Identifying a loop in an external network

A non-transitory computer-readable storage medium storing instructions that when executed by a processor of a computer cause the computer to perform a method, the method comprising:

• learning, by a switch in a first network, a media access control (MAC) address of a packet received from a second network via a first ingress port of the switch, wherein the MAC address is learned in association with an aggregate virtual local area network (VLAN) configured on the first network for traffic from the second network;
• inspecting the packet to determine an external VLAN configured on the second network;
• sending, via the first ingress port, a loop detection packet on the external VLAN, wherein a source address and a detector address of the loop detection packet are both a local address of the switch, and wherein a destination address of the loop detection packet is a multi-destination address;
• and
• in response to identifying the local address as the detector address in an ingress packet received from a second ingress port of the switch coupling a second switch of the first network:
• identifying a loop in the second network on the external VLAN;
• and
• disabling transmission via the first ingress port.

A computer system, comprising:

• a processor;
• a memory device;
• a set of ports, wherein at least one port participates in a first network;
• and
• a non-transitory machine-readable medium comprising instructions executable by the processor to:
• learn a media access control (MAC) address of a packet received from a second network via a first ingress port in the set of ports, wherein the MAC address is learned in association with an aggregate virtual local area network (VLAN) configured on the first network for traffic from the second network;
• and
• inspect the packet to determine an external VLAN configured on the second network;
• send, via the first ingress port, a loop detection packet on the external VLAN, wherein a source address and a detector address of the loop detection packet are both a local address of the computer system, and wherein a destination address of the loop detection packet is a multi-destination address;
• identify the local address as the detector address in an ingress packet received from a