Usage of Layer 2 Attributes Extended Community in EVPN
draft-yu-bess-evpn-l2-attributes-04
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|---|---|---|---|
| Authors | Tianpeng Yu , Haibo Wang | ||
| Last updated | 2019-03-10 (Latest revision 2019-01-21) | ||
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draft-yu-bess-evpn-l2-attributes-04
BESS Workgroup T. Yu, Ed.
Internet-Draft
Intended status: Standards Track H. Wang
Expires: September 11, 2019 Huawei Technologies
March 10, 2019
Usage of Layer 2 Attributes Extended Community in EVPN
draft-yu-bess-evpn-l2-attributes-04
Abstract
This document adopts Layer 2 Attributes Extended Community defined in
[RFC8214] to EVPN allowing signalling L2 information in control
plane.
An interoperability mechanism of control word is described for EVPN
and VPWS in this document.
Also flow label signalling mechanism is described for EVPN and VPWS.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on September 11, 2019.
Copyright Notice
Copyright (c) 2019 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
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publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Specification of Requirements . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. EVPN Layer 2 Attributes Extended Community . . . . . . . . . 3
4.1. Control Flag Attribute . . . . . . . . . . . . . . . . . 4
4.2. L2 MTU Attribute . . . . . . . . . . . . . . . . . . . . 6
5. Control Word Indicator Extended Community . . . . . . . . . . 6
6. Usage of Control Word . . . . . . . . . . . . . . . . . . . . 7
6.1. EVPN ELAN . . . . . . . . . . . . . . . . . . . . . . . . 7
6.1.1. Deterministic mode . . . . . . . . . . . . . . . . . 7
6.1.2. Interoperable mode . . . . . . . . . . . . . . . . . 7
6.2. EVPN VPWS . . . . . . . . . . . . . . . . . . . . . . . . 8
6.2.1. Deterministic mode . . . . . . . . . . . . . . . . . 8
6.2.2. Interoperable mode . . . . . . . . . . . . . . . . . 8
7. Usage of Flow Label . . . . . . . . . . . . . . . . . . . . . 8
8. Instructions on Using Control Word and Flow Label . . . . . . 9
9. Other Considerations . . . . . . . . . . . . . . . . . . . . 9
10. Security Considerations . . . . . . . . . . . . . . . . . . . 9
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
12.1. Normative References . . . . . . . . . . . . . . . . . . 10
12.2. Informative References . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
EVPN [RFC7432] lacks of a negotiation mechanism on L2 capabilities.
Lacking of such capabilities will lead to malformed packets on
forwarding plane without any prevention from control plane
signalling. [RFC8214] defines Layer 2 Attributes Extended Community
but there is no defination on how it can used in EVPN ELAN. This
document aims to describe how Layer 2 Attributes Extended Community
to be used in EVPN ELAN.
To achieve better load balancing on EVPN ELAN and VPWS services, flow
label function in EVPN is described in this document.
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2. Specification of Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Terminology
EVPN: BGP MPLS-Based Ethernet VPN defined in [RFC7432].
EVPN ELAN: In order to distinguish EVPN VPWS, EVPN ELAN specifies
EVPN defined in [RFC7432].
EVI: An EVPN Instance spanning the Provider Edge (PE) devices
participating in that EVPN ELAN.
EVPN VPWS: EVPN Virtual Private Wire Service, refers to [RFC8214].
EVPN E-Tree: Ethernet VPN Ethernet-Tree defined in [RFC8317].
CW: Control Word defined in [RFC4448].
CI: Control Word Indicator, defined in Section 4 of this document.
PE: Provider Edge device.
FL: Flow-Aware Transport Label, defined in [RFC6391].
BUM: Broadbast, Unknown-Unicast, Multicast.
P2MP: Point to Multi-Point.
MP2P: Multi-Point to Point.
LSP: Label-Switched Path.
4. EVPN Layer 2 Attributes Extended Community
The definition of EVPN Layer 2 Attributes Extended Community is same
with [RFC8214]. it is listed as below for convenience.
