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layer2_ecmp.md

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1. Introduction

Contrail control-node can peer with set of PE nodes which may have a multihome CE device(multihomed to mentioned set of PE). This set of PE are in all-active multihoming mode. EVPN route originating because of this CE will be exported to contrail with two paths(via set of PE). Contrail should be able to load balance between the multiple links.

2. Problem statement

Though contrail-control supports this scenario but contrail-vrouter-agent does not. It picks first nexthop from the nexthop list received in evpn route. This results in skewed traffic flow.

Use case

Support multi-homed TOR.

3. Proposed solution

Honor all the nexthop sent for evpn route from control-node and compose ecmp out of same.

3.1 Alternatives considered

NA

3.2 API schema changes

NA

3.3 User workflow impact

NA

3.4 UI changes

NA

3.5 Notification impact

There were no changes made in logs, UVEs or alarms.

4. Implementation

4.1 Work items

Config Schema

NA

Control-node

NA

Control-vrouter-agent

Agent will accept multiple nexthops appearing in xmpp messages. As this is a feature implementing ECMP evpn routes from multihoming CE, no locally generated (e.g. multiple VMI with same mac on compute) will be considered for ECMP. In other words agent will not publish any ECMP evpn routes and will only act on control-node published routes.

Proxy Arp

EVPN routes will provide the mac/IP binding for arp. This will remain same as of regular arp entries programmed by EVPN. There is an inherent assumption in vrouter(data plane) to not look at binding when nexthop is ecmp composite. This will be modified to pick up the mac from binding and not rely on type of nexthop.

Tunnel tracking

Flows will be used for tracking the tunnels as in L3 ECMP. Every flow will carry one ecmp index computed using SIP, DIP, sport, dport and protocol type. Reverse flow is also programmed at same so that source and destination never change for a flow in forward/reverse direction.

Selection logic of ecmp composite NH is described here: https://github.com/Juniper/contrail-controller/wiki/Flow-processing

Contrail-UI

NA

5. Performance and scaling impact

5.1 API and control plane

No impact

5.2 Forwarding performance

No impact

6. Upgrade

No impact

7. Deprecations

There are no deprecations when this change is made.

8. Dependencies

There are no dependencies for this feature.

9. Testing

9.1 Unit tests

Unit Test Cases will be added to validate added code

9.2 Dev tests

  • Verify ECMP NH is formed for bridge/evpn routes when more than one nexthop is seen.
  • Verify flows and forwarding.
  • Verify traffic is distributed across multiple NH.

9.3 System tests

  • Verify traffic flow with multihomed CE (say two PE). Contrail will peer with
  • both gateway. Traffic to CE should be distributed.

10. Documentation Impact

NA

11. References

NA