![background image](http://html1.mh-extra.com/html/foundry-networks/fastiron-edge-switch-x424/fastiron-edge-switch-x424_manual_2324269526.webp)
Foundry Configuration Guide for the FESX, FSX, and FWSX
20 - 2
© Foundry Networks, Inc.
December 2005
•
Not-So-Stubby Area (NSSA) external link
OSPF is built upon a hierarchy of network components. The highest level of the hierarchy is the
Autonomous
System (AS)
. An autonomous system is defined as a number of networks, all of which share the same routing
and administration characteristics.
An AS can be divided into multiple
areas
as shown in Figure 20.1 on page 20-3. Each area represents a
collection of contiguous networks and hosts. Areas limit the area to which link-state advertisements are
broadcast, thereby limiting the amount of flooding that occurs within the network. An area is represented in OSPF
by either an IP address or a number.
You can further limit the broadcast area of flooding by defining an area range. The area range allows you to
assign an aggregate value to a range of IP addresses. This aggregate value becomes the address that is
advertised instead all of the individual addresses it represents being advertised. You can assign up to 32 ranges
in an OSPF area.
An OSPF router can be a member of multiple areas. Routers with membership in multiple areas are known as
Area Border Routers (ABRs)
. Each ABR maintains a separate topological database for each area the router is
in. Each topological database contains all of the LSA databases for each router within a given area. The routers
within the same area have identical topological databases. The ABR is responsible for forwarding routing
information or changes between its border areas.
An
Autonomous System Boundary Router (ASBR)
is a router that is running multiple protocols and serves as a
gateway to routers outside an area and those operating with different protocols. The ASBR is able to import and
translate different protocol routes into OSPF through a process known as
redistribution
. For more details on
redistribution and configuration examples, see “Enable Route Redistribution” on page 20-27.
Summary of Contents for FastIron Edge Switch X424
Page 36: ...Foundry Configuration Guide for the FESX FSX and FWSX 2 12 Foundry Networks Inc December 2005...
Page 56: ...Foundry Configuration Guide for the FESX FSX and FWSX 3 20 Foundry Networks Inc December 2005...
Page 70: ...Foundry Configuration Guide for the FESX FSX and FWSX 4 14 Foundry Networks Inc December 2005...
Page 198: ...Foundry Configuration Guide for the FESX FSX and FWSX 8 38 Foundry Networks Inc December 2005...
Page 316: ...Foundry Configuration Guide for the FESX FSX and FWSX 12 26 Foundry Networks Inc December 2005...
Page 350: ...Foundry Configuration Guide for the FESX FSX and FWSX 15 12 Foundry Networks Inc December 2005...
Page 458: ...Foundry Configuration Guide for the FESX FSX and FWSX 18 18 Foundry Networks Inc December 2005...
Page 712: ...Foundry Configuration Guide for the FESX FSX and FWSX 22 32 Foundry Networks Inc December 2005...
Page 760: ...Foundry Configuration Guide for the FESX FSX and FWSX A 34 Foundry Networks Inc December 2005...
Page 796: ...Foundry Configuration Guide for the FESX FSX and FWSX C 18 Foundry Networks Inc December 2005...
Page 820: ...Foundry Configuration Guide for the FESX FSX and FWSX E 10 Foundry Networks Inc December 2005...