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In: Auth48
SIDR                                                           W. George
Intended status: Standards Track                               S. Murphy
Expires: June 10, 2017                   SPARTA, Inc., a Parsons Company
                                                        December 7, 2016

                 BGPSec Considerations for AS Migration


   This document discusses considerations and methods for supporting and
   securing a common method for AS-Migration within the BGPSec protocol.

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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on June 10, 2017.

Copyright Notice

   Copyright (c) 2016 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
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   (http://trustee.ietf.org/license-info) in effect on the date of
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   2
     1.2.  Documentation note  . . . . . . . . . . . . . . . . . . .   3
   2.  General Scenario  . . . . . . . . . . . . . . . . . . . . . .   3
   3.  RPKI Considerations . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Origin Validation . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Path Validation . . . . . . . . . . . . . . . . . . . . .   5
       3.2.1.  Outbound announcements (PE-->CE)  . . . . . . . . . .   5
       3.2.2.  Inbound announcements (CE-->PE) . . . . . . . . . . .   6
   4.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Solution  . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     5.1.  Outbound (PE->CE) . . . . . . . . . . . . . . . . . . . .   8
     5.2.  Inbound (CE->PE)  . . . . . . . . . . . . . . . . . . . .   8
     5.3.  Other considerations  . . . . . . . . . . . . . . . . . .   9
     5.4.  Example . . . . . . . . . . . . . . . . . . . . . . . . .   9
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  13
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   8.  Note for RFC Editor . . . . . . . . . . . . . . . . . . . . .  14
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  14
     10.2.  Informative References . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   A method of managing a BGP Autonomous System Number (ASN) migration
   is described in RFC7705 [RFC7705].  Since it concerns the handling of
   AS_PATH attributes, it is necessary to ensure that the process and
   features are properly supported in BGPSec
   [I-D.ietf-sidr-bgpsec-protocol], because BGPSec is explicitly
   designed to protect against changes in the BGP AS_PATH, whether by
   choice, by misconfiguration, or by malicious intent.  It is critical
   that the BGPSec protocol framework is able to support this
   operationally necessary tool without creating an unacceptable
   security risk or exploit in the process.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

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1.2.  Documentation note

   This document uses Autonomous System Numbers (ASNs) from the range
   reserved for documentation as described in RFC 5398 [RFC5398].  In
   the examples used here, they are intended to represent Globally
   Unique ASNs, not ASNs reserved for private use as documented in RFC
   1930 [RFC1930] section 10.

2.  General Scenario

   This document assumes that the reader has read and understood the ASN
   migration method discussed in RFC7705 [RFC7705] including its
   examples (see section 2 of the referenced document), as they will be
   heavily referenced here.  The use case being discussed in the
   referenced document is as follows: For whatever the reason, a
   provider is in the process of merging two or more ASes, where
   eventually one subsumes the other(s).  BGP AS Confederations RFC 5065
   [RFC5065] is not enabled between the ASes, but a mechanism is being
   used to modify BGP's default behavior and allow the migrating
   Provider Edge router (PE) to masquerade as the old ASN for the
   Provider Edge to Customer Edge (PE-CE) eBGP session, or to manipulate
   the AS_PATH, or both.  While BGPSec [I-D.ietf-sidr-bgpsec-protocol]
   does have a method to handle standard confederation implementations,
   it is not applicable in this exact case.  This migration requires a
   slightly different solution in BGPSec than for a standard
   confederation because unlike in a confederation, eBGP peers may not
   be peering with the "correct" external ASN, and the forward-signed
   updates are for a public ASN, rather than a private one, so there is
   no expectation that the BGP speaker would strip the affected
   signatures before propagating the route to its eBGP neighbors.

   In the following examples (section 5.4) (Section 5.4), AS64510 is
   being subsumed by AS64500, and both ASNs represent a Service Provider
   (SP) network (see Figures 1 & 2 in RFC7705 [RFC7705]).  AS64496 and
   64499 represent end customer networks.  References to PE, CE, and P
   routers mirror the diagrams and references in the above cited draft.

