BGPSEC Potential Optimizations for AS-PATH Prepending and Transparent Route Servers.

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sidr wg / Québec C ity 2011.07.28 Doug Montgomery <dougm @ nist.gov> Randy Bush <randy @ psg.com>. BGPSEC Potential Optimizations for AS-PATH Prepending and Transparent Route Servers. bgpsec-00 Level Set. Requirements : Provide cryptographic assurance that:
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sidr wg / Québec City2011.07.28Doug Montgomery <dougm@nist.gov>Randy Bush <randy@psg.com>BGPSEC PotentialOptimizations for AS-PATH Prependingand Transparent Route Servers.bgpsec-00 Level Set
  • Requirements: Provide cryptographic assurance that:
  • Origin AS was authorized by IP holder to announce route.
  • Every AS in the AS_Path explicitly authorized the advertisement of the route to the subsequent AS in the AS_Path.
  • Semantics:
  • Each AS’s Signature computed over Target AS for the update (forward chaining of path) and previous AS Sig (backward chaining of authorization).
  • Expire Time & beaconing subject of another presentation …..
  • AS0 (origin) Path SignatureHash(…) Signed by Router Key AS0.rtr-xx  Sig0AS1 Path Signature Hash(…) Signed by RouterKey AS1.rtr-yy  Sig1Exp TimeNLRIAS0Algo IDAS1Sig0Sig1AS1Algo IDAS2bgpsec-00 Path_Sigs
  • Syntax:
  • BGPSEC Path_Signatures attribute elements correspond 1-1 with AS_Path attribute elements.
  • AS_Path attribute umodified, nor is Path data (ASNs) replicated in Path_Sig.
  • bgpsec-00 – focus on requirements and semantics – purposefully ignore syntax optimizations until we get the first two right.
  • See: draft-sriram-bgpsec-design-choices-00
  • BGPSEC Path_Signatures Attribute……..Exp TimeAlgo ID^A0.RtrCert ^A1.RtrCert Sig0 Sig1 ……..AS_SeqASN 0ASN 1BGP AS_PATH AttributeOptimizations / Enhancements
  • From recent WG discussions:
  • AS_Path Prepending– current 1-1 correspondence of elements would require repeating signatures when using Path prepending.
  • Transparent Route Servers: - AS_Path does not reflect the actual sequence of AS’s that the update traversed.
  • Going Forward:
  • Important to separate the requirement, semantics and syntax discussions of how we address these and future enhancements.
  • Requirement? – ensure BGPSEC doesn’t interfere with some current/proposed use case, or enhance BGPSEC to protect use case?
  • Depending upon which BGP services / capabilities / uses we are trying to preserve / protect there are numerous ways to spec solutions.
  • Strawman Approaches in response to recent discussions …
  • PrependingStrawman
  • Requirements:
  • Support current uses of prepending without incurring expense of repeating Path_Signature elements.
  • Use BGPSEC to protect prepended AS’s from modification.
  • Semantics:
  • Prepend Count (pCNT) included as input to ASx signature noting how many times ASx appears in the actual AS_PATH.
  • Normally pCNT=1.
  • AS0 (origin) Path SignatureHash(…) Signed by Router Key AS0.rtr-xx  Sig0AS1 Path Signature Hash(…) Signed by RouterKey AS1.rtr-yy  Sig1AS2Sig1Exp TimeNLRIAS0Algo IDpCNTAS1Sig0pCNTAS1Algo IDTransparent Route Servers
  • Use Case:
  • Multi-Lateral Peering where sender does not know all the receivers.
  • Router Server’s AS not included in AS_PATH so as to not contribute to the Path Length for purposes of downstream best path computation.
  • BGPSEC Issue:
  • BGPSEC speaker can’t forward sign to other RS customers – not peering with them directly, may not even explicitly know them, defeats the transmission efficiency of RS architectures.
  • Total transparency – violates the fundamental service of BGPSEC to provide a cryptographically verified sequence of route authorizations.
  • “Translucent” RS Strawman
  • Requirements:
  • Support current business/use model of transparent RS’s.
  • Use BGPSEC to protect / verify the complete AS_PATH (including RS AS) without impacting AS_Path_Length computations.
  • Be completely transparent when sending updates to non-BGPSEC peers.
  • Semantics:
  • RS AS fully participates in BGPSEC to/from its customer AS’s, including explicitly carrying the RS AS# in the update.
  • Use previously proposed Prepend Count (pCNT=0) to indicate that an AS is operating as a transparent RS.
  • BGPSEC validates complete AS_PATH, but pCNT=0 hops do not contribute to Path_Length.
  • When sending to non-BGPSEC peer, RS AS# is stripped.
  • Further Details …
  • Not important now … unless we agree on the requirements/semantics:
  • … if we do agree on the basic approach, then we can consider further details.
  • Tradeoffs between optimization and minimizing BGPSEC changes to current BGP attributes / behaviors.
  • Strawman Syntax:
  • Extend BGPSEC Path_Signatures Field to carry pCNT for each Sig.
  • Modify Sig generation / verification procedures to address pCNT.
  • Modify Path_Length computation on BGPSEC implementations to ignore pCNT=0 hops.
  • Add rules to strip RS AS when sending to non-BGPSEC peer.
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