BGPsec Operations: BGPsec Operational Considerations

Internet Engineering Task Force (IETF)                           R. Bush
Request for Comments: 8207                     Internet Initiative Japan
BCP: 211                                                  September 2017
Category: Best Current Practice
ISSN: 2070-1721


                   BGPsec Operational Considerations

Abstract

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

Status of This Memo

   This memo documents an Internet Best Current Practice.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   BCPs is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc8207.

Copyright Notice

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

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Table of Contents

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

1.  Introduction

   Origin validation based on the Resource Public Key Infrastructure
   (RPKI) [RFC6811] is in its early phases.  As BGPsec [RFC8205] 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 that this document
   attempts to describe.  As with most operational practices, they will
   likely change over time.

   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 Autonomous System's (AS's)
   eBGP-speaking border routers.  It is designed so that it can be used
   to protect announcements that 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.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Suggested Reading

   It is assumed that the reader understands BGP [RFC4271], BGPsec
   [RFC8205], the RPKI [RFC6480], the RPKI Repository Structure
   [RFC6481], and Route Origin Authorizations (ROAs) [RFC6482].

3.  RPKI Distribution and Maintenance

   The considerations for RPKI objects (Certificates, Certificate
   Revocation Lists (CRLs), manifests [RFC6481], and Ghostbusters
   Records [RFC6493]), Trust Anchor Locators (TALs) [RFC7730], cache
   behaviors of synchronization, 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 [KEY], 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
   Certification Authority (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 that there is
   no propagation delay for provisioning the new key.

5.  Within a Network

   BGPsec is spoken by edge routers in a network, specifically those
   that border other networks/ASes.

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

   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 that face more critical peers or upstreams or
   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 the 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 a 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 that 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 ASes 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 that support
   BGPsec.

7.  Routing Policy

   As BGPsec-signed paths cannot traverse non-BGPsec topology, partial
   BGPsec deployment forms islands of assured paths.  As islands grow to
   touch each other, they become larger islands.

   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 a 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 the
   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 that 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
   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 that 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 that are forward signed to R.  But
   the sending router cannot generate signatures to all the possible
   clients.  Therefore, a BGPsec-aware route server needs to validate
   the incoming BGPsec_PATH and to forward updates that can be validated
   by clients that 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
   [RFC8205].  The route server uses a pCount of 0 to not increase the
   effective AS hop count, thereby retaining the intent of
   'transparency'.

   If it is known that a BGPsec neighbor is a transparent route server,
   or otherwise may validly use a pCount of 0 (e.g., see [RFC8206]), the
   router SHOULD be configured to accept and process a received pCount
   of 0.  Routers MUST disallow a pCount of 0 by default.

   To prevent exposure of the internals of the 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 ASes are used.

8.  Notes

   For protection from attacks replaying BGP data on the order of a day
   or longer old, rekeying routers with new keys (previously)
   provisioned in the RPKI is sufficient.  For one approach, see
   [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
   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 that 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
   [RFC8205].

10.  IANA Considerations

   This document does not require any IANA actions.

11.  References

11.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC6493]  Bush, R., "The Resource Public Key Infrastructure (RPKI)
              Ghostbusters Record", RFC 6493, DOI 10.17487/RFC6493,
              February 2012, <https://www.rfc-editor.org/info/rfc6493>.

   [RFC6811]  Mohapatra, P., Scudder, J., Ward, D., Bush, R., and R.
              Austein, "BGP Prefix Origin Validation", RFC 6811,
              DOI 10.17487/RFC6811, January 2013,
              <https://www.rfc-editor.org/info/rfc6811>.

   [RFC7115]  Bush, R., "Origin Validation Operation Based on the
              Resource Public Key Infrastructure (RPKI)", BCP 185,
              RFC 7115, DOI 10.17487/RFC7115, January 2014,
              <https://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,
              <https://www.rfc-editor.org/info/rfc7730>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8205]  Lepinski, M., Ed. and K. Sriram, Ed., "BGPsec Protocol
              Specification", RFC 8205, DOI 10.17487/RFC8205, September
              2017, <http://www.rfc-editor.org/info/rfc8205>.

11.2.  Informative References

   [KEY]      Bush, R., Turner, S., and K. Patel, "Router Keying for
              BGPsec", Work in Progress, draft-ietf-sidr-rtr-keying-13,
              April 2017.

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,
              <https://www.rfc-editor.org/info/rfc4271>.

   [RFC5065]  Traina, P., McPherson, D., and J. Scudder, "Autonomous
              System Confederations for BGP", RFC 5065,
              DOI 10.17487/RFC5065, August 2007,
              <https://www.rfc-editor.org/info/rfc5065>.

   [RFC5905]  Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
              "Network Time Protocol Version 4: Protocol and Algorithms
              Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
              <https://www.rfc-editor.org/info/rfc5905>.

   [RFC6480]  Lepinski, M. and S. Kent, "An Infrastructure to Support
              Secure Internet Routing", RFC 6480, DOI 10.17487/RFC6480,
              February 2012, <https://www.rfc-editor.org/info/rfc6480>.

   [RFC6481]  Huston, G., Loomans, R., and G. Michaelson, "A Profile for
              Resource Certificate Repository Structure", RFC 6481,
              DOI 10.17487/RFC6481, February 2012,
              <https://www.rfc-editor.org/info/rfc6481>.

   [RFC6482]  Lepinski, M., Kent, S., and D. Kong, "A Profile for Route
              Origin Authorizations (ROAs)", RFC 6482,
              DOI 10.17487/RFC6482, February 2012,
              <https://www.rfc-editor.org/info/rfc6482>.

   [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, <https://www.rfc-editor.org/info/rfc6916>.

   [RFC8206]  George, W. and S. Murphy, "BGPsec Considerations for
              Autonomous System (AS) Migration", RFC 8206,
              DOI 10.17487/RFC8206, September 2017,
              <http://www.rfc-editor.org/info/rfc8206>.

   [ROLLOVER] Weis, B., Gagliano, R., and K. Patel, "BGPsec Router
              Certificate Rollover", Work in Progess,
              draft-ietf-sidrops-bgpsec-rollover-02, August 2017.

Acknowledgements

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

Author's Address

   Randy Bush
   Internet Initiative Japan
   5147 Crystal Springs
   Bainbridge Island, Washington  98110
   United States of America

   Email: randy@psg.com