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Secure Inter-Domain Routing                                   R. Barnes
Working Group                                                   S. Kent
Internet Draft                                         BBN Technologies
Intended status: Informational                        February 23, 2007
Expires: August 2007

           An Infrastructure to Support Secure Internet Routing

Status of this Memo

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   BCP 79.

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Copyright Notice

   Copyright (C) The IETF Trust (2007).


   This document describes an architecture for an infrastructure to
   support secure Internet routing. The foundation of this architecture
   is a public key infrastructure (PKI) that represents the allocation
   hierarchy of IP address space and Autonomous System Numbers;

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   certificates from this PKI are used to verify signed objects that
   authorize autonomous systems to originate routes for specified IP
   address prefixes. The data objects that comprise the PKI, as well as
   other signed objects necessary for secure routing, are stored and
   disseminated through a distributed repository system. This document
   also describes at a high level how this architecture can be used to
   add security features to common operations such as IP address space
   allocation and route filter construction.

Conventions used in this document

   In examples, "C:" and "S:" indicate lines sent by the client and
   server respectively.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC-2119 [1].

Table of Contents

   1. Introduction...................................................3
   2. PKI for Internet Number Resources..............................4
      2.1. Role in the overall architecture..........................4
      2.2. CA Certificates...........................................5
      2.3. End-Entity Certificates...................................5
      2.4. Trust Anchors.............................................6
   3. Route Origination Authorizations...............................6
      3.1. Role in the overall architecture..........................7
      3.2. Syntax and semantics......................................7
      3.3. Revocation................................................8
   4. Repository system..............................................8
      4.1. Role in the overall architecture..........................9
      4.2. Contents and structure....................................9
      4.3. Access protocols.........................................10
      4.4. Access control...........................................10
   5. Common Operations.............................................11
      5.1. Certificate issuance.....................................11
      5.2. ROA management...........................................12
         5.2.1. Single-homed subscribers (without portable allocations)
         5.2.2. Multi-homing........................................13
         5.2.3. Portable allocations................................13
      5.3. Route filter construction................................13
   6. Security Considerations.......................................14
   7. IANA Considerations...........................................14
   8. Acknowledgments...............................................14

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   9. References....................................................15
      9.1. Normative References.....................................15
      9.2. Informative References...................................15
   Author's Addresses...............................................15
   Intellectual Property Statement..................................16
   Disclaimer of Validity...........................................16

1. Introduction

   This document describes an architecture for an infrastructure to
   support improved security for BGP routing [2] for the Internet.  The
   architecture described by this document supports, at a minimum, two
   types of routing security: It enables an entity to verifiably assert
   that it is the legitimate holder of a set IP addresses or a set of
   Autonomous System (AS) numbers, and it allows the holder of IP
   address space to explicitly and verifiably authorize an AS to
   originate routes to that address space.  In addition to these initial
   applications, however, this architecture could also support, without
   extension, more advanced security protocols such as S-BGP [7] or
   soBGP [8].  This architecture is applicable to routing of both IPv4
   and IPv6 datagrams.

   In order to facilitate deployment, the architecture takes advantage
   of existing technologies and practices.  The structure of the
   architecture corresponds to the existing resource allocation
   structure, so that management of this architecture is a natural
   extension of the resource-management functions of organizations that
   are already responsible for IP address and AS number resource
   allocation. Likewise, existing resource allocation and revocation
   practices have well-defined correspondents in this architecture.  To
   ease implementation, existing IETF standards are used wherever
   possible; for example, extensive use is made of the X.509 certificate
   profile defined by PKIX [3] and the extensions for IP Addresses and
   AS numbers defined in RFC 3779 [4].

   The architecture is comprised of three main components: An X.509
   public-key infrastructure (PKI) where certificates attest to holdings
   of IP address space and AS numbers; signed objects called Route
   Origination Authorizations (ROAs) that enable an address space holder
   to explicitly authorize an AS to originate routes to portions of the
   IP address space; and a distributed repository system that makes
   these objects available for use by ISPs in making routing decisions.
   These three basic components enable several security functions; this
   document describes how they can be used to improve route filter
   generation, and to perform several other common operations in such a
   way as to make them cryptographically verifiable.