3.  RPKI Considerations

   The methods and implementation discussed in RFC7705 [RFC7705] are
   widely used during network integrations resulting from mergers and
   acquisitions, as well as network redesigns, and therefore it is
   necessary to support this capability on any BGPSec-enabled routers/
   ASNs.  What follows is a discussion of the potential issues to be
   considered regarding how ASN-migration and BGPSec
   [I-D.ietf-sidr-bgpsec-protocol] validation might interact.

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   One of the primary considerations for this document and migration is
   that service providers (SPs) rarely stop after one
   merger/acquisition/divestiture, and end up accumulating several
   legacy ASNs over time.  Since they are using methods to migrate that
   are transparent to and therefore do not require coordination with
   customers, they do not have a great deal of control over the length
   of the transition period as they might with something completely
   under their administrative control (e.g. a key roll).  Because they
   are not forcing a simultaneous migration (i.e. both ends switch to
   the new ASN at an agreed-upon time), there is no incentive for a
   given customer to complete the move from the old ASN to the new.
   This leaves many SPs with multiple legacy ASNs which don't go away
   very quickly, if at all.  As solutions were being proposed for RPKI
   implementations to solve this transition case, the WG carefully
   considered operational complexity and hardware scaling issues
   associated with maintaining multiple legacy ASN keys on routers
   throughout the combined network.  While SPs who choose to remain in
   this transition phase indefinitely invite added risks because of the
   operational complexity and scaling considerations associated with
   maintaining multiple legacy ASN keys on routers throughout the
   combined network, saying "don't do this" is of limited utility as a
   solution.  As a result, this solution attempts to minimize the
   additional complexity during the transition period, on the assumption
   that it will likely be protracted.  Note: While this document
   primarily discusses service provider considerations, it is not solely
   applicable to SPs, as enterprises often migrate between ASNs using
   the same functionality.  What follows is a discussion of origin and
   path validation functions and how they interact with ASN migrations.

3.1.  Origin Validation

   Route Origin Validation as defined by RFC 6480 [RFC6480] does not
   modification to enable AS migration, as the existing protocol and
   procedure allows for a solution.  In the scenario discussed in RFC
   7705 [RFC7705], AS64510 is being replaced by AS64500.  If there are
   any existing routes originated by AS64510 on the router being moved
   into the new ASN, this simply requires generating new Route
   Origination Authorizations (ROAs) for the routes with the new ASN and
   treating them as new routes to be added to AS64500.  However, we also
   need to consider the situation where one or more other PEs are still
   in AS64510, and are originating one or more routes that may be
   distinct from any that the router under migration is originating.
   PE1 (which is now a part of AS64500 and instructed to use Replace Old
   AS as defined in RFC 7705 [RFC7705] to remove AS64510 from the path)
   needs to be able to properly handle routes originated from AS64510.
   If the route now shows up as originating from AS64500, any downstream
   peers' validation check will fail unless a ROA is *also* available
   for AS64500 as the origin ASN.  In addition to generating a ROA for

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   65400 for any prefixes originated by the router being moved, it may
   be necessary to generate ROAs for 65400 for prefixes that are
   originating on routers still in 65410, since the AS replacement
   function will change the origin AS in some cases.  This means that
   there will be multiple ROAs showing different ASes authorized to
   orignate the same prefixes until all routers originating prefixes
   from AS64510 are migrated to AS64500.  Multiple ROAs of this type are
   permissible per RFC 6480 [RFC6480] section 3.2, and so managing
   origin validation during a migration like this is merely applying the
   defined case where a set of prefixes are originated from more than
   one ASN.  Therefore, for each ROA that authorizes the old ASN (e.g.
   AS64510) to originate a prefix, a new ROA MUST also be created that
   authorizes the replacing ASN (e.g.  AS64500) to originate the same

3.2.  Path Validation

   BGPSec Path Validation requires that each router in the AS Path
   cryptographically sign its update to assert that "Every AS on the
   path of ASes listed in the update message has explicitly authorized
   the advertisement of the route to the subsequent AS in the path."
   (see intro of [I-D.ietf-sidr-bgpsec-protocol]) Since the referenced
   AS migration technique is explicitly modifying the AS_PATH between
   two eBGP peers who are not coordinating with one another (are not in
   the same administrative domain), no level of trust can be assumed,
   and therefore it may be difficult to identify legitimate manipulation
   of the AS_PATH for migration activities when compared to manipulation
   due to misconfiguration or malicious intent.

