Operation Manual – IPv4 Routing
H3C S3610&S5510 Series Ethernet Switches
Chapter 3 OSPF Configuration
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Wide scope: Supports networks of various sizes and up to several hundred routers
in an OSPF routing domain.
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Fast convergence: Transmits updates instantly after network topology changes for
routing information synchronization in the AS.
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Loop-free: Computes routes with the shortest path first (SPF) algorithm according
to the collected link states, so no route loops are generated.
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Area partition: Allows an AS to be split into different areas for ease of management
and the routing information transmitted between areas is summarized to reduce
network bandwidth consumption.
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Equal-cost multi-route: Supports multiple equal-cost routes to a destination.
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Routing hierarchy: Supports a four-level routing hierarchy that prioritizes the
routes into intra-area, inter-area, external Type-1, and external Type-2 routes.
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Authentication: Supports interface-based packet authentication to guarantee the
security of packet exchange.
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Multicast: Supports packet multicasting on some types of links.
3.1.1 Basic Concepts
I. Autonomous System
A set of routers using the same routing protocol to exchange routing information
constitute an Autonomous System (AS).
II. OSPF route computation
OSPF route computation is described as follows:
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Based on the network topology around itself, each router generates Link State
Advertisements (LSA) and sends them to other routers in update packets.
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Each OSPF router collects LSAs from other routers to compose a LSDB (Link
State Database). An LSA describes the network topology around a router, so the
LSDB describes the entire network topology of the AS.
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Each router transforms the LSDB to a weighted directed graph, which actually
reflects the topology architecture of the entire network. All the routers have the
same graph.
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Each router uses the SPF algorithm to compute a Shortest Path Tree that shows
the routes to the nodes in the autonomous system. The router itself is the root of
the tree.
III. Router ID
To run OSPF, a router must have a Router ID, which is a 32-bit unsigned integer, the
unique identifier of the router in the AS.
You may assign a Router ID to an OSPF router manually. If no Router ID is specified,
the system automatically selects one for the router as follows:
