Internet DRAFT - draft-gs-bess-evpn-l2-attribute-cw
draft-gs-bess-evpn-l2-attribute-cw
BESS Workgroup Gangadhara Reddy Chavva
Ericsson
Satishkumar Rodd
Internet-Draft Ericsson
Intended status: Standards Track
Expires: June 24, 2019 December 24, 2018
EVPN VPWS layer 2 Attributes Extended community for
Control-Word behavior
draft-gs-bess-evpn-l2-attribute-cw-00
Abstract
This document aims to define a negotiation mechanism for L2
capabilities in an EVPN scenario spefic to EVPN-VPWS control word
behavior.
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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Task Force (IETF). Note that other groups may also distribute
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Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Specification of Requirements . . . . . . . . . . . . . . . . 2
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
4. EVPN Layer 2 Attributes Extended Community . . . . . . . . . 3
5. Usage of Control Flags . . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
8. Normative References . . . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
EVPN [RFC7432] is ambiguous about the VPWS session
if the control-word(C-flag) in L2 attributes between PE devices are
different.
The objective of this document is to explain the mechanism to
negaotiate C-flag between PE devices which helps establish EVPN-VPWS
session where PE C-flags don't align initially.
2. Specification of Requirements
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 [RFC2119].
3. Terminology
EVPN: BGP MPLS-Based Ethernet VPN defined in [RFC7432]
EVPN ELAN: In order to distinguish EVPN VPWS, EVPN ELAN speficies
EVPN defined in [RFC7432]
CW: Control Word defined in [RFC4448]
PE: Provider Edge
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4. EVPN Layer 2 Attributes Extended Community
EVPN Layer 2 Attributes Extended Community is defined in EVPN VPWS
[RFC8214]. A mechanism to achieve interoperability between devices
with different CW capabilities is defined in this document.
EVPN Layer 2 Attributes Extended Community is advertised
along with Ethernet Auto-discovery(E-AD). The definition of
EVPN Layer 2 Attributes Extended Community is same with [RFC8214].
it is listed as below for convenience.
+-------------------------------------------+
| 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
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 |C|P|B| (MBZ = MUST Be Zero)
+-+-+-+-+-+-+-+-+-+-+--+-+-+-+-+
Figure 2: Control Flags
The P bit and B bit operations are defined in [RFC8214].
C bit represents the control word capability of the PE. It indicates
if set to C=0 that, PE is not capable of processing control-word(CW)
in the data traffic. C bit SHOULD be same among PEs belonging to same
Ethernet Segment(ESI).
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Other bits in Control Flags are reserved for future investigation and
MUST be zero.
If local PE does not support EVPN Layer 2 Attributes Extended
Community, this community MUST be ignored.
5. Usage of Control Flags
The description below is based on the network topology showed in
Figure 3:
+--------+ +--------+
| PE1 | | PE2 |
| (CW) |-------| (NCW) |
+--------+ +--------+
Figure 3: Network Topology for Control Word Interoperability
PE1 is control-word capable where as PE2 is not capable of control-word.
PE2 capability for CW is either Disabled or Not supported.
With the setup mentioned in Figure 3, the current EVPN-VPWS RFC[RFC8214]
does not explicitly mention the state of the VPWS session between two
PEs. It also states PE2 MUST put control-word for any data to be sent
to PE1 over that link. But here the problem is PE2 may not be capable of
prepending control-word to traffic. Hence PE1 will receive the packets
without control-word even when its expecting with CW.
This document proposes a solution for the above problem. It clearly
defines the behavior for a PE in this scenario.
The solution require but does not mandate an administrative command
enforce-cw. The behavior of this is exaplined in following statements.
enforce-cw enabled:
-------------------
1) When PE1 receives E-AD(C-bit=0) from PE2, PE1 MUST NOT fall back
to C-bit=0, but the VPWS session state will be brought DOWN.
2) When PE2 receives E-AD(C-bit=1) from PE1, PE2 will establish session
in DOWN state.
enforce-cw disabled:
------------------
1) When PE1 receives E-AD(C-bit=0) from PE2, PE1 MUST fall back
to C-bit=0, and initiate new E-AD message towards PE2 with C-bit=0.
And mark VPWS session UP.
2) When PE2 receives E-AD(C-bit=1) from PE1, PE2 will establish session
in DOWN state.
This document does not suppress any E-AD messages in any scenario. Every PE
MUST be sending their E-AD message at-least once per VPWS-session.
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C-bit Handling Procedures Diagram where enforce-cw is disabled.
------------------
Y | Received | N
-------| E-AD message |--------------
| ------------------ |
-------------- |
| | |
------- ------- |
| C=0 | | C=1 | |
------- ------- |
| | |
| ---------------- |
| | Control Word | N |
| | Capable? |----------- |
| ---------------- | |
| Y | | |
| | | |
| ---------------- | |
| | Control Word | N | |
| | enabled? |---- | |
| ---------------- | | |
| Y | | | |
| | | | ----------------
| | | | | Control Word |
| | | | | enabled? |
| | | | ----------------
| | | | N | Y |
| | | | | |
Send Send Send Send Send Send
C=0 C=1 C=0 C=0 C=0 C=1
| | | |
----------------------------------
| If receive the same as sent, |
| VPWS setup is complete. If not:|
----------------------------------
| | | |
------------------- -----------
| Receive | | Receive |
| C=1 | | C=0 |
------------------- -----------
| |
Make session DOWN |
Wait for the next Send
message C=0
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C-bit Handling Procedures Diagram where enforce-cw is enabled.
------------------
Y | Received | N
-------| E-AD message |-------------------
| ------------------ |
------------------------------ |
| | |
------- ------- |
| C=0 | | C=1 | |
------- ------- |
| | |
| | ----------------
| | | Control Word | N
| | | enabled? |---
| | ---------------- |
| | Y | |
| | | |
---------------- ---------------- | |
| Control Word | N | Control Word | N | |
| enabled? |------- | enabled? |---- | |
---------------- | ---------------- | | |
Y | | Y | | | |
| | | | | |
| | | | | |
| | | | | |
| | | | | |
| | | | | |
| | | | | |
Send Send Send Send Send Send
C=1 C=0 C=1 C=0 C=1 C=0
| | | |
-------------- ------------- ------------- --------------
| Make VPWS | | Make VPWS | | Make VPWS | | Make VPWS |
|Session DOWN| | Session UP| | Session UP| |Session DOWN|
-------------- ------------- ------------- --------------
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6. Security Considerations
There are no new security considerations due to the text of this
document.
7. IANA Considerations
This document does not make any requests from IANA.
8. 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>.
[RFC4447] Martini, L., El-Aawar, N., Heron, G., Rosen, E., Tappan,
D., and T. Smith, "Pseudowire Setup and Maintenance
using the Label Distribution Protocol (LDP)", RFC 4447,
April 2006.
<https://www.rfc-editor.org/info/rfc4447>
[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>.
[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>.
[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>.
[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>.
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Author's Address
Gangadhara Reddy Chavva
Ericsson.
EMail: meetgangadhara@gmail.com
Satishkumar Rodd
Ericsson.
EMail: rodd.satish@gmail.com
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