OSPF Configuration in a Broadcast Multi Access Topology

This section discusses Open Shortest Path First (OSPF) operation and configuration in a broadcast multi-access environment such as Ethernet or Token Ring.

Broadcast Network EO 10.64.0.2

Point-to-Point Network SO

Broadcast Network EO 10.64.0.2

interface EthernetO ip address 10.64.0.1 2 55.255.255.0

router ospf 1 network 10.0.0.0 0.255.255.255 area 0

Can assign network or interface address-

Point-to-Point Network SO

172.16.14.1

interface EthernetO ip address 1O.64.O.2 2 55.255.255.0

interface SerialO

ip address 172.16.14.4 255.255.255.0 router ospf 50 network 172.16.14.4 0.0.0.0 area 0 network 10.64.0.2 0.0.0.0 area 0

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Cisco CCIE Prep v1.0—Module 7-11

As with other routing protocols, enabling OSPF requires that you create an OSPF routing process and specify the networks to be associated with the routing process. However, OSPF requires the use of an inverse mask with the network command to control exactly which interfaces on the router participate in OSPF. Also, the interfaces specified with the network command must be assigned to a particular area with the area parameter.

Table 6-1: OSPF Routing Process

Steps

Command

Purpose

<process-id>

Enables OSPF routing on the router. The process ID is an internally used number to identify the OSPF processes running on the router. The process-id does not need to match process-ids on other routers to share routing information. Running multiple OSPF processes on the same router is not recommended because it creates multiple database instances that add extra overhead.

Step 2:

network address wildcard-mask area area-id

Defines the interfaces on which OSPF will run and the area ID for those interfaces.

address - Can be the network address, subnet, or the actual Internet Protocol (IP) address of the interface. This parameter instructs the router on which interfaces to send and listen for LSAs and what networks to advertise.

wildcard-mask - An inverse mask used to determine the range of interfaces to run OSPF on. The mask has wildcard bits, where 0 is a match and 1 is the "don't care" bit. For example, 172.16.0.0 0.0.255.255 indicates a match in the first two bytes of 172.16. The router will enable OSPF on all interfaces that fall within the 172.16.x.x range. If specifying an actual interface address, use the mask 0.0.0.0 to match all four bytes of the address. An address and wildcard-mask combination of 0.0.0.0 255.255.255.255 will match all interfaces on the router.

area - Specifies the area that the interfaces will be assigned to. This parameter can be specified in decimal (0-65,535) or dotted decimal (A.B.C.D, similar to an IP address) format.

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