One document matched: draft-huston-sidr-roa-validation-00.txt
Individual Submission G. Huston
Internet-Draft G. Michaelson
Intended status: Informational APNIC
Expires: August 11, 2008 February 8, 2008
Validation of Route Origin Authorizations in BGP using the Resource
Certificate PKI
draft-huston-sidr-roa-validation-00.txt
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Copyright (C) The IETF Trust (2008).
Abstract
This document defines an application of the Resource Public Key
Infrastructure to validate the origination of routes advertised in
the Border Gateway Protocol. The proposed application is intended to
fit within the requirements for adding security to inter-domain
routing, including the ability to support incremental and piecemeal
deployment, and does not require any changes to the specification of
BGP.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Validation Outcomes of a BGP Route Object using ROAs . . . . . 3
3. Applying Validation Outcomes to BGP Route Selection . . . . . 5
3.1. Using ROA Validation Outcomes to reject BGP
advertisements . . . . . . . . . . . . . . . . . . . . . . 7
4. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
7. Normative References . . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
Intellectual Property and Copyright Statements . . . . . . . . . . 11
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1. Introduction
This document defines an application of the Resource Public Key
Infrastructure (RPKI) to validate the origination of routes
advertised in the Border Gateway Protocol (BGP) [RFC4271].
The RPKI is based on on Resource Certificates. Resource Certificates
are X.509 certificates that conform to the PKIX profile [RFC3280],
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 PKI is structured such that each current Resource
Certificate matches a current resource allocation or assignment.
This is described in [I-D.ietf-sidr-arch].
Route Origin Authorizations (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 an 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].
This document describes how ROA validation outcomes can be used in
the BGP route selection process, and how the proposed application are
intended to fit within the requirements for adding security to inter-
domain routing [ID.ietf-rpsec-bgpsecrec], including the ability to
support incremental and piecemeal deployment, and, furthermore, does
not require any changes to the specification of BGP.
2. Validation Outcomes of a BGP Route Object using ROAs
A BGP Route Object is an address prefix and a set of attributes. In
terms of ROA validation the prefix value and the origin AS are used
in the validation operation.
[Note: If the origination of the prefix is an AS Set then ??. The
draft authors do not have a clear idea as to what to propose here!]
ROA validation is described in [I-D.ietf-sidr-roa-format], and the
outcome of the validation operation is that the ROA is valid in the
context of the RPKI or validation has failed.
There appears to be two means of matching a route object to a ROA:
decoupled and linked.
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The decoupled approach where the ROAs are managed and distributed
independently of the operation of the routing protocol and a local
BGP speaker has access to a local cache of the complete set of ROAs
and the RPKI data set when performing a validation operation. In
this case the route object does not refer to a ROA, a certificate
validation path, CRLs nor Trust Anchors, and it is the role of the
relying party to match a route object to one or more candidate ROAs
and perform the validation operation on a selected ROA in order to
determine the appropriate local actions to perform on the route
object. The second approach is where the route object references a
ROA, either by explicit inclusion of the ROA itself as an attribute
of the route object that is carried in BGP or by reference where some
identification of the ROA is carried as an attribute of the object.
The more general case here is the decoupled approach where a set of
ROAs are selected where the address prefix in the ROA is an exact
match, or the address prefix in the ROA is a covering aggregate of
the address prefix in the route object and the ROA has the
requireExactMatch set to FALSE.The following outcomes are possible
using the defined ROA validation procedure for each ROA in this set:
o An "exact match" is a valid ROA where the address prefix in the
route object exactly matches a prefix listed in the ROA and the
origin AS in the route object matches the origin AS listed in the
ROA.
o A "covering match" is a valid ROA where the address prefix in the
ROA is a covering aggregate of the prefix in the route object, and
the ROA has the requireExactMatch value of TRUE, and the origin AS
in the route object matches the AS listed in the ROA.
o An "exact failure" is a ROA where the address prefix in the route
object exactly matches a prefix listed in the ROA, the origin AS
matches the AS listed in the ROA, but the EE certificate of the
ROA signature fails to validate within the context of the RPKI.
o A "covering failure" is a ROA where the address prefix in the ROA
is a covering aggregate of the prefix in the update, and the ROA
has the requireExactMatch value FALSE, and the origin AS in the
update matches the origin AS listed in the ROA, but the EE
certificate that is associated with the ROA's digital signature
fails to validate within the context of the RPKI.
o An "exact mismatch" is a ROA where the address prefix in the route
object exactly matches a prefix listed in the ROA and the origin
AS of the route object does not match the AS listed in the ROA.
