BGP Prefix Origin Validation
draft-ietf-sidr-pfx-validate-05
Network Working Group P. Mohapatra
Internet-Draft Cisco Systems
Intended status: Standards Track J. Scudder
Expires: October 19, 2012 Juniper Networks
D. Ward
Cisco Systems
R. Bush
Internet Initiative Japan, Inc.
R. Austein
Dragon Research Labs
April 17, 2012
BGP Prefix Origin Validation
draft-ietf-sidr-pfx-validate-05
Abstract
To help reduce well-known threats against BGP including prefix mis-
announcing and monkey-in-the-middle attacks, one of the security
requirements is the ability to validate the origination AS of BGP
routes. More specifically, one needs to validate that the AS number
claiming to originate an address prefix (as derived from the AS_PATH
attribute of the BGP route) is in fact authorized by the prefix
holder to do so. This document describes a simple validation
mechanism to partially satisfy this requirement.
Status of this Memo
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Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 5
2. Prefix-to-AS Mapping Database . . . . . . . . . . . . . . . . 5
2.1. Pseudo-Code . . . . . . . . . . . . . . . . . . . . . . . 7
3. Policy Control . . . . . . . . . . . . . . . . . . . . . . . . 7
4. Interaction with Local Cache . . . . . . . . . . . . . . . . . 8
5. Deployment Considerations . . . . . . . . . . . . . . . . . . 8
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
8. Security Considerations . . . . . . . . . . . . . . . . . . . 9
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
9.1. Normative References . . . . . . . . . . . . . . . . . . . 9
9.2. Informational References . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
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1. Introduction
A BGP route associates an address prefix with a set of autonomous
systems (AS) that identify the interdomain path the prefix has
traversed in the form of BGP announcements. This set is represented
as the AS_PATH attribute in BGP [RFC4271] and starts with the AS that
originated the prefix. To help reduce well-known threats against BGP
including prefix mis-announcing and monkey-in-the-middle attacks, one
of the security requirements is the ability to validate the
origination AS of BGP routes. More specifically, one needs to
validate that the AS number claiming to originate an address prefix
(as derived from the AS_PATH attribute of the BGP route) is in fact
authorized by the prefix holder to do so. This document describes a
simple validation mechanism to partially satisfy this requirement.
The Resource Public Key Infrastructure (RPKI) describes an approach
to build a formally verifiable database of IP addresses and AS
numbers as resources. The overall architecture of RPKI as defined in
[RFC6480] consists of three main components:
o A public key infrastructure (PKI) with the necessary certificate
objects,
o Digitally signed routing objects,
o A distributed repository system to hold the objects that would
also support periodic retrieval.
The RPKI system is based on resource certificates that define
extensions to X.509 to represent IP addresses and AS identifiers
[RFC3779], thus the name RPKI. Route Origin Authorizations (ROA)
[RFC6482] are separate digitally signed objects that define
associations between ASes and IP address blocks. Finally the
repository system is operated in a distributed fashion through the
IANA, RIR hierarchy, and ISPs.
In order to benefit from the RPKI system, it is envisioned that
relying parties either at AS or organization level obtain a local
copy of the signed object collection, verify the signatures, and
process them. The cache must also be refreshed periodically. The
exact access mechanism used to retrieve the local cache is beyond the
scope of this document.
Individual BGP speakers can utilize the processed data contained in
the local cache to validate BGP announcements. The protocol details
to retrieve the processed data from the local cache to the BGP
speakers is beyond the scope of this document (refer to
[I-D.ietf-sidr-rpki-rtr] for such a mechanism). This document
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proposes a means by which a BGP speaker can make use of the processed
data in order to assign a "validation state" to each prefix in a
received BGP UPDATE message.
Note that the complete path attestation against the AS_PATH attribute
of a route is outside the scope of this document.
Although RPKI provides the context for this draft, it is equally
possible to use any other database which is able to map prefixes to
their authorized origin ASes. Each distinct database will have its
own particular operational and security characteristics; such
characteristics are beyond the scope of this document.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2. Prefix-to-AS Mapping Database
The BGP speaker loads validated objects from the cache into local
storage. The objects loaded have the content (IP address, prefix
length, maximum length, origin AS number). We refer to such a
locally stored object as a "Validated ROA Payload" or "VRP".
We define several terms in addition to "VRP". Where these terms are
used, they are capitalized:
o Prefix: (IP address, prefix length), interpreted as is customary
(see [RFC4632]).
o Route: Data derived from a received BGP UPDATE, as defined in
[RFC4271], Section 1.1. The Route includes one Prefix and an
AS_PATH; it may include other attributes to characterize the
prefix.
o VRP Prefix: The Prefix from a VRP.
o VRP ASN: The origin AS number from a VRP.
o Route Prefix: The Prefix derived from a route.
o Route Origin ASN: The origin AS number derived from a Route. The
origin AS number is the rightmost AS in the final segment of the
AS_PATH attribute in the Route if that segment is of type
AS_SEQUENCE, or the distinguished value "NONE" if the final
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segment of the AS_PATH attribute is of any type other than
AS_SEQUENCE.
o Covered: A Route Prefix is said to be Covered by a VRP when the
VRP prefix length is less than or equal to the Route prefix length
and the VRP prefix address matches the Route prefix address for
all bits specified by the VRP prefix length. (This is simply a
statement of the well-known concept of determining a prefix
match.)
o Matched: A Route Prefix is said to be Matched by a VRP when the
Route Prefix is Covered by that VRP and in addition, the Route
prefix length is less than or equal to the VRP maximum length and
the Route Origin ASN is equal to the VRP ASN.
Given these definitions, any given BGP Route will be found to have
one of the following "validation states":
o NotFound: No VRP Covers the Route Prefix.
o Valid: At least one VRP Matches the Route Prefix.
o Invalid: At least one VRP Covers the Route Prefix, but no VRP
Matches it.
We observe that no VRP can have the value "NONE" as its VRP ASN.
Thus a Route whose Origin ASN is "NONE" cannot be Matched by any VRP.
Similarly, no valid Route can have an Origin ASN of zero
[I-D.ietf-idr-as0]. Thus no Route can be Matched by a VRP whose ASN
is zero.
When a BGP speaker receives an UPDATE from a neighbor, it SHOULD
perform a lookup as described above for each of the Routes in the
UPDATE message. The lookup SHOULD also be applied to routes which
are redistributed into BGP from another source, such as another
protocol or a locally defined static route. An implementation MAY
provide configuration options to control which routes the lookup is
applied to. The "validation state" of the Route MUST be set to
reflect the result of the lookup. The implementation should consider
the "validation state" as described in the document as a local
property or attribute of the Route. If validation is not performed
on a Route, the implementation SHOULD initialize the "validation
state" of such a route to "NotFound".
Use of the validation state is discussed in Section 3 and Section 5.
An implementation MUST NOT exclude a route from the Adj-RIB-In or
from consideration in the decision process as a side-effect of its
validation state, unless explicitly configured to do so.
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We observe that a Route can be Matched or Covered by more than one
VRP. This procedure does not mandate an order in which VRPs must be
visited; however, the "validation state" output is fully determined.
2.1. Pseudo-Code
The following pseudo-code illustrates the procedure above. In case
of ambiguity, the procedure above, rather than the pseudo-code,
should be taken as authoritative.
result = BGP_PFXV_STATE_NOT_FOUND;
//Iterate through all the Covering entries in the local VRP
//database, pfx_validate_table.
entry = next_lookup_result(pfx_validate_table, route_prefix);
while (entry != NULL) {
prefix_exists = TRUE;
if (route_prefix_length <= entry->max_length) {
if (route_origin_as != NONE
&& entry->origin_as != 0
&& route_origin_as == entry->origin_as) {
result = BGP_PFXV_STATE_VALID;
return (result);
}
}
entry = next_lookup_result(pfx_validate_table, input.prefix);
}
//If one or more VRP entries Covered the route prefix, but
//no one Matched, return "Invalid" validation state.
if (prefix_exists == TRUE) {
result = BGP_PFXV_STATE_INVALID;
}
return (result);
3. Policy Control
An implementation MUST provide the ability to match and set the
validation state of routes as part of its route policy filtering
function. Use of validation state in route policy is elaborated in
Section 5. For more details on operational policy considerations,
see [I-D.ietf-sidr-origin-ops].
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An implementation MUST support Four-Octet AS Numbers, [RFC4893].
4. Interaction with Local Cache
Each BGP speaker supporting prefix validation as described in this
document is expected to communicate with one or more RPKI caches,
each of which stores a local copy of the global RPKI database. The
protocol mechanisms used to gather and validate these data and
present them to BGP speakers are described in
[I-D.ietf-sidr-rpki-rtr].
The prefix-to-AS mappings used by the BGP speaker are expected to be
updated over time. When a mapping is added or deleted, the
implementation MUST re-validate any affected prefixes. An "affected
prefix" is any prefix that was matched by a deleted or updated
mapping, or could be matched by an added mapping.
5. Deployment Considerations
Once a Route is selected for validation, it is categorized according
the procedure given in Section 2. Subsequently, routing policy as
discussed in Section 3 can be used to take action based on the
validation state.
Policies which could be implemented include filtering routes based on
validation state (for example, rejecting all "invalid" routes) or
adjusting a route's degree of preference in the selection algorithm
based on its validation state. The latter could be accomplished by
adjusting the value of such attributes as LOCAL_PREF. Considering
invalid routes for BGP decision process is a pure local policy matter
and should be done with utmost care.
In some cases (particularly when the selection algorithm is
influenced by the adjustment of a route property that is not
propagated into IBGP) it could be necessary for routing correctness
to propagate the validation state to the IBGP peer. This can be
accomplished on the sending side by setting a community or extended
community based on the validation state, and on the receiving side by
matching the (extended) community and setting the validation state.
6. Acknowledgments
The authors wish to thank Rex Fernando, Hannes Gredler, Mouhcine
Guennoun, Russ Housley, Junaid Israr, Miya Kohno, Shin Miyakawa, Taka
Mizuguchi, Hussein Mouftah, Keyur Patel, Tomoya Yoshida, Kannan
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Varadhan, and Wes George. The authors are grateful for the feedback
from the members of the SIDR working group.
Junaid Israr's contribution to this specification was part of his PhD
research work and thesis at University of Ottawa.
7. IANA Considerations
8. Security Considerations
Although this specification discusses one portion of a system to
validate BGP routes, it should be noted that it relies on a database
(RPKI or other) to provide validation information. As such, the
security properties of that database must be considered in order to
determine the security provided by the overall solution. If
"invalid" routes are blocked as this specification suggests, the
overall system provides a possible denial-of-service vector, for
example if an attacker is able to inject or remove one or more
records in the validation database, it could lead an otherwise valid
route to be marked as invalid.
In addition, this system is only able to provide limited protection
against a determined attacker -- the attacker need only prepend the
"valid" source AS to a forged BGP route announcement in order to
defeat the protection provided by this system.
This mechanism does not protect against "AS in the middle attacks" or
provide any path validation. It only attempts to verify the origin.
In general, this system should be thought of more as a protection
against misconfiguration than as true "security" in the strong sense.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[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.
[RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing
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(CIDR): The Internet Address Assignment and Aggregation
Plan", BCP 122, RFC 4632, August 2006.
[RFC4893] Vohra, Q. and E. Chen, "BGP Support for Four-octet AS
Number Space", RFC 4893, May 2007.
[RFC6482] Lepinski, M., Kent, S., and D. Kong, "A Profile for Route
Origin Authorizations (ROAs)", RFC 6482, February 2012.
9.2. Informational References
[I-D.ietf-idr-as0]
Kumari, W., Bush, R., Schiller, H., and K. Patel,
"Codification of AS 0 processing.", draft-ietf-idr-as0-03
(work in progress), January 2012.
[I-D.ietf-sidr-origin-ops]
Bush, R., "RPKI-Based Origin Validation Operation",
draft-ietf-sidr-origin-ops-15 (work in progress),
March 2012.
[I-D.ietf-sidr-rpki-rtr]
Bush, R. and R. Austein, "The RPKI/Router Protocol",
draft-ietf-sidr-rpki-rtr-26 (work in progress),
February 2012.
[RFC6480] Lepinski, M. and S. Kent, "An Infrastructure to Support
Secure Internet Routing", RFC 6480, February 2012.
Authors' Addresses
Pradosh Mohapatra
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
USA
Email: pmohapat@cisco.com
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John Scudder
Juniper Networks
1194 N. Mathilda Ave
Sunnyvale, CA 94089
USA
Email: jgs@juniper.net
David Ward
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
USA
Email: dward@cisco.com
Randy Bush
Internet Initiative Japan, Inc.
5147 Crystal Springs
Bainbridge Island, Washington 98110
USA
Email: randy@psg.com
Rob Austein
Dragon Research Labs
Email: sra@hactrn.net
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