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Configuring an Interface on a Nonbroadcast, Multiaccess Network

When configuring OSPFv2 on an NBMA network, you can use nonbroadcast mode rather than point-to-multipoint mode. Using this mode offers no advantages over point-to-multipoint mode, but it has more disadvantages than point-to-multipoint mode. Nevertheless, you might occasionally find it necessary to configure nonbroadcast mode to interoperate with other equipment.

Nonbroadcast mode treats the NBMA network as a partially connected LAN, electing designated and backup designated routers. All routers must have a direct connection to both the designated and backup designated routers, or unpredictable results occur.

To configure nonbroadcast mode, include the following statements:




interface interface-name {

interface-type nbma;

neighbor address <eligible>;

poll-interval seconds;
}

For a list of hierarchy levels at which you can configure these statements, see the statement summary sections for these statements.

Specify the interface by IP address or interface name. For more information about interface names, see the JUNOS Network Interfaces Configuration Guide.

Note: For nonbroadcast interfaces, specify the IP address of the nonbroadcast interface as the interface-name.

To configure multiple neighbors, include a neighbor statement for each neighbor.

OSPF routers normally discover their neighbors dynamically by listening to the broadcast or multicast hello packets on the network. Because an NBMA network does not support broadcast (or multicast), the router cannot discover its neighbors dynamically, so you must configure all the neighbors statically. Do this by including the neighbor statement and specifying the IP address of each neighboring router in the address option. To configure multiple neighbors, include multiple neighbor statements. If the neighbor is allowed to become the designated router, include the eligible keyword.

By default, the router sends hello packets out the interface every 120 seconds before it establishes adjacency with a neighbor. To modify this interval, include the poll-interval statement.

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