[Idr] route-capability explained
"Samita Chakrabarti" <samitac@ipinfusion.com> Thu, 31 July 2008 16:36 UTC
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From: Samita Chakrabarti <samitac@ipinfusion.com>
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Date: Thu, 31 Jul 2008 06:47:02 -0700
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Subject: [Idr] route-capability explained
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Reference: draft-chakrabarti-idr-as4-route-cap-01.txt Slides: http://www.ietf.org/proceedings/08jul/slides/idr-7.ppt Purpose of the proposal: Optimize to dynamically handle the BGP configuration mismatch when As4byte extended- community attributes are not understood by the legacy BGP implementations. Where is the problem? draft-rekhter-as4octet-ext-community-03.txt defines AS4octet extended communities and RFC4893 describes AS4 capability in general. But there is no explicit specification which says whether the AS4octet extended community feature must be turned on when an implementation is compliant to RFC4893. The following questions come up for interoperability (Assuming there are more than one or two routing vendor implementations in the community): 1. How do we handle interoperability between AS2-byte extended community compliant peer and AS4-byte implementation that supports or does not support as4octet-ext-comm ? 2. What if a PE is connected with two different PEs where one does not support AS4 extended community format and one that does? 1. Correct configuration on each PE for its corresponding peer is the current answer 3. Does the manual configuration scale reasonably in a large provider network where number of PEs are quite large? Or what if when there is no administrative control over Inter-AS provider network option C PE implementing draft-rekhter-as4octet-ext-community or not? 4. Should we optimize to find out the ext-communities capability from the peer during the transition of AS4 extended -communities? Here is the optimization scenario described in draft-chakrabarti-idr-as4-route-cap-01.txt: PE1 ------------------------------------------PE2 implements AS4octet-ext-comm Does not implement AS4octet-ext-comm and unaware of PE2's or it is configured for 2byte-support AS4octet-ext-comm exports RT 1:2 imports RT 1:2 ext-format-A: ext-format-B: X:000000010002 Y:000100000002 X= Type-subtype for AS4 Y= Type-subtype for regular ext-community Now PE1 sends ext-format-A to ext-format-B , one can see that 8byte comparison of ext-community will not match. (X and Y are different and value fields are different) If a route-capability is introduced then, dynamically PE1 can discover that PE2 is not capable of supporting AS4-ext-community and it can send 2byte format, even though it might store the ext-community in AS4octet format. NOTE: I understand that this problem scenario exists when there is a configuration issue due to lack of knowledge about the implementation and configuration of the peer. BGP may have traditionally designed for simplicity and manual configuration only, but it does not really scale well without spending time debugging problems. My point is to make the AS4 transition easy for the operators so that the transition is easy accross different versions of same implementation and different vendor's implementations. Alternately, an AS4octet-ext-community implementation SHOULD check whether its peer is capable of EXTENDED_AS CAPABLE (RFC4893 compliant) and then use the AS4-ext-format or 2b:4b format. But, as per current specifications there is no guarantee that an implementation supporting RFC 4893 would also support AS4Octet-ext-community. If we do not want a separate route-capability, then we should specify in the rekhter-as4-ext-community document that AS4-ext-community formatted attribute should be sent to the PE only when it is AS4-capable. At the idr meeting at IETF on Wednesday, we were told, this is operational or implementation issue - not a protocol issue. I agree it is not exactly a protocol issue. But, given that IETF is all about running "interoperable" code across many vendors, I strongly believe this issue should be addressed to clarify the specification such that there are less issues during the AS4 transition. So here are a few alternatives that make sense in my mind: 1. draft-rekhter-as4octet-ext-community-03.txt can specify handling of AS4byte and AS2byte extendend-communities. 2. Provide capability exchange to find out if my peer is capable of understanding AS4byte-extended-community for importing or for deciphering Site-Of-Origin or received RD values correctly 3. Update RFC4360 to incorporate as4octet-ext-community and discuss transition sceanrios _______________________________________________ Idr mailing list Idr@ietf.org https://www.ietf.org/mailman/listinfo/idr
- [Idr] route-capability explained Samita Chakrabarti
- Re: [Idr] route-capability explained Paul Jakma
- Re: [Idr] route-capability explained Samita Chakrabarti
- Re: [Idr] route-capability explained Paul Jakma
- Re: [Idr] route-capability explained Samita Chakrabarti
- Re: [Idr] route-capability explained Paul Jakma
- Re: [Idr] route-capability explained Samita Chakrabarti