EVPN Layer 2 Attributes Extended Community Usage in EVPN
draft-yu-bess-evpn-l2-attributes-01
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| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Expired".
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|---|---|---|---|
| Author | Tianpeng Yu | ||
| Last updated | 2018-12-05 (Latest revision 2018-11-03) | ||
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draft-yu-bess-evpn-l2-attributes-01
BESS Workgroup T. Yu
Internet-Draft Huawei Technologies
Intended status: Standards Track December 5, 2018
Expires: June 8, 2019
EVPN Layer 2 Attributes Extended Community Usage in EVPN
draft-yu-bess-evpn-l2-attributes-01
Abstract
This document aims to define a negotiation mechanism for L2
capabilities in an EVPN scenario.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on June 8, 2019.
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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. L2 MTU Processing . . . . . . . . . . . . . . . . . . . . . . 7
7. Instructions of using control word and Flow Label . . . . . . 7
8. Security Considerations . . . . . . . . . . . . . . . . . . . 8
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
10. Normative References . . . . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
EVPN [RFC7432] is lacking a negotiation mechanism on L2 capabilities.
If the L2 capabilities between PE devices are different, they are not
able to communicate properly.
This document aims to define a negotiation mechanism for L2
capabilities in an EVPN scenario.
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]
CI: Control word indicator, defined in Section 4 of this document
PE: Provider Edge
FL: Flow label, defined in [RFC6391]
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4. EVPN Layer 2 Attributes Extended Community
EVPN Layer 2 Attributes Extended Community is defined in EVPN VPWS
[RFC8214]. This document describes the behaviors how it adapts to
EVPN ELAN. A mechanism to achieve interoperability between devices
with and without CW capabilities is defined. Flow Label mechanism is
defined. EVPN Layer 2 Attributes Extended Community is advertised
along with Ethernet Auto-discovery. 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 |CI|F|C|P|B| (MBZ = MUST Be Zero)
+-+-+-+-+-+-+-+-+-+-+--+-+-+-+-+
Figure 2: Control Flags
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 of known unicast
traffic. C bit MUST set 0 when advertising A-D route if PE has no
capability of processing control word. C bit SHOULD 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 when working in ELAN mode.
CI bit is defined to achieve interoperability between devices with
and without control word capability. Control Word Indicator is one
octet with value 0xFF. CI bit MUST NOT set 1 if C bit is set 0. The
usage of CI bit is described in Section 4.
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F bit is 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 the capability of both sending and
receiving flow label. F bit MUST be same across all Ethernet
Segments within one EVI on a local PE. BUM traffic SHOULD NOT
include Flow label when forwarded no matter F bit is set to 1 or 0
when working in ELAN mode.
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.
If local PE does not support EVPN Layer 2 Attributes Extended
Community, this community MUST be ignored.
When a PE receives A-D routes with C, CI or F bits enabled, the
behavior SHOULD be spreaded to all MAC tables towards the
corresponding ES when applicable.
5. Usage of Control Flags
The description below is based on the network topology showed in
Figure 3:
+--------+ +--------+
| PE1 | | PE2 |
| (CW) |-------| (CW) |
+--------+ +--------+
\ /
\ /
+--------+
| PE3 |
| (NCW) |
+--------+
Figure 3: Network Topology for Control Word Interoperability
PE1 and PE2 are routers with control word capability and PE3 is
router control word disabled or without control word capability. It
is assumed that PE1, PE2 and PE3 are working in same EVI.
When local PE receives auto-discovery routes from remote PE, if CI=0,
then goes process A, if CI=1, then goes to process B.
Process A:
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Compare the value of C bit with local control word enable status. If
same, local PE treats remote PE as a valid EVPN destination. If not
same, local PE treats remote PE as an invalid EVPN destination.
After such process, PE1 treat PE2 as a valid destination and PE3 as
an invalid destination. PE2 treat PE1 as a valid destination and PE3
as an invalid destination. PE3 treat both PE1 and PE2 as an invalid
destination. PE1 and PE2 will forward traffic with control word
encapsulated. PE1 and PE2 will not be able to interoperate with PE3,
due to control word status difference.
