Internet DRAFT - draft-keyupate-bess-fat-pw-bgp
draft-keyupate-bess-fat-pw-bgp
Bess K. Patel
Internet-Draft S. Boutros
Intended status: Standards Track J. Liste
Expires: October 31, 2015 Cisco Systems
B. Wen
Comcast
J. Rabadan
Alcatel-Lucent
April 29, 2015
Extensions to BGP Signaled Pseudowires to support Flow-Aware Transport
Labels
draft-keyupate-bess-fat-pw-bgp-00.txt
Abstract
[RFC6391] describes a mechanism that uses an additional label (Flow
Label) in the MPLS label stack that allows 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 [RFC4447].
This draft defines protocol extensions required to synchronize flow
label states among PEs when using the BGP-based signaling procedures
defined in [RFC4761]. These protocol extensions are equally
applicable to point-to-point L2VPNs defined in [RFC6624].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on October 31, 2015.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Modifications to Layer 2 Info Extended Community . . . . . . 3
3. Signaling the Presence of the Flow Label . . . . . . . . . . 5
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
5. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
A pseudowire (PW)[RFC3985] is normally transported over one single
network path, even if multiple 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
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service. 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], [RFC4928].
Using the principles defined in [RFC6391], this draft augments the
BGP-signaling procedures of [RFC4761] and [RFC6624] to allow an
OPTIONAL mode that may be employed when the use of ECMPs is known to
be beneficial to the operation of the PW.
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 [section 3.4.2] of [RFC4761] 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.
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. Modifications to Layer 2 Info Extended Community
The Layer 2 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:
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+------------------------------------+
| Extended community type (2 octets) |
+------------------------------------+
| Encaps Type (1 octet) |
+------------------------------------+
| Control Flags (1 octet) |
+------------------------------------+
| Layer-2 MTU (2 octet) |
+------------------------------------+
| Reserved (2 octets) |
+------------------------------------+
Layer 2 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|T|R|Z|C|S| (Z = MUST Be Zero)
+-+-+-+-+-+-+-+-+
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.
Z Must be set to Zero.
T When the bit value is 1, the PE is requesting 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
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].
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3. Signaling the Presence of the Flow Label
As part of the Pseudowire signaling procedures described in
[RFC4761], a Layer 2 Info Extended Community is advertised in the
VPLS BGP NLRI. This draft recommends that the Control Flags field of
this extended community be used to synchronize the flow label states
amongst PEs for a given L2VPN.
A PE that wishes to send a flow label in a Pseudowire packet MUST
include in its VPLS BGP NLRI a Layer 2 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 Layer 2 Info Extended Community
using Control Flags field with R = 1.
A PE that receives a VPLS BGP NLRI containing a Layer 2 Info Extended
Community with R = 0 NUST 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.
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
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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
7. Security Considerations
This extension to BGP does not change the underlying security issues
inherent in the existing [RFC4271].
8. References
8.1. Normative References
[I-D.ietf-l2vpn-vpls-multihoming]
Kothari, B., Kompella, K., Henderickx, W., Balus, F.,
Uttaro, J., Palislamovic, S., and W. Lin, "BGP based
Multi-homing in Virtual Private LAN Service", draft-ietf-
l2vpn-vpls-multihoming-06 (work in progress), July 2013.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3985] Bryant, S. and P. Pate, "Pseudo Wire Emulation Edge-to-
Edge (PWE3) Architecture", RFC 3985, March 2005.
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[RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
Protocol 4 (BGP-4)", RFC 4271, January 2006.
[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, February 2006.
[RFC4447] Martini, L., Rosen, E., El-Aawar, N., Smith, T., and G.
Heron, "Pseudowire Setup and Maintenance Using the Label
Distribution Protocol (LDP)", RFC 4447, April 2006.
[RFC4761] Kompella, K. and Y. Rekhter, "Virtual Private LAN Service
(VPLS) Using BGP for Auto-Discovery and Signaling", RFC
4761, January 2007.
[RFC4928] Swallow, G., Bryant, S., and L. Andersson, "Avoiding Equal
Cost Multipath Treatment in MPLS Networks", BCP 128, RFC
4928, June 2007.
[RFC6391] Bryant, S., Filsfils, C., Drafz, U., Kompella, V., Regan,
J., and S. Amante, "Flow-Aware Transport of Pseudowires
over an MPLS Packet Switched Network", RFC 6391, November
2011.
8.2. Informative References
[RFC2842] Chandra, R. and J. Scudder, "Capabilities Advertisement
with BGP-4", RFC 2842, May 2000.
[RFC2858] Bates, T., Rekhter, Y., Chandra, R., and D. Katz,
"Multiprotocol Extensions for BGP-4", RFC 2858, June 2000.
[RFC6624] Kompella, K., Kothari, B., and R. Cherukuri, "Layer 2
Virtual Private Networks Using BGP for Auto-Discovery and
Signaling", RFC 6624, May 2012.
Authors' Addresses
Keyur Patel
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
USA
Email: keyupate@cisco.com
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Sami Boutros
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
USA
Email: sboutros@cisco.com
Jose Liste
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
USA
Email: jliste@cisco.com
Bin Wen
Comcast
1701 John F Kennedy Blvd
Philadelphia, PA 19103
USA
Email: bin_wen@cable.comcast.com
Jorge Rabadan
Alcatel-Lucent
777 E. Middlefield Road
Mountain View, CA 94043
USA
Email: jorge.rabadan@alcatel-lucent.com
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