Internet DRAFT - draft-ietf-bess-evpn-mh-pa
draft-ietf-bess-evpn-mh-pa
BESS Working Group P. Brissette, Ed.
Internet-Draft LA. Burdet, Ed.
Intended status: Standards Track Cisco Systems
Expires: 5 September 2024 B. Wen
Comcast
E. Leyton
Verizon Wireless
J. Rabadan
Nokia
4 March 2024
EVPN Port-Active Redundancy Mode
draft-ietf-bess-evpn-mh-pa-10
Abstract
The Multi-Chassis Link Aggregation Group (MC-LAG) technology enables
establishing a logical link-aggregation connection with a redundant
group of independent nodes. The purpose of multi-chassis LAG is to
provide a solution to achieve higher network availability while
providing different modes of sharing/balancing of traffic. RFC7432
defines EVPN-based MC-LAG with Single-active and All-active
multi-homing redundancy modes. This document expands on existing
redundancy mechanisms supported by EVPN and introduces a new Port-
Active redundancy mode.
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 5 September 2024.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Multi-Chassis Link Aggregation (MC-LAG) . . . . . . . . . . . 3
3. Port-Active Redundancy Mode . . . . . . . . . . . . . . . . . 4
3.1. Overall Advantages . . . . . . . . . . . . . . . . . . . 4
3.2. Port-Active Redundancy Procedures . . . . . . . . . . . . 5
4. Designated Forwarder Algorithm to Elect per Port-Active PE . 6
4.1. Capability Flag . . . . . . . . . . . . . . . . . . . . . 6
4.2. Modulo-based Algorithm . . . . . . . . . . . . . . . . . 7
4.3. HRW Algorithm . . . . . . . . . . . . . . . . . . . . . . 7
4.4. Preference-based DF Election . . . . . . . . . . . . . . 8
4.5. AC-Influenced DF Election . . . . . . . . . . . . . . . . 8
5. Convergence considerations . . . . . . . . . . . . . . . . . 8
5.1. Primary / Backup per Ethernet-Segment . . . . . . . . . . 8
5.2. Backward Compatibility . . . . . . . . . . . . . . . . . 9
6. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 10
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
8. Security Considerations . . . . . . . . . . . . . . . . . . . 10
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 11
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
11.1. Normative References . . . . . . . . . . . . . . . . . . 11
11.2. Informative References . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
EVPN [RFC7432] defines the All-Active and Single-Active redundancy
modes. All-Active redundancy provides per-flow load-balancing for
multi-homing, and Single-active redundancy provides service carving
where only one of the PEs in a redundancy relationship is active per
service.
While these two multi-homing scenarios are most widely utilized in
data center and service provider access networks, there are scenarios
where an active/standby multi-homing at the interface level is useful
and required. The main consideration for this new mode of
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load-balancing is the determinism of traffic forwarding through a
specific interface rather than statistical per-flow load-balancing
across multiple PEs providing multi-homing. The determinism provided
by active/standby multi-homing at the interface level is also
required for certain QoS features to work. While using this mode,
customers also expect fast convergence during failure and recovery.
This document defines the Port-Active redundancy mode as a new type
of multi-homing in EVPN and describes how this new mode operates and
is to be supported via EVPN.
1.1. Requirements Language
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.
2. Multi-Chassis Link Aggregation (MC-LAG)
When a CE is multi-homed to a set of PE nodes using the
[IEEE.802.1AX_2014] Link Aggregation Control Protocol (LACP), the PEs
must act as if they were a single LACP speaker for the Ethernet links
to form and operate as a Link Aggregation Group (LAG). To achieve
this, the PEs connected to the same multi-homed CE must synchronize
LACP configuration and operational data between them. Interchassis
Communication Protocol (ICCP) [RFC7275] has historically been used to
achieve this. EVPN in [RFC7432] describes the case where a CE is
multihomed to multiple PE nodes, using a LAG as a means to greatly
simplify the procedure. The simplification, however, comes with a
few assumptions:
* a CE device connected to EVPN multi-homing PEs MUST have a single
LAG with all its links connected to the EVPN multi-homing PEs in a
redundancy group.
* identical LACP parameters MUST be configured on peering PEs such
as system id, port priority, and port key.
This document relies on proper LAG operation as in [RFC7432].
Discrepancies from the list above are out of the scope of this
document, as are LAG misconfiguration and miswiring detection across
peering PEs.
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+-----+
| PE3 |
+-----+
+-----------+
| MPLS/IP |
| CORE |
+-----------+
+-----+ +-----+
| PE1 | | PE2 |
+-----+ +-----+
| |
I1 I2
\ /
\ /
+---+
|CE1|
+---+
Figure 1: MC-LAG Topology
Figure 1 shows a MC-LAG multi-homing topology where PE1 and PE2 are
part of the same redundancy group providing multi-homing to CE1 via
interfaces I1 and I2. Interfaces I1 and I2 are members of a LAG
running LACP. The core, shown as IP or MPLS enabled, provides a wide
range of L2 and L3 services. MC-LAG multi-homing functionality is
decoupled from those services in the core and it focuses on providing
multi-homing to the CE. In Port-Active redundancy mode, only one of
the two interfaces I1 or I2 would be in forwarding and the other
interface will be in standby. This also implies that all services on
the active interface are in active mode and all services on the
standby interface operate in standby mode.
3. Port-Active Redundancy Mode
3.1. Overall Advantages
The use of Port-Active redundancy brings the following benefits to
EVPN networks:
a. Open standards-based active/standby redundancy at the interface
level which eliminates the need to run ICCP and LDP (e.g., they
may be running VXLAN or SRv6 in the network).
b. Agnostic of underlay technology (MPLS, VXLAN, SRv6) and
associated services (L2, L3, Bridging, E-LINE, etc).
c. Provides a way to enable deterministic QoS over MC-LAG attachment
circuits.
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d. Fully compliant with [RFC7432], does not require any new protocol
enhancement to existing EVPN RFCs.
e. Can leverage various Designated Forwarder (DF) election
algorithms e.g. modulo, HRW, etc.
f. Replaces legacy MC-LAG ICCP-based solution, and offers the
following additional benefits:
* Efficiently supports 1+N redundancy mode (with EVPN using BGP
RR) whereas ICCP requires a full mesh of LDP sessions among
PEs in the redundancy group.
* Fast convergence with mass-withdraw is possible with EVPN, no
equivalent in ICCP.
3.2. Port-Active Redundancy Procedures
The following steps describe the proposed procedure with EVPN LAG to
support Port-Active redundancy mode:
a. The Ethernet-Segment Identifier (ESI) MUST be assigned per access
interface as described in [RFC7432], which may be auto-derived or
manually assigned. The access interface MAY be a Layer-2 or
Layer-3 interface. The use of ESI over a Layer-3 interface is
newly described in this document.
b. Ethernet-Segment (ES) MUST be configured in Port-Active
redundancy mode on peering PEs for specific access interface.
c. When ESI is configured on a Layer-3 interface, the Ethernet-
Segment (ES) route (Route Type-4) may be the only route exchanged
by PEs in the redundancy group.
d. PEs in the redundancy group leverage the DF election defined in
[RFC8584] to determine which PE keeps the port in active mode and
which one(s) keep it in standby mode. While the DF election
defined in [RFC8584] is per [ES, Ethernet Tag] granularity, the
DF election is done per [ES] in Port-Active redundancy mode. The
details of this algorithm are described in Section 4.
e. DF router MUST keep corresponding access interface in up and
forwarding active state for that Ethernet-Segment
f. Non-DF routers SHOULD implement a bidirectional blocking scheme
for all traffic comparable to [RFC7432] Single-Active blocking
scheme, albeit across all VLANs.
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* Non-DF routers MAY bring and keep peering access interface
attached to it in an operational down state.
* If the interface is running LACP protocol, then the non-DF PE
MAY also set the LACP state to OOS (Out of Sync) as opposed to
an interface down state. This allows for better convergence
on standby to active transition.
g. The primary/backup bits of EVPN Layer 2 Attributes Extended
Community [RFC8214] SHOULD be used to achieve better convergence
as decribed in section Section 5.1.
4. Designated Forwarder Algorithm to Elect per Port-Active PE
The ES routes, running in Port-Active redundancy mode, are advertised
with the new Port Mode Load-Balancing capability bit in the DF
Election Extended Community defined in [RFC8584]. Moreover, the ES
associated with the port leverages the existing procedure of Single-
Active, and signals Single-Active Multihomed site redundancy mode
along with Ethernet-AD per-ES route (Section 7.5 of [RFC7432]).
Finally the ESI label-based split-horizon procedures in Section 8.3
of [RFC7432] should be used to avoid transient echo'ed packets when
Layer-2 circuits are involved.
The various algorithms for DF Election are discussed in Sections 4.2
to 4.5 for completeness even though the choice of algorithm in this
solution doesn't affect complexity or performance as in other
redundancy modes.
4.1. Capability Flag
[RFC8584] defines a DF Election extended community, and a Bitmap (2
octets) field to encode "capabilities" to use with the DF election
algorithm in the DF algorithm field:
Bit 0: D bit or 'Don't Preempt' bit, as explained in
[I-D.ietf-bess-evpn-pref-df].
Bit 1: AC-DF Capability (AC-Influenced DF election), as explained
in [RFC8584].
1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|D|A| |P| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Amended Bitmap field in the DF Election Extended Community
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This document defines the following value and extends the Bitmap
field:
Bit 5: Port Mode Designated Forwarder Election (P bit hereafter),
determines that the DF Election algorithm should be
modified to consider the port ES only and not the Ethernet
Tags.
4.2. Modulo-based Algorithm
The default DF Election algorithm, or modulus-based algorithm as in
[RFC7432] and updated by [RFC8584], is used here, at the granularity
of ES only. Given that ES-Import Route Target extended community may
be auto-derived and directly inherits its auto-derived value from ESI
bytes 1-6, many operators differentiate ESI primarily within these
bytes. As a result, bytes 3-6 are used to determine the designated
forwarder using Modulo-based DF assignment, achieving good entropy
during Modulo calculation across ESIs:
Assuming a redundancy group of N PE nodes, the PE with ordinal i is
the DF for an <ES> when (Es mod N) = i, where Es represents bytes 3-6
of that ESI.
4.3. HRW Algorithm
Highest Random Weight (HRW) algorithm defined in [RFC8584] MAY also
be used and signaled, and modified to operate at the granularity of
<ES> rather than per <ES, VLAN>.
Section 3.2 of [RFC8584] describes computing a 32-bit CRC over the
concatenation of Ethernet Tag and ESI. For Port-Active redundancy
mode, the Ethernet Tag is simply omitted from the CRC computation and
all references to (V, Es) are replaced by (Es), as repeated and
summarised below.
DF(Es) denotes the DF and BDF(Es) denote the BDF for the Ethernet
Segment Es; Si is the IP address of PE i; and Weight is a function of
Si, and Es.
1. DF(Es) = Si| Weight(Es, Si) >= Weight(Es, Sj), for all j. In the
case of a tie, choose the PE whose IP address is numerically the
least. Note that 0 <= i,j < number of PEs in the redundancy
group.
2. BDF(Es) = Sk| Weight(Es, Si) >= Weight(Es, Sk), and Weight(Es,
Sk) >= Weight(Es, Sj). In the case of a tie, choose the PE whose
IP address is numerically the least.
Where:
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* DF(Es) is defined to be the address Si (index i) for which
Weight(Es, Si) is the highest; 0 <= i < N-1.
* BDF(Es) is defined as that PE with address Sk for which the
computed Weight is the next highest after the Weight of the DF. j
is the running index from 0 to N-1; i and k are selected values.
4.4. Preference-based DF Election
When the new capability 'Port Mode' is signaled, the preference-based
DF Election algirithm in [I-D.ietf-bess-evpn-pref-df] is modified to
consider the port only and not any associated Ethernet Tags.
Furthermore, the Port Mode capability MUST be compatible with the
'Don't Preempt' bit. When an interface recovers, a peering PE
signaling D bit will enable non-revertive behavior at the port level.
4.5. AC-Influenced DF Election
The AC-DF bit defined in [RFC8584] MUST be set to 0 when advertising
Port Mode Designated Forwarder Election capability (P=1). When an AC
(sub-interface) goes down, it does not influence the DF Election.
The peer's Ethernet A-D per EVI is ignored in all Port Mode
DF Election algorithms.
Upon receiving the AC-DF bit set (A=1) from a remote PE, it MUST be
ignored when performing Port Mode DF Election.
5. Convergence considerations
To improve the convergence, upon failure and recovery, when the Port-
Active redundancy mode is used, some advanced synchronization between
peering PEs may be required. Port-Active is challenging in the sense
that the "standby" port may be in a down state. It takes some time
to bring a "standby" port to an up state and settle the network. For
IRB and L3 services, ARP / ND cache may be synchronized. Moreover,
associated VRF tables may also be synchronized. For L2 services, MAC
table synchronization may be considered.
Finally, for members of a LAG running LACP the ability to set the
"standby" port in "out-of-sync" state a.k.a "warm-standby" can be
leveraged.
5.1. Primary / Backup per Ethernet-Segment
The EVPN Layer 2 Attributes Extended Community ("L2-Attr") defined in
[RFC8214] SHOULD be advertised in the Ethernet A-D per ES route for
fast convergence.
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Only the P and B bits of the Control Flags field in the L2-Attr
Extended Community are relevant to this document, and only in the
context of Ethernet A-D per ES routes:
* When advertised, the L2-Attr Extended Community SHALL have only P
or B bits in the Control Flags field set, and all other bits and
fields MUST be zero.
* A remote PE receiving the optional L2-Attr Extended Community in
Ethernet A-D per ES routes SHALL consider only P and B bits and
ignore other values.
For L2-Attr Extended Community sent and received in Ethernet A-D
per EVI routes used in [RFC8214], [RFC7432] and
[I-D.ietf-bess-evpn-vpws-fxc]:
* P and B bits received SHOULD be considered overridden by "parent"
bits when advertised in the Ethernet A-D per ES.
* Other fields and bits of the extended community are used according
to the procedures of those documents.
5.2. Backward Compatibility
Implementations that comply with [RFC7432] or [RFC8214] only (i.e.,
implementations that predate this specification) will not advertise
the EVPN Layer 2 Attributes Extended Community in Ethernet A-D per ES
routes. That means that all remote PEs in the ES will not receive P
and B bit per ES and will continue to receive and honour the P and B
bits received in Ethernet A-D per EVI route(s). Similarly, an
implementation that complies with [RFC7432] or [RFC8214] only and
that receives an L2-Attr Extended Community in Ethernet A-D per ES
routes will ignore it and continue to use the default path resolution
algorithm:
* The remote ESI Label Extended Community ([RFC7432]) signals
Single-Active (Section 4)
* the remote MAC and/or Ethernet A-D per EVI routes are unchanged,
and since the L2-Attr Extended Community in Ethernet A-D per ES
route is ignored, the P and B bits in the L2-Attr Extended
Community in Ethernet A-D per EVI routes are used.
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6. Applicability
A common deployment is to provide L2 or L3 service on the PEs
providing multi-homing. The services could be any L2 EVPN such as
EVPN VPWS, EVPN [RFC7432], etc. L3 service could be in a VPN context
[RFC4364] or in a global routing context. When a PE provides first
hop routing, EVPN IRB could also be deployed on the PEs. The
mechanism defined in this document is used between the PEs providing
L2 and/or L3 services, when active/standby redundancy at the
interface level is desired.
A possible alternate solution to the one described in this document
is MC-LAG with ICCP [RFC7275] active-standby redundancy. However,
ICCP requires LDP to be enabled as a transport of ICCP messages.
There are many scenarios where LDP is not required e.g. deployments
with VXLAN or SRv6. The solution defined in this document with EVPN
does not mandate the need to use LDP or ICCP and is independent of
the underlay encapsulation.
7. IANA Considerations
This document solicits the allocation of the following values from
the "BGP Extended Communities" registry group :
* Bit 5 in the [RFC8584] DF Election Capabilities registry, "P bit -
Port Mode Designated Forwarder Election".
8. Security Considerations
The same Security Considerations described in [RFC7432] and [RFC8584]
are valid for this document.
By introducing a new capability, a new requirement for unanimity (or
lack thereof) between PEs is added. Without consensus on the new
DF Election procedures and Port Mode, the DF Election algorithm falls
back to the default DF Election as provided in [RFC8584] and
[RFC7432]. This behavior could be exploited by an attacker that
manages to modify the configuration of one PE in the ES so that the
DF Election algorithm and capabilities in all the PEs in the ES fall
back to the default DF Election. If that is the case, the PEs will
be exposed to the same unfair load balancing, service disruption, and
possibly black-holing or duplicate traffic mentioned in those
documents and their security sections.
9. Acknowledgements
The authors thank Anoop Ghanwani for his comments and suggestions and
Stephane Litkowski for his careful review.
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10. Contributors
In addition to the authors listed on the front page, the following
coauthors have also contributed to this document:
Ali Sajassi
Cisco Systems
United States of America
Email: sajassi@cisco.com
Samir Thoria
Cisco Systems
United States of America
Email: sthoria@cisco.com
11. References
11.1. Normative References
[I-D.ietf-bess-evpn-pref-df]
Rabadan, J., Sathappan, S., Lin, W., Drake, J., and A.
Sajassi, "Preference-based EVPN DF Election", Work in
Progress, Internet-Draft, draft-ietf-bess-evpn-pref-df-13,
9 October 2023, <https://datatracker.ietf.org/doc/html/
draft-ietf-bess-evpn-pref-df-13>.
[IEEE.802.1AX_2014]
IEEE, "IEEE Standard for Local and metropolitan area
networks -- Link Aggregation", IEEE 802.1AX-2014,
DOI 10.1109/IEEESTD.2014.7055197, 24 December 2014,
<http://ieeexplore.ieee.org/servlet/
opac?punumber=6997981>.
[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>.
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[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>.
[RFC8584] Rabadan, J., Ed., Mohanty, S., Ed., Sajassi, A., Drake,
J., Nagaraj, K., and S. Sathappan, "Framework for Ethernet
VPN Designated Forwarder Election Extensibility",
RFC 8584, DOI 10.17487/RFC8584, April 2019,
<https://www.rfc-editor.org/info/rfc8584>.
11.2. Informative References
[I-D.ietf-bess-evpn-vpws-fxc]
Sajassi, A., Brissette, P., Uttaro, J., Drake, J.,
Boutros, S., and J. Rabadan, "EVPN VPWS Flexible Cross-
Connect Service", Work in Progress, Internet-Draft, draft-
ietf-bess-evpn-vpws-fxc-08, 24 October 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-bess-
evpn-vpws-fxc-08>.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
2006, <https://www.rfc-editor.org/info/rfc4364>.
[RFC7275] Martini, L., Salam, S., Sajassi, A., Bocci, M.,
Matsushima, S., and T. Nadeau, "Inter-Chassis
Communication Protocol for Layer 2 Virtual Private Network
(L2VPN) Provider Edge (PE) Redundancy", RFC 7275,
DOI 10.17487/RFC7275, June 2014,
<https://www.rfc-editor.org/info/rfc7275>.
Authors' Addresses
Patrice Brissette (editor)
Cisco Systems
Ottawa ON
Canada
Email: pbrisset@cisco.com
Luc Andre Burdet (editor)
Cisco Systems
Canada
Email: lburdet@cisco.com
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Bin Wen
Comcast
United States of America
Email: Bin_Wen@comcast.com
Edward Leyton
Verizon Wireless
United States of America
Email: edward.leyton@verizonwireless.com
Jorge Rabadan
Nokia
United States of America
Email: jorge.rabadan@nokia.com
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