NBMA Overview

NBMA Overview
Non-broadcast multi-access networks (for example, Frame Relay and ATM) present a special
challenge for OSPF. As you know, multi-access networks use an election process to select a DR
and a BDR to represent all OSPF routers on the network. This election process requires the participation
of all routers on the multi-access network. However, Hello packets are used to facilitate
the communication for the election process. This works fine on broadcast multi-access because the
connected devices on the network can hear the AllSPFRouters multicast address for the subnet.
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 OSPF on NBMA networks, it’s important to know which
configuration, or environment, will be the most effective solution. The next section discusses
some possible solutions for implementing OSPF over NBMA networks.