3.2.1.  Outbound announcements (PE-->CE)

   When PE1 is moved from AS64510 to AS64500, it will be provisioned
   with the appropriate keys for AS64500 to allow it to forward-sign
   routes using AS64500.  However, there is no guidance in the BGPSec
   protocol specification [I-D.ietf-sidr-bgpsec-protocol] on whether or
   not the forward-signed ASN value is required to match the configured
   remote AS to validate properly.  That is, if CE1's BGP session is
   configured as "remote AS 64510", the presence of "local AS 64510" on
   PE1 will ensure that there is no ASN mismatch on the BGP session
   itself, but if CE1 receives updates from its remote neighbor (PE1)
   forward-signed from AS64500, there is no guidance as to whether the
   BGPSec validator on CE1 still considers those valid by default.
   RFC4271 [RFC4271] section 6.3 mentions this match between the ASN of
   the peer and the AS_PATH data, but it is listed as an optional
   validation, rather than a requirement.  We cannot assume that this
   mismatch will be allowed by vendor implementations and thus using it
   as a means to solve this migration case is likely to be problematic.

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3.2.2.  Inbound announcements (CE-->PE)

   Inbound is more complicated, because the CE doesn't know that PE1 has
   changed ASNs, so it is forward-signing all of its routes with
   AS64510, not AS64500.  The BGPSec speaker cannot manipulate previous
   signatures, and therefore cannot manipulate the previous AS Path
   without causing a mismatch that will invalidate the route.  If the
   updates are simply left intact, the ISP would still need to publish
   and maintain valid and active public-keys for AS 64510 if it is to
   appear in the BGPSec_Path_Signature in order that receivers can
   validate the BGPSEC_Path_Signature arrived intact/whole.  However, if
   the updates are left intact, this will cause the AS Path length to be
   increased, which is unacceptable as discussed in RFC7705 [RFC7705].

4.  Requirements

   In order to be deployable, any solution to the described problem
   needs to consider the following requirements, listed in no particular
   order.  BGPSec:

   o  MUST support AS Migration for both inbound and outbound route
      announcements (see Section 3.2.1 and 3.2.2) without reducing
      BGPSec's protections for route path

   o  MUST NOT require any reconfiguration on the remote eBGP neighbor

   o  SHOULD NOT require global (i.e. network-wide) configuration
      changes to support migration.  The goal is to limit required
      configuration changes to the devices (PEs) being migrated.

   o  MUST NOT lengthen AS Path during migration

   o  MUST operate within existing trust boundaries e.g. can't expect
      remote side to accept pCount=0 (see Section 4.2 of
      [I-D.ietf-sidr-bgpsec-protocol]) from untrusted/non-confed

5.  Solution

   As noted in [I-D.ietf-sidr-bgpsec-protocol], section 4.2, BGPSec
   already has a solution for hiding ASNs where increasing the AS Path
   length is undesirable.  So a simple solution would be to retain the
   keys for AS64510 on PE1, and forward-sign towards CE1 with AS64510
   and pCount=0.  However, this would mean passing a pCount=0 between
   two ASNs that are in different administrative and trust domains such
   that it could represent a significant attack vector to manipulate
   BGPSec-signed paths.  The expectation for legitimate instances of

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   pCount=0 (to make a route-server that is not part of the transit path
   invisible) is that there is some sort of existing trust relationship
   between the operators of the route-server and the downstream peers
   such that the peers could be explicitly configured by policy to
   accept pCount=0 announcements only on the sessions where they are
   expected.  For the same reason that things like "Local AS" [RFC7705]
   are used for ASN migration without end customer coordination, it is
   unrealistic to assume any sort of coordination between the SP and the
   administrators of CE1 to ensure that they will by policy accept
   pCount=0 signatures during the transition period, and therefore this
   is not a workable solution.

