3Com Switch 7754, Configuration Manual

Page: 382 / 940

382 C
HAPTER
37: IP R
OUTING
P
OLICY
C
ONFIGURATION
n
Among the items defined in an IP prefix list, at least one item should be in permit
mode. The items in deny mode can be used to quickly filter out undesired routing
information. But if all the items are in deny mode, no route will pass the filter of
the IP prefix list. You can define an item
permit 0.0.0.0 0 greater-equal 0
less-equal 32 after the deny-mode items to permit all other routes to pass
through.
AS Path List
Configuration
A BGP routing information packet contains an AS path field. AS path list can be
used to match the AS path field in BGP routing information to filter out the
routing information that does not match.
By default, no AS path list is defined.
Community List
Configuration
In BGP, community attributes are optional transitive. Some community attributes
are globally recognized and they are called standard community attributes. Some
are for special purposes and they can be customized.
A route can have one or more community attributes. The speaker of multiple
community attributes of a route can act based on one, multiple or all attributes. A
router can decide whether to change community attributes before forwarding a
route to other peer entity.
Community list is used to identify community information. It falls in to two types:
basic community list and advanced community list. The former one’s value ranges
from 1 to 99, and the latter one’s ranges from 100 to 199.
By default, no BGP community list is defined.
Applying Routing Policy
to Route Import
For a routing protocol, you can import the routes discovered by other routing
protocols to it to enrich its route knowledge. When doing this, you can adopt a
route-policy to filter routing information, so as to import only needed routes. For
an import operation, if the destination routing protocol cannot directly use the
Table 312 AS path list configuration
Operation Command Description
Enter system view system-view -
Configure AS path list ip as-path-acl acl-number { permit |
deny } as-regular-expression
Optional
Table 313 Community list configuration
Operation Command Description
Enter system view system-view -
Configure basic community
list ip community-list
basic-comm-list-number { per
mit | deny } [ aa:nn ]
&<1-12> [ internet |
no-export-subconfed |
no-advertise | no-export ]*
Optional
Configure advanced
community list ip community-list
adv-comm-list-number { per
mit | deny }
comm-regular-expression
Optional