Installing and Administering Internet Services

Chapter 8 263

Conﬁguring gated

Conﬁguring the OSPF Protocol

address, name, wildcard name, all.) Multiple interface statements may

be speciﬁed with different clauses. If a clause is speciﬁed more than once,

the instance with the most speciﬁc interface reference is used.

The cost clause can optionally be speciﬁed to deﬁne a cost of sending a

packet on the interface. This cost is advertised as the link cost for this

interface. See “Cost” on page 274 for more information about setting

interface costs.

You can also enable or disable the interface deﬁnition. If disable is

not explicitly speciﬁed, an interface deﬁnition is assumed to be enabled.

OSPF supports three types of network interfaces:

• A multicast (or “broadcast”) network is a network that supports two

or more attached routers and allows a single message to be addressed

to a set of network nodes at the same time. An example of a multicast

network is an Ethernet LAN.

• A non-broadcast multi-access (NBMA) network is a network that

supports multiple attached routers, but does not support

broadcasting of messages. An example of an NBMA network is an

X.25 PDN.

• A point-to-point network is a network that joins a single pair of

routers. An example of a point-to-point network is a 56Kb serial line.

The deﬁnition for each type of interface is described separately in the

following sections.

Multicast Interfaces. On multicast networks, an OSPF router

dynamically detects its neighbor routers through the OSPF Hello

message. The following statements are deﬁned for a multicast type

interface:

retransmitinterval is the number of seconds between

retransmission of link states, database description, and link state

request packets. This value should exceed the expected round-trip delay

between any two routers in the network. A sample value for a LAN is 5

seconds.

Default: None (you must specify a value)

Range: Integer between 0 - 65535