wdiff draft-ietf-sidr-roa-validation-01.txt draft-ietf-sidr-roa-validation-02.txt

Secure Inter-Domain Routing (SIDR) G. Huston
Internet-Draft G. Michaelson
Intended status: Informational APNIC
Expires: April 9, February 5, 2010 August 4, 2009 October 6, 2008

Validation of Route Origination in BGP using the Resource Certificate
PKI
draft-ietf-sidr-roa-validation-01.txt
draft-ietf-sidr-roa-validation-02.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
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
3. Applying Validation . . . . . . . . . . . . . Outcomes to BGP Route Selection . . . . . . 4
2.2. Linked Validation . .
4. Further Considerations . . . . . . . . . . . . . . . . . . 6
3. Applying Validation Outcomes to BGP Route Selection . . 5
5. Security Considerations . . . 6
3.1. Validation Outcomes and Rejection of BGP Route Objects . . 9
4. Further Considerations . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . 9
5. Security Considerations . . . . . . . . . . . . . . . . . 7
7. Changes -01 to -02 . . 10
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
7. 7
8. Normative References . . . . . . . . . . . . . . . . . . . . . 11 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
Intellectual Property and Copyright Statements . . . . . . . . . . 13 8

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].

Bogon Origin Attestations (BOAs) are digitally signed objects that
describe a collection of address prefixes and AS numbers that are not
authorised by the right-of-use holder to be advertised in the inter-
domain routing system [I-D.ietf-sidr-boa].

This document describes how ROA and BOA validation outcomes can be
used in the BGP route selection process, and how the proposed
application of ROAs and BOAs are intended to fit within the
requirements for adding security to inter-domain routing
[ID.ietf-rpsec-bgpsecrec], routing, including
the ability to support incremental and piecemeal deployment.

This document describes the semantic interpretation of a valid ROA,
with particular reference to application in BGP relating to the
origination of route objects. The document does not describe any
application of a ROA to validation of the AS Path.

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 "Route Object" is an address prefix and a set of attributes.
In terms of ROA and BOA validation of the Route Object the prefix value and the
origin AS attribute 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.

BOA validation is described in [I-D.ietf-sidr-boa], and the outcome
of the validation operation

It is assumed here that the BOA 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.

2.1. Decoupled Validation

The decoupled approach is where the ROAs are managed and distributed
independently of the operation of the routing protocol BGP itself, 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

A BGP route object does not refer to a specific ROA. ROA that should be
used by a Relying Party (RP) to validate the origination information
contained in the route object, nor does it refer to the set of
certificates that the RP should use to validate the ROA's digital
signature. The relying party RP needs to match a route object to one or more
candidate valid ROAs and BOAs in order to determine the appropriate local
actions to perform on the route object.

The relying party selects the set of 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

To validate 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 object the ROA's prefix length and
greater then or equal to RP would undertake the ROA's corresponding maxLength attribute.

The following outcomes are possible using the defined ROA validation
procedure for each ROA in this set:

Exact Match:
A
steps:

1. Select all valid ROA exists, where the address prefix in the route object
exactly matches a prefix listed in the ROA, or the ROA contains ROAs that include a
covering aggregate and the prefix length of the route object is
smaller than ROAIPAddress value that
either matches, 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.

Covering Match:
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.

Exact 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 of, the origin AS of the route object does not match the AS listed
in the ROA.

Covering 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.

No ROA:
There are no Exact Matches, Covering Matches, no Exact Mismatches
or Covering Mismatches in the RPKI repository.

The ROA to be used for the validation function is selected from object.
2. If the set of candidate ROAs in the order given above. In other words an Exact Match is preferred over a Covering Match, which, in turn, is preferred over
an Exact Mismatch which is preferred over a Covering Mismatch.

The set of BOAs that are used for empty the validation function are
composed of the set of valid BOAs where the origin AS of the route
object matches an AS described in a BOA, or where an address prefix
in a valid BOA that is process
stops with an exact match or a covering aggregate of the
route object. In the case that the validation outcome using ROAs is
one of Exact Mismatch, Covering Mismatch or No ROA, then the
validation outcome of the BOA changes the overall validation result
to "Bogon".

Bogon:
A valid BOA exists where an address prefix in the BOA is a an
exact match for the prefix in the route object, or is a covering
aggregate of the prefix in the route object, or "unknown".
3. If any ROA has an AS in the BOA asID value that matches the originating AS in
the BOA. In addition, there is no
valid ROA that is an Exact Match or a Covering Match with the
route object.

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 and either the route object can be compared against the ROA, as per the
previous section, giving one of five possible results: Exact Match,
Covering Match, Exact Mismatch, Covering Mismatch, and No Match,
which is defined as:

No Match:
The valid ROA does not comtain any object's address prefix that exactly
precisely matches the an address prefix in the route object, ROA, or the route object's
address prefix is a covering
aggregate more specific prefix of the address prefix in the route object.

In the case of a Mismatch or a No Match condition, the relying party
should check for the presence of valid BOAs where the origin AS of
ROA and the route object matches an AS described in a BOA, or where an
address prefix in a valid BOA that length value is an exact match less than or a covering
aggregate of equal to the route object. If a valid BOA can be found that
matches either of these conditions that
ROAIPAddress's maxLength value, then the overall route object validation of a route object process stops
with a linked ROA an outcome of "valid".
4. Otherwise, the validation outcome is changed to "Bogon". "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 set, which is then used locally by placing installing it in
the
loc-RIB, loc-RIB [RFC4271], and is announced to peers as the local "best"
route.

It is proposed here that the ROA validation outcome of "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].

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 a strong 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, unless the object is described in a BOA.

In the case of a partial deployment scenario of RPKI route
attestation objects, where some address prefixes and AS numbers are
described in ROAs or BOAs and others are not, then the relative
ranking of validation outcomes from the highest (most preferred) to
the lowest (least preferred) degree of preference are proposed to be
as specified int he following list. The exact values to apply to a
Local Preference setting are left as a matter of local policy and
local configuration.

1. Exact Match

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

This is slightly less preferred because it is possible that the
address holder of the aggregate has allocated the prefix in
question to a different party. It is also possible that the
originating AS is using more specific advertisements as part of a
traffic engineering scenario.

3. No ROA

In the case of partial deployment of ROAs, the absence of
validation credentials is a neutral outcome, in that there is no
grounds proposed addition to increase or decrease the relative local degree of preference
for the route object.

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 "valid" 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. 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.

6. No Match

Here the route object has referenced a ROA that preferred over "unknown" over "invalid".

It is not valid, or
does not include an address prefix that matcehs the route object,
or the referenced ROA could not be located. This could be an
attempt to create a false route object and use an invalid ROA.

7. Bogon

Here the right-of-use holder of the AS or address prefix has
explicitly tagged the address prefix or the AS as a "bogon".
This implies that the announcement has been made without the
appropriate authority, and the local preference of the route
object should be ranked at a level commensurate with rejecting
the route object.

In the case of comprehensive deployment of RPKI route attestion
objects the absence matter of a specific ROA origination authority for the
route object should render it as an unusable for routing. In this
case the local preference BGP selection policy in setting for the whether
"invalid" route object is as follows:

1. Exact Match

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, No ROA, Covering Mismatch, Exact Mismatch, No
Match

The local preference of objects are discarded from further consideration in
the route object should be ranked at a
level of least preferred, due to the constraints noted in selection process, however the following section.

3. Bogon

Here the right-of-use holder of the AS or address prefix has
explicitly tagged the address prefix or the AS as a "bogon".
This implies that the announcement has been made without the
appropriate authority, and the local preference of the route
object consideration
should be ranked at a level commensurate with rejecting
the route object.

3.1. Validation Outcomes and Rejection of BGP Route Objects

In the case of comprehensive deployment of ROAs, the use of a
validation outcome other than an Exact Match as sufficient grounds to
reject taken into account in such a route object should be undertaken with care. 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 proposed that, even in the case of
comprehensive deployment of ROAs, a missing ROA or a mismatch advised that local policy settings should not be
result in "unknown" validation outcomes being considered as
sufficient grounds to reject a route
advertisement outright. Alternate approaches object outright from
consideration as a local "best" route.

A local policy setting may be considered such that "invalid"
validation outcomes would be sufficient grounds to reject the route
object. However, due to the considerations of circular dependence
and differing propagation times as noted above, a local policy
setting may be considered that would involve the use of a local timer
to accept the route as feasible for an interim period of time until
there is an acceptable level of assurance that all reasonable efforts
to local obtain a valid ROA for the object have been undertaken.

4. Further Considerations

This document provides a description of how ROAs and BOAs 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 relevant to
the operation of a BGP speaker that are not specified here.

These considerations include:

o It is not specified when validation of an advertised prefix should
be performed by a BGP speaker. Is It is considered to be a matter of
local policy whether it is considered to be strictly necessary required to perform validation
at a point prior to loading the object into the Adj-RIB-In structure,
structure [RFC4271], 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 at the time when expiration of
which the routing object should be revalidated. re-tested for validity. 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 whther 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. intervals.

o It is a matter of local configuration as to whther 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 de-coupled framework of
validation service of ROAs and the loading of outcomes into BGP speakers
are not considered here.

5. Security Considerations

This approach to orgination validation does not allow for
'deterministic' origination validation in terms uses a model of positive
security, where information that cannot be validated within the ability RPKI
framework is intended to interpreted by a RP as invalid.

However, the considerations of accommodating environments of partial
adoption, where only a BGP speker subset of valid route objects have associated
ROAs within the structure of the RPKI imply some modification to
accept or reject the
model of positive security. Here it is assumed that once an advertised address
prefix is described in a ROA, then this ROA "protects" all address
prefixes that are more specific than that described in the ROA.
Thus, any more specific address prefix and originating AS combination
of a valid ROA, that does not have a matching valid ROA is considered
to be "invalid".

The match condition of a route object outright, given that
there remains some issues against a single ROA is
summarized in the following table:

In an environment of potential circularity a collection of dependence ROAs, a route object is
considered "valid" if any ROA provides a "valid" outcome, and
time lags between
"invalid" if one or more ROAs provide an "invalid" outcome and no
ROAs provide a "valid" outcome. The "unknown" outcome occurs when no
ROA produces a "valid" or an "invalid" outcome.

6. IANA Considerations

[There are no IANA considerations in this document.]

7. Changes -01 to -02

Following WG review of the propagation means of information specification of denial in the
routing
system and propagation of information authorizations in the RPKI.

There are also issues context of the most appropirate RPKI at IETF 74 and IETF
75, it appears that there is no general WG support for the use of an
explicit denial object (termed a 'BOA'). The alternative approach,
explored in previous iterations of this draft, used a more restricted
interpretation of a ROA that yielded only "valid" or "unknown"
outcomes (by using "unknown" where validation "invalid" is used in this revision
of the authenticity of document). To allow for "invalid" outcomes the route object has
not been possible in draft used the context of partial adoption of
BOA to undertake the RPKI, role of a 'disavow' constraint, where a route
object was considered to be "invalid" if it was the absense subject of validation information does a
valid BOA and was not necessarily
constitute sufficient grounds considered to interpret the route object as an
invalidly originated object. be "valid" by any valid ROA. The consequence of these considerations is that while
reasons advanced to support the use dropping of ROAs
can increase the confidence in BOA was the validity increased
complexity of origination RP systems through the use of a second object in route
objects that match
validation, a valid ROA, ROAs cannot perform potentially confusing mismatch in the opposite,
namely interpretation
scope between the rejection ROA and the BOA, where the ROA's scope was limited
to set of route objects that cannot be validated by
ROAs. To assist prefixes described in the case of rejecting some forms ROA, while the BOA's scope
included all possible more specifics of route objects
that cannot be explicitly validated, the prefixes listed in the
BOA, and the ability to reconstruct the semantic equivalent of a BOA has been
through the use of a ROA that used as a means restricted-use AS as its asID.
Accordingly, this draft has been revised to remove all references to
the use of an explicit rejection denial object and uses the implicit semantics
of certain classes route objects. The
implication is that publishers denial in the RPKI should publish both ROAs
and BOAs a ROA object.

There appears to be no WG interest in order consideration of validation in
a "linked" model, where a ROA is bound to provide the greatest level of information route object that
will allow relying parties it is
intended to make appropriate choices in terms validate. Accordingly this section of
route preference selection.

6. IANA Considerations

[There are no IANA considerations in the text has also
been dropped from this document.]

7. version.

8. Normative References

[I-D.ietf-sidr-arch]
Lepinski, M., Kent, S., M. and R. Barnes, S. Kent, "An Infrastructure to Support
Secure Internet Routing", draft-ietf-sidr-arch (work in
progress), February 2008.

[I-D.ietf-sidr-boa]
Huston, G., Manderson, T., and G. Michaelson, "Profile for
Bogon Origin Attestations (BOAs)", draft-ietf-sidr-bogons
(work in progress), August 2008. July 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), July 2008.

[ID.ietf-rpsec-bgpsecrec]
Christian, B. and T. Tauber, "BGP Security Requirements",
draft-ietf-sidr-roa-format (work in progress),
November 2007. 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.

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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