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Point-to-Multipoint networks have been
designed to work simply and naturally when faced with partial mesh
connectivity. In Point-to-Multipoint mode, OSPF treats all
router-to-router connections on the non-broadcast network as if they were
point-to-point links. No Designated Router is elected for the network, nor
is there an LSA generated for the network. It may be necessary to
configure the set of neighbors that are directly reachable over the
Point-to-Multipoint network. Each neighbor is identified by its IP address
on the Point-to-Multipoint network. Because no Designated Routers are
elected on Point-to-Multipoint networks, the Designated Router eligibility
of configured neighbors is undefined.
Alternatively, neighbors on Point-to-Multipoint networks may be
dynamically discovered by lower-level protocols such as Inverse ARP. In
contrast to NBMA networks, Point-to-Multipoint networks have the following
properties:
- Adjacencies are established between all neighboring routers.
There is no Designated Router or Backup Designated Router for a
Point-to-MultiPoint network. No network-LSA is originated for
Point-to-MultiPoint networks. Router Priority is not configured for
Point-to-MultiPoint interfaces, nor for neighbors on Point-to-MultiPoint
networks.
- When originating a router-LSA, Point-to-MultiPoint interface is
reported as a collection of "point-to-point links" to all of
the interface's adjacent neighbors, together with a single stub link
advertising the interface's IP address with a cost of 0.
- When flooding out a non-broadcast interface (when either in NBMA
or Point-to-MultiPoint mode) the Link State Update or Link State
Acknowledgment packet must be replicated in order to be sent to each
of the interface's neighbors.
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Lab
Activity |
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In
this lab, you will learn how to configure OSPF to
function correctly in a non-broadcast environment. |
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