EVPN Layer 2 Attributes Extended Community Usage in EVPN ELAN
draft-yu-bess-evpn-l2-attributes-00

Abstract

This document aims to define a negotiation mechanism for L2 capabilities in an EVPN ELAN scenario.

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 Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on May 7, 2019.

Copyright 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 (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect 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. EVPN Layer 2 Attributes Extended Community
• 3. Control Flags Processing
• 4. L2 MTU Processing
• 5. Other Considerations
• 6. Security Considerations
• 7. IANA Considerations
• 8. Normative References
• Author's Address

1. Introduction

EVPN [RFC7432] is lacking a negotiation mechanism on L2 capabilities. If the L2 capablities between Ethernet Segments are different, they are not able to communicate properly.

This document aims to define a negotiation mechanism for L2 capabilities in an EVPN ELAN scenario.

2. EVPN Layer 2 Attributes Extended Community

EVPN Layer 2 Attributes Extended Community is defined in RFC 8214 [RFC8214]. This document describes the behaviors how it adapts to EVPN ELAN. EVPN Layer 2 Attributes Extended Community is advertised along with Ethernet Auto-discovery. The definition of EVPN Layer 2 Attributes Extended Community 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                 |F|C|MBZ|  (MBZ = MUST Be Zero)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 2: Control Flags

The P bit and B bit defined in RFC 8214 [RFC8214] must be zero when used in ELAN mode. This is because RFC 7432 has defined ESI Label Extended Community to achieve single-active redundancy mode.

C bit indicates the control word enable status of known unicast traffic. If set to 1, then a control word [RFC4448] MUST be present when sending known unicast EVPN packets to this PE. It is recommended that the control word be included in the absence of an entropy label [RFC6790]. C bit MUST set 0 if PE has no capability of processing control word. C bit MUST be same across all Ethernet Segments within one EVI on a local PE.

BUM traffic SHOULD NOT include control word when forwarded no matter C bit is set to 1 or 0.

F bit is newly defined to achieve Flow-Aware Transport Labels [RFC6391] in EVPN. It can be used in both EVPN ELAN and VPWS. When F bit is set to 1, the PE announces it has capability of both sending and receiving flow label.

Other bits in Control Flags are reserved for future investigation and MUST be zero.

L2 MTU is a 2-octet value indicating the CE-PE link MTU in bytes. It MUST be same across all ES within one EVI on a local PE.

3. Control Flags Processing

When a PE receives Auto-discovery routes, handing procedures of Control Word Extended Community is as below: If EVPN Layer 2 Attributes Extended Community is included, PE MUST validate if Control Flags status is same with local behavior. If there is a is mismatch, the local PE MUST NOT add the remote PE as a valid EVPN destination for corresponding EVI.

If local PE does not support EVPN Layer 2 Attributes Extended Community, this community MUST be ignored. If EVPN Layer 2 Attributes Extended Community is not included, local PE MUST always the remote PE as a valid EVPN destination. When a PE receives A-D routes with C or F bits enabled, the behavior will spread to all MAC tables towards the corresponding ES. When interoperating with devices not supporting EVPN Layer 2 Attributes Extended Community, A-D routes received will not contain such community. Local PE SHOULD assume the behavior of all remote PE is same with local.

When data plane is not using MPLS, both C and F bit MUST NOT set 1. Control word and FAT is only applicable to MPLS data plane.

4. L2 MTU Processing

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 destination.

5. Other Considerations

To achieve interoperability with remote PE without support for EVPN Layer 2 Attributes Extended Community, a route policy can be implemented to specify L2 behavior manually. This function SHOULD be used only for interoperability. A PE SHOULD NOT overwrite existing EVPN Layer 2 Attributes Extended Community in a received route.

It is strongly encouraged to keep control word and flow label behavior consistent within the same EVI.

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

Author's Address