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EVPN-VXLAN Lightweight Leaf to Server Loop Detection

Configure EVPN-VXLAN lightweight leaf to server loop detection to quickly detect and break local area network (LAN) Ethernet loops downstream on the leaf-to-server port side. This feature detects and breaks loops for:

  • Inaccurate wiring of the fabric components

  • Inaccurate wiring or misconfiguration of third party switches to EVPN fabric devices (such as when connecting customer edge (CE) switches)

This feature helps repair loops that the EVPN control plane (on QFX5120 and QFX52xx JUNOS-based platforms) cannot detect without having to rely on the state of BGP EVPN signaling.

With this feature configured, the device transmits periodic multicast PDUs on PE to CE ports for loop detection. The device can then block the port upon receiving these self-generated PDUs. When the device receives a loop detection PDU, it breaks the loop by blocking (operationally shutting down) the ingress port. The device sets a new error log statement:

After breaking and clearing the loop, you can bring the port back online as follows:

  • Implicitly through manual intervention.

  • Explicitly by automatic after-timeout commands.

Loop Detect Scenarios

The following three loop detection scenarios demonstrate that looping can take place with different Ethernet segment identifiers (ESIs), with the same ESIs, or with no ESIs.

Figure 1: Different ESI Looped

When different ESIs are looped, you can enable a range of fabric RID on which the loop detection will be triggered (mandatory), or build the list automatically using RIDs/RD based on EVPN Type 1 (auto-discovery) route signaling (optional).

Different ESI Looped
Figure 2: Same ESI Looped

When the same ESI is looped, the CE switch is not using the same bridged interface when connecting to Leaf1/Leaf3.

Same ESI Looped
Figure 3: No ESI on Looped Ports

When no ESI exists on one of the looped ports, the loop goes through the CE switch from Leaf1 to Leaf3.

No ESI on Looped Ports

Loop Detect PE-CE Use Cases using L2 Heartbeats

The following two use cases show that the loop is occurring through the switch due to misconfiguration of the switch (use case 1), or that the loop is caused by misalignment of cable connections on the switch (use case 2). In both of the following two use cases, functionality is not dependent on the BGP speed of control-plane advertisement, and this lightweight PC-CE loop detection is independent of configured ESI values.

EVPN-VXLAN Lightweight Leaf Server Loop Detection Use Case 1

In this first case, the loop occurs at Leaf3 and neither CE-switch1 nor CE-switch2 are enabled with Connectivity Fault Management (CFM); Only eaf1 and eaf3 are CFM enabled. L2 packet CFM is using proprietary type, length, value (TLV) format.

Figure 4: Scenario 1 Scenario 1

EVPN-VXLAN Lightweight Leaf to Server Loop Detection Use Case 2

The L2 packet CFM is using a proprietary type, length, and value (TLV) and the loop occurs on Leaf1. Instead of relying on the speed of BGP, the MAC route reflections speed, and the duplicate MAC or MAC move detections in larger DC fabrics, the lightweight loop detection is independent of the state of the BGP EVPN signaling.

Figure 5: Scenario 2 Scenario 2

Enable Loop Detection on Logical Interface

To enable loop detection, use the loop-detect enhanced interface ifl statement at the [edit protocols] hierarchy level.

Sample Configuration

The following sample configuration enables loop detection on interface ge-0/0/1.0, which is a trunk interface with vlan-id 100.

CLI Commands to Display or Clear Loop Detection Status

Use the show loop-detect enhanced interface command to display loop status on an interface or all interfaces.

Use the clear loop-detect enhanced interface command to restore an interface or all interfaces to their prior state after the device detects a loop and applies a configured action to break the loop.

Show command without any loop

Show command with loop detect status