   A better solution presents itself when considering how to handle
   routes coming from the CE toward the PE, where the routes are
   forward-signed to AS64510, but will eventually need to show AS64500
   in the outbound route announcement.  Because both AS64500 and AS64510
   are in the same administrative domain, a signature from AS64510
   forward-signed to AS64500 with pCount=0 would be acceptable as it
   would be within the appropriate trust boundary so that each BGP
   speaker could be explicitly configured to accept pCount=0 where
   appropriate between the two ASNs.  At the very simplest, this could
   potentially be used at the eBGP boundary between the two ASNs during
   migration.  Since the AS_PATH manipulation described above usually
   happens at the PE router on a per-session basis, and does not happen
   network-wide simultaneously, it is not generally appropriate to apply
   this AS hiding technique across all routes exchanged between the two
   ASNs, as it may result in routing loops and other undesirable
   behavior.  Therefore the most appropriate place to implement this is
   on the local PE that still has eBGP sessions with peers expecting to
   peer with AS64510 (using the transition mechanisms detailed in
   RFC7705 [RFC7705]).  Since that PE has been moved to AS64500, it is
   not possible for it to forward-sign AS64510 with pCount=0 without
   some minor changes to the BGPSec behavior to address this use case.

   AS migration is using AS_PATH and remote AS manipulation to act as if
   a PE under migration exists simultaneously in both ASNs even though
   it is only configured with one global ASN.  This document describes
   applying a similar technique to the BGPSec signatures generated for
   routing updates processed through this migration machinery.  Each
   routing update that is received from or destined to an eBGP neighbor
   that is still using the old ASN (64510) will be signed twice, once
   with the ASN to be hidden and once with the ASN that will remain
   visible.  In essence, we are treating the update as if the PE had an
   internal BGP hop and the update was passed across an eBGP session
   between AS64500 and AS64510, configured to use and accept pCount=0,
   while eliminating the processing and storage overhead of creating an
   actual eBGP session between the two ASNs within the PE router.  This
   will result in a properly secured AS Path in the affected route

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   updates, because the PE router will be provisioned with valid keys
   for both AS64500 and AS64510.  An important distinction here is that
   while AS migration under standard BGP4 is manipulating the AS_PATH
   attribute, BGPSec uses an attribute called the Secure_Path (see
   Section 3.1 of [I-D.ietf-sidr-bgpsec-protocol]), and BGPSec capable
   neighbors do not exchange AS_PATH information in their route
   announcements.  However, a BGPSec neighbor peering with a non-BGPSec-
   capable neighbor will use the information found in Secure_Path to
   reconstruct a standard AS_PATH for updates sent to that neighbor.
   Unlike in Secure_Path where the ASN to be hidden is still present,
   but ignored when considering AS Path (due to pCount=0), when
   reconstructing an AS_PATH for a non-BGPSec neighbor, the pCount=0
   ASNs will not appear in the AS_PATH at all (see section 4.4 of the
   [I-D.ietf-sidr-bgpsec-protocol]).  This document is not changing
   existing AS_PATH reconstruction behavior, merely highlighting it for

   The procedure to support AS Migration in BGPSec is slightly different
   depending on whether the PE under migration is receiving the routes
   from one of its eBGP peers ("inbound" as in section 3.2.2) or
   destined toward the eBGP peers ("outbound" as in section 3.2.1).

5.1.  Outbound (PE->CE)

   When a PE router receives an update destined for an eBGP neighbor
   that is locally configured with AS-migration mechanisms as discussed
   in RFC7705 [RFC7705], it MUST generate a valid BGPSec signature as
   defined in [I-D.ietf-sidr-bgpsec-protocol] for _both_ configured
   ASNs.  It MUST generate a signature from the new (global) ASN forward
   signing to the old (local) ASN with pCount=0, and then it MUST
   generate a forward signature from the old (local) ASN to the target
   eBGP ASN with pCount=1 as normal.

