Operation Manual – IPv4 Routing
H3C S3610&S5510 Series Ethernet Switches
Chapter 3 OSPF Configuration
3-3
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If the loopback interfaces are configured, select the highest IP address among
them.
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If no loopback interface is configured, select the highest IP address among
addresses of active interfaces on the router.
IV. OSPF packets
OSPF uses five types of packets:
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Hello packet: Periodically sent to find and maintain neighbors, containing the
values of some timers, information about the DR, BDR and known neighbors.
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DD packet (database description packet): Describes the digest of each LSA in the
LSDB, exchanged between two routers for data synchronization.
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LSR (link state request) packet: Requests needed LSAs from the neighbor. After
exchanging the DD packets, the two routers know which LSAs of the neighbor are
missing from the local LSDBs. In this case, they send an LSR packet to each other,
requesting the missing LSAs. The LSA packet contains the digest of the missing
LSAs.
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LSU (link state update) packet: Transmits the needed LSAs to the neighbor.
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LSAck (link state acknowledgment) packet: Acknowledges received LSU packets.
It contains the headers of received LSAs (a packet can acknowledge multiple
LSAs).
V. LSA types
OSPF sends routing information in LSAs, which, as defined in RFC 2328, have the
following types:
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Router LSA: Type-1 LSA, originated by all routers, flooded throughout a single
area only. This LSA describes the collected states of the router's interfaces to an
area.
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Network LSA: Type-2 LSA, originated for broadcast and NBMA networks by the
designated router, flooded throughout a single area only. This LSA contains the
list of routers connected to the network.
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Network Summary LSA: Type-3 LSA, originated by ABRs (Area Border Routers),
and flooded throughout the LSA's associated area. Each summary-LSA describes
a route to a destination outside the area, yet still inside the AS (an inter-area
route).
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ASBR Summary LSA: Type-4 LSA, originated by ABRs and flooded throughout
the LSA's associated area. Type 4 summary-LSAs describe routes to ASBR
(Autonomous System Boundary Router).
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AS External LSA: Type-5 LSA, originated by ASBRs, and flooded throughout the
AS (except stub and NSSA areas). Each AS-external-LSA describes a route to
another AS.