Process B:
In this process, if C is set 0, then remote PE is treated as valid
EVPN destination. If C is set 1, then only when CI and C bit status
is same with local, remote PE is treated as a valid EVPN destination.
When local PE forwards a packet to remote PE, if remote PE is control
word enabled, then the unicast packet MUST be encapsulated with a
control word indicator before control word. If remote PE is control
word disabled or no control word capability, then unicast packet is
directly encapsulated after MPLS label as payload.
For example:
PE1 advertises A-D route with CI and C bit set 1, packet forwarding
behavior is as below:
PE2->PE1: Transport Label + EVPN Label to PE1 + CI + CW + Payload
PE3->PE1: Transport Label + EVPN Label to PE1 + Payload
PE2 advertises A-D route with CI and C bit set 1, PE3 advertise A-D
route with CI and C bit set 0, packet forwarding from PE1 to PE2 and
PE3 is as below::
PE1->PE2: Transport Label + EVPN Label to PE2 + CI + CW + Payload
PE1->PE3: Transport Label + EVPN Label to PE3 + Payload
After a PE receives a packet, after looking into EVPN label, if the
first byte is "0xFF", it indicates control word is included behind.
If the first byte is not "0xFF", it indicates control word is not
included behind.
The control word interoperability mechanism described above is not
applicable to EVPN VPWS, it is applicable to EVPN ELAN.
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When working in EVPN VPWS mode, in case of C bit status is not
consistent on both ends, VPWS SHOULD be teared up and behave like
control word not enabled.
+--------+ +--------+
| PE1 | | PE2 |
| (FL) |-------| (FL) |
+--------+ +--------+
\ /
\ /
+--------+
| PE3 |
| (NFL) |
+--------+
Figure 4: Network Topology for Flow Label Interoperability
Flow label is introduced allowing to archieve better load-balancing
in the network in conditions mentioned below:
o Services in EVPN instance is not sensitive to misordering.
o Transit network has no capability parsing payload inside MPLS
label as hash factor.
PE1 and PE2 are routers with flow label capability and flow label
enabled and PE3 is router flow label disabled or without flow label
capability. It is assumed that PE1, PE2 and PE3 are working in same
EVI.
When local PE receives auto-discovery routes from remote PE, F bit
does not impact validation process of EVPN auto-discovery routes.
Even F bit of remote PE does not match with local status, local PE
SHOULD still add remote PE as a valid EVPN destination.
When sending traffic from PE1 towards PE2 and PE3, as PE1 has already
learnt the FL status of PE2 and PE3, packet encapulation is as below:
PE1->PE2: Transport Label + EVPN Label to PE2 + FL + Payload
PE1->PE3: Transport Label + EVPN Label to PE3 + Payload
When sending traffic from PE2 and PE3 towarding PE1, packet
encapulation is as below:
PE2->PE1: Transport Label + EVPN Label to PE1 + FL + Payload
PE3->PE1: Transport Label + EVPN Label to PE1 + Payload
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When PE1 recieves packets, after looking at EVPN label, it can be
both bottom of stack or not. When EVPN label is bottom of stack, and
flow label enabled locally, packet MUST be treated as valid and parse
following bytes as payload.
The flow label mechanism described above is applicable to both EVPN
ELAN and EVPN VPWS.
When interoperating with devices not supporting EVPN Layer 2
Attributes Extended Community, A-D routes received will not contain
such community. Local PE MAY assume the behavior of all remote PE is
same with local.
When data plane is not using MPLS, all bits in control flags MUST be
0. Control word and Flow Label are only applicable to MPLS data
plane.
6. 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.
7. Instructions of 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 of 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 MUST NOT be used in EVPN carrying services sensitive to
misordering. 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 MUST be disabled, otherwise control word will be treated as
part of MAC address mistakenly.
Similarly, entropy label [RFC6790] MUST NOT be used in EVPN carrying
services sensitive to misordering.
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8. Security Considerations
There are no new security considerations due to the text of this
document.
9. IANA Considerations
This document does not make any requests from IANA.
10. 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>.
[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>.
[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>.
[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
Tianpeng Yu
Huawei Technologies
EMail: yutianpeng.ietf@gmail.com
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