One document matched: draft-singh-l2vpn-bgp-vpls-control-flags-00.txt
L2VPN Working Group R. Singh
INTERNET-DRAFT K. Kompella
Intended Status: Proposed Standard Juniper Networks
Expires: April 24, 2014 October 21, 2013
Updated processing of control flags for BGP VPLS
draft-singh-l2vpn-bgp-vpls-control-flags-00
Abstract
This document updates the meaning of the "control flags" fields
inside the "layer2 info extended community" used for BGP-VPLS NLRI.
Status of this Memo
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INTERNET DRAFT Control Flags for BGP VPLS October 21, 2013
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Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3 Updated meaning of control flags in the layer2 info extended
community . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4 Using p2mp LSP as transport for CW-marked VPLS frames . . . . . 4
5 Illustrative diagram . . . . . . . . . . . . . . . . . . . . . 5
6 Security Considerations . . . . . . . . . . . . . . . . . . . . 5
7 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
8 References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1 Normative References . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6
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1 Introduction
The use of control word (CW) helps prevent mis-ordering of IPv4 or
IPv6 PW traffic over ECMP-paths/LAG-bundles. [RFC4385] describes the
format for control-word that may be used over point-2-point PWs and
over a VPLS.
[RFC4761] describes the concepts and signaling for using BGP to bring
up a VPLS. It specifies as part of its BGP VPLS NLRI that a PE may
require other PEs in the same VPLS to include (or not) control-word
and sequencing information in VPLS frames sent to this PE.
However, [RFC4761] does not describe the behavior of PEs in a mixed
environment where some PEs support control-word/sequencing and others
do not.
1.1 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 [RFC2119].
2 Problem
[RFC4761] uses a VPLS BGP NLRI to specify the required behavior off
multiple PEs. The behavior required off the multiple PEs identified
by the NLRI indicates the VPLS label they should use in the VPLS
traffic being forwarded to this PE. Additionally, by using the
"control flags" it specifies whether the other PEs (in the same VPLS)
should use control-word or sequenced-delivery for packets forwarded
to this PE. These are respectively indicated by the C and the S bits
in the "control flags" as specified in section 3.2.4 in [RFC4761].
[RFC4761] requires that if the advertising PE sets the C and S bits,
the receiving PE MUST honor the same by inserting control word (CW)
and by including sequence numbers respectively.
However, in a BGP VPLS deployment there would often be cases where a
PE receiving the VPLS BGP NLRI may not have the ability to insert a
CW or include sequencing information inside PW frames. In that case
the behavior of BGP VPLS needs to be further specified.
This document enhances the meaning of the control flags in layer2
extended community in the BGP VPLS NLRI for an environment where not
every PE in a a VPLS has the ability or the configuration to honor
the control flags received from the PE advertising the BGP NLRI.
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3 Updated meaning of control flags in the layer2 info extended
community
Currently, the CW setting is not negotiated. Rather, if a PE sets the
C-bit, it expects to receive VPLS packets with a control word, and
will send packets the same way. If the PEs at both ends of a
pseudowire don't agree on the setting of the C-bit, the PW doesn't
come up. Similarly for the S-bit.
This memo changes the meaning of the C-bit and the S-bit in the
control flags. If a PE sets the C-bit in its NLRI, it means that the
PE can send and receive packets with a control word. If the PEs at
both ends of a PW set the C-bit, control words are used in both
directions of the PW. If both PEs send a C-bit of 0, control words
are not used on the PW. These two cases behave as before.
However, if the PEs don't agree on the setting of the C-bit, control
words are not used on that PW. This behavior is new; the old
behavior is that the PW doesn't come up.
The behavior for the S-bit is similar.
4 Using p2mp LSP as transport for CW-marked VPLS frames
BGP VPLS can be used over either point-2-point LSPs acting as
transport between the VPLS PEs. Alternately, BGP VPLS may also be
used over p2mp LSPs with the source of the p2mp LSPs rooted at the PE
advertising the VPLS BGP NLRI.
In a network that uses p2mp LSPs as transport for BGP VPLS, in a
given VPLS there may be some PEs that support control-word while
others do not. In such a setup, a source PE that supports control-
word / sequenced-delivery should setup 2 different p2mp trees - one
which has as its leaves those VPLS PEs that are advertising the C/S-
bits as 1, and another p2mp LSP whose leaves are PEs that are not
advertising C/S-bits as 1.
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5 Illustrative diagram
-----
/ A1 \
---- ____CE1 |
/ \ -------- -------- / | |
| A2 CE2- / \ / PE1 \ /
\ / \ / \___/ | \ -----
---- ---PE2 | \
| | \ -----
| Service Provider Network | \ / \
| | CE5 A5
| ___ | / \ /
\ / \ PE4_/ -----
PE3 / \ /
|------/ \------- -------
---- / | ----
/ \/ \ / \ CE = Customer Edge Device
| A3 CE3 --CE4 A4 | PE = Provider Edge Router
\ / \ /
---- ---- A<n> = Customer site n
Figure 1: Example of a VPLS
In the above topology, let there be a VPLS configured with the PEs as
displayed. Let PE1 be the PE under consideration that is CW enabled.
Let PE2 and PE3 also be CW enabled. Let PE4 not be CW enabled. PE1
will advertise a VPLS BGP NLRI, containing the C/S bits marked as 1.
PE2 and PE3 on learning of NLRI from PE1, shall include the control
word in VPLS frames being forwarded to PE1. However, PE4 which does
not have the ability to include control-word.
As per [RFC4761], PE1 would have an expectation that all other PEs
forward traffic to it by including CW.
However, to support the mixed-CW environment as above, PE1 will bring
up the PW with PE4 despite the CW mismatch. Additionally, it will
setup its data-plane such that it will strip the control-word only
for those VPLS packets that are received from PEs that are themselves
indicating their desire to receive CW marked packets. So, PE1 will
setup its data plane to strip-off the CW only for VPLs frames
received from PEs PE2 and PE3. PE1 will setup its data plane to not
strip CW from frames received from PE4.
6 Security Considerations
No new security issues.
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7 IANA Considerations
None.
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.
[RFC4761] Kompella, K., Y. Rekhter, Virtual Private LAN Service
(VPLS) Using BGP for Auto-Discovery and Signaling,
RFC 4761, January 2007.
[RFC4385] Bryant, S., Swallow G., Martini L., D. McPherson,
Pseudowire Emulation Edge-to-Edge (PWE3) Control Word,
RFC 4385, February 2006.
Authors' Addresses
Ravi Singh
Juniper Networks
1194 N. Mathilda Ave.
Sunnyvale, CA 94089
US
EMail: ravis@juniper.net
Kireeti Kompella
Juniper Networks
1194 N. Mathilda Ave.
Sunnyvale, CA 94089
US
EMail: kireeti@juniper.net
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