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+-------------------------------------------+
| Type (0x06) / Sub-type (0x04) (2 octets) |
+-------------------------------------------+
| Control Flags (2 octets) |
+-------------------------------------------+
| L2 MTU (2 octets) |
+-------------------------------------------+
| Reserved (2 octets) |
+-------------------------------------------+
Figure 1: EVPN Layer 2 Attributes Extended Community
Layer 2 Attributes Extended Community SHOULD be included in Ethernet
Auto-discovery Route route and Inclusive Multicast Ethernet Tag
Route.
For an EVPN ELAN, Layer 2 Attributes Extended Community included in
Auto-discovery route applies to unicast traffic and Inclusive
Multicast Ethernet Tag Route applies to BUM traffic.
Layer 2 Attributes Extended Community for unicast MUST be same across
all Ethernet Segments in Auto-discovery routes within one EVI on a
local PE when used in EVPN ELAN. Layer 2 Attributes Extended
Community for BUM MUST be same across EVIs sharing the same P-Tunnel
within a PE. Layer 2 Attributes Extended Community MAY be different
between Auto-discovery route and Inclusive Multicast Ethernet Tag
Route.
When a PE recieves routes without L2 Attributes Extended Community,
local PE SHOULD assume the values of Layer 2 Attributes Extended
Community of all corresponding PEs are same with local. This allows
backward compatibility of introducing L2 Attributes Extended
Community into EVPN ELAN.
If a local PE does not support EVPN Layer 2 Attributes Extended
Community, this community MUST be ignored.
4.1. Control Flag Attribute
The definition of Control Flags is as below:
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+--+-+-+-+-+
| MBZ |CI|F|C|P|B| (MBZ = MUST Be Zero)
+-+-+-+-+-+-+-+-+-+-+--+-+-+-+-+
Figure 2: Control Flags in EVPN Layer 2 Attributes Extended Community
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The P bit and B bit defined in [RFC8214] must be zero when used in
EVPN ELAN mode. This is because [RFC7432] has defined ESI Label
Extended Community to achieve single-active redundancy mode.
C bit indicates the control word enable status:
o When C bit is set to 1, the PE announces it has the capability of
both sending and receiving CW.
o C bit MUST set 0 if PE has no capability of sending or receiving
control word.
o C bit SHOULD not set 1 if Layer 2 Attributes Extended Community is
used on P2MP or MP2MP LSPs.
F bit is defined to achieve flow label signalling capability in EVPN:
o When F bit is set to 1, the PE announces it has the capability of
both sending and receiving flow label.
o F bit MUST set 0 if PE has no capability of sending or receiving
flow label.
o F bit SHOULD not set 1 if Layer 2 Attributes Extended Community is
used on P2MP or MP2MP LSPs.
CI bit is defined to achieve interoperability between devices with
and without control word capability. Control Word Indicator is a
MPLS label. CI bit MUST NOT set 1 if C bit is set 0.
CI label MUST NOT be a MPLS reserved label [RFC3032], MUST be with
TTL=1 and MUST be Bottom-of-Stack. CI label MUST NOT be used to
direct forwarding behavior in any cases.
When a PE sends packets with CI label, it MUST keep value CI labels
consistent for traffic towards the same ES. Due to CI usage is to
indicate the existance of CW and will never direct fowarding, CI MPLS
label can be any none-reserved MPLS label.
There are two ways of filling CWI label value:
o Use the label value advertised in Control Word Indicator Extended
Community (refer to section 5).
o In case absense of Control Word Indicator Extended Community, EVPN
service label MAY be copied into CWI.
The usage of CI bit is described in Section 6.
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Other bits in Control Flag are reserved for future investigation and
MUST be zero.
When a PE receives Auto-discovery routes with C or F bit enabled, the
behavior SHOULD be spread to all MAC tables towards the corresponding
ES.
4.2. L2 MTU Attribute
L2 MTU is a 2-octet value indicating the CE-PE link MTU in bytes. If
a non-zero MTU attribute is received, it MUST be checked against
local MTU value if the local value is not zero. If there is a
mismatch, the local PE MUST NOT add the remote PE as the EVPN ELAN or
VPWS destination.
