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Chapter 10 Routing
USG20(W)-VPN Series User’s Guide
242
Each type of area is illustrated in the following figure.
Figure 158
OSPF: Types of Areas
This OSPF AS consists of four areas, areas 0-3. Area 0 is always the backbone. In this example,
areas 1, 2, and 3 are all connected to it. Area 1 is a normal area. It has routing information about
the OSPF AS and networks X and Y. Area 2 is a stub area. It has routing information about the OSPF
AS, but it depends on a default route to send information to networks X and Y. Area 3 is a NSSA. It
has routing information about the OSPF AS and network Y but not about network X.
OSPF Routers
Every router in the same area has the same routing information. They do this by exchanging Hello
messages to confirm which neighbor (layer-3) devices exist, and then they exchange database
descriptions (DDs) to create a synchronized link-state database. The link-state database contains
records of router IDs, their associated links and path costs. The link-state database is then
constantly updated through Link State Advertisements (LSA). Each router uses the link state
database and the Dijkstra algorithm to compute the least cost paths to network destinations.
Like areas, each router has a unique 32-bit ID in the OSPF AS, and there are several types of
routers. Each type is really just a different role, and it is possible for one router to play multiple
roles at one time.
• An internal router (IR) only exchanges routing information with other routers in the same area.
• An Area Border Router (ABR) connects two or more areas. It is a member of all the areas to
which it is connected, and it filters, summarizes, and exchanges routing information between
them.
• An Autonomous System Boundary Router (ASBR) exchanges routing information with routers in
networks outside the OSPF AS. This is called redistribution in OSPF.
• A backbone router (BR) has at least one interface with area 0. By default, every router in area 0
is a backbone router, and so is every ABR.
Table 97
OSPF: Redistribution from Other Sources to Each Type of Area
SOURCE \ TYPE OF AREA
NORMAL
NSSA
STUB
Static routes
Yes
Yes
No
RIP
Yes
Yes
Yes
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Страница 151: ...Chapter 9 Interfaces USG20 W VPN Series User s Guide 151 Configuration Network Interface Ethernet Edit External Type ...
Страница 152: ...Chapter 9 Interfaces USG20 W VPN Series User s Guide 152 Configuration Network Interface Ethernet Edit External Type ...
Страница 154: ...Chapter 9 Interfaces USG20 W VPN Series User s Guide 154 Configuration Network Interface Ethernet Edit Internal Type ...
Страница 155: ...Chapter 9 Interfaces USG20 W VPN Series User s Guide 155 Figure 121 Configuration Network Interface Ethernet Edit OPT ...
Страница 156: ...Chapter 9 Interfaces USG20 W VPN Series User s Guide 156 Configuration Network Interface Ethernet Edit OPT ...
Страница 170: ...Chapter 9 Interfaces USG20 W VPN Series User s Guide 170 Figure 127 Configuration Network Interface PPP Add ...
Страница 178: ...Chapter 9 Interfaces USG20 W VPN Series User s Guide 178 Figure 129 Configuration Network Interface Cellular Add Edit ...
Страница 194: ...Chapter 9 Interfaces USG20 W VPN Series User s Guide 194 Figure 139 Configuration Network Interface VLAN Add Edit ...
Страница 206: ...Chapter 9 Interfaces USG20 W VPN Series User s Guide 206 Figure 141 Configuration Network Interface Bridge Add Edit ...
Страница 282: ...Chapter 15 UPnP USG20 W VPN Series User s Guide 282 Figure 190 Network Connections My Network Places Properties Example ...
Страница 340: ...Chapter 21 IPSec VPN USG20 W VPN Series User s Guide 340 Figure 226 Configuration VPN IPSec VPN VPN Connection Edit IKE ...
Страница 348: ...Chapter 21 IPSec VPN USG20 W VPN Series User s Guide 348 Figure 228 Configuration VPN IPSec VPN VPN Gateway Add Edit ...
Страница 378: ...Chapter 22 SSL VPN USG20 W VPN Series User s Guide 378 Create a Web Application SSL Application Object ...
Страница 591: ...Chapter 31 Log and Report USG20 W VPN Series User s Guide 591 Figure 418 Configuration Log Report Email Daily Report ...
Страница 659: ...Appendix B Legal Information USG20 W VPN Series User s Guide 659 Environmental Product Declaration ...