Secure Inter-Domain Routing (SIDR) G. Huston
Internet-Draft G. Michaelson
Intended status: Informational APNIC
Expires: September 4, 2010 March 3, 2010
Validation of Route Origination using the Resource Certificate PKI and
ROAs
draft-ietf-sidr-roa-validation-04.txt
Abstract
This document defines the semantics of a Route Origin Authorization
in terms of the context of an application of the Resource Public Key
Infrastructure to validate the origination of routes advertised in
the Border Gateway Protocol.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
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."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on September 4, 2010.
Copyright Notice
Copyright (c) 2010 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
(http://trustee.ietf.org/license-info) in effect on the date of
Huston & Michaelson Expires September 4, 2010 [Page 1]
Internet-Draft Route Validation March 2010
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. ROA Validation Outcomes for a Route Object . . . . . . . . . . 3
3. Applying Validation Outcomes to Route Selection . . . . . . . . 5
4. Disavowal of Routing Origination . . . . . . . . . . . . . . . 6
5. Route Object Validation Lifetime . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Normative References . . . . . . . . . . . . . . . . . . . 8
8.2. Informative References . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8
Huston & Michaelson Expires September 4, 2010 [Page 2]
Internet-Draft Route Validation March 2010
1. Introduction
This document defines the semantics of a Route Origin Authorization
(ROA) in terms of the context of an application of the Resource
Public Key Infrastructure (RPKI) [I-D.ietf-sidr-arch] to validate the
origination of routes advertised in the Border Gateway Protocol (BGP)
[RFC4271].
The RPKI is based on a hierarchy of Resource Certificates that are
aligned to the Internet number resource allocation structure.
Resource Certificates are X.509 certificates that conform to the PKIX
profile [RFC5280], and to the extensions for IP addresses and AS
identifiers [RFC3779]. A Resource Certificate describes an action by
an issuer that binds a list of IP address blocks and Autonomous
System (AS) numbers to the Subject of a certificate, identified by
the unique association of the Subject's private key with the public
key contained in the Resource Certificate. The RPKI is structured
such that each current Resource Certificate matches a current
resource allocation or assignment. This is further described in
[I-D.ietf-sidr-arch].
ROAs are digitally signed objects that bind an address to an AS
number, signed by the address holder. A ROA provides a means of
verifying that an IP address block holder has authorized a particular
AS to originate route objects in the inter-domain routing environment
for that address block. ROAs are described in
[I-D.ietf-sidr-roa-format]. ROAs are intended to fit within the
requirements for adding security to inter-domain routing.
This document describes the semantic interpretation of a ROA, with
particular reference to application in inter-domain routing relating
to the origination of route objects, and the intended scope of the
authority that is conveyed in the ROA.
2. ROA Validation Outcomes for a Route Object
A "route object" is an address prefix and an associated set of
routing attributes. In terms of validation of the route object in
the context of BGP [RFC4271]the address prefix value and the "origin
AS" are used in the ROA validation operation. The route object's
origin AS is the final element of the route object's AS_PATH
attribute. If the final AS_PATH element is an AS Set, indicating
that the route object is an aggregate, then the origin AS is taken as
the AS component of the AGGREGATOR attribute [RFC4271].
It is assumed here that a Relying Party (RP) has access to a local
cache of the complete set of valid ROAs when performing validation of
Huston & Michaelson Expires September 4, 2010 [Page 3]
Internet-Draft Route Validation March 2010
a route object. (Valid ROAs are defined as ROAs that are determined
to be syntactically correct and are signed using a signature that can
be verified using the RPKI, as described in
[I-D.ietf-sidr-roa-format].) The RP needs to match a route object to
one or more candidate valid ROAs in order to determine a validation
outcome, which, in turn, can be used to determine the appropriate
local actions to perform on the route object.