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2. PKI for Internet Number Resources

   Because the holder of a block IP address space is entitled to define
   the topological destination of IP datagrams whose destinations fall
   within that block, decisions about inter-domain routing are
   inherently based on knowledge the allocation of the IP address space.
   Thus, a basic function of this architecture is to provide
   cryptographically verifiable attestations as to these allocations. In
   current practice, the allocation of IP address is hierarchic: The
   holder of a set of IP addresses may sub-allocate portions of that
   set, either to itself (e.g., to a particular unit of the same
   organization), or to another organization.  Because of this
   structure, IP address allocations can be described naturally by a
   hierarchic public-key infrastructure, in which each certificate
   attests to an allocation of IP addresses, and signing of subordinate
   certificates corresponds to sub-allocation of IP addresses.  The
   above reasoning holds true for AS number resources as well, with the
   difference that, by convention, AS numbers may not be sub-allocated
   except by registries. Thus allocations of both IP addresses and AS
   numbers can be expressed by the same PKI.  Such a PKI is a central
   component of this architecture.

2.1. Role in the overall architecture

   Certificates in this PKI are called Resource Certificate, and conform
   to the certificate profile for such certificates [5].  Resource
   certificates attest to the allocation by the (certificate) issuer of
   IP addresses or AS numbers to the subject.  They do this by binding
   the public key contained in the Resource Certificate to the IP
   addresses or AS numbers included in the certificate's IP Address
   Delegation or AS Identifier Delegation Extensions.  An important
   property of this PKI is that the names assigned to certificate
   issuers and subjects are not intended to be meaningful; this is in
   contrast to most PKIs where considerable effort is expended to ensure
   that the subject name in a certificate is properly associated with
   the entity that holds the private key corresponding to the public key
   in the certificate. This PKI is different because it is an
   authorization PKI, not an authentication PKI. Because issuers need
   not verify the right of an entity to use a subject name in a
   certificate, they avoid the costs and liabilities of such
   verification. This makes it easier for these entities to take on the
   additional role of CA. Only the basic PKI requirement, that a CA not
   associate the same name with two distinct subjects to whom it issues
   certificates, is imposed.

   The certificates in the PKI assert the basic facts on which the rest
   of the infrastructure operates.  Certificates within the CA hierarchy

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   attest to IP address space and AS number holdings.  End-entity
   certificates are issued by resource holders to delegate the authority
   attested by their allocation certificates, the primary use for this
   being the signing of ROAs.  These certificates and corresponding
   certificate revocation lists will comprise a significant portion of
   the data stored in the repository system.

2.2. CA Certificates

   Any holder of Internet Number Resources who is authorized to sub-
   allocate them must be able to issue Resource Certificates to
   correspond to these sub-allocations.  Thus, for example, CA
   certificates will be associated with each of the Regional Internet
   Registries, National Internet Registries, and Local Internet
   Registries, as well as with all ISPs.  A CA certificate is also
   necessary for a resource holder to issue ROAs (because it must also
   issue the corresponding end-entity certificates used to validate
   ROAs), so many subscribers also will need to have CA certificates for
   their allocations (in particular, multi-homed subscribers, and
   subscribers with portable allocations).

   Each Resource Certificate attests to an allocation of resources to
   its holder, so entities that have allocations from multiple sources
   will have multiple CA certificates. (A CA also may issue distinct
   certificates for each distinct allocation to the same entity, if the
   issuer and the resource holder agree that such an arrangement will
   facilitate management and use of the certificates.)

2.3. End-Entity Certificates

   Although the private key corresponding to public key contained in an
   end-entity certificate is not used to sign other certificates in the
   PKI, the primary function of end-entity certificates in this PKI is
   the verification of signed objects that relate to the usage of the
   resources described in the certificate, e.g., ROAs.  For this
   purpose, there is a one-to-one correspondence between end-entity
   certificates and signed objects, i.e., the private key corresponding
   to each end-entity certificate is used to sign exactly one object,
   and each object is signed with one key.  This property allows the PKI
   itself to be used to revoke these signed objects. When the end-entity
   certificate used to sign an object has been revoked, the signature on
   that object (and any corresponding assertions) will be considered
   invalid, so a signed object can be effectively revoked by revoking
   the end-entity certificate used to sign it.

   A secondary advantage to this one-to-one correspondence is that the
   private key corresponding to the public key in a certificate is used

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   exactly once in its lifetime, and thus can be destroyed after it has
   been used to sign its one object.  This fact should simplify key
   management, since only the public portions of end-entity certificates
   will need to be retained for any significant length of time.

