10G Core Routing Switch User Manual
陈泽科技有限公司
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switchB(config-router)#
network 110.11.2.0
switchB(config-router)#
network 196.38.165.0
# Configure Switch C
switchC(config)#
router rip
switchC(config-router)#
network 110.11.2.0
switchC(config-router)#
network 117.102.0.0
OSPF Configuration
OSPF Overview
Introduction to OSPF
Open Shortest Path First (OSPF) is an Interior Gateway Protocol based on the link state developed by IETF. At present,
OSPF version 2 (RFC2328) is used, which is available with the following features:
Applicable scope: It can support networks in various sizes and can support several hundred routers at maximum.
Fast convergence: It can transmit the update packets instantly after the network topology changes so that the
change is synchronized in the AS.
Loop-free: Since the OSPF calculates routes with the shortest path tree algorithm according to the collected link
states, it is guaranteed that no loop routes will be generated from the algorithm itself.
Area partition: It allows the network of AS to be divided into different areas for the convenience of management
so that the routing information transmitted between the areas is abstracted further, hence to reduce the network
bandwidth consumption.
Equal-cost multi-route: Support multiple equal-cost routes to a destination.
Routing hierarchy: OSPF has a four-level routing hierarchy. It prioritizes the routes to be intra-area, inter-area,
external type-1, and external type-2 routes.
Authentication: It supports the interface-based packet authentication so as to guarantee the security of the route
calculation.
Multicast transmission: Support multicast address to receive and send packets.
Process of OSPF Route Calculation
The routing calculation process of the OSPF protocol is as follows:
Each OSPF-capable router maintains a Link State Database (LSDB), which describes the topology of the whole AS.
According to the network topology around itself, each router generates a Link State Advertisement (LSA). The
routers on the network transmit the LSAs among them by transmitting the protocol packets to each others. Thus,
each router receives the LSAs of other routers and all these LSAs compose its LSDB.
LSA describes the network topology around a router, so the LSDB describes the network topology of the whole
network. Routers can easily transform the LSDB to a weighted directed graph, which actually reflects the topology
architecture of the whole network. Obviously, all the routers get a graph exactly the same.
A router uses the SPF algorithm to calculate the shortest path tree with itself as the root, which shows the routes
to the nodes in the autonomous system. The external routing information is leave node. A router, which advertises
the routes, also tags them and records the additional information of the autonomous system. Obviously, the
Routing tables obtained by different routers are different.
