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In: Auth48done
Network Working Group                                            R. Bush
Internet-Draft                                 Internet Initiative Japan
Intended status: Best Current Practice                   January 5, 2017
Expires: July 9, 2017


                   BGPsec Operational Considerations
                     draft-ietf-sidr-bgpsec-ops-16

Abstract

   Deployment of the BGPsec architecture and protocols has many
   operational considerations.  This document attempts to collect and
   present the most critical and universal.  It is expected to evolve as
   BGPsec is formalized and initially deployed.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to
   be interpreted as described in RFC 2119 [RFC2119] only when they
   appear in all upper case.  They may also appear in lower or mixed
   case as English words, without normative meaning.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on July 9, 2017.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents



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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Suggested Reading . . . . . . . . . . . . . . . . . . . . . .   3
   3.  RPKI Distribution and Maintenance . . . . . . . . . . . . . .   3
   4.  AS/Router Certificates  . . . . . . . . . . . . . . . . . . .   3
   5.  Within a Network  . . . . . . . . . . . . . . . . . . . . . .   3
   6.  Considerations for Edge Sites . . . . . . . . . . . . . . . .   4
   7.  Routing Policy  . . . . . . . . . . . . . . . . . . . . . . .   5
   8.  Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   7
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     12.1.  Normative References . . . . . . . . . . . . . . . . . .   7
     12.2.  Informative References . . . . . . . . . . . . . . . . .   8
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   Origin Validation based on the Resource Public Key Infrastructure
   (RPKI), [RFC6811], is in its early phases.  As BGPsec,
   [I-D.ietf-sidr-bgpsec-protocol] may require larger memory and/or more
   modern CPUs, it expected to be deployed incrementally over a longer
   time span.  BGPsec is a new protocol with many operational
   considerations which this document attempts to describe.  As with
   most operational practices, this document will likely evolve.

   BGPsec relies on widespread propagation of the RPKI [RFC6480].  How
   the RPKI is distributed and maintained globally and within an
   operator's infrastructure may be different for BGPsec than for origin
   validation.

   BGPsec needs to be spoken only by an AS's eBGP-speaking border
   routers.  It is designed so that it can be used to protect
   announcements which are originated by resource constrained edge
   routers.  This has special operational considerations, see Section 6.

   Different prefixes may have different timing and replay protection
   considerations.



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2.  Suggested Reading

   It is assumed that the reader understands BGP, see [RFC4271], BGPsec,
   [I-D.ietf-sidr-bgpsec-protocol], the RPKI, see [RFC6480], the RPKI
   Repository Structure, see [RFC6481], and Route Origin Authorizations
   (ROAs), see [RFC6482].

3.  RPKI Distribution and Maintenance

   The considerations for RPKI objects (Certificates, Certificate
   Revocation Lists (CRLs), manifests, Ghostbusters Records [RFC6481]),
   Trust Anchor Locators (TALs) [RFC7730], cache behaviours of
   synchronisation and validation from the section on RPKI Distribution
   and Maintenance of [RFC7115] apply.  Specific considerations relating
   to ROA objects do not apply to this document.

4.  AS/Router Certificates

   As described in [I-D.ietf-sidr-rtr-keying] BGPsec-speaking routers
   are capable of generating their own public/private key-pairs and
   having their certificates signed and published in the RPKI by the
   RPKI CA system, and/or are given public/private key-pairs by the
   operator.

   A site/operator may use a single certificate/key in all their
   routers, one certificate/key per router, or any granularity in
   between.

   A large operator, concerned that a compromise of one router's key
   would make other routers vulnerable, may deploy a more complex
   certificate/key distribution burden to reduce this exposure.

   At the other end of the spectrum, an edge site with one or two
   routers may choose to use a single certificate/key.

   In anticipation of possible key compromise, a prudent operator SHOULD
   pre-provision each router's 'next' key in the RPKI so there is no
   propagation delay for provisioning the new key.

5.  Within a Network

   BGPsec is spoken by edge routers in a network, those which border
   other networks/ASs.

   In an AS where edge routers speak BGPsec and therefore inject BGPsec
   paths into the iBGP, Route Reflectors MUST have BGPsec enabled if and
   only if there are eBGP speakers in their client cone, i.e. an RR
   client or the transitive closure of a client's customers.



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   A BGPsec capable router MAY use the data it receives to influence
   local policy within its network, see Section 7.  In deployment this
   policy should fit into the AS's existing policy, preferences, etc.
   This allows a network to incrementally deploy BGPsec enabled border
   routers.

   eBGP speakers which face more critical peers or up/downstreams would
   be candidates for early deployment.  Both securing one's own
   announcements and validating received announcements should be
   considered in partial deployment.

   An operator should be aware that BGPsec, as any other policy change,
   can cause traffic shifts in their network.  And, as with normal
   policy shift practice, a prudent operator has tools and methods to
   predict, measure, modify, etc.

   On the other hand, an operator wanting to monitor router loading,
   shifts in traffic, etc. might deploy incrementally while watching
   those and similar effects.

