Brocade Communications Systems FastIron SX 800 Configuration Manual page 437

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.
Protocols are automatically notified when a route filter is created, deleted or modified. In addition, when a protocol is notified of a
filter change, appropriate steps are taken to apply the new or updated filter to existing routes.
Filter update delay and BGP
The filter-changes-update-delay command applies (remove only) to changes of filters that are already used or referenced by
applications. If the content of a filter is changed, the new filter action takes effect after filter-changes-update-delay for existing routes.
The notification delay also applies to situations where the usage or reference of a filter is changed in BGP.
For example, the following BGP neighbor command sets or changes the route-map filter on a neighbor:
device(config-bgp)# neighbor x.x.x.x route-map map_abc out
In this case, the device applies the route-map "map_abc" to the peer, and updates the neighbor out-bound routes after a delay.
If the delay-time is 0, BGP does not start peer out-bound policy updates immediately.
Use the clear filter-change-update or clear ip bgp neighbor soft-out commands to trigger BGP policy updates.
Similarly, the filter-changes-update-delay command also applies to the neighbor in-bound policy change.
NOTE
The auto-update action for a BGP peer filter is newly introduced in release 08.0.01. In previous releases, a user needs to
manually issue the clear ip bgp neighbor soft out command to cause the device to apply the new route-map retroactively to
existing routes.
The general guideline is to define a policy first , then apply it to a BGP peer.
BGP4 policy processing order
The order of application of policies when processing inbound and outbound route advertisements on the device is:
1. lp prefix-list
2. Outbound Ip prefix-list ORF, if negotiated
3. Filter-list (using As-path access-list)
4. Distribute list (using IP ACL - IPv4 unicast only)
5. Route-map
FastIron Ethernet Switch Layer 3 Routing
53-1003627-04
Configuring a static BGP4 network
437