In OSPFv3, addresses for these LSAs are expressed as "prefix
and prefix length" instead of "address and mask." The default route is expressed as a prefix with length 0.
Inter-area-prefix and intra-area-prefix LSAs carry all IPv6 prefix information that, in IPv4, is included in
router LSAs and network LSAs. The Options field in certain LSAs (router LSAs, network LSAs, interarea-router
LSAs, and link LSAs) has been expanded to 24 bits to provide support for OSPF in IPv6.
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are flooded within an area only. The LSA indicates whether the router is an ABR or ASBR and if it is
one end of a virtual link. Type 1 LSAs are also used to advertise stub networks. In OSPFv3, these LSAs
have no address information and are network protocol independent. In OSPFv3, router interface
information may be spread across multiple router LSAs. Receivers must concatenate all router LSAs
originated by a given router before running the SPF calculation.
multiaccess network segment. This LSA lists all OSPF routers that have interfaces attached to the network
segment. Only the elected designated router for the network segment can generate and track the network
LSA for the segment. In OSPFv3, network LSAs have no address information and are
network-protocol-independent.
routes). Type 3 LSAs may represent a single network or set of networks aggregated into one prefix.
Only ABRs generate Type 3 LSAs. In OSPFv3, addresses for these LSAs are expressed as "prefix and
prefix length" instead of "address and mask." The default route is expressed as a prefix with length 0.
are trying to reach an external network use these advertisements to determine the best path to the next
hop. ABRs generate Type 4 LSAs.
usually from a different routing protocol into OSPF. In OSPFv3, addresses for these LSAs are expressed
as "prefix and prefix length" instead of "address and mask." The default route is expressed as a prefix
with length 0.
an NSSA. Type 7 LSAs may be originated by and advertised throughout an NSSA. NSSAs do not receive
or originate Type 5 LSAs. Type 7 LSAs are advertised only within a single NSSA. They are not flooded
into the backbone area or into any other area by border routers.
is associated. Link LSAs provide the link-local address of the router to all other routers attached to the
link or network segment, inform other routers attached to the link of a list of IPv6 prefixes to associate
with the link, and allow the router to assert a collection of Options bits to associate with the network
LSA that is originated for the link.
or transit network, each with a unique link-state ID. The link-state ID for each intra-area-prefix LSA
describes its association to either the router LSA or network LSA and contains prefixes for stub and
transit networks.
Implementing OSPF
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