   BGPsec does not sign over communities, so they are not formally
   trustable.  Additionally, outsourcing verification is not prudent
   security practice.  Therefore an eBGP listener SHOULD NOT strongly
   trust unsigned security signaling, such as communities, received
   across a trust boundary.

6.  Considerations for Edge Sites

   An edge site which does not provide transit and trusts its
   upstream(s) may only originate a signed prefix announcement and not
   validate received announcements.

   An Operator might need to use hardware with limited resources.  In
   such cases, BGPsec protocol capability negotiation allows for a
   resource constrained edge router to hold only its own signing key(s)
   and sign its announcements, but not receive signed announcements.
   Therefore, the router would not have to deal with the majority of the
   RPKI, potentially saving the need for additional hardware.

   As the vast majority of ASs are stubs, and they announce the majority
   of prefixes, this allows for simpler and less expensive incremental
   deployment.  It may also mean that edge sites concerned with routing
   security will be attracted to upstreams which support BGPsec.








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7.  Routing Policy

   Unlike origin validation based on the RPKI, BGPsec marks a received
   announcement as Valid or Not Valid, there is no explicit NotFound
   state.  In some sense, an unsigned BGP4 path is the equivalent of
   NotFound.  How this is used in routing is up to the operator's local
   policy, similar to origin validation as in [RFC6811].

   As BGPsec will be rolled out over years and does not allow for
   intermediate non-signing edge routers, coverage will be spotty for a
   long time.  This presents a dilemma; should a router evaluating an
   inbound BGPsec_Path as Not Valid be very strict and discard it?  On
   the other hand, it might be the only path to that prefix, and a very
   low local-preference would cause it to be used and propagated only if
   there was no alternative.  Either choice is reasonable, but we
   recommend dropping because of the next point.

   Operators should be aware that accepting Not Valid announcements, no
   matter the local preference, will often be the equivalent of treating
   them as fully Valid.  Local preference affects only routes to the
   same set of destinations.  Consider having a Valid announcement from
   neighbor V for prefix 10.0.0.0/16 and an Not Valid announcement for
   10.0.666.0/24 from neighbor I.  If local policy on the router is not
   configured to discard the Not Valid announcement from I, then longest
   match forwarding will send packets to neighbor I no matter the value
   of local preference.

   Validation of signed paths is usually deployed at the eBGP edge.

   Local policy on the eBGP edge MAY convey the validation state of a
   BGP signed path through normal local policy mechanisms, e.g.  setting
   a BGP community for internal use, or modifying a metric value such as
   local-preference or multi-exit discriminator (MED).  Some may choose
   to use the large Local-Pref hammer.  Others may choose to let AS-Path
   rule and set their internal metric, which comes after AS-Path in the
   BGP decision process.

   As the mildly stochastic timing of RPKI propagation may cause version
   skew across routers, an AS Path which does not validate at router R0
   might validate at R1.  Therefore, signed paths that are Not Valid and
   yet propagated (because they are chosen as best path) MUST NOT have
   signatures stripped and MUST be signed if sent to external BGPsec
   speakers.

   This implies that updates which a speaker judges to be Not Valid MAY
   be propagated to iBGP peers.  Therefore, unless local policy ensures
   otherwise, a signed path learned via iBGP may be Not Valid.  If




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   needed, the validation state should be signaled by normal local
   policy mechanisms such as communities or metrics.

   On the other hand, local policy on the eBGP edge might preclude iBGP
   or eBGP announcement of signed AS Paths which are Not Valid.

   A BGPsec speaker receiving a path SHOULD perform origin validation
   per [RFC6811] and [RFC7115].

   A route server is usually 'transparent', i.e. does not insert an AS
   into the path so as not to increase the AS hop count and thereby
   affect downstream path choices.  But, with BGPsec, a client router R
   needs to be able to validate paths which are forward signed to R.
   But the sending router can not generate signatures to all the
   possible clients.  Therefore a BGPsec-aware route server needs to
   validate the incoming BGPsec_Path, and to forward updates which can
   be validated by clients which must therefore know the route server's
   AS.  This implies that the route server creates signatures per client
   including its own AS in the BGPsec_Path, forward signing to each
   client AS, see [I-D.ietf-sidr-bgpsec-protocol].  The route server
   uses pCount of zero to not increase the effective AS hop count,
   thereby retaining the intent of 'transparency'.

   If it is known that a BGPsec neighbor is not a transparent route
   server, or is otherwise validly using pCount=0 (e,g, see
   [I-D.ietf-sidr-as-migration]), and the router provides a knob to
   disallow a received pCount (of zero, that knob SHOULD be applied.
   Routers should disallow pCount 0 by default.

   To prevent exposure of the internals of BGP Confederations [RFC5065],
   a BGPsec speaker exporting to a non-member removes all intra-
   confederation Secure_Path segments.  Therefore signing within the
   confederation will not cause external confusion even if non-unique
   private ASs are used.

8.  Notes

   For protection from attacks replaying BGP data on the order of a day
   or longer old, re-keying routers with new keys (previously)
   provisioned in the RPKI is sufficient.  For one approach, see
   [I-D.ietf-sidr-bgpsec-rollover]

   A router that once negotiated (and/or sent) BGPsec should not be
   expected to always do so.

