INTERNET-DRAFT Patrice Brissette
Intended Status: Proposed Standard Samir Thoria
Ali Sajassi
Cisco Systems
Expires: September 12, 2019 March 11, 2019
EVPN multi-homing port-active load-balancing
draft-brissette-bess-evpn-mh-pa-03
Abstract
The Multi-Chassis Link Aggregation Group (MC-LAG) technology enables
the establishment of a logical port-channel 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. EVPN
standard defines EVPN based MC-LAG with single-active and all-active
multi-homing load-balancing mode. The current draft expands on
existing redundancy mechanisms supported by EVPN and introduces
support of port-active load-balancing mode. In the current draft,
port-active load-balancing mode is also referred to as per interface
active/standby.
Status of this Memo
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Copyright and License Notice
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Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Multi-Chassis Ethernet Bundles . . . . . . . . . . . . . . . . 4
3. Port-active load-balancing procedure . . . . . . . . . . . . . 4
4. Algorithm to elect per port-active PE . . . . . . . . . . . . . 5
5. Convergence considerations . . . . . . . . . . . . . . . . . . 5
6. Applicability . . . . . . . . . . . . . . . . . . . . . . . . . 6
7. Overall Advantages . . . . . . . . . . . . . . . . . . . . . . 6
8 Security Considerations . . . . . . . . . . . . . . . . . . . . 8
9 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
11 References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
11.1 Normative References . . . . . . . . . . . . . . . . . . . 8
11.2 Informative References . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
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1 Introduction
EVPN, as per [RFC7432], provides all-active per flow load balancing
for multi-homing. It also defines single-active with service carving
mode, where one of the PEs, in 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 active-standby per interface multi-homing redundancy is useful
and required. Main consideration for this mode of redundancy is the
determinism of traffic forwarding through specific interface rather
than statistical per flow load balancing across multiple PEs
providing multi-homing. The determinism provided by active-standby
per interface is also required for certain QOS features to work.
While using this mode, customers also expect minimized convergence
during failures. A new term of load-balancing mode "port-active load-
balancing" is then defined.
This draft describes how that new redundancy mode can be supported
via EVPN.
+-----+
| 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 Bundle-Ethernet
interfaces running LACP protocol. The core, shown as IP or MPLS
enabled, provides wide range of L2 and L3 services. MC-LAG multi-
homing functionality is decoupled from those services in the core and
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it focuses on providing multi-homing to CE. With per-port
active/standby redundancy, only one of the two interface I1 or I2
would be in forwarding, 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. When EVPN is used to provide MC-LAG functionality, we refer to
it as EVLAG in this draft.
1.1 Terminology
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 RFC 2119 [RFC2119].
2. Multi-Chassis Ethernet Bundles
When a CE is multi-homed to a set of PE nodes using the [802.1AX]
Link Aggregation Control Protocol (LACP), the PEs must act as if they
were a single LACP speaker for the Ethernet links to form a bundle,
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 among them. ICCP-based protocol
has been used for that purpose. EVPN LAG simplifies greatly that
solution. Along with the simplification comes few assumptions:
- Links in the Ethernet Bundle MUST operate in all-active load-
balancing mode
- Same LACP parameters MUST be configured on peering PEs such as
system id, port priority, etc.
Any discrepancies from this list is left for future study.
Furthermore, mis-configuration and mis-wiring detection across
peering PEs are also left for further study.
3. Port-active load-balancing procedure
Following steps describe the proposed procedure with EVPN LAG to
support port-active load-balancing mode:
1- ESI MUST be assigned per access interface as described in
[RFC7432], which may be auto derived or manually assigned. Access
interface MAY be a Layer-2 or Layer3 interface.
2- Ethernet-Segment MUST be configured in port-active load-balancing
mode on peering PEs for specific interface
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3- Peering PEs MAY exchange only Ethernet-Segment route (Route Type-
4)
4- PEs in the redundancy group leverages DF election defined in
[EVPN-DF] 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 [EVPN-DF] is per <ES, VLAN> granularity, for port-active mode of
multi-homing, the DF election is done per <ES>. The details of this
algorithm are described in Section 4.
5- DF router MUST keep corresponding access interface in up and
forwarding active state for that Ethernet-Segment
6- Non-DF routers MAY bring and keep peering access interface
attached to it in 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 interface state down. This allows for
better convergence on standby to active transition.