5. Control Word Indicator Extended Community
This extended community is a new transitive extended community having
a Type field value of 0x06 (EVPN) and the Sub-Type TBD. It is used
for Control Word Indicator of known unicast and BUM traffic. It
indicates that the frame contains a CW after MPLS Bottom-of-Stack.
This extended community MAY be advertised along Ethernet Auto-
discovery Route route and Inclusive Multicast Ethernet Tag Route when
CI bit is 1 in EVPN Layer 2 Attributes Extended Community. When a PE
advertising the communnity, it MUST ensure CWI label same across
Ethernet Segments within one EVI and EVIs sharing the same P-Tunnel.
CI label value advertised SHOULD NOT be same with EVPN service
lables. Control Word Indicator Extended Community MUST NOT be
included if CI is 0.
If a PE contains Control Word Indicator Extended Community when
establishing the MP2P LSP, when receiving packets from MP2P LSP, it
uses the CI label value been advertised to identify existance of CW.
If a PE does not contain Control Word Indicator Extended Community
when establishing the MP2P LSP, it relies on the MPLS Bottom-of-Stack
bit to identify existance of CW.
When CI bit and F bit set 1 together, Control Word Indicator Extended
Community MUST be included. The packet encapulation from ingress PE
is: transport label(s) + EVPN service label(s) + FL + CI + CW +
payload. Forwarding plane on egress PE MUST use CI value in the
extended community to identify CW and identify FL in between if
exits. When working in such mode, source PE MUST ensure FL value
calaulated locally does not equal CI value learnt from EVPN routes.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=0x06 | Sub-Type=TBD | Flags(1 Octet)| Reserved=0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved=0 | CI Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Control Word Indicator Extended Community
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| MBZ |C| (MBZ = MUST Be Zero)
+-+-+-+-+-+-+-+-+
Figure 4: Flags in Control Word Indicator Extended Community
6. Usage of Control Word
6.1. EVPN ELAN
6.1.1. Deterministic mode
PE advertises CW local enable status via Layer 2 Attributes Extended
Community. A validation procedure is added in procedure of Auto-
discovery and Inclusive Multicast Ethernet Tag Route. Only if C bit
status in L2 attribute of recieved routes are same with local statue,
the recieved routes are treated valid. CI bit is not used in this
mode.
6.1.2. Interoperable mode
1. Disable CW function on all devices and keep CW status consistent
within EVI, then the EVI can work in the deterministic mode.
2. An interoperable mode based on CI MAY be implemented to achieve
interoperability with such devices.
An egress PE can receive packets from MP2P LSP with same EVPN label
but with different CW status from different remote PEs. This brings
challenge on CW interoperate mechanism. To overcome this challenge,
CI is introduced to allow a PE identifying CW status on forwarding
plane.
When an EVPN ELAN working in interoperable mode, if CW on a PE is
enabled, the PE MUST set both C and CI bit = 1. If CW on a PE is
disabled or the PE is not capable to add CW, the PE MUST set both C
and CI bit = 0.
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In this mode, A validation procedure is added in procedure of Auto-
discovery and Inclusive Multicast Ethernet Tag Route. Only if C bit
= CI bit in L2 attribute of recieved routes, recieved routes are
treated valid.
With such procedure, an egress PE is able to identify existance of CW
on fowarding plane via CI for packets recieved from MP2P LSP.
6.2. EVPN VPWS
6.2.1. Deterministic mode
When an EVPN VPWS working in deterministic mode, each PE advertises
CW capability based on local status in Auto-discovery route via l2
attribute. After a PE receives EVPN Auto-discovery route, it
compares the value of C bit with local control word enable status.
If not same, local PE MUST NOT bring up the EVPN VPWS.
6.2.2. Interoperable mode
Considering some devices has no capability of adding and parsing CW,
there are two ways to interoperate such devices:
1. Disable CW function on PE1 and keep CW status consistent within
EVPN VPWS towards PE3, then the EVPN VPWS can work in the
deterministic mode.
2. An interoperable mode MAY be implemented to achieve
interoperability with such devices.
When an EVPN VPWS working in interoperable mode, in case of C bit
status is not consistent on both ends, VPWS MUST tear up.
When working in interoperable mode, impact of lacking complete CW
between PEs SHOULD be evaluated based on section 8 of this document.
