Brocade Virtual ADX Switch and Router Guide (Supporting ADX v03.1.00) - Manual (Page 275)

Brocade Virtual ADX Switch and Router Guide 261
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Filtering
8
Dynamic route filter update
Routing protocols use various route filters to control the distribution of routes. Route filters are
used to filter routes received from and advertised to other devices. Protocols also use route-map
policies to control route redistribution from other routing protocols. In addition, route filter policies
are used to select routes to be installed in the routing tables, and used by forwarding engine to
forward traffic.
There are currently 5 different types of route filters defined for use in a device:
• Access List (ACL)
• Prefix-List
• BGP4 as-path Access-list
• BGP4 community-list
• Route-map
Not every protocol uses all of these route filters. A protocol will usually use two or three filter types.
The filters used by BGP4, OSPF, and OSPFv3 protocols are described in
Table 37 .
When a route filter is changed (created, modified or deleted) by a user, the filter change notification
will be sent to all relevant protocols, so that protocols can take appropriate actions. For example if
BGP4 is using a route-map (say MapX) to control the routes advertised to a particular peer, the
change of route-map (MapX) will cause BGP4 to re-evaluate the advertised routes, and make the
appropriate advertisements or withdrawals according to the new route-map policy.
A route filter change action can happen in three ways.
1. A new filter is defined (created).
This filter name may be already referenced by an application. The application needs to be
notified of the addition of the new filter, and will bind to and use the new filter. In general, if a
filter name is referenced by an application, but is not actually defined, the application assumes
the default deny action for the filter.
2. An existing filter is undefined (removed).
If the deleted filter is already used and referenced by an application, the application will unbind
itself from the deleted filter.
3. An existing filter is modified (updated).
If the filter is already used and referenced by an application, the application will be notified.
TABLE 37 Route filters used by each protocol
Protocol Route
map Prefix
list Community- list As-path
access- list ACL
BGP4 X X BGP4 does not use
Community- List filters
directly. It does use them
indirectly through route-map
filters that contain
Community-List filters. X X
OSPF X X X
OSPFv3 X X