3Com Switch 7757, Configuration Manual

Page: 357 / 940

Configuring the Way to Advertise/Receive Routing Information 357
Importing Routes With BGP employed, an AS can send its interior routing information to its
neighbor ASs. However, the interior routing information is not generated by BGP,
it is obtained by importing IGP routing information to BGP routing table. Once IGP
routing information is imported to BGP routing table, it is advertised to BGP peers.
You can filter IGP routing information by routing protocols before the IGP routing
information is imported to BGP routing table.
c
CAUTION:
■
If a route is imported to the BGP routing table through the import-route
command, its Origin attribute is Incomplete.
■
The network segment route to be advertised must be in the local IP routing
table. You can use routing policy to control route advertising with more
flexibility.
■
The Origin attribute of the network segment routes advertised to BGP routing
table through the
network command is IGP.
Configuring BGP Route
Aggregation
In a medium-/large-sized BGP network, you can reduce the number of the routes
to be advertised to BGP peers through route aggregation to save the spaces of
BGP peer routing tables. BGP supports two route aggregation modes: automatic
aggregation mode and manual aggregation mode.
■
Automatic aggregation mode, where IGP sub-network routes imported by BGP
are aggregated. In this mode, only the aggregated routes are advertised. The
imported IGP sub-network routes are not advertised. Note that the default
routes and the routes imported by using the
network command cannot be
automatically aggregated.
■
Manual aggregation mode, where local BGP routes are aggregated. The
priority of manual aggregation is higher than that of automatic aggregation.
Table 291 Import routes
Operation Command Description
Enter system view system-view -
Enable BGP, and enter BGP
view bgp as-number Required
By default, BGP is disabled.
Import and advertise routing
information generated by
other protocols. import-route protocol
[ process-id ] [ med
med-value | route-policy
route-policy-name ]*
Required
By default, BGP does not
import nor advertise the
routing information generated
by other protocols.
Advertise network segment
routes to BGP routing table network network-address
[ mask ] [ route-policy
route-policy-name ]
Optional
By default, BGP does not
advertise any network segment
routes. Optional
By default, BGP does not
advertise any network segment
routes. Optional
By default, BGP does not
advertise any network segment
routes.