Brocade FastIron Ethernet Switch Layer 3 Routing Configuration Guide - Manual (Page 476)

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.
Filter update delay and BGP
476 FastIron Ethernet Switch Layer 3 Routing Configuration Guide
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