Secure Inter-Domain Routing (SIDR) G. Huston
Internet-Draft G. Michaelson
Intended status: Informational APNIC
Expires: November 27, 2009 May 26, 2009
Validation of Route Origination in BGP using the Resource Certificate
PKI
draft-huston-sidr-roa-validation-01.txt
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Abstract
This document defines an application of the Resource Public Key
Infrastructure to validate the origination of routes advertised in
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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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Validation Outcomes of a BGP Route Object . . . . . . . . . . . 3
2.1. Decoupled Validation . . . . . . . . . . . . . . . . . . . 4
2.2. Linked Validation . . . . . . . . . . . . . . . . . . . . . 5
3. Applying Validation Outcomes to BGP Route
Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Validation Outcomes and Rejection of BGP Route
Objects . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Further Considerations . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
7. Changes from draft-ietf-sidr-roa-validation-01 . . . . . . . . 8
8. Normative References . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
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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 Resource Certificates. 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 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 of
ROAs is intended to fit within the requirements for adding security
to inter-domain routing, including the ability to support incremental
and piecemeal deployment. This proposed application does not require
any changes to the specification of BGP protocol elements. The
application may be used as part of BGP's local route selection
algorithm [RFC4271].
2. Validation Outcomes of a BGP Route Object
A BGP Route Object is an address prefix and a set of attributes. In
terms of ROA and BOA validation the prefix value and the origin AS
are used in the validation operation.
If the route object is an aggregate and the AS Path contains an AS
Set, then the origin AS is considered to be the AS described as the
AGGREGATOR [RFC4271] of the route object.
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.
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There appears to be two means of matching a route object to a ROA:
decoupled and linked.
2.1. Decoupled Validation
The decoupled approach is 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 BGP route object does not refer to a specific ROA.
The relying party needs to match a route object to one or more
candidate valid ROAs in order to determine the appropriate local
actions to perform on the route object.
The relying party selects a set of valid ROAs where the address
prefix in the route object either exactly matches an ROAIPAddress
(matching both the address prefix value and the prefix length), or
where the route object spans a block of addresses that is included in
the span described by the ROA's address prefix value and length and
where the route object's prefix length is less than the ROA's prefix
length.
If the set of ROAs is empty then the validation outcome can be
classified as "unknown".
Otherwise the route object should be tested against the set of valid
ROAS. The following outcomes are possible using the defined ROA
validation procedure for each ROA in this set:
Exact Match:
A valid ROA exists, where the address prefix in the route object
exactly matches a prefix listed in the ROA, or the ROA contains a
covering aggregate and the prefix length of the route object is
smaller than or equal to the ROA's associated maxLength attribute,
and the origin AS in the route object matches the origin AS listed
in the ROA.
More Specific:
A valid ROA exists, where an address prefix in the ROA is a
covering aggregate of the prefix in the route object, and the
prefix length of the route object is greater than the ROA's
associated maxLength attribute, and the origin AS in the route
object matches the AS listed in the ROA.
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AS Mismatch:
A valid ROA exists where the address prefix in the route object
exactly matches a prefix listed in the ROA, or the ROA contains a
covering aggregate and the prefix length of the route object is
smaller than or equal to the ROA's associated maxLength attribute,
and the origin AS of the route object does not match the AS listed
in the ROA.
More Specific AS Mismatch:
A valid ROA exists where an address prefix in the ROA is a
covering aggregate of the prefix in the route object, the prefix
length of the route object is greater than the ROA's associated
maxLength attribute, and the origin AS of the route object does
not match the AS listed in the ROA.
If any of the ROAs in the set provide an "Exact Match" outcome then
the BGP route object can be interpreted by the Relying Party as
"valid", otherwise the route object can be regarded as "invalid".
2.2. Linked Validation
The linked approach requires the route object to reference a ROA
either by inclusion of the ROA as an attribute of the route object,
or inclusion of a identity field in an attribute of the route object
as a means of identifying a particular ROA.