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o A "covering mismatch" is a ROA where the address prefix in the ROA
is a covering aggregate of the prefix in the route object, the ROA
has the requireExactMatch value FALSE, and the origin AS of the
route object does not match the AS listed in the ROA.
o "ROA missing" is where there are no exact or covering matches, no
exact or covering mismatches and no exact of covering failures in
the RPKI repository.
In this case the ROA that would be used for the validation function
is selected from the set such that the most specific valid ROA that
matches or covers the route object address prefix and where the route
object origin AS matches the ROA AS. If there is no such ROA in the
set, then the most specific valid ROA is selected. If there is no
such ROA in the set then the most specific ROA is selected.
The linked approach requires the route object to reference a ROA
either buy inclusion of the ROA as an attribute of the route object,
or inclusion of a identity field as a means of identifying a
particular ROA. In this case the set of outcomes of ROA validation
is a subset of the decoupled approach, as follows:
o "exact match"
o "covering match"
o "exact failure"
o "covering failure"
o "ROA missing"
3. Applying Validation Outcomes to BGP Route Selection
Within the framework of the abstract model of BGP operation, a
received prefix announcement from a peer is compared to all
announcements for this prefix received from other peers and a route
selection procedure is used to select the "best" route object from
this candiudate set which is then used locally by placing it in the
loc-RIB, and is announced to peers as the local "best" route.
It is proposed that the validation outcome be used as part of the
determination of the local degree of preference as defined in section
9.1.1 of the BGP specification [RFC4271].
In the case of a partial deployment scenario, when some prefixes are
described in ROAs and others are not, then the relative ranking of
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validation outcomes from the highest (most preferred) to the lowest
(least preferred) degree of preference are proposed as follows:
1. "exact match"
An exact match indicates that the prefix has been allocated and
is routeable, and that the prefix right-of-use holder has
authorized the originating AS to originate precisely this
announcement.
2. "covering match"
A covering match is slightly less preferred becuase it is
possible that the address holder of the aggregate has allocated
the prefix in question to a different party, and both the
aggregate address holder and the prefix holder have signed ROAs
and are advertising the prefix.
3. "ROA missing"
In the case of partial deployment of ROAs the absence of
validation credentials is neutral, in that there is no grounds to
increase or decrease the relative degree of preference for the
prefix.
4. "covering mismatch"
A covering mismatch is considered to be less preferable than a
neutral position in that the address holder of a covering
aggregate has indicated an originating AS that is not the
originating AS of this announcement. On the other hand it may be
the case that this prefix has been validly allocated to another
party who has not generated a ROA for this prefix even through
the announcement is valid.
5. "covering failure"
A convering failure indicates that the ROA is not valid in terms
of the PKI, but this still admit the possibility that the prefix
has been allocated to another party who has not generated a ROA.
6. An "exact mismatch"
Here the exact match prefix holder has validly provided an
authority for origination by an AS that is not the AS that is
originating this announcement. This would appear to be a bogus
announcement by inference.
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7. "exact failure"
Here the authority to originate is not valid, indicating t6hat
either the authority has expired or that the authority infomation
has been constructed by someone other than the prefix owner.
This implies that the announcement is made without authority.
In the case of comprehensive deployment of ROAs the relative local
degree of preference can be adjusted such that cases 3 through 5 of
the above list have an equal level of lesser preference, as in this
case there is no "missing" ROA so that a validation failure need not
be interpreted as a potentially valid route object that does not have
an associated ROA.
