3Com Switch 7700 Configuration Manual page 118

110 C 5: IP R
HAPTER OUTING
P O
ROTOCOL PERATION
As you configure the network type, consider the following points:
NBMA means that a network is non-broadcast and multi-accessible. ATM is a
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typical example. You can configure the polling interval for hello packets before
the adjacency of neighboring routers is formed.
Configure the interface type to nonbroadcast on a broadcast network without
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multi-access capability.
Configure the interface type to P2MP if not all the routers are directly
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accessible on an NBMA network.
Change the interface type to P2P if the router has only one peer on the NBMA
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network.
The differences between NBMA and P2MP are listed below:
In OSPF, NBMA refers to the networks that are fully connected, non-broadcast
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and multi-accessible. However, a P2MP network is not required to be fully
connected.
DR and BDR are required on a NBMA network but not on a P2MP network.
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NBMA is the default network type. For example, if ATM is adopted as the link
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layer protocol, OSPF defaults the network type on the interface to NBMA,
regardless of whether the network is fully connected. P2MP is not the default
network type. No link layer protocols are regarded as P2MP. You must change
the network type to P2MP manually. The most common method is to change a
partially connected NBMA network to a P2MP network.
NBMA forwards packets by unicast and requires neighbors to be configured
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manually. P2MP forward packets by multicast.
Perform the following configuration in VLAN interface view.
Table 27 Configuring a Network Type on the Interface that Starts OSPF
Operation
Configure network type on the interface
After the interface has been configured with a new network type, the original
network type is removed automatically.
Configuring the Cost for Sending Packets on an Interface
The user can control the network traffic by configuring different message sending
costs for different interfaces. Otherwise, OSPF automatically calculates the cost
according to the baud rate on the current interface.
Perform the following configuration in VLAN interface view.
Table 28 Configuring the Cost for Sending Packets on the Interface
Operation
Configure the cost for sending packets on
interface
Restore the default cost for packet
transmission on the interface
Command
ospf network-type { broadcast | NBMA |
P2MP | P2P }
Command
ospf cost value
undo ospf cost