This approach to route object origination validation uses a model of
"positive" attestations, where route objects that cannot be validated
within the RPKI framework would conventionally be treated by a RP as
"invalid". However, the considerations of accommodating environments
of partial adoption of the use of ROAs, where only a subset of
validly advertised address prefixes have associated published ROAs
within the structure of the RPKI, imply some modification to this
model of positive attestation. In the context of route object
validation it is assumed that once an address prefix is described in
a ROA, then this ROA speifically encompasses all address prefixes
that are more specific than that described in the ROA. Thus, any
route object for more specific address prefix than that described by
any valid ROA that does not itself have a matching valid ROA is
considered to be "invalid". However, routes objects for address
prefixes that are not fully described by any single ROA, i.e., those
route objects whose address prefixes may be an aggregate of address
prefixes described in a valid ROA, or have address prefixes where
there is no intersection with any ROA, and are not matched by any ROA
and are not a more specific of any ROA cannot be reliably classified
as "invalid" in a partial deployment scenario. Such route objects
have a validation outcome of "unknown".
The validation condition of a route object with a prefix and an
origin AS when using single ROA for validation is summarized in the
following table:
Prefix matching non-matching
AS AS
+---------+-------------+
Covering | unknown | unknown |
Aggregate | | |
+---------+-------------+
match ROA | valid | invalid |
prefix | | |
+---------+-------------+
More | invalid | invalid |
Specific | | |
than ROA | | |
+---------+-------------+
Huston & Michaelson Expires September 4, 2010 [Page 4]
Internet-Draft Route Validation March 2010
In an environment of a collection of ROAs, a route object is
considered to be "valid" if any ROA provides a "valid" outcome. It
is considered to be "invalid" if one (or more) ROAs provide an
"invalid" outcome and no ROAs provide a "valid" outcome. It is
considered to be "unknown" when no ROA produces either a "valid" or
an "invalid" outcome.
Route object validation is defined by the following procedure:
1. Select all valid ROAs that include a ROAIPAddress value that
either matches, or is a covering aggregate of, the address
prefix in the route object.
2. If the set of candidate ROAs is empty then the validation
procedure stops with an outcome of "unknown".
3. If any of the selected ROAs has an asID value that matches the
origin AS in the route object, and either the route object's
address prefix precisely matches a ROAIPAddress in the ROA, or
the route object's address prefix is a more specific prefix of
a ROAIPAddress, and the route object's prefix length value is
less than or equal to the ROAIPAddress' maxLength value, then
the validation procedure stops with an outcome of "valid".
4. Otherwise, the validation procedure stops with an outcome of
"invalid".
3. Applying Validation Outcomes to Route Selection
Within the framework of the abstract model of the operation of inter-
domain routing using BGP [RFC4271], a received prefix announcement
from a routing peer is compared to all announcements for this prefix
received from other routing peers and a route selection procedure is
used to select the "best" route object from this candidate set.
The route object validation outcome, described in Section 2, of
"unknown", "valid" or "invalid" may be used as part of the
determination of the local degree of preference, in which case the
local order of preference is as follows:
"valid" is to be preferred over
"unknown", which itself is to be preferred over
"invalid".
It is a matter of local routing policy as to the actions to be
undertaken by a routing entity in processing route objects with
"unknown" validation outcomes. Due to considerations of partial use
Huston & Michaelson Expires September 4, 2010 [Page 5]
Internet-Draft Route Validation March 2010
of ROAs in heterogeneous environments, such as in the public
Internet, it is advised that local policy settings should not result
in "unknown" validation outcomes being considered as sufficient
grounds to reject a route object outright from further consideration
as a local "best" route.
It is a matter of local routing policy as to whether "invalid" route
objects are considered to be ineligible for further consideration in
a route selection process. A possible consideration here is one of
potential circularity of dependence. If the authoritative
publication point of the repository of ROAs, or that of any
certificate used in relation to an address prefix, is located at an
address that lies within the address prefix described in a ROA, then
the repository can only be accessed by the RP once a route for the
prefix has been accepted by the RP's local routing domain. It is
also noted that the propagation time of RPKI objects may be different
to the propagation time of route objects, and that route objects may
be received before the RP's local repository cache picks up the
associated ROAs and recognises them as valid within the RPKI.
4. Disavowal of Routing Origination
A ROA is a positive attestation that a prefix holder has authorized
an AS to originate a route for this prefix into the inter-domain
routing system. It is possible for a prefix holder to construct an
authorization where no valid AS has been granted any such authority
to originate a route object for an address prefix. This is acheived
by using a ROA where the ROA's subject AS is one that must never be
used in any routing context. Specifically, AS 0 is reserved by the
IANA such that it "may be use [sic] to identify non-routed networks"
[IANA.AS-Registry].
