Internet DRAFT - draft-ietf-bess-fat-pw-bgp
draft-ietf-bess-fat-pw-bgp
INTERNET-DRAFT K. Patel
Intended Status: Standard Track Arrcus
Updates: 4761 S. Boutros
VMware
J. Liste
Cisco
B. Wen
Comcast
J. Rabadan
Nokia
Expires: September 3, 2018 March 2, 2018
Extensions to BGP Signaled Pseudowires to support Flow-Aware Transport
Labels
draft-ietf-bess-fat-pw-bgp-04
Abstract
This draft defines protocol extensions required to synchronize flow
label states among Provider Edges PE(s) when using the BGP-based
signaling procedures. These protocol extensions are equally
applicable to point-to-point Layer2 Virtual Private Networks
(L2VPNs). This draft updates RFC 4761 by defining new flags in the
Control Flags field of the Layer2 Info Extended Community.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
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Copyright and License Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Requirements Language . . . . . . . . . . . . . . . . . . . 4
2. Modifications to Layer2 Info Extended Community . . . . . . . . 5
3. Signaling the Presence of the Flow Label . . . . . . . . . . . 6
4 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 7
5 Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Normative References . . . . . . . . . . . . . . . . . . . 8
8.2. Informative References . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
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1 Introduction
The mechanism described in [RFC6391] uses an additional label (Flow
Label) in the MPLS label stack to allow Label Switch Routers to
balance flows within Pseudowires at a finer granularity than the
individual Pseudowires across the Equal Cost Multiple Paths (ECMPs)
that exists within the Packet Switched Network (PSN).
Furthermore, [RFC6391] defines the LDP protocol extensions required
to synchronize the flow label states between the ingress and egress
PEs when using the signaling procedures defined in the [RFC8077].
A pseudowire (PW) [RFC3985] is transported over one single network
path, even if Equal Cost Multiple Paths (ECMPs) exist between the
ingress and egress PW provider edge (PE) equipment. This is required
to preserve the characteristics of the emulated service.
This draft introduces an optional mode of operation allowing to
transport a PW over ECMPs, for example when the use of these is known
to be beneficial to the operation of the PW. This specification uses
the principles defined in [RFC6391], and augments the BGP-signaling
procedures of [RFC4761] and [RFC6624]. The use of a single path to
preserve the packet delivery order remains the default mode of
operation of a PW, and is described in [RFC4385] and [RFC4928].
High bandwidth Ethernet-based services are a prime example that
benefits from the ability to load-balance flows in a PW over multiple
PSN paths. In general, load-balancing is applicable when the PW
attachment circuit bandwidth and PSN core link bandwidth are of same
order of magnitude.
To achieve the load-balancing goal, [RFC6391] introduces the notion
of an additional Label Stack Entry (LSE) (Flow label) located at the
bottom of the stack (right after PW LSE). Label Switching Routers
(LSRs) commonly generate a hash of the label stack in order to
discriminate and distribute flows over available ECMPs. The presence
of the Flow label (closely associated to a flow determined by the
ingress PE) will normally provide the greatest entropy.
Furthermore, following the procedures for Inter-AS scenarios
described in [RFC4761] section 3.4, the Flow label should never be
handled by the ASBRs, only the terminating PEs on each AS will be
responsible for popping or pushing this label. This is equally
applicable to Method B [RFC4761] section 3.4.2 where ASBRs are
responsible for swapping the PW label as traffic traverses from ASBR
to PE and ASBR to ASBR directions. Therefore, the Flow label will
remain untouched across AS boundaries.
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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].
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2. Modifications to Layer2 Info Extended Community
The Layer2 Info Extended Community is used to signal control
information about the pseudowires to be setup. The extended community
format is described in [RFC4761]. The format of this extended
community is described as:
+------------------------------------+
| Extended community type (2 octets) |
+------------------------------------+
| Encaps Type (1 octet) |
+------------------------------------+
| Control Flags (1 octet) |
+------------------------------------+
| Layer-2 MTU (2 octet) |
+------------------------------------+
| Reserved (2 octets) |
+------------------------------------+
Figure 1: Layer2 Info Extended Community
Control Flags:
This field contains bit flags relating to the control information
about pseudowires. This field is augmented with a definition of 2 new
flags field.
