Which two statements about BGP prefix-based outbound filtering are true? (Choose two.)
A.
It must be configured per address family.
B.
It can use prefix lists and route maps for filtering.
C.
It can be configured under the global BGP routing process.
D.
It can be configured for external peering sessions only.
E.
It can increase the processing load on the router.
F.
It supports IP multicast routes.
A & E are correct.
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Only A is correct.
B and C are incorrect by definition.
E is incorrect because ORF’s goal is to decrease the load.
Cisco says that ORF doesn’t support multicast (making F invalid) and can be configured for external sessions only (making D valid). But actually ORF works fine on internal sessions too. You can easily simulate this.
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C is also relevant because you can setup neighbor #.#.#.# capability orf prefix-list both under global process.
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E is accurate because it reduces the load on the customer router since he no longer has to process all the routes but it increases the load on the Provider Edge router (which is where the ORF is configured) since he now has to do all the filtering for the Customer Edge router.
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Restrictions for BGP Prefix-Based Outbound Route Filtering
•The BGP Prefix-Based Outbound Route Filtering feature does not support IP multicast routes.
•IP addresses that are used for outbound route filtering must be defined in an IP prefix-list. BGP distribute lists and IP access lists are not supported.
•Outbound route filtering is configured on only a per-address family basis and cannot be configured under the general session or BGP routing process (Router(config-router)#).
•Outbound route filtering is configured for only external peering sessions.
http://www.cisco.com/c/en/us/td/docs/ios/12_2s/feature/guide/fsbgporf.html
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http://www.cisco.com/c/en/us/td/docs/ios/12_2s/feature/guide/fsbgporf.html#wp1053890
No discussion, as doc says that, that was the referrence for the question…
Restrictions
•The BGP Prefix-Based Outbound Route Filtering feature does not support multicast.
•IP addresses that are used for outbound route filtering must be defined in an IP prefix-list. BGP distribute lists and IP access lists are not supported.
•Outbound route filtering is configured on only a per-address family basis and cannot be configured under the general session or BGP routing process (Router(config-router)#).
•Outbound route filtering is configured for only external peering sessions.
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