   Like the DNS, the global RPKI presents only a loosely consistent
   view, depending on timing, updating, fetching, etc.  Thus, one cache
   or router may have different data about a particular prefix or router



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   than another cache or router.  There is no 'fix' for this, it is the
   nature of distributed data with distributed caches.

   Operators who manage certificates SHOULD have RPKI GhostBuster
   Records (see [RFC6493]), signed indirectly by End Entity
   certificates, for those certificates on which others' routing depends
   for certificate and/or ROA validation.

   Operators should be aware of impending algorithm transitions, which
   will be rare and slow-paced, see [RFC6916].  They should work with
   their vendors to ensure support for new algorithms.

   As a router must evaluate certificates and ROAs which are time
   dependent, routers' clocks MUST be correct to a tolerance of
   approximately an hour.  The common approach is for operators to
   deploy servers that provide time service, such as [RFC5905], to
   client routers.

   If a router has reason to believe its clock is seriously incorrect,
   e.g. it has a time earlier than 2011, it SHOULD NOT attempt to
   validate incoming updates.  It SHOULD defer validation until it
   believes it is within reasonable time tolerance.

9.  Security Considerations

   This document describes operational considerations for the deployment
   of BGPsec.  The security considerations for BGPsec are described in
   [I-D.ietf-sidr-bgpsec-protocol].

10.  IANA Considerations

   This document has no IANA Considerations.

11.  Acknowledgments

   The author wishes to thank Thomas King, Arnold Nipper, and Alvaro
   Retana, and the BGPsec design group.

12.  References

12.1.  Normative References

   [I-D.ietf-sidr-bgpsec-protocol]
              Lepinski, M., "BGPSEC Protocol Specification", draft-ietf-
              sidr-bgpsec-protocol-07 (work in progress), February 2013.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.



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   [RFC6493]  Bush, R., "The Resource Public Key Infrastructure (RPKI)
              Ghostbusters Record", RFC 6493, February 2012.

   [RFC6811]  Mohapatra, P., Scudder, J., Ward, D., Bush, R., and R.
              Austein, "BGP Prefix Origin Validation", RFC 6811, January
              2013.

   [RFC7115]  Bush, R., "Origin Validation Operation Based on the
              Resource Public Key Infrastructure (RPKI)", BCP 185,
              RFC 7115, DOI 10.17487/RFC7115, January 2014,
              <http://www.rfc-editor.org/info/rfc7115>.

   [RFC7730]  Huston, G., Weiler, S., Michaelson, G., and S. Kent,
              "Resource Public Key Infrastructure (RPKI) Trust Anchor
              Locator", RFC 7730, DOI 10.17487/RFC7730, January 2016,
              <http://www.rfc-editor.org/info/rfc7730>.

12.2.  Informative References

   [I-D.ietf-sidr-as-migration]
              George, W. and S. Murphy, "BGPSec Considerations for AS
              Migration", draft-ietf-sidr-as-migration-06 (work in
              progress), December 2016.

   [I-D.ietf-sidr-bgpsec-rollover]
              Gagliano, R., Patel, K., and B. Weis, "BGPSEC router key
              rollover as an alternative to beaconing", draft-ietf-sidr-
              bgpsec-rollover-01 (work in progress), October 2012.

   [I-D.ietf-sidr-rtr-keying]
              Turner, S., Patel, K., and R. Bush, "Router Keying for
              BGPsec", draft-ietf-sidr-rtr-keying-01 (work in progress),
              February 2013.

   [RFC4271]  Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
              Protocol 4 (BGP-4)", RFC 4271, January 2006.

   [RFC5065]  Traina, P., McPherson, D., and J. Scudder, "Autonomous
              System Confederations for BGP", RFC 5065, August 2007.

   [RFC5905]  Mills, D., Martin, J., Burbank, J., and W. Kasch, "Network
              Time Protocol Version 4: Protocol and Algorithms
              Specification", RFC 5905, June 2010.

   [RFC6480]  Lepinski, M. and S. Kent, "An Infrastructure to Support
              Secure Internet Routing", RFC 6480, February 2012.





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   [RFC6481]  Huston, G., Loomans, R., and G. Michaelson, "A Profile for
              Resource Certificate Repository Structure", RFC 6481,
              February 2012.

   [RFC6482]  Lepinski, M., Kent, S., and D. Kong, "A Profile for Route
              Origin Authorizations (ROAs)", RFC 6482, February 2012.

   [RFC6916]  Gagliano, R., Kent, S., and S. Turner, "Algorithm Agility
              Procedure for the Resource Public Key Infrastructure
              (RPKI)", BCP 182, RFC 6916, DOI 10.17487/RFC6916, April
              2013, <http://www.rfc-editor.org/info/rfc6916>.

Author's Address

   Randy Bush
   Internet Initiative Japan
   5147 Crystal Springs
   Bainbridge Island, Washington  98110
   US

   Email: randy@psg.com






























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