When you move to a non-broadcast form of multi-access network, you
lose the assurance that all connected devices are receiving the Hello packets
and are participating in the DR/BDR election.
Because of the difficulty in running OPSF on NBMA networks, it is
important to know which configuration, or environment, will be the most
effective solution. The following section, "NBMA Environments," discusses
some possible solutions for implementing OSPF over NBMA networks.
arlier, we mentioned that there are three types of networks: broad-
cast multi-access, non-broadcast multi-access, and point-to-point. Although
NBMA requires somewhat more configuration to make OSPF operational, it
also gives you the option of deciding how you want it to behave.
With extended configurations on NBMA interfaces, an administrator can
cause OSPF to behave as if it were running on one of the following four net-
In order to achieve a broadcast implementation of OSPF on an NBMA net-
work, a full mesh must exist among the routers. Figure 4.4 depicts what the
NBMA network would have to look like. You can see that each router has
a permanent virtual circuit (PVC) configured with all of the other routers.
Copyright ©2001 SYBEX , Inc., Alameda, CA