3Com 3C13636 Configuration Manual page 607

3Com Router 3000 Ethernet Family
Configuration Guide
Broadcast: If Ethernet or FDDI is adopted, OSFP defaults the network type to
broadcast.
Non-Broadcast Multi-access (NBMA): If Frame Relay, ATM, HDLC or X.25 is
adopted as a link layer protocol, OSPF defaults the network type to NBMA.
Point-to-Multipoint (p2mp): No link layer protocol is regarded to be p2mp by
default. A p2mp network must be compulsorily changed from other network types.
The common practice is to change a non fully-matched NBMA into a p2mp
network.
Point-to-point (p2p): When the link layer protocol is PPP or LAPB, the default
network type of OSPF is p2p.
NBMA network refers to a non-broadcast and multi-accessible network. ATM is a
typical example for it. The period for sending a polling hello packet before a router
forms neighboring relationship with its peer router can be specified by configuring the
polling interval.
On a broadcast network, which has no multi-access capability, an interface can be
configured into NBMA.
Configure the interface type to p2mp if not all the routers are directly accessible on an
NBMA network.
Change the interface type to p2p if the router has only one peer on the NBMA network.
Differences between NBMA and p2mp:
In OSPF, NBMA refers to a network that is fully matched, non-broadcast and
multi-accessible. While a p2mp network is unnecessarily fully matched.
On a NBMA network, it is necessary to elect DR and BDR; while a p2mp network
has no DR and BDR.
NBMA is the default network type. For example, if ATM is adopted as the link layer
protocol, OSPF defaults the network type on the interface to NBMA, regardless of
whether the network is fully connected. In contrast, p2mp is not a default network
type. No link layer protocol is regarded as p2mp by default. A p2mp network must
be compulsorily changed from other networks types. The common practice is to
change a non fully-matched NBMA into a p2mp network.
NBMA forwards packets by unicast and neighbors shall be configured manually.
While p2mp forwards packets by multicast.
Perform the following configuration in interface view.
Table 4-6 Configure the network type of an OSPF interface
Configure the network type of an OSPF
interface
Operation
3Com Corporation
4-12
Chapter 4 OSPF Configuration
Command
ospf network-type { broadcast | nbma
| p2mp | p2p }