Installing and Administering Internet Services

276 Chapter 8
Configuring gated
Configuring the OSPF Protocol
Externally-defined routing information is kept separately from the OSPF
routing information. In addition, the externally-defined routing
information can be tagged, where the source of the information is
identified and stored along with the route information.
Statements in the Control class of the /etc/gated.conf file control the
importing of routes from routing protocols to a gated forwarding table
and the exporting of routes from the gated forwarding table. See
“Importing and Exporting Routes” on page 292.
The defaults statements in the OSPF protocol configuration are
specified for AS boundary routers only. These statements specify how
external routing information is handled by the OSPF protocol. The
following can be defined in the defaults statements:
• preference specifies the preference value given to the ASE routes
imported from other autonomous systems. The preference value
determines the order of routes to the same destination in the routing
table. gated allows one route to a destination per protocol for each
autonomous system. In the case of multiple routes, the route used is
determined by the lowest preference value. (See “Specifying Route
Preference” on page 289.) If a preference value is not specified, ASE
routes are imported with a preference of 150.
Default: 150
Range: 0 (most preferred) - 255 (least preferred)
• cost specifies the cost associated with an OSPF route that is
exported to other AS boundary routers.
Default: 0
Range: 0 - 65535
• tag specifies an OSPF tag placed on all routes exported by gated
into OSPF. Each external route can be tagged by the AS boundary
router to identify the source of the routing information. The tag
value can be an unsigned 31-bit number. Or, you can specify tag as
as_tag, where as_tag is an unsigned 12-bit number that is
automatically assigned.
• type determines how ASE routes imported into OSPF are treated.
Type 1 routes should be routes from internal gateway protocols with
external metrics that are directly comparable to OSPF metrics. When
OSPF is selecting a route, OSPF will use a type 1 route’s external
metric and add the OSPF internal cost to the AS border router. Type