3.1. Using ROA Validation Outcomes to reject BGP advertisements
In the case of partial deployment of ROAs there are a very limited
set of circumstances where the outcome of ROA validation can be used
as grounds to reject all consideration of the route object as an
invalid advertisement. While the presence of a valid ROA that
matches the advertisement is astrong indication that an advertisement
matches the authority provided by the prefix holder to advertise the
prefix into the routing system, the absence of a ROA or the
invalidity of a covering ROA does not provide a conclusive indication
that the advertisement has been undertaken without the address
holder's permission.
In the case of comprehensive deployment of ROAs an invalid ROA could
be considered grounds for rejection of the route object advertisement
were it not for the issue of circular dependence. If the
authoritative publication point of the repository of ROAs or any
certificates used to related to an address prefix is stored at a
location that lies within the address prefix, then the repository can
only be accessed once a route for the prefix has been accepted. If
the local BGP speaker is in a position to use some mechanism to check
for circular dependencies then in the case of comprehensive
deployment of ROAs an invalid ROA would be sufficient grounds to
reject a route object.
It is noted that validation of a ROA infers two properties of the
address, namely that the address prefix itself is "valid" and is not
part of a "reserved" pool held by the IANA, an RIR or any LIR, and
secondly that the origination of the address in the routing system
has been undertaken with the explicit permission of the address
holder. Accepting an advertisement of an address prefix that has
failed ROA validation admits the possibility of accepting an
advertisment for an invalid address that is drawn from a reserved
pool. In the case of comprehensive deployment of ROAS the validation
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outcome of "ROA missing" is a strong indication that the address
itself is invalid, as in the comprehensive deployment model all
validly advertised address space is, by definition, covered by a ROA.
The issue of circularity dependency between the address and the
publication point of the ROA would still need to be addressed in this
case.
4. Open Issues
This document provides a description of how ROA validation could be
used by a BGP speaker. It is noted that the proposed procedure
requires no changes to the operation of BGP. It is also noted that
the decoupled and linked approach are not mutually exclusive, and the
same procedure can be applied to route objects that contain an
explicit pointer to the associated ROA and route objects where the
local BGP speaker has to create a set of candidate ROAs that could be
applied to a route object. However, there are a number of ques5tions
about this approach that are not resolved here.
Some open issues at this point are:
o When should validation of an advertised prefix be performed by a
BGP speaker? Is it strictly necessary to perform validation at a
point prior to loading the object into the Adj-RIB-In structure,
or once the object has been loaded into Adj-RIB-IN, or at a later
time that is determined by a local configuration setting? Should
validation be performed each time a route object is updated by a
peer even when the origin AS has not altered?
o What is the lifetime of a validation outcome? When should the
routing object be revalidated? Should the validation outcome be
regarded as valid until the route object is withdrawn or further
updated, or should validation occur at more frequent intervals?
o Are there circumstances that would allow a route object to be
removed from further consideration in route selection upon a
validation failure, similar to the actions of Route Flap Damping?
o Can ROA validation be performed on a per-AS basis rather than a
per-BGP speaker? What BGP mechanisms would be appropriate to
support such a mode of operation?
5. Security Considerations
[to be completed]
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6. IANA Considerations
[There are no IANA considerations in this document at this stage.
Later iterations of this draft propose to add a ROA identifier into
the BGP route attribute set]
7. Normative References
[I-D.ietf-sidr-arch]
Lepinski, M., Kent, S., and R. Barnes, "An Infrastructure
to Support Secure Internet Routing", draft-ietf-sidr-arch
(work in progress), November 2007.
[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), July 2007.
[ID.ietf-rpsec-bgpsecrec]
Christian, B. and T. Tauber, "BGP Security Requirements",
draft-ietf-sidr-roa-format (work in progress),
November 2007.
[RFC3280] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet
X.509 Public Key Infrastructure Certificate and
Certificate Revocation List (CRL) Profile", RFC 3280,
April 2002.
[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.
Authors' Addresses
Geoff Huston
Asia Pacific Network Information Centre
Email: gih@apnic.net
URI: http://www.apnic.net
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George Michaelson
Asia Pacific Network Information Centre
Email: ggm@apnic.net
URI: http://www.apnic.net
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