7. Usage of Flow Label
PE advertises FL local enable status via Layer 2 Attributes Extended
Community. Different from CW, flow label signalling on control plane
uses a loose validation procedure, which means FL status in received
routes MAY be different from local.
For MP2P LSP, when sending packet towards remote PE, FL is added if
both local and remote PEs are enabled. If a PE has no FL capability,
it will not receive packets with FL from MP2P LSP as all source PEs
will not send packets with FL towards this PE. If a PE has FL
capability, it MAY receive packets with and without FL from MP2P LSP
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as source PEs MAY have or haven't FL capability. In such case, the
PE SHOULD treat packet without FL valid on forwarding plane even
though local FL status is enabled. MPLS Bottom-of-Stack bit is used
to identify whether FL is containted in the packets.
The flow label mechanism described above is applicable to both EVPN
ELAN, E-Tree and EVPN VPWS.
8. Instructions on Using Control Word and Flow Label
In EVPN, CW is used avoid misordering caused by transit node using
MPLS payload as hash factor. The detailed reason for this refers to
[RFC8469]. CW is mandatory for an EVPN carrying misordering
sensitive service, when CW is not available, mitigations described in
section 6 of [RFC8469] also apply to EVPN.
Flow Label MAY be used to achieve better load-balancing in network,
when transit node has no capability to look inside MPLS payload as
hash factor.
It has been recognized that some transit nodes treat payload after
MPLS label as MAC address info and use as hash factor directly. When
it is bearing services sensitive to misordering, such load balancing
function SHOULD be disabled, otherwise control word will be treated
as part of MAC address mistakenly.
9. Other Considerations
When data plane is not using MPLS, C, F and CI bits in control flags
MUST be 0. Control word and Flow Label are only applicable to MPLS
data plane.
10. Security Considerations
This document updates the behavior specified in [RFC7432] and
[RFC8214]. The security considerations listed in these two documents
apply. However, there are no new security considerations due to the
text of this document.
11. IANA Considerations
IANA is requested to allocate a new "EVPN Extended Community Sub-
Types" registry defined in [RFC7153] as follow:
SUB-TYPE VALUE NAME Reference
-------------------------------------------------------------------
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TBD Control Word Indicator Extended Community This document
12. References
12.1. 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,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC7432] Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based
Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February
2015, <https://www.rfc-editor.org/info/rfc7432>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8214] Boutros, S., Sajassi, A., Salam, S., Drake, J., and J.
Rabadan, "Virtual Private Wire Service Support in Ethernet
VPN", RFC 8214, DOI 10.17487/RFC8214, August 2017,
<https://www.rfc-editor.org/info/rfc8214>.
[RFC8317] Sajassi, A., Ed., Salam, S., Drake, J., Uttaro, J.,
Boutros, S., and J. Rabadan, "Ethernet-Tree (E-Tree)
Support in Ethernet VPN (EVPN) and Provider Backbone
Bridging EVPN (PBB-EVPN)", RFC 8317, DOI 10.17487/RFC8317,
January 2018, <https://www.rfc-editor.org/info/rfc8317>.
[RFC8469] Bryant, S., Malis, A., and I. Bagdonas, "Recommendation to
Use the Ethernet Control Word", RFC 8469,
DOI 10.17487/RFC8469, November 2018,
<https://www.rfc-editor.org/info/rfc8469>.
12.2. Informative References
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,
<https://www.rfc-editor.org/info/rfc3032>.
[RFC4448] Martini, L., Ed., Rosen, E., El-Aawar, N., and G. Heron,
"Encapsulation Methods for Transport of Ethernet over MPLS
Networks", RFC 4448, DOI 10.17487/RFC4448, April 2006,
<https://www.rfc-editor.org/info/rfc4448>.
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[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,
<https://www.rfc-editor.org/info/rfc6391>.
[RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and
L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
RFC 6790, DOI 10.17487/RFC6790, November 2012,
<https://www.rfc-editor.org/info/rfc6790>.
Authors' Addresses
Tianpeng Yu (editor)
EMail: yutianpeng.ietf@gmail.com
Haibo Wang
Huawei Technologies
EMail: rainsword.wang@huawei.com
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