Network Working Group James Uttaro
Internet Draft AT&T
Intended status: Standards Track Matthieu Texier
July 5, 2013 Arbor Networks
Expires: Jan 5, 2014 David Smith
Cisco Systems
Wim Henderickx
Adam Simpson
Alcatel-Lucent
BGP Flow-Spec Extended Community for Traffic Redirect to IP Next Hop
draft-ietf-idr-flowspec-redirect-ip-00.txt
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Abstract
Flow-spec is an extension to BGP that allows for the dissemination
of traffic flow specification rules. This has many possible
applications but the primary one for many network operators is the
distribution of traffic filtering actions for DDoS mitigation. The
flow-spec standard [RFC 5575] defines a redirect-to-VRF action for
policy-based forwarding but this mechanism can be difficult to use,
particularly in networks without L3 VPNs.
This draft proposes a new redirect-to-IP flow-spec action that
provides a simpler method of policy-based forwarding. This action is
indicated by the presence of a new BGP extended community in the
flow-spec route. Many routers already support a redirect-to-IP
filter action and, in this case, the only new functionality implied
by this draft is the ability to signal the action using flow-spec.
Table of Contents
1. Introduction...................................................3
2. Terminology....................................................3
3. Redirect to IP Extended Community..............................3
4. Security Considerations........................................5
5. Acknowledgments................................................6
6. Contributors...................................................6
7. IANA Considerations............................................6
8. References.....................................................6
8.1. Normative References......................................6
8.2. Informative References....................................6
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1. Introduction
Flow-spec is an extension to BGP that allows for the dissemination
of traffic flow specification rules. This has many possible
applications but the primary one for many network operators is the
distribution of traffic filtering actions for DDoS mitigation.
Every flow-spec route is effectively a rule, consisting of a
matching part (encoded in the NLRI field) and an action part
(encoded as a BGP extended community). The flow-spec standard [RFC
5575] defines widely-used filter actions such as discard and rate
limit; it also defines a redirect-to-VRF action for policy-based
forwarding. Using the redirect-to-VRF action for redirecting traffic
towards an alternate destination is useful for DDoS mitigation but
it can be complex and cumbersome, particularly in networks without
L3 VPNs.
This draft proposes a new redirect-to-IP flow-spec action that
provides a simpler method of policy-based forwarding. This action is
indicated by the presence of a new BGP extended community in the
flow-spec route. Many routers already support a redirect-to-IP
filter action and, in this case, the only new functionality implied
by this draft is the ability to signal the action using flow-spec.
2. Terminology
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].
3. Redirect to IP Extended Community
This document proposes a new BGP extended community called "Flow
spec redirect/mirror to IP next-hop" with type value 0x0800
(assigned from the "BGP Extended Communities Type - extended,
transitive" registry). The new extended community, simply called
"redirect to IP" in the remainder of this document, can be added to
any UPDATE message announcing the reachability of one or more flow-
spec NLRI. The encoding of the attribute is shown in Figure 1. In
the 6 bytes of data after the 2-byte type value the least-
significant bit is the 'C' (copy) bit. If 'C' is equal to 1 the
originator of the flow-spec route is requesting a mirror action:
routers that install this flow-spec route should create a copy of
every matching packet and forward the copies towards a specified
next-hop address while still forwarding the original packets
normally (i.e. based on longest-prefix-match forwarding table
lookups). If 'C' is equal to 0 the originator of the flow-spec route
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is requesting a simple redirect action: routers that install this
flow-spec route should forward the matching packets (the original
versions, not copies) towards a new next-hop address. All bits other
than the 'C' bit in the 6-byte data portion of the extended
community should be set to 0 by the originating BGP speaker and
ignored by receiving BGP speakers.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x08 | 0x00 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (Set to zero and |
| ignored on receipt) |C|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Flow-spec Redirect/Mirror to IP Next-hop Extended Community
Figure 1
The redirect-to-IP extended community is valid with any other set of
flow-spec extended communities except if that set includes a
redirect-to-VRF extended community (type 0x8008) and in that case
the redirect-to-IP extended community should be ignored.
When a BGP speaker receives an UPDATE message with the redirect-to-
IP extended community it is expected to create a traffic filtering
rule for every flow-spec NLRI in the message that has this path as
its best path. The filter entry matches the IP packets described in
the NLRI field and redirects them (C=0) or copies them (C=1) towards
the IPv4 or IPv6 address specified in the 'Network Address of Next-
Hop' field of the associated MP_REACH_NLRI. More specifically: if an
IPv4 [or IPv6] packet with destination address D that is normally
forwarded to a next-hop A matches a filter entry of the type
described above it MUST instead be redirected (C=0) or mirrored
(C=1) to next-hop B, where B is found by FIB lookup of the IPv4 [or
IPv6] address contained in the MP_REACH_NLRI next-hop field (i.e. a
longest-prefix-match lookup). Signaling and applying constraints
beyond longest-prefix-match on the types of interfaces or tunnels
that can be used as the redirection next-hop B are not precluded by
this specification but are nevertheless outside its scope.
