Extreme Networks ExtremeWare XOS 11.3, Руководство пользователя

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ExtremeWare XOS 11.3 Concepts Guide
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28 OSPFv3
This chapter covers the following topics:
●
Overview of OSPFv3 on page 557
●
Route Redistribution on page 561
Overview of OSPFv3
Open Shortest Path First (OSPF) is a link state protocol that distributes routing information between
routers belonging to a single IP domain; the IP domain is also known as an
autonomous system (AS). In a
link-state routing protocol, each router maintains a database describing the topology of the AS. Each
participating router has an identical database for an area maintained from the perspective of that router.
From the link state database (LSDB), each router constructs a tree of shortest paths, using itself as the
root. The shortest path tree provides the route to each destination in the AS. When several equal-cost
routes to a destination exist, traffic can be distributed among them. The cost of a route is described by a
single metric.
OSPFv3 supports IPv6, and uses commands only slightly modified from that used to support IPv4.
OSPFv3 has retained the use of the four-byte, dotted decimal numbers for router IDs, LSA IDs, and area
IDs.
OSPFv3 is an interior gateway protocol (IGP), as is the other common IGP for IPv6, RIPng. OSPFv3 and
RIPng are compared in
Chapter 26 , “RIPng” on page 539 .
Licensing
To use OSPFv3, you must have a Core license installed on your switch. The BlackDiamond 10K ships
with a Core, or Advanced Core license. Other platforms can be upgraded to a Core license. See the
section
“Software Licensing” on page 33 for more information about licensing.
Link State Database
Upon initialization, each router transmits a link state advertisement (LSA) on each of its interfaces.
LSAs are collected by each router and stored into the LSDB of each router. Once all LSAs are received,
the router uses the LSDB to calculate the best routes for use in the IP routing table. OSPFv3 uses
flooding to distribute LSAs between routers. Any change in routing information is sent to all of the
routers in the network. All routers within an area have the exact same LSDB.
Table 69 describes LSA
type numbers.
Table 69: Selected OSPFv3 LSA types
Type Number Description
0x0008 Link LSA
0x2001 Router LSA