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Cisco ONS 15454 Reference Manual, R7.0
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Chapter 13 Management Network Connectivity
13.2 13.2.6 IP Scenario 6: Using OSPF
13.2.6 IP Scenario 6: Using OSPF
Open Shortest Path First (OSPF) is a link state Internet routing protocol. Link state protocols use a “hello
protocol” to monitor their links with adjacent routers and to test the status of their links to their
neighbors. Link state protocols advertise their directly connected networks and their active links. Each
link state router captures the link state “advertisements” and puts them together to create a topology of
the entire network or area. From this database, the router calculates a routing table by constructing a
shortest path tree. Routes are recalculated when topology changes occur.
ONS 15454s use the OSPF protocol in internal ONS 15454 networks for node discovery, circuit routing,
and node management. You can enable OSPF on the ONS 15454s so that the ONS 15454 topology is
sent to OSPF routers on a LAN. Advertising the ONS 15454 network topology to LAN routers
eliminates the need to manually enter static routes for ONS 15454 subnetworks. Figure 13-8 shows a
network enabled for OSPF. Figure 13-9 shows the same network without OSPF. Static routes must be
manually added to the router for CTC computers on LAN A to communicate with Nodes 2 and 3 because
these nodes reside on different subnets.
OSPF divides networks into smaller regions, called areas. An area is a collection of networked end
systems, routers, and transmission facilities organized by traffic patterns. Each OSPF area has a unique
ID number, known as the area ID. Every OSPF network has one backbone area called “area 0.” All other
OSPF areas must connect to area 0.
When you enable an ONS 15454 OSPF topology for advertising to an OSPF network, you must assign
an OSPF area ID in decimal format to the ONS 15454 network. Coordinate the area ID number
assignment with your LAN administrator. All DCC-connected ONS 15454s should be assigned the same
OSPF area ID.