Cisco IOS Cookbook, 2nd Edition

Changing the Network Type on an Interface

Problem

You want to change the default OSPF network type on an interface.

Solution

OSPF supports several different types of logical networks on interfaces. The default values are often exactly what you want, but it is sometimes useful to change them:

Router9#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router9(config)#interface FastEthernet0/0
Router9(config-if)#ip ospf network ?
  broadcast            Specify OSPF broadcast multi-access network
  non-broadcast        Specify OSPF NBMA network
  point-to-multipoint  Specify OSPF point-to-multipoint network
  point-to-point       Specify OSPF point-to-point network

Router9(config-if)#

Discussion

Before altering the OSPF network type on an interface, it is useful to understand the differences between the different network types and what the defaults are. Table 8-3 shows the default OSPF network types for a variety of common media.

Table 8-3. OSPF default network types for several common media

Media type	Type or layer 2 encapsulation	Default OSPF network
Serial, ISDN, Async, Dialer	HDLC	Point-to-point
	PPP	Point-to-point
	LAPB	Point-to-point
	Frame Relay	Nonbroadcast
	ATM-DXI	Nonbroadcast
	X.25	Nonbroadcast
	SMDS	Nonbroadcast
ATM	N/A	Nonbroadcast
Point-to-point subinterface	Frame Relay, ATM, etc.	Point-to-point
Multipoint subinterface	Frame Relay, ATM, etc.	Nonbroadcast
Ethernet, FastEthernet, GigabitEthernet	N/A	Broadcast
Ethernet VLAN, Subinterface	ISL, dot1Q	Broadcast
Loopback	N/A	Loopback
Tunnel	N/A	Point-to-point

The configuration ...