A ROA with a subject of AS 0 is an attestation by the holder of a
prefix that the prefix described in the ROA, and any more specific
prefix, SHOULD NOT be used in a routing context.
The route object validation procedure, described in Section 2, will
provide a "valid" outcome if any ROA matches the address prefix and
origin AS, even if other valid ROAs would provide an "invalid"
validation outcome if used in isolation. Consequently, an AS 0 ROA
has a lower preference than any other ROA that has a routeable AS as
its subject. This allows a prefix holder to use an AS 0 ROA to
declare a default condition that any route object that is equal to,
or more specific than the prefix to be considered to be invalid,
while also allowing other concurrently issued ROAs to describe valid
origination authorizations for more specific prefixes.
Huston & Michaelson Expires September 4, 2010 [Page 6]
Internet-Draft Route Validation March 2010
By convention, an AS 0 ROA SHOULD have a maxLength value of 32 for
IPv4 addresses and 128 for IPv6 addresses, although in terms of route
object validation the same outcome would be achieved with any valid
maxLength value, or even if the maxLength element were to be omitted
from the ROA.
Also by convention, an AS 0 ROA SHOULD be the only ROA issued for a
given address prefix, although again this is not a strict
requirement. An AS 0 ROA can coexist with ROAs that have different
subject AS values, although in such cases the presence of the AS 0
ROA does not alter the route object validation outcome in any way.
5. Route Object Validation Lifetime
The "lifetime" of a validation outcome refers to the time period
during which the original validation outcome can be still applied.
The implicit assumption here is that when the validation lifetime
expires the routing object SHOULD be re-tested for validity.
The validation lifetime for a ROA is controlled by the Valid times
specified in the End Entity (EE) Certificate used to sign the ROA,
and the valid times of those certificates in the certification path
used to validate the EE Certificate. A ROA validation "expires" at
the Validity To field of the signing EE certificate, or at such a
time when there is no certification path that can validate the ROA.
A ROA issuer may prematurely invalidate a ROA by revoking the EE
certificate that was used to sign the ROA.
6. Security Considerations
ROA issuers should be aware of the validation implication in issuing
a ROA, in that a ROA implicitly invalidates all route objects that
have more specific prefixes with a prefix length greater than
maxLength, and all originating AS's other than the AS listed in the
collection of ROAs for this prefix.
A conservative operational practice would be to ensure the issuing of
ROAs for all more specific prefixes with distinct origination AS's
prior to the issuing of ROAs for larger encompassing address blocks,
in order to avoid inadvertent invalidation of valid route objects
during ROA generation.
ROA issuers should also be aware that if they generate a ROA for one
origin AS, then if the prefix holder authorises multiple AS's to
originate route objects it is necessary for a ROA be generated for
every such authorized AS.
Huston & Michaelson Expires September 4, 2010 [Page 7]
Internet-Draft Route Validation March 2010
7. IANA Considerations
[There are no IANA Considerations.]
8. References
8.1. Normative References
[I-D.ietf-sidr-arch]
Lepinski, M. and S. Kent, "An Infrastructure to Support
Secure Internet Routing", draft-ietf-sidr-arch (work in
progress), October 2009.
[I-D.ietf-sidr-roa-format]
Lepinski, M., Kent, S., and D. Kong, "An Infrastructure to
Support Secure Internet Routing",
draft-ietf-sidr-roa-format (work in progress),
October 2009.
[RFC3779] Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP
Addresses and AS Identifiers", RFC 3779, June 2004.
[RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
Protocol 4 (BGP-4)", RFC 4271, January 2006.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, May 2008.
8.2. Informative References
[IANA.AS-Registry]
IANA, "IANA Autonomous System Number Registry",
March 2010.
Authors' Addresses
Geoff Huston
Asia Pacific Network Information Centre
Email: gih@apnic.net
Huston & Michaelson Expires September 4, 2010 [Page 8]
Internet-Draft Route Validation March 2010
George Michaelson
Asia Pacific Network Information Centre
Email: ggm@apnic.net
Huston & Michaelson Expires September 4, 2010 [Page 9]
