Dynamically refreshing routes – Brocade Virtual ADX Switch and Router Guide (Supporting ADX v03.1.00) User Manual
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Brocade Virtual ADX Switch and Router Guide
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Filtering
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Dynamically requesting a route refresh from a BGP4 neighbor
You can easily apply changes to filters that control BGP4 routes received from or advertised to a
neighbor, without resetting the BGP4 session between the device and the neighbor. For example, if
you add, change, or remove a BGP4 IP prefix list that denies specific routes received from a
neighbor, you can apply the filter change by requesting a route refresh from the neighbor. If the
neighbor also supports dynamic route refreshes, the neighbor resends its Adj-RIB-Out, its table of
BGP4 routes. Using the route refresh feature, you do not need to reset the session with the
neighbor.
The route refresh feature is based on the following specifications:
•
RFC 2842. This RFC specifies the Capability Advertisement, which a BGP4 device uses to
dynamically negotiate a capability with a neighbor.
•
RFC 2858 for Multi-protocol Extension.
•
RFC 2918, which describes the dynamic route refresh capability
The dynamic route refresh capability is enabled by default and cannot be disabled. When the
device sends a BGP4 OPEN message to a neighbor, the device includes a Capability Advertisement
to inform the neighbor that the device supports dynamic route refresh.
NOTE
The option for dynamically refreshing routes received from a neighbor requires the neighbor to
support dynamic route refresh. If the neighbor does not support this feature, the option does not
take effect and the software displays an error message. The option for dynamically re-advertising
routes to a neighbor does not require the neighbor to support dynamic route refresh.
Dynamically refreshing routes
The following sections describe how to refresh BGP4 routes dynamically to put new or changed
filters into effect.
To request a dynamic refresh of all routes from a neighbor, enter a command such as the following.
Virtual ADX(config-bgp)# clear ip bgp neighbor 192.168.1.170 soft in
This command asks the neighbor to send its BGP4 table (Adj-RIB-Out) again. The device applies its
filters to the incoming routes and adds, modifies, or removes BGP4 routes as necessary.
Syntax: clear ip bgp neighbor all | ip-addr | as-num [soft-outbound | soft [in | out]]
The all | ip-addr | as-num parameters specify the neighbor. The ip-addr parameter specifies a
neighbor by its IP interface with the device. The as-num parameter specifies all neighbors within
the specified AS. The all parameter specifies all neighbors.
The soft-outbound parameter updates all outbound routes by applying the new or changed filters,
but sends only the existing routes affected by the new or changed filters to the neighbor.
The soft [in | out] parameter specifies whether you want to refresh the routes received from the
neighbor or sent to the neighbor:
•
soft in does one of the following:
•
If you enabled soft reconfiguration for the neighbor, soft in updates the routes by
comparing the route policies against the route updates that the device has stored. Soft
reconfiguration does not request additional updates from the neighbor or otherwise affect
the session with the neighbor. Refer to