Unanswered Question
Jun 27th, 2007

Anybody know how is ORF implemeted in SP network ? what is need for it?


I have this problem too.
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Edison Ortiz Wed, 06/27/2007 - 12:31

ORF is very useful since you can configure a prefix-list indicating what routes are sent to you. Doing this, saves a tremendous amount of bandwidth in some environment and you have the power to modify the requested network(s) from your end instead of the ISP end.

The prefix-list you send via ORF (from the client side) would be placed as an outgoing prefix-list in the ISP side.

Without ORF, placing an incoming prefix-list to block incoming networks at the client side, means that traffic has consumed precious bandwidth.

mohammedmahmoud Wed, 06/27/2007 - 13:33


Routers exchange their inbound filters in order to be used as outbound filters on neighbor routers, these filters are described in the ORF entries which are part of the route refresh message --> reduces resources (BW + CPU).

ORF capabilities needs to be negotiated by the router for each ORF type supported in the ORF message --> each neighbor monitors his neighbor for his ORF capabilities.

"neighbor capability orf prefix-list { both | send | receive }" --> enables the negotiation of prefix-list ORF capabilities during the BGP session setup.

Accordingly, it can be used to be sent to the ISP to be used as an outbound prefix-list @ the ISP in order not to waste resources (the ISP sending all the routes and then the customer filters them after receiving them).


ISP side:

neighbor remote-as

neighbor capability ORF prefix-list receive

Customer side:

neighbor remote-as

neighbor capability orf prefix-list send

neighbor prefix-list in

ip prefix-list seq permit


Mohammed Mahmoud.

ksnarayan43 Wed, 06/27/2007 - 14:00

Thank you Mohammed and Edison.

From a BGP prespective, typically customers have the option to recieve "Full routing table" or directly connected routes from SP or recieve defaults routes only.

How would ORF help? when you have default route, why would u need tens and thousands of routes on your router. What is the benefit ?

thank you

mohammedmahmoud Wed, 06/27/2007 - 14:12


In the case of receiving a default route, ORF has no benefits, its main benefits is when you receive many routes and need to inbound filter some of them.


Mohammed Mahmoud.

Edison Ortiz Wed, 06/27/2007 - 15:48

You have no benefits, whatsover, with ORF while receiving just the default route from the ISP.

ORF is only useful for full or partial BGP routing table where bandwidth and cpu usage may be a factor.

ksnarayan43 Wed, 06/27/2007 - 15:53

Thank you Edison.

What is the benefit of full or partial BGP routing table versus default to customers ?


Edison Ortiz Wed, 06/27/2007 - 16:01

With full BGP routing table, you have the power to filter external networks at the edge. With a partial BGP routing table, you have limited capability while with a default route, you have no way of filtering external networks.

I'm sure there are other advantages of running a full BGP routing table vs a partial one, but the reason above, is the only one that comes to mind at the moment.

sundar.palaniappan Wed, 06/27/2007 - 15:59

"How would ORF help? when you have default route, why would u need tens and thousands of routes on your router. What is the benefit ?"

If I understand your question correct you seem to want to know what's the benefit of learning partial or full BGP routing table update rather than just the default route. If that indeed is the question if the network is multi-homed to the provider(s) and learning specific routes it makes the customer Edge routers choose the optimal/shorter route to a destination. With just a default route the routing may or may not occur in a optimal way in such a case.



ksnarayan43 Wed, 06/27/2007 - 16:37

Thank you Edison and Sundar.

Yes, The question was the benefit of partial versus full BGP route. And in which scenario u would use ORF.

Also, just trying to understand the ORF and its application wrt to BGP, have seen few customers looking for few thousand routes support on the CE routers. Was wondering the benefits of it.Why would they need it?. Does not look like multi-homed scenario


mohammedmahmoud Wed, 06/27/2007 - 22:49


Just to make sure that you are caution with receiving a full internet routing table, the internet routing table has exceeded 220,000 route, thus always make sure that the routers you are dealing with are capable of handling this amount if routes.


Mohammed Mahmoud.

Pavel Bykov Thu, 06/28/2007 - 02:28

As a general rule of thumb, if the topology is simple enough to use static routing, don't use BGP at all.

If you have only one link to ISP, and you are certain you can detect link failure at interface level, than don't use BGP. But if you can't detect link failure, than BGP can help, because it creates neighbor relations using TCP and has keepalive mechanism.


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