Chapter 19
| Unicast Routing
Configuring the Open Shortest Path First Protocol (Version 2)
– 722 –
Default Information
◆ Originate Default Route
22
– Generates a default external route into an
autonomous system. Note that the Advertise Default Route field must also be
properly configured. (Default: Disabled)
When this feature is used to redistribute routes into a routing domain (that is,
an Autonomous System), this router automatically becomes an Autonomous
System Boundary Router (ASBR). This allows the router to exchange routing
information with boundary routers in other autonomous systems to which it
may be attached. If a router is functioning as an ASBR, then every other router
in the autonomous system can learn about external routes from this device.
Figure 487: AS Boundary Router
◆ Advertise Default Route
22
– The router can advertise a default external route
into the autonomous system (AS). (Options: Not Always, Always;
Default: Not Always)
■
Always – The router will advertise itself as a default external route for the
local AS, even if a default external route does not actually exist. (To define a
default route, see “Configuring Static Routes” on page 681.)
■
NotAlways – It can only advertise a default external route into the AS if it
has been configured to import external routes through RIP or static routes,
and such a route is known. (See “Redistributing External Routes” on
page 734.)
◆ External Metric Type
22
– The external link type used to advertise the default
route. Type 1 route advertisements add the internal cost to the external route
metric. Type 2 routes do not add the internal cost metric. When comparing
Type 2 routes, the internal cost is only used as a tie-breaker if several Type 2
routes have the same cost. (Default: Type 2)
◆ Default External Metric
22
– Metric assigned to the default route.
(Range: 0-16777215; Default: 20)
The metric for the default external route is used to calculate the path cost for
traffic passed from other routers within the AS out through the ASBR.
Redistribution of routing information from other protocols is controlled by the
Redistribute function (see page 734).
22. These are configured with the “default-information originate”
command.
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