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|Z|Z|Z|Z|T|R|C|S| (Z = MUST Be Zero)
+-+-+-+-+-+-+-+-+
Figure 2: Control Flags Bit Vector
With reference to the Control Flags Bit Vector, the following bits in
the Control Flags are defined; the remaining bits, designated Z, MUST
be set to zero when sending and MUST be ignored when receiving this
Extended Community.
T When the bit value is 1, the PE announce the ability
to send a Pseudowire packet that includes a flow label.
When the bit value is 0, the PE is indicating that it will
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not send a Pseudowire packet containing a flow label.
R When the bit value is 1, the PE is able to receive a
Pseudowire packet with a flow label present. When the bit
value is 0, the PE is unable to receive a Pseudowire packet
with the flow label present.
C Defined in [RFC4761].
S Defined in [RFC4761].
3. Signaling the Presence of the Flow Label
As part of the Pseudowire signaling procedures described in
[RFC4761], a Layer2 Info Extended Community is advertised in the VPLS
BGP NLRI.
A PE that wishes to send a flow label in a Pseudowire packet MUST
include in its VPLS BGP NLRI a Layer2 Info Extended Community using
Control Flags field with T = 1.
A PE that is willing to receive a flow label in a Pseudowire packet
MUST include in its VPLS BGP NLRI a Layer2 Info Extended Community
using Control Flags field with R = 1.
A PE that receives a VPLS BGP NLRI containing a Layer2 Info Extended
Community with R = 0 MUST NOT include a flow label in the Pseudowire
packet.
Therefore, a PE sending a Control Flags field with T = 1 and
receiving a Control Flags field with R = 1 MUST include a flow label
in the Pseudowire packet. Under all other combinations, a PE MUST
NOT include a flow label in the Pseudowire packet.
A PE MAY support the configuration of the flow label (T and R bits)
on a per-service (e.g., VPLS VFI) basis. Furthermore, it is also
possible that on a given service, PEs may not share the same flow
label settings. The presence of a flow label is therefore determined
on a per-peer basis and according to the local and remote T and R bit
values. For example, a PE part of a VPLS and with a local T = 1,
must only transmit traffic with a flow label to those peers that
signaled R = 1. And if the same PE has local R = 1, it must only
expect to receive traffic with a flow label from peers with T = 1.
Any other traffic must not have a flow label. A PE expecting to
receive traffic from a remote peer with a flow label MAY drop traffic
that has no flow label. A PE expecting to receive traffic from a
remote peer with no flow label MAY drop traffic that has flow label.
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Modification of flow label settings may impact traffic over a PW as
these could trigger changes in the PEs data-plane programming (i.e.
imposition / disposition of flow label). This is an implementation
specific behavior and outside the scope of this draft.
The signaling procedures in [RFC4761] state that the unspecified bits
in the Control Flags field (bits 0-5) MUST be set to zero when
sending and MUST be ignored when receiving. The signaling procedure
described here is therefore backwards compatible with existing
implementations. A PE not supporting the extensions described in
this draft will always advertise a value of ZERO in the position
assigned by this draft to the R bit and therefore a flow label will
never be included in a packet sent to it by one of its peers.
Similarly, it will always advertise a value of ZERO in the position
assigned by this draft to the T bit and therefore a peer will know
that a flow label will never be included in a packet sent by it.
Note that what is signaled is the desire to include the flow LSE in
the label stack. The value of the flow label is a local matter for
the ingress PE, and the label value itself is not signaled.
4 Acknowledgements
The authors would like to thank Bertrand Duvivier and John Drake for
their review and comments.
