Open Shortest Path First (Ospfv2 And Ospfv3); Protocol Overview; Autonomous System (As) Areas - Dell S4048–ON Configuration Manual

Open Shortest Path First (OSPFv2 and OSPFv3)

Open shortest path first (OSPFv2 for IPv4) and OSPF version 3 (OSPF for IPv6) are supported on Dell Networking OS.
This chapter provides a general description of OSPFv2 (OSPF for IPv4) and OSPFv3 (OSPF for IPv6) as supported in the Dell
Networking Operating System (OS).
NOTE: The fundamental mechanisms of OSPF (flooding, DR election, area support, SPF calculations, and so on) are the
same between OSPFv2 and OSPFv3. This chapter identifies and clarifies the differences between the two versions of
OSPF. Except where identified, the information in this chapter applies to both protocol versions.
OSPF protocol standards are listed in the

Protocol Overview

OSPF routing is a link-state routing protocol that calls for the sending of link-state advertisements (LSAs) to all other routers within
the same autonomous system (AS) areas.
Information on attached interfaces, metrics used, and other variables is included in OSPF LSAs. As OSPF routers accumulate link-
state information, they use the shortest path first (SPF) algorithm to calculate the shortest path to each node.
OSPF routers initially exchange HELLO messages to set up adjacencies with neighbor routers. The HELLO process is used to
establish adjacencies between routers of the AS. It is not required that every router within the AS areas establish adjacencies. If two
routers on the same subnet agree to become neighbors through the HELLO process, they begin to exchange network topology
information in the form of LSAs.
In OSPFv2 neighbors on broadcast and NBMA links are identified by their interface addresses, while neighbors on other types of
links are identified by RID.

Autonomous System (AS) Areas

OSPF operates in a type of hierarchy.
The largest entity within the hierarchy is the autonomous system (AS), which is a collection of networks under a common
administration that share a common routing strategy. OSPF is an intra-AS (interior gateway) routing protocol, although it is capable
of receiving routes from and sending routes to other ASs.
You can divide an AS into a number of areas, which are groups of contiguous networks and attached hosts. Routers with multiple
interfaces can participate in multiple areas. These routers, called area border routers (ABRs), maintain separate databases for each
area. Areas are a logical grouping of OSPF routers identified by an integer or dotted-decimal number.
Areas allow you to further organize your routers within in the AS. One or more areas are required within the AS. Areas are valuable in
that they allow sub-networks to "hide" within the AS, thus minimizing the size of the routing tables on all routers. An area within the
AS may not see the details of another area's topology. AS areas are known by their area number or the router's IP address.
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Open Shortest Path First (OSPFv2 and OSPFv3)
Standards Compliance chapter.
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