5.2.  Inbound (CE->PE)

   When a PE router receives an update from an eBGP neighbor that is
   locally configured with AS-migration mechanisms (i.e. the opposite
   direction of the previous route flow), it MUST generate a signature
   from the old (local) ASN forward signing to the new (global) ASN with
   pCount=0.  It is not necessary to generate the second signature from
   the new (global) ASN because the Autonomous System Border Router
   (ASBR) will generate that when it forward signs towards its eBGP
   peers as defined in normal BGPSec operation.  Note that a signature
   is not normally added when a routing update is sent across an iBGP
   session.  The requirement to sign updates in iBGP represents a change
   to the normal behavior for this specific AS-migration scenario only.

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5.3.  Other considerations

   In this case, the PE is adding BGPSec attributes to routes received
   from or destined to an iBGP neighbor, and using pCount=0 to mask
   them.  While this is not prohibited by BGPSec
   [I-D.ietf-sidr-bgpsec-protocol], BGPSec-capable routers that receive
   updates from BGPSec-enabled iBGP neighbors MUST accept updates with
   new (properly-formed) BGPSec attributes, including the presence of
   pCount=0 on a previous signature, or they will interfere with this
   method.  In similar fashion, any BGPSec-capable route-reflectors in
   the path of these updates MUST reflect them transparently to their
   BGPSec-capable clients.

   In order to secure this set of signatures, the PE router MUST be
   provisioned with valid keys for _both_ configured ASNs (old and new),
   and the key for the old ASN MUST be kept valid until all eBGP
   sessions are migrated to the new ASN.  Downstream neighbors will see
   this as a valid BGPSec path, as they will simply trust that their
   upstream neighbor accepted pCount=0 because it was explicitly
   configured to do so based on a trust relationship and business
   relationship between the upstream and its neighbor (the old and new

   Additionally, section 4 of RFC7705 [RFC7705] discusses methods in
   which AS migrations can be completed for iBGP peers such that a
   session between two routers will be treated as iBGP even if the
   neighbor ASN is not the same ASN on each peer's global configuration.
   As far as BGPSec is concerned, this requires the same procedure as
   when the routers migrating are applying AS migration mechanisms to
   eBGP peers, but the router functioning as the "ASBR" between old and
   new ASN is different.  In eBGP, the router being migrated has direct
   eBGP sessions to the old ASN and signs from old ASN to new with
   pCount=0 before passing the update along to additional routers in its
   global (new) ASN.  In iBGP, the router being migrated is receiving
   updates (that may have originated either from eBGP neighbors or other
   iBGP neighbors) from its downstream neighbors in the old ASN, and
   MUST sign those updates from old ASN to new with pCount=0 before
   sending them on to other peers.

5.4.  Example

   The following example will illustrate the method being used above.
   As with previous examples, PE1 is the router being migrated, AS64510
   is the old ASN, which is being subsumed by AS64500, the ASN to be
   permanently retained. 64505 is another external peer, used to
   demonstrate what the announcements will look like to a third party
   peer that is not part of the migration.  Some additional notation is
   used to delineate the details of each signature as follows:

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   The origin BGPSEC signature attribute takes the form: sig(<Target
   ASN>, Origin ASN, pCount, NLRI Prefix) key

   Intermediate BGPSEC signature attributes take the form: sig(<Target
   ASN>, Signer ASN, pCount, <most recent sig field>) key

   Equivalent AS_PATH refers to what the AS_PATH would look like if it
   was reconstructed to be sent to a non-BGPSec peer, while Secure_Path
   shows the AS Path as represented between BGPSec peers.