   Although this document defines only one use for end-entity
   certificates, additional uses will likely be defined in the future.
   For example, end-entity certificates could be used as a more general
   authorization for their subjects to act on behalf of the holder of
   the indicated resources.  This could facilitate authentication of
   inter-ISP interactions, or authentication of interactions with the
   repository system.  These additional uses for end-entity
   certificates, however, may require retention of the corresponding
   private keys, even though this is not required for the private keys
   associated with end-entity certificates keys used for verification of
   ROAs, as described above.

2.4. Trust Anchors

   In any PKI, each relying party (RP) is free to choose its own set of
   trust anchors. In this case, the hierarchy of this PKI is structured
   according to the IP address space and AS number allocation hierarchy,
   so since administrative control of the IP address space (the root of
   the allocation hierarchy) rests with IANA and the RIRs , these
   entities form a natural set of default trust anchors for this PKI.
   Nonetheless, every relying party is free to choose a different set of
   trust anchors to use for certificate validation operations.

   For example, an RP could create one or more self-signed certificates
   to which all address space and/or all AS numbers are assigned, and
   for which the RP knows the corresponding private key. The RP could
   then issue certificates under these trust anchors to whatever
   entities in the PKI it wishes, with the result that the certificate
   paths terminating at these locally-installed trust anchors will
   satisfy the RFC 3779 validation requirements.

   An RP who elects to create and manage its own set of trust anchors
   may fail to detect allocation errors that arise under such
   circumstances, but the resulting vulnerability is local to the RP.

3. Route Origination Authorizations

   The information on IP address allocation provided by the PKI is not
   in itself sufficient to guide routing decisions.  In particular, BGP
   is based on the assumption that the AS that originates routes for a
   particular block of IP address space is authorized to do so by the
   holder of that block; the PKI contains no information about these

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   authorizations.  A Route Origination Authorization (ROA) make such
   authorization explicit, allowing a holder of address space to create
   an object that explicitly and verifiably asserts that an AS is
   authorized originate routes to that address space.

3.1. Role in the overall architecture

   A ROA is an attestation that the holder of a set of IP addresses has
   authorized an autonomous system to originate routes for that set of
   IP addresses.  A ROA is structured according to format described in
   [6].  The validity of this authorization depends on the issuer of the
   ROA being the owner of the set of IP addresses in the ROA; this fact
   is asserted by an end-entity certificate from the PKI, whose
   corresponding private key is used to sign the ROA.  The repository
   system will be the primary mechanism for disseminating ROAs, since
   the operators of repositories already provide other types routing
   information.  In addition, ROAs could also be distributed in BGP
   UPDATE messages or via other communication paths, since route
   filtering is their primary application.

3.2. Syntax and semantics

   A ROA constitutes an explicit authorization for a single AS to
   originate routes to one or more prefixes, and is signed by the holder
   of those prefixes.  A ROA thus have three essential components:

   1. An AS number

   2. One or more IP address prefixes

   3. A digital signature

   In addition, a ROA has a version number, to accommodate changes in
   syntax (or semantics) over time. The AS number contained in a ROA is
   that of an AS authorized to originate routes for the indicated IP
   address prefixes.  Only one AS number is contained in a ROA in order
   to simplify ROA management, e.g., to avoid the complexity that might
   arise is AS numbers for multiple ISPs were referenced from a single
   ROA. If an ISP serving a subscriber has multiple AS numbers, and
   wants the address space holder to authorize advertisement of the same
   set of prefixes by any of these ASes, the ISP should request the
   subscriber to issue multiple ROAs, each specifying a distinct AS
   number. Similarly, a multi-homed address space holder must generate
   multiple ROAs, one for each ISP that will originate routes for it.

   A ROA is signed using the private key whose public key is contained
   in an end-entity certificate in the PKI, from which the ROA inherits

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   two properties.  First, The IP prefixes listed in the ROA are the
   ones that the indicated AS is authorized to originate; in order for
   this authorization (i.e., the ROA) to be valid, the prefixes
   contained in a ROA must be exactly the same as the set of IP
   addresses in the IP Address Delegation Extension of the end-entity
   certificate used to sign the ROA.  Second, the ROA is valid only as
   long as the certificate used to sign it is valid; a ROA is
   invalidated by revoking the end-entity certificate corresponding to
   the public key used to verify it, and the validity interval of the
   ROA is implicitly that of the validity interval of the corresponding