7- For EVPN-VPWS service, the usage of primary/backup bits of EVPN
Layer2 attributes extended community [RFC8214] is highly recommended
to achieve better convergence.
4. Algorithm to elect per port-active PE
The default DF Election algorithm, or modulus-based algorithm as in
[RFC7432], is used here also, at the granularity of <ES> only. For
Modulo calculation, byte 10 of the ESI is used.
Highest Random Weight (HRW) algorithm defined in [EVPN-DF] MAY also
be used and signaled, and modified to operate at the granularity of
<ES> rather than per <ES, VLAN>.
Let Active(ESI) denote the PE that will be the active PE for port
with Ethernet segment identifier - ESI. The other PEs in the
redundancy group will be standby PE(s) for the same port (ES). Ai is
the address of the PEi and weight() is a pseudorandom function of ESi
and Ai, Wrand() function defined in [EVPN-DF] is used as the Weight()
function.
Active(ESI) = PEi: if Weight(ESI, Ai) >= Weight(ESI, Aj), for all j,
0 <= I,j <= Number of PEs in the redundancy group. In case of a tie,
choose the PE whose IP address is numerically the least.
5. Convergence considerations
To improve the convergence, upon failure and recovery, when port-
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active load-balancing mode is used, some advanced synchronization
between peering PEs may be required. Port-active is challenging in a
sense that the "standby" port is in down state. It takes some time to
bring a "standby" port in up-state and settle the network. For IRB
and L3 services, ARP / MLD cache may be synchronized. Moreover,
associated VRF tables may also be synchronized. For L2 services, MAC
table synchronization may be considered. Finally, using bundle-
Ethernet interface, where LACP is running, is usually a smart thing
since it provides the ability to set the "standby" port in "out-of-
sync" state aka "warm-standby".
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 VPN context
[RFC4364] or in global routing context. When a PE provides first hop
routing, EVPN IRB could also be deployed on the PEs. The mechanism
defined in this draft is used between the PEs providing the L2 and/or
L3 service, when the requirement is to use per port active.
A possible alternate solution is the one described in this draft 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 draft with EVPN does not
mandate the need to use LDP or ICCP and is independent of the
underlay encapsulation.
7. Overall Advantages
There are many advantages in EVPN LAG to support port-active load-
balancing mode. Here is a non-exhaustive list:
- Open standards based per interface single-active redundancy
mechanism that eliminates the need to run ICCP and LDP.
- Agnostic of underlay technology (MPLS, VXLAN, SRv6) and associated
services (L2, L3, Bridging, E-LINE, etc).
- Provides a way to enable deterministic QOS over MC-LAG attachment
circuits
- Fully compliant with RFC-7432, does not require any new protocol
enhancement to existing EVPN RFCs.
- Can leverage various DF election algorithms e.g. modulo, HRW, etc.
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- Replaces legacy MC-LAG ICCP-based solution, and offers following
additional benefits:
- Efficiently supports 1+N redundancy mode (with EVPN using BGP
RR) where as ICCP requires full mesh of LDP sessions among PEs in
redundancy group
- Fast convergence with mass-withdraw is possible with EVPN, no
equivalent in ICCP
- Customers want per interface single-active redundancy, but don't
want to enable LDP (e.g. they may be running VXLAN or SRv6 in the
network). Currently there is no alternative to this.
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8 Security Considerations
The same Security Considerations described in [RFC7432] are valid for
this document.
9 IANA Considerations
There are no new IANA considerations in this document.
10. Acknowledgements
Authors would like to thank Luc Andre Burdet for valuable reviews and
inputs.
11 References
11.1 Normative References
[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>.
[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>.
[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>.
[EVPN-DF] Rabadan J., Mohanty S. et al. "Framework for EVPN
Designated Forwarder Election Extensibility", draft-
ietf-bess-evpn-df-election- framework-07, work-in-
progress, December, 2018.
11.2 Informative 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>.
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[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>.
Authors' Addresses
Patrice Brissette
Cisco Systems
EMail: pbrisset@cisco.com
Samir Thoria
Cisco Systems
EMail: sthoria@cisco.com
Ali Sajassi
Cisco Systems
EMail: sajassi@cisco.com
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