5 Contributors
In addition to the authors listed above, the following individuals
also contributed to this document:
Eric Lent
John Brzozowski
Steven Cotter
6. IANA Considerations
Although [RFC4761] defined a Control Flags Bit Vector as part of the
Layer2 Info Extended Community, it did not ask for the creation of a
registry.
This document requests that IANA creates a registry for this bit
vector and that it be called the "Layer2 Info Extended Community
Control Flags Bit Vector" registry.
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This registry should be created here:
https://www.iana.org/assignments/bgp-extended-communities/bgp-
extended-communities.xhtml.
Considering [RFC4761] and this document, the initial registry is as
follows:
Value Name Reference
----- -------------------------------- --------------
S Sequenced delivery of frames RFC4761
C Presence of a Control Word RFC4761
T Request to send a flow label This document
R Ability to receive a flow label This document
As per [RFC4761] and this document, the remaining bits are
unassigned, and MUST be set to zero when sending and MUST be ignored
when receiving the Layer2 Info Extended Community.
7. Security Considerations
This extension to BGP does not change the underlying security issues
inherent in the existing [RFC4271] and [RFC4761].
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March
1997, <http://www.rfc-editor.org/info/rfc2119>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271, DOI 10.17487/RFC4271,
January 2006, <http://www.rfc-editor.org/info/rfc4271>.
[RFC4761] Kompella, K., Ed. and Y. Rekhter, Ed., "Virtual Private
LAN Service (VPLS) Using BGP for Auto-Discovery and Signaling", RFC
4761, DOI 10.17487/RFC4761, January 2007, <http://www.rfc-
editor.org/info/rfc4761>.
[RFC6391] Bryant, S., Ed., Filsfils, C., Drafz, U., Kompella, V.,
Regan, J., and S. Amante, "Flow-Aware Transport of Pseudowires over
an MPLS Packet Switched Network", RFC 6391, DOI 10.17487/RFC6391,
November 2011, <http://www.rfc-editor.org/info/rfc6391>.
[RFC8126] M. Cotton, et al., "Guidelines for Writing an IANA
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Considerations Section in RFCs", RFC 8126, DOI 10.17487/RFC6391, June
2017, <http://www.rfc-editor.org/info/rfc8126>.
8.2. Informative References
[RFC3985] Bryant, S., Ed. and P. Pate, Ed., "Pseudo Wire Emulation
Edge-to-Edge (PWE3) Architecture", RFC 3985, DOI 10.17487/RFC3985,
March 2005, <http://www.rfc-editor.org/info/rfc3985>.
[RFC4385] Bryant, S., Swallow, G., Martini, L., and D. McPherson,
"Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for Use over
an MPLS PSN", RFC 4385, DOI 10.17487/RFC4385, February 2006,
<http://www.rfc-editor.org/info/rfc4385>.
[RFC8077] Martini, L., and G. Heron, "Pseudowire Setup and
Maintenance Using the Label Distribution Protocol (LDP)", RFC 8077,
DOI 10.17487/RFC8077, February 2017, <http://www.rfc-
editor.org/info/rfc8077>.
[RFC4928] Swallow, G., Bryant, S., and L. Andersson, "Avoiding Equal
Cost Multipath Treatment in MPLS Networks", BCP 128, RFC 4928, DOI
10.17487/RFC4928, June 2007, <http://www.rfc-
editor.org/info/rfc4928>.
[RFC6624] Kompella, K., Kothari, B., and R. Cherukuri, "Layer 2
Virtual Private Networks Using BGP for Auto-Discovery and Signaling",
RFC 6624, DOI 10.17487/RFC6624, May 2012, <http://www.rfc-
editor.org/info/rfc6624>.
Authors' Addresses
Keyur Patel
Arrcus
Email: keyur@arrcus.com
Sami Boutros
VMware
Email: sboutros@vmware.com
Jose Liste
Cisco
Email: jliste@cisco.com
Bin Wen
Comcast
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Email: bin_wen@cable.comcast.com
Jorge Rabadan
Nokia
Email: jorge.rabadan@nokia.com
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