   Note: The representation of signature attribute generation is being
   simplified here somewhat for the sake of brevity; the actual details
   of the signing process are as described Sections 4.1 and 4.2 in
   [I-D.ietf-sidr-bgpsec-protocol].  For example, what is covered by the
   signature also includes Flags, Algorithm Suite ID, NLRI length, etc.
   Also, the key is not carried in the update, instead the SKI is

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   Before Merger

           ISP B                     ISP A
 CE-1 <--- PE-1 <------------------- PE-2 <--- CE-2
 64496     Old_ASN: 64510   Old_ASN: 64500     64499

 CE-2 to PE-2:  sig(<64500>, O=64499, pCount=1, N)K_64499-CE2  [sig1]
                Equivalent AS_PATH=(64499)

 PE-2 to 64505: sig(<64505>, 64500, pCount=1, <sig1>)K_64500-PE2  [sig2]
                sig(<64500>, 64499, pCount=1, N)K_64499-CE2  [sig1]
                Equivalent AS_PATH=(64500,64499)

 PE-2 to PE-1:  sig(<64510>, 64500, pCount=1, <sig1>)K_64500-PE2  [sig3]
                sig(<64500>, 64499, pCount=1, N)K_64499-CE2  [sig1]
                Equivalent AS_PATH=(64500,64499)

 PE-1 to CE-1:  sig(<64496>, 64510, pCount=1, <sig3>)K_64510-PE1  [sig4]
                sig(<64510>, 64500, pCount=1, <sig1>)K_64500-PE2  [sig3]
                sig(<64500>, 64499, pCount=1, N)K_64499-CE2  [sig1]
                Equivalent AS_PATH= (64510,64500,64499)

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   Migrating, route flow outbound PE-1 to CE-1

          ISP A'                    ISP A'
CE-1 <--- PE-1 <------------------- PE-2 <--- CE-2
64496     Old_ASN: 64510   Old_ASN: 64500     64499
          New_ASN: 64500   New_ASN: 64500

CE-2 to PE-2:  sig(<64500>, 64499, pCount=1, N)K_64499-CE2  [sig11]
               Equivalent AS_PATH=(64499)

PE-2 to 64505: sig(<64505>, 64500, pCount=1, <sig11>)K_64500-PE2  [sig12]
               sig(<64500>, 64499, pCount=1, N)K_64499-CE2  [sig11]
               Equivalent AS_PATH=(64500,64499)

PE-2 to PE-1:  sig(<64500>, 64499, pCount=1, N)K_64499-CE2  [sig11]
               Equivalent AS_PATH=(64499)
#PE-2 sends to PE-1 (in iBGP) the exact same update
#as received from AS64499.

PE-1 to CE-1:  sig(<64496>, 64510, pCount=1, <sig13>)K_64510-PE1  [sig14]
               sig(<64510>, 64500, pCount=0, <sig11>)K_64500-PE2  [sig13]
               sig(<64500>, 64499, pCount=1, N)K_64499-CE2  [sig11]
               Equivalent AS_PATH=(64510,64499)
               Secure_Path=(64510, 64500(pCount=0),64499)
               length=sum(pCount)=2 (length is NOT 3)
#PE1 adds [sig13] acting as AS64500
#PE1 accepts [sig13] with pCount=0 acting as AS64510,
#as it would if it received sig13 from an eBGP peer

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   Migrating, route flow inbound CE-1 to PE-1

          ISP A'                    ISP A'
CE-1 ---> PE-1 -------------------> PE-2 ---> CE-2
64496     Old_ASN: 64510   Old_ASN: 64500     64499
          New_ASN: 64500   New_ASN: 64500

CE-1 to PE-1:  sig(<64510>, 64496, pCount=1, N)K_64496-CE1   [sig21]
               Equivalent AS_PATH=(64496)

PE-1 to PE-2:  sig(<64500>, 64510, pCount=0, <sig21>)K_64510-PE1  [sig22]
               sig(<64510>, 64496, pCount=1, N)K_64496-CE1   [sig21]
               Equivalent AS_PATH=(64496)
               Secure_Path=(64510 (pCount=0),64496)
               length=sum(pCount)=1 (length is NOT 2)
#PE1 adds [sig22] acting as AS64510
#PE1 accepts [sig22] with pCount=0 acting as AS64500,
#as it would if it received sig22 from an eBGP peer

PE-2 to 64505: sig(<64505>, 64500, pCount=1, <sig22>)K_64500-PE2  [sig23]
               sig(<64500>, 64510, pCount=0, <sig21>)K_64510-PE1  [sig22]
               sig(<64510>, 64496, pCount=1, N)K_64496-CE1   [sig21]
               Equivalent AS_PATH=(64500,64496)
               Secure_Path=(64500,64510 (pCount=0), 64496)
               length=sum(pCount)=2 (length is NOT 3)

PE-2 to CE-2:  sig(<64499>, 64500, pCount=1, <sig22>)K_64500-PE2  [sig24]
               sig(<64500>, 64510, pCount=0, <sig21>)K_64510-PE1  [sig22]
               sig(<64510>, 64496, pCount=1, N)K_64496-CE1   [sig21]
               Equivalent AS_PATH=(64500,64496)
               Secure_Path=(64500, 64510 (pCount=0), 64496)
               length=sum(pCount)=2 (length is NOT 3)

6.  Acknowledgements

   Thanks to Kotikalapudi Sriram, Shane Amante, Warren Kumari, Terry
   Manderson, Keyur Patel, Alia Atlas, and Alvaro Retana for their
   review comments.

   Additionally, the solution presented in this document is an amalgam
   of several SIDR interim meeting discussions plus a discussion at
   IETF85, collected and articulated thanks to Sandy Murphy.

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7.  IANA Considerations

   This memo includes no request to IANA.

8.  Note for RFC Editor

   This section can be removed prior to publication.

   RFC Editor - this document updates draft-ietf-sidr-bgpsec-protocol,
   but the normal Updates= metadata method cannot be used until an RFC
   number is assigned to the document being updated.  Please ensure that
   the metadata is corrected when the bgpsec-protocol document has been
   assigned an RFC number.

9.  Security Considerations

   RFC7705 [RFC7705] discusses a process by which one ASN is migrated
   into and subsumed by another.  Because this process involves
   manipulating the AS_Path in a BGP route to make it deviate from the
   actual path that it took through the network, this migration process
   is attempting to do exactly what BGPSec is working to prevent.
   BGPSec MUST be able to manage this legitimate use of AS_Path
   manipulation without generating a vulnerability in the RPKI route
   security infrastructure, and this document was written to define the
   method by which the protocol can meet this need.

   The solution discussed above is considered to be reasonably secure
   from exploitation by a malicious actor because it requires both
   signatures to be secured as if they were forward-signed between two
   eBGP neighbors.  This requires any router using this solution to be
   provisioned with valid keys for both the migrated and subsumed ASN so
   that it can generate valid signatures for each of the two ASNs it is
   adding to the path.  If the AS's keys are compromised, or zero-length
   keys are permitted, this does potentially enable an AS_PATH
   shortening attack, but these are existing security risks for BGPSec.

10.  References

10.1.  Normative References

              Lepinski, M. and K. Sriram, "BGPsec Protocol
              Specification", draft-ietf-sidr-bgpsec-protocol-20 (work
              in progress), December 2016.

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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC7705]  George, W. and S. Amante, "Autonomous System Migration
              Mechanisms and Their Effects on the BGP AS_PATH
              Attribute", RFC 7705, DOI 10.17487/RFC7705, November 2015,

10.2.  Informative References

   [RFC1930]  Hawkinson, J. and T. Bates, "Guidelines for creation,
              selection, and registration of an Autonomous System (AS)",
              BCP 6, RFC 1930, DOI 10.17487/RFC1930, March 1996,

   [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,

   [RFC5065]  Traina, P., McPherson, D., and J. Scudder, "Autonomous
              System Confederations for BGP", RFC 5065,
              DOI 10.17487/RFC5065, August 2007,

   [RFC5398]  Huston, G., "Autonomous System (AS) Number Reservation for
              Documentation Use", RFC 5398, DOI 10.17487/RFC5398,
              December 2008, <http://www.rfc-editor.org/info/rfc5398>.

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

Authors' Addresses

   Wesley George

   Email: wesgeorge@puck.nether.net

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   Sandy Murphy
   SPARTA, Inc., a Parsons Company
   7110 Samuel Morse Drive
   Columbia, MD  21046

   Phone: +1 443-430-8000
   Email: sandy@tislabs.com

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