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• OSPF looks at more than just the simple hop count. When adding the
shortest path to any node into the tree, the optimal path is chosen on
the basis of delay, throughput and connectivity. OSPF utilizes IP
multicast to reduce the amount of routing traffic required when
sending or receiving routing path updates. The separate routing area
scheme used by OSPF further reduces the amount of routing traffic,
and thus inherently provides another level of routing protection. In
addition, all routing protocol exchanges can be authenticated. Finally,
the OSPF algorithms have been tailored for efficient operation in
TCP/IP Internets.
• OSPFv2 is a compatible upgrade to OSPF. It involves enhancements
to protocol message authentication, and the addition of a
point-to-multipoint interface which allows OSPF to run over
non-broadcast networks, as well as support for overlapping area
ranges.
• When using OSPF, you must organize your network (i.e., autonomous
system) into normal, stub, or not-so-stubby areas; configure the ranges
of subnet addresses that can be aggregated by link state
advertisements; and configure virtual links for areas that do not have
direct physical access to the OSFP backbone.
- To implement OSPF for a large network, you must first organize
the network into logical areas to limit the number of OSPF routers
that actively exchange Link State Advertisements (LSAs). You can
then define an OSPF interface by assigning an IP interface
configured on this router to one of these areas. This OSPF
interface will send and receive OSPF traffic to neighboring OSPF
routers.
- You can further optimize the exchange of OSPF traffic by
specifying an area range that covers a large number of subnetwork
addresses. This is an important technique for limiting the amount
of traffic exchanged between Area Border Routers (ABRs).