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Loop Detection in Pure L2 Mode

Juniper Cloud-Native Router supports Layer 2 loop detection mechanisms by detecting frequent MAC address movements between ports.

Juniper Cloud-Native Router supports Layer 2 loop detection mechanism in the vRouter data path. Frequent MAC address movements between ports, many a times resulting from incorrect wiring, can result in L2 loops, resulting in network instability, broadcast storms, and degragded performance. Traditional loop detection mechanisms such as Spanning Tree Protocol (STP) may not always be feasible in modern data center environments.

Cloud-Native Router implements a loop detection mechanism that identifies MAC address learning loops by monitoring the frequency of MAC address movements between ports. The vRouter uses the MAC-MOVE table to track these MAC movemements, including source MAC, VLAN tag, hit count, and timestamp. The vRouter detects high hit counts on the same MAC address entry in the MAC_MOVE table, indicating continuous movement of the MAC address between two ports within a short interval of time.

You can use the purel2cli --mac-move-table show command on the vRouter shell to view the MAC_MOVE table:

The vRouter also logs the detected loop and shuts down affected ports.

A Syslog notification is also generated when the loop is detected: