Network Working Group James Uttaro
Internet Draft AT&T
Updates: 5575 Clarence Filsfils
Intended Status: Proposed Standard Pradosh Mohapatra
Expiration Date: July 2013 David Smith
Cisco
January 22, 2013
Revised Validation Procedure for BGP Flow Specifications
draft-ietf-idr-bgp-flowspec-oid-01
Abstract
This document describes a modification to the validation procedure
defined in RFC 5575 for the dissemination of BGP flow specifications.
RFC 5575 requires that the originator of the flow specification
matches the originator of the best-match unicast route for the
destination prefix embedded in the flow specification. This allows
only BGP speakers within the data forwarding path (such as autonomous
system border routers) to originate BGP flow specifications. Though
it is possible to disseminate such flow specifications directly from
border routers, it may be operationally cumbersome in an autonomous
system with a large number of border routers having complex BGP
policies. The modification proposed herein enables flow
specifications to be originated from a centralized BGP route
controller.
Status of this Memo
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Uttaro, et al. [Page 1]
Internet Draft Revised Flowspec Validation Procedure June 2012
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This Internet-Draft will expire on July 1, 2013.
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Table of Contents
1 Specification of Requirements ...................... 2
2 Motivation ......................................... 3
3 Introduction ....................................... 5
4 Revised Validation Procedure ....................... 6
5 Security Considerations ............................ 7
6 IANA Considerations ................................ 7
7 Normative References ............................... 7
8 Acknowledgements ................................... 8
9 Authors' Addresses ................................. 8
1. Specification of Requirements
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 [RFC2119].
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2. Motivation
Step (a) of the validation procedure in [RFC5575], section 6 is
defined with the underlying assumption that the flow specification
NLRI traverses the same path, in the inter-domain and intra-domain
route distribution graph, as that of the longest-match unicast route
for the destination prefix embedded in the flow specification.
In the case of inter-domain traffic filtering, for example, the flow
specification originator at the egress border routers of ASN1 (RTR-D
and RTR-E in figure 1) matches the EBGP neighbor that advertised the
longest match destination prefix (RTR-F and RTR-G respectively).
Similarly, at the ingress border routers of ASN1 (RTR-A and RTR-B in
figure 1), the flow specification originator matches the egress IBGP
border routers that had advertised the unicast route for the best-
match destination prefix (RTR-D and RTR-E respectively). This is true
even when ingress border routers select paths from different egress
border routers as best path based upon IGP distance (as an example,
RTR-A chooses RTR-D's path as best; RTR-B chooses RTR-E as the best
path).
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Internet Draft Revised Flowspec Validation Procedure June 2013
/ - - - - - - - - - - - - - -
| ASN1 |
+-------+ +-------+
| | | | | |
| RTR-A | | RTR-B |
| | | | | |
+-------+ +-------+
| \ / |
IBGP \ / IBGP
| \ / |
+-------+
| | | |
| RTR-C |
| | RC | |
+-------+
| / \ |
/ \
| IBGP / \ IBGP |
+-------+ +-------+
| | RTR-D | | RTR-E | |
| | | |
| | | | | |
+-------+ +-------+
| | | |
- - -|- - - - - - - - -|- - -/
| EBGP EBGP |
- - -|- - - - - - - - -|- - -/
| | | |
+-------+ +-------+
| | | | | |
| RTR-F | | RTR-G |
| | | | | |
+-------+ +-------+
| ASN2 |
/ - - - - - - - - - - - - - -
Figure 1
It is highly desirable that each ASN is able to protect itself
independently from network security attacks using the BGP flow
specification NLRI for intra-domain purposes only. Network operators
often deploy a dedicated Security Operations Center (SOC) within
their ASN to monitor and detect such security attacks. To mitigate
attacks in a scalable intra-domain manner, operators require the
ability to originate intra-domain flow specification NLRIs from a
central BGP route controller (or router reflector per [RFC4456]) that
is not within the data forwarding plane. In this way, operators can
direct border routers within their ASN with specific attack
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Internet Draft Revised Flowspec Validation Procedure June 2013
mitigation actions (drop the traffic, forward to a clean-pipe center,
etc.). To originate a flow specification NLRI, a central BGP route
controller (or route reflector) must set itself as the originator in
the flowspec NLRI. This is necessary given the route controller is
originating the flow specification not reflecting it, and to avoid
the complexity of having to determine the egress border router whose
path was chosen as the best in each of the ingress border routers. It
thus becomes necessary to modify step (a) of the RFC 5575 validation
procedure such that an IBGP peer that is not within the data
forwarding plane may originate flow specification NLRIs.
3. Introduction
RFC 5575 defined a new BGP capability that can be used to distribute
traffic flow specifications amongst BGP speakers in support of
traffic filtering. The primary intention of RFC 5575 is to enable
downstream autonomous systems to signal traffic filtering policies to
upstream autonomous systems. In this way, traffic is filtered closer
to the source and the upstream autonomous system(s) avoid carrying
the traffic to the downstream autonomous system only to be discarded.
RFC 5575 also enables more granular traffic filtering based upon
upper layer protocol information (e.g., protocol port numbers) as
opposed to coarse IP destination prefix-based filtering. Flow
specification NLRIs received from a BGP peer are subject to validity
checks before being considered feasible and subsequently installed
within the respective Adj-RIB-In. The validation procedure defined
within RFC 5575 requires that the originator of the flow
specification NLRI matches the originator of the best-match unicast
route for the destination prefix embedded in the flow specification.
This allows only BGP speakers [RFC4271] within the data forwarding
path (such as autonomous system border routers) to originate BGP flow
specification NLRIs. Though it is possible to disseminate such flow
specification NLRIs directly from border routers, it may be
operationally cumbersome in an autonomous system with a large number
of border routers having complex BGP policies. This document
describes a modification to the RFC 5575 validation procedure
allowing flow specification NLRIs to be originated from a centralized
BGP route controller within the local autonomous system that is
neither in the data forwarding path nor serving as a BGP route
reflector [RFC4456]. While the proposed modification cannot be used
for inter-domain coordination of traffic filtering, it greatly
simplifies distribution of intra-domain traffic filtering policies in
an autonomous system with a large number of border routers having
complex BGP policies. By relaxing the validation procedure for IBGP,
the proposed modification allows flow specifications to be
distributed in a standard and scalable manner throughout an
autonomous system.
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4. Revised Validation Procedure
Step (a) of the validation procedure specified in RFC 5575, section 6
is redefined as follows:
a) One of the following conditions MUST hold true:
o The originator of the flow specification matches the
originator of the best-match unicast route for the
destination prefix embedded in the flow specification.
o The AS_PATH and AS4_PATH attribute of the flow
specification are empty.
o The AS_PATH and AS4_PATH attribute of the flow
specification does not contain AS_SET and AS_SEQUENCE
segments.
An empty AS_PATH and AS4_PATH attribute indicates per [RFC4271] that
the flow specification NLRI originated in the same autonomous system
as the local BGP speaker. Similarly, lack of AS_SET and AS_SEQUENCE
segments within an AS_PATH and AS4_PATH attribute that is not empty
indicates that the flow specification NLRI originated in the same
autonomous system as the local BGP speaker but that the autonomous
system includes a BGP confederation [RFC5065]. With this proposed
modification to the RFC 5575 validation procedure, it is now possible
for an IBGP peer that is not within the data forwarding path to
originate flow specification NLRIs. This applies with and without the
presence of a BGP confederation within the autonomous system.
Further, RFC 5575 states that "BGP (flow specification)
implementations MUST also enforce that AS_PATH attribute of a route
received via the External Border Gateway Protocol (eBGP) contains the
neighboring AS in the left-most position of the AS_PATH attribute".
This rule is not valid for all topologies. For example, it prevents
exchange of BGP flow specification NLRIs at Internet exchanges with
BGP route servers. Therefore, this document also redefines the RFC
5575 AS_PATH and AS4_PATH validation procedure referenced above as
follows.
BGP flow specification implementations MUST enforce that the last AS
added within the AS_PATH and AS4_PATH attribute of a EBGP learned
flow specification NLRI MUST match the last AS added within the
AS_PATH and AS4_PATH attribute of the best-match unicast route for
the destination prefix embedded in the flow specification. This
proposed modification enables the exchange of BGP flow specification
NLRIs at Internet exchanges with BGP route servers while at the same
time, for security reasons, prevents an EBGP peer from advertising an
inter-domain flow specification for a destination prefix that it does
not provide reachability information for. Note, comparing only the
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last ASNs is sufficient for EBGP learned flow specification NLRIs.
Requiring a full AS_PATH and AS4_PATH match would limit origination
of inter-domain flow specifications to the origin (or first) AS of
the best-match unicast route for the destination prefix embedded in
the flow specification only. As such, a full AS_PATH and AS4_PATH
validity check may prevent transit ASNs from originating inter-domain
flow specifications which is not desirable.
5. Security Considerations
No new security issues are introduced by relaxing the validation
procedure for IBGP learned flow specifications. With this proposal,
the security characteristics of BGP flow specifications remain
equivalent to the existing security properties of BGP unicast
routing. Traffic flow specifications learned from IBGP peers are
trusted, hence, its not required to validate that the originator of
an intra-domain traffic flow specification matches the originator of
the best-match unicast route for the flow destination prefix.
Conversely, this proposal continues to enforce the validation
procedure for EBGP learned traffic flow specifications. In this way,
the security properties of RFC 5575 are maintained such that an EBGP
peer cannot cause a denial-of-service attack by advertising an
inter-domain flow specification for a destination prefix that it does
not provide reachability information for.
6. IANA Considerations
This document has no actions for IANA.
7. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4271] Rekhter, Y., Li, T., and Hares, S., "A Border Gateway
Protocol 4 (BGP-4)", RFC 4271, January 2006.
[RFC4456] Bates, T., Chen, E., and Chandra, R., "BGP Route
Reflection: An Alternative to Full Mesh Internal BGP (IBGP)", RFC
4456, April 2006.
[RFC5065] Traina, P., McPherson, D., and Scudder, J., "Autonomous
System Confederations for BGP", August 2007.
[RFC5575] Marques, P., Sheth, N., Raszuk, R., Greene, B., Mauch, J.,
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Internet Draft Revised Flowspec Validation Procedure June 2013
and McPherson, D., "Dissemination of Flow Specification Rules", RFC
5575, August 2009.
8. Acknowledgements
The authors would like to thank Han Nguyen for his direction on this
work as well as Waqas Alam, Keyur Patel, Robert Raszuk, Eric Rosen
and Shyam Sethuram for their review comments.
9. Authors' Addresses
James Uttaro
AT&T
200 S. Laurel Avenue
Middletown, NJ 07748
USA
Email: ju1738@att.com
Clarence Filsfils
Cisco
Brussels 1000
BE
Email: cf@cisco.com
Pradosh Mohapatra
Cisco
170 W. Tasman Drive
San Jose, CA 95134
USA
Email: pmohapat@cisco.com
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David J. Smith
Cisco
111 Wood Avenue South
Iselin, NJ 08830
USA
E-mail: djsmith@cisco.com
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