If the ROA can be located is valid within the context of the RPKI
then the route object can be compared against the ROA, as per the
previous section, and can be validated if there is an "Exact Match"
and otherwise be regarded as invalid.
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 candidate 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 here that the validation outcome (or "unknown",
"valid" or "invalid") 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].
The proposed addition to the local degree of preference is "valid" is
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to be preferred over "unknown" over "invalid".
3.1. Validation Outcomes and Rejection of BGP Route
Objects
It is a matter of local preference setting whether "invalid" route
objects are discarded from further consideration in the route
selection process, however the following consideration should be
taken into account in such a situation.
The consideration here is one of potential circularity of dependence.
If the authoritative publication point of the repository of ROAs or
any certificates used in relation to an address prefix is stored at a
location that lies within the address prefix described in a ROA, then
the repository can only be accessed once a route for the prefix has
been accepted by the local routing domain. It is also noted that the
propagation time of RPKI objects may be different to the propagation
time of route objects in BGP, and that route objects may be received
before the relying party's local repository cache picks up the
associated ROAs and recognises them as valid within the RPKI.
For these reasons it is advised that, even in the case of
comprehensive deployment of ROAs, "unknown" and "invalid" validations
should not be considered as sufficient grounds to reject a route
advertisement outright. Alternate approaches may involve the use of
a local timer to accept the route for an interim period of time until
there is an acceptable level of assurance that all reasonable efforts
to local a valid ROA have been undertaken.
4. Further Considerations
This document provides a description of how ROAs 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 considerations about this approach to
origination validation that are not specified here.
These considerations include:
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o It is not specified when validation of an advertised prefix should
be performed by a BGP speaker. Is is considered to be a matter of
local policy whether it is considered to be 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. It is also not specified whether
origination validation should be performed each time a route
object is updated by a peer even when the origin AS has not
altered.
o The lifetime of a validation outcome is not specified here. This
specifically refers to the time period during which the original
validation outcome can be still applied, and the time when the
routing object be revalidated. It is a matter of local policy
setting as to whether a validation outcome be regarded as valid
until the route object is withdrawn or further updated, or whether
validation of a route object should occur at more frequent
intervals?
o It is a matter of local policy as to whether there are
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 It is a matter of local configuration as to whether ROA validation
is performed on a per-AS basis rather than a per-BGP speaker, and
the appropriate BGP mechanisms to support such a per-AS iBGP route
validation service are not considered here.
5. Security Considerations
This approach to origination validation does not allow for
'deterministic' validation in terms of the ability of a BGP speaker
to accept or reject an advertised route object outright, given that
there remains some issues of potential circularity of dependence and
time lags between the propagation of information in the routing
system and propagation of information in the RPKI.
There are also issues of the most appropriate interpretation of
outcomes where validation of the authenticity of the route object has
not been possible in the context of partial adoption of the RPKI,
where the absence of validation information does not necessarily
constitute sufficient grounds to interpret the route object as an
invalidly originated object.
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6. IANA Considerations
[There are no IANA considerations in this document.]
7. Changes from draft-ietf-sidr-roa-validation-01
Following WG discussion at IETF 74 on the appropriate means of
specification of denial in routing authorizations in the context of
the RPKI, it appears to the authors that there is no general WG
support for the inclusion of an explicit denial capability. Instead,
the authors are of the view there was visible WG support, to the
level of some form of rough consensus, for the approach where a valid
ROA acts as an implicit "denial" for those route objects that have
address prefixes that are more specific than the set of prefixes
specified in the ROA, and for those route objects which have
originating AS numbers other than those listed in valid ROAs that
span the address prefix listed in the route object. This draft has
been revised to remove all references to the use of an explicit
denial object in ROA validation, and uses only the semantics of a ROA
to define an "invalid" route object in this context. The remainder
of the WG internet draft has been left largely intact.
8. 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), March 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),
nOVEMBER 2008.
[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.
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Authors' Addresses
Geoff Huston
Asia Pacific Network Information Centre
Email: gih@apnic.net
George Michaelson
Asia Pacific Network Information Centre
Email: ggm@apnic.net
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