   Address holders that have allocations from multiple sources must
   issue multiple ROAs.  If an address holder has allocations from
   multiple sources, then these allocations will be described by
   multiple CA certificates in the PKI, each issued by the provider of
   the respective allocation; the sets of IP addresses contained in end-
   entity certificates issued by this address holder are required to be
   subsets of these allocations.  Because end-entity certificates are in
   one-to-one correspondence with ROAs, this means that the set of IP
   addresses contained in a ROA must be drawn from an allocation by a
   single source; hence ROAs cannot combine allocations from multiple

3.3. Revocation

   If an address holder decides that an AS should no longer originate
   routes for addresses that it holds (e.g., if the address holder
   transfers from one ISP to another), then it will be necessary to
   invalidate the ROAs that attest to any such authorization.  Since
   ROAs are in one-to-one correspondence with end-entity certificates,
   the standard method for revoking a ROA is to revoke the corresponding
   end-entity certificate in the PKI.  There is no independent
   revocation mechanism for ROAs.

4. Repository system

   In order for ROAs (and other objects to be verified using
   certificates from the PKI) to be validated, the objects necessary to
   validate them must be universally accessible.  The primary function
   of the distributed repository system described here is to store these
   objects and to make them available for download. The repository
   system is also a point of enforcement for access controls for the
   signed objects stored in it, e.g., ensuring that records related to
   an allocation of resources can be manipulated only by authorized
   parties. This requirement exists to prevent denial of service attacks
   based on deletion of or tampering with repository objects. Although

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   any unauthorized modification is detectable by relying parties,
   because all the objects are digitally signed, it is preferable that
   the repository system prevent unauthorized modifications.

4.1. Role in the overall architecture

   The repository system is the central clearing-house for the objects
   required for validation of signed objects like ROAs.  When
   certificates and CRLs are created, they are uploaded to this
   repository, and then downloaded for use by relying parties.  In
   addition, signed objects that require universal distribution can also
   be made accessible through the repository system; ROAs are the only
   such objects defined by this document, but other types of signed
   objects may be added to this architecture in the future.  The
   repository system also must ensure the integrity of the data it
   contains by enforcing appropriate controls on access to the
   repository and on modifications to entries in it.  This document
   describes the controls necessary for PKI objects and ROAs, but does
   not assume that they are applicable to other types of objects; if
   other types of objects are to be included in the repository system in
   the future, any necessary controls on them must be defined.

4.2. Contents and structure

   The primary function of the repository system is to provide universal
   distribution of objects necessary for the function of this
   architecture.  First among these are the objects that comprise the
   PKI, namely Resource Certificates and their corresponding CRLs; these
   objects require universal distribution so that all relying parties
   have access to the PKI components required to validate signed objects
   used by this architecture.  In addition, it may be necessary to make
   other types of signed objects available through the repository
   system.  ROAs are a prime example of such a type, since routes whose
   origination is authorized by a ROA are distributed through the entire
   routing infrastructure, any component of which may, by local policy,
   examine the route origin for consistency with the ROA.

   Although there is a single repository system that is accessed by
   relying parties, it is comprised of multiple databases. These
   databases will be distributed among RIRs and ISPs that participate in
   the architecture.  At a minimum, the database operated by each RIR
   will contain certificates and CRLs issued by that RIR; it may also
   contain repository objects submitted by holders of addresses that
   fall within that RIR's scope or copies of data from other RIRs,
   according to local policy.

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4.3. Access protocols

   Repository operators will choose one or more access protocols that
   relying parties can use to access the repository system.  These
   protocols will be used by numerous participants in the infrastructure
   (e.g., all registries, ISPs, and multi-homed subscribers) to maintain
   their respective portions of it.  In order to support these
   activities, certain basic functionality is required of the suite of
   access protocols, as described below.  No single access protocol need
   implement all of these functions (although this may be the case), but
   each function must be implemented by at least one access protocol.

   Download: Access protocols MUST support the bulk download of
   repository contents and subsequent download of changes to the
   downloaded contents, since this will be the most common way in which
   relying parties interact with the repository system.  Other types of
   download interactions (e.g., download of a single object) MAY also be

   Upload/change/delete: Access protocols MUST also support mechanisms
   for the issuers of certificates, CRLs, and other signed objects to
   add them to the repository, and to remove them.  Mechanisms for
   modifying objects in the repository MAY also be provided.  All access
   protocols that allow modification to the repository (through
   addition, deletion, or modification of its contents) MUST support
   verification of the authorization of the entity performing the
   modification, so that appropriate access controls can be applied (see
   Section 4.4).