If an MP_REACH_NLRI containing one or more flow-spec NLRI does not
have a valid IPv4 or IPv6 address in its next-hop field, or the
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length of the next-hop is 0, then the redirect-to-IP extended
community, if present, should be ignored.
The scope of application (in terms of router interfaces/contexts) of
the filter rules derived from the redirect-to-IP extended community
is outside the scope of this specification except for noting that
filter rules derived from VPNv4 and VPNv6 flow-spec routes should
only be installed in the VRF contexts that import the routes.
The redirect-to-IP extended community is transitive across AS
boundaries. When a flow-spec route with this community is advertised
to an EBGP peer the next-hop address in the MP_REACH_NLRI SHOULD be
reset to an address of the advertising router by default, per normal
BGP procedures. Alternatively, the advertising router MAY be
configured to keep the next-hop unchanged, if it is known that the
destination AS has a valid route to the next-hop address.
The validation check described in [RFC 5575] and revised in
[VALIDATE] SHOULD be applied by default to received flow-spec routes
with the redirect-to-IP extended community, as it is to all types of
flow-spec routes. This means that a flow-spec route with a
destination prefix subcomponent SHOULD NOT be accepted from an EBGP
peer unless that peer also advertised the best path for the matching
unicast route. BGP speakers that support the redirect-to-IP extended
community MUST also, by default, enforce the following check when
receiving a flow-spec route from an EBGP peer:
. If the flow-spec route has an IP next-hop X and includes a
redirect-to-IP extended community, then the BGP speaker
SHOULD discard the redirect-to-ip extended community (and
not propagate it further with the flow-spec route) if the
last AS in the AS_PATH or AS4_PATH attribute of the longest
prefix match for X does not match the AS of the EBGP peer.
It MUST be possible to disable this additional validation check on a
per-EBGP session basis.
4. Security Considerations
A system that originates a flow-spec route with a redirect-to-IP
extended community can cause many receivers of the flow-spec route
to send traffic to a single next-hop, overwhelming that next-hop and
resulting in inadvertent or deliberate denial-of-service. This is
particularly a concern when the redirect-to-IP extended community is
allowed to cross AS boundaries. The validation check described in
section 3 significantly reduces this risk.
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5. Acknowledgments
The authors would like to thank Han Nguyen and Robert Raszuk for
their feedback and suggestions.
This document was prepared using 2-Word-v2.0.template.dot.
6. Contributors
Pradosh Mohapatra
Cumulus Networks
Email: pmohapat@cumulusnetworks.com
7. IANA Considerations
IANA is requested to update the reference for the following
assignment in the "BGP Extended Communities Type - extended,
transitive" registry:
Type value Name Reference
---------- ---------------------------------------- ---------
0x0800 Flow spec redirect/mirror to IP next-hop [this
document]
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
8.2. Informative References
[RFC5575] P. Marques, N. Sheth, R. Raszuk, B. Greene, J.
Mauch, D. McPherson, "Dissemination of Flow
Specification Rules", RFC 5575, August 2009.
[IPV6-FLOW] R. Raszuk, B. Pithawala, D. McPherson,
"Dissemination of Flow Specification Rules for
IPv6", draft-ietf-idr-flow-spec-v6-00, June 2011.
[VALIDATE] Uttaro, J., Filsfils, C., Mohapatra, P., Smith, D.,
"Revised Validation Procedure for BGP Flow
Specifications", draft-ietf-idr-bgp-flowspec-oid-
00, June 2012.
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Authors' Addresses
James Uttaro
AT&T
200 S. Laurel Avenue
Middletown, NJ 07748
USA
Email: ju1738@att.com
David Smith
Cisco
111 Wood Avenue South
Iselin, NJ 08830
USA
E-mail: djsmith@cisco.com
Wim Henderickx
Alcatel-Lucent
Copernicuslaan 50
2018 Antwerp, Belgium
Email: wim.henderickx@alcatel-lucent.be
Adam Simpson
Alcatel-Lucent
600 March Road
Ottawa, Ontario K2K 2E6
Canada
Email: adam.simpson@alcatel-lucent.com
Matthieu Texier
Arbor Networks
38 Rue de Berri
75008 Paris
Email: mtexier@arbor.net
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