BGP Event-Based VPN Import

[Andrew Xue Zheng Lay]

Hi Guys,

I came across this command, but have problem understanding what it does or how to use it:

Router(config-router-af)# import path selection {all | bestpath [strict] | multipath [strict]}

It falls under the "BGP Event-Based VPN Import" section:

http://www.cisco.com/c/en/us/td/docs/ios/ios_xe/iproute_bgp/configuration/guide/2_xe/irg_xe_book/irg_event_vpn_import_xe.html#wp1059052

Does anyone know what this does or how this works?

[Ashok Kumar]

Hi,

It specifies the BGP import path selection policy for a specific VRF instance.

You might be aware on VRF-LITE, that's the VPNs without MPLS.

BGP Event-Based VPN Import

The BGP Event-Based VPN Import feature introduces a modification to the existing BGP path import process. BGP Virtual Private Network (VPN) import provides importing functionality for BGP paths where BGP paths are imported from the BGP VPN table into a BGP virtual routing and forwarding (VRF) topology. In the existing path import process, when path updates occur, the import updates are processed during the next scan time, which is a configurable interval of 5 to 15 seconds. The scan time adds a delay in the propagation of routes. The enhanced BGP path import is driven by events; when a BGP path changes, all of its imported copies are updated as soon as processing is available.
When you use the BGP Event-Based VPN Import feature, convergence times are significantly reduced because provider edge (PE) routers can propagate VPN paths to customer edge (CE) routers without the scan time delay. Configuration changes such as adding imported route targets (RT) to a VRF are not processed immediately, and are still handled during the 60-second periodic scanner pass.
Import Path Selection Policy

Event-based VPN import introduces three path selection policies:
•All—Import all available paths from the exporting net that match any route target (RT) associated with the importing VRF instance.

•Best path—Import the best available path that matches the RT of the VRF instance. If the best path in the exporting net does not match the RT of the VRF instance, a best available path that matches the RT of the VRF instance is imported.

•Multipath—Import the best path and all paths marked as multipaths that match the RT of the VRF instance. If there are no best path or multipath matches, then the best available path is selected.

- Ashok

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[Andrew Xue Zheng Lay]

Any examples?