   Current efforts to implement a repository system use RSYNC [9] as the
   single access protocol.  RSYNC, as used in this implementation,
   provides all of the above functionality.

4.4. Access control

   In order to maintain the integrity of information in the repository,
   controls must be put in place to prevent addition, deletion, or
   modification of objects in the repository by unauthorized parties.
   The identities of parties attempting to make such changes can be
   authenticated through the relevant access protocols.  Although
   specific access control policies are subject to the local control of
   repository operators, it is recommended that repositories allow only
   the issuers of signed objects to add, delete, or modify them.
   Alternatively, it may be advantageous in the future to define a
   formal delegation mechanism to allow resource holders to authorize
   other parties to act on their behalf, as is suggested in Section 2.3

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5. Common Operations

   Creating and maintaining the infrastructure described above will
   entail the addition of security operations to normal resource
   allocation and routing authorization procedures.  For example, a
   multi-homed subscriber entering a relationship with a new ISP will
   need to issue one or more ROAs to that ISP, in addition to conducting
   any other necessary technical or business procedures.  The current
   primary use of this infrastructure is for route filter construction;
   using ROAs, route filters can be constructed in an automated fashion
   with high assurance that the holder of the advertised prefix has
   authorized the first- hop AS to originate an advertised route.

5.1. Certificate issuance

   In order to participate in this infrastructure, resource holders will
   require certificates in the PKI that attest to their allocations.
   Each such certificate will show the issuer of the allocation as the
   certificate issuer, the recipient of the allocation as subject, and a
   description of the allocated resources in the appropriate RFC 3779
   extensions.  The two operations defined in this architecture that
   require a resource holder to have resource certificates for his
   allocations are (1) issuance of certificates for sub-allocations and
   (2) management of ROAs (and corresponding end-entity certificates).

   In particular, there are several operational scenarios that require
   certificates to be issued.  Any allocation that may be sub-allocated
   requires a CA certificate so that certificates can be issued as
   necessary for sub-allocations. Multi-homed subscribers require
   certificates for their allocations so that they can issue ROAs to
   their ISPs.  Holders of "portable" address allocations must have
   certificates, so that a ROA can be issued to each ISP that is
   authorized to originate a route to the allocation, since the
   allocation does not come from any ISP.

   As a resource holder receives multiple allocations over time, it will
   accrue a collection of resource certificates to attest to them.  It
   may be the case that multiple of a resource holder's allocations are
   from the same source.  A set of resource certificates that are all
   issued by the same CA could be combined into a single resource
   certificate by consolidating their IP Address Delegation and AS
   Identifier Delegation Extensions into a single extension of each
   type.  However, if the certificates for these allocations contain
   different validity intervals, creating a certificate that combines
   them might create problems, and thus is NOT RECOMMENDED. If a
   resource holder's allocations come from different sources, they will
   be signed by different CAs, and cannot be combined.  When a set of

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   resources is no longer allocated to a resource holder, any
   certificates attesting to such an allocation must be revoked. A
   resource holder MAY choose to use the same public key in multiple CA
   certificates that issued by the same or differing authorities,
   although such reuse of a key pair does complicate path construction.

5.2. ROA management

   Whenever a holder of IP address space wants to authorize an AS to
   originate routes for a prefix within his holdings, he must issue an
   end-entity certificate containing that prefix and use the
   corresponding private key to sign a ROA containing the designated
   prefix and an AS number identifying the designated AS.  As a
   prerequisite, then, any address holder that issues ROAs for a prefix
   must have a resource certificate for an allocation containing that
   prefix.  The standard procedure for issuing a ROA is as follows:

   1. Create an end-entity certificate containing the prefixes to be
      authorized in the ROA

   2. Construct the payload of the ROA, including the prefixes in the
      end-entity certificate and the AS number to be authorized

   3. Sign the ROA using the private key corresponding to the end-entity
      certificate (the ROA is comprised of the payload encapsulated in a
      CMS signed message [ROA format I-D])

   4. Upload the end-entity certificate and the ROA to the repository

   The standard procedure for revoking a ROA is to revoke the
   corresponding end-entity certificate by creating an appropriate CRL
   and uploading it to the repository system.  The revoked ROA and end-
   entity certificate SHOULD BE removed from the repository system.

5.2.1. Single-homed subscribers (without portable allocations)

   In BGP, a single-homed subscriber with a non-portable allocation does
   not need to explicitly authorize routes to be originated for the
   prefix (or prefixes) it is using, since its ISP will already
   advertise a more general prefix and route traffic for the
   subscriber's prefix as an internal function.  Since no routes are
   originated specifically for prefixes held by these subscribers, no
   ROAs need to be issued under their allocations; rather, the
   subscriber's ISP will issue any necessary ROAs for its more general
   prefixes under resource certificates its own allocation. Thus,

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   single-homed subscribers with non-portable allocations do not need to
   issue (or otherwise manage) ROAs.

5.2.2. Multi-homing

   If a multi-homed subscriber wants multiple ASes to originate routes
   for prefixes that it holds, then it must explicitly authorize each of
   them to do so by issuing a ROA for each AS in question.

5.2.3. Portable allocations

   A resource holder is said to have a portable allocation if the
   resource holder received its allocation from a registry.  Because
   these allocations are not taken from any larger allocations held by
   an ISP, there is no ISP that holds and advertises a more general
   prefix.  If the holder of a portable allocation wants to authorize an
   ISP to originate routes to its allocation, then it must issue a ROA
   to this ISP; none of the ISP's existing ROAs authorize it to
   originate routes to that portable allocation.

5.3. Route filter construction

   The goal of this architecture is to support improved routing
   security.  One way to do this is to use ROAs to construct route
   filters that reject routes that conflict with the origination
   authorizations asserted by current ROAs, which can be accomplished
   with the following procedure:

   1. Obtain current certificates, CRLs, and ROAs from the repository
      system (e.g., update a previous download)

   2. Verify each end-entity certificate by constructing and verifying
      a certification path for the certificate (including checking
      relevant CRLs).

   3. Verify each ROA by verifying that it is signed by a valid end-
      entity certificate that matches the address allocation in the ROA.

   4. Based on validated ROAs, construct a table of prefixes and
      corresponding authorized origin ASes (or vice versa).

   In addition to this basic route-filtering technique, the
   infrastructure can be used to support more advanced routing-security
   systems, such as S-BGP [7] and soBGP [8].

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   The first three steps in the above procedure would incur a
   prohibitive amount of overhead if all objects in the repository
   system were downloaded and validated every time a route filter was
   constructed.  Instead, it will be more efficient for users of the
   infrastructure to initially download all of the objects
   (certificates, CRLs, and ROAs), perform necessary validations, then
   perform incremental downloads and validations on a regular basis.  A
   typical ISP using the infrastructure might have a daily schedule to
   download updates from the repository, upload any modifications it has
   made, and construct route filters.

6. Security Considerations

   The focus of this document is security; hence security considerations
   permeate this specification.

   The security mechanisms provided by and enabled by this architecture
   depend on the integrity and availability of the infrastructure it
   describes.  The integrity of objects within the infrastructure is
   ensured by appropriate controls on the repository system, as
   described in Section 4.4. Likewise, because the repository system is
   structured as a distributed database, it should be inherently
   resistant to denial of service attacks; nonetheless, appropriate
   precautions should also be taken, both through replication and backup
   of the constituent databases and through the physical security of
   database servers

7. IANA Considerations

   This document makes no request of IANA.

   Note to RFC Editor: this section may be removed on publication as an

8. Acknowledgments

   This document was prepared using 2-Word-v2.0.template.dot.

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9. References

9.1. Normative References

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

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

   [3]   Housley, R., et al., "Internet X.509 Public Key Infrastructure
         Certificate and Certificate Revocation List (CRL) Profile", RFC
         3280, April 2002.

   [4]   Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP
         Addresses and AS Identifiers", RFC 3779, June 2004.

   [5]   Huston, G., Michaelson, G., and Loomans, R., "A Profile for
         X.509 PKIX Resource Certificates", draft-ietf-sidr-res-certs-
         03, February 2007.

   [6]   Kong, D., and Kent, S., " A Profile for Route Origin
         Authorizations (ROA)", draft-ietf-sidr-roa-format-00, February

9.2. Informative References

   [7]   [S-BGP]

   [8]   [soBGP]

   [9]   [rsync]

Author's Addresses

   Richard Barnes
   BBN Technologies

   Email: rbarnes@bbn.com

   Stephen Kent
   BBN Technologies

   Email: kent@bbn.com

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