Extreme Networks ExtremeWare 7.3.0, Справочник по командам

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ExtremeWare Software 7.3.0 Command Reference Guide 1257
17
IGP Commands
This chapter documents commands used for the following interior gateway protocols:
• OSPF
• Integrated IS-IS
• RIP
OSPF is a link-state protocol that distributes routing information between routers belonging to a single
IP domain, also known as an
autonomous system (AS). In a link-state routing protocol, each router
maintains a database describing the topology of the autonomous system. Each participating router has
an identical database 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 autonomous system. When
several equal-cost routes to a destination exist, traffic can distributed among them. The cost of a route is
described by a single metric.
OSPF allows parts of a networks to be grouped together into areas . The topology within an area is
hidden from the rest of the autonomous system. Hiding this information enables a significant reduction
in LSA traffic, and reduces the computations needed to maintain the LSDB. Routing within the area is
determined only by the topology of the area.
The three types of routers defined by OSPF are as follows:
• Internal Router (IR )—An internal router has all of its interfaces within the same area.
• Area Border Router (ABR) —An ABR has interfaces belonging to two or more areas. It is responsible
for exchanging summary advertisements with other ABRs.
• Autonomous System Border Router (ASBR) —An ASBR acts as a gateway between OSPF and other
routing protocols, or other autonomous systems.
Each switch that is configured to run OSPF must have a unique router ID. It is recommended that you
manually set the router ID of the switches participating in OSPF, instead of having the switch
automatically choose its router ID based on the highest interface IP address. Not performing this
configuration in larger, dynamic environments could result in an older LSDB remaining in use.
NOTE
Do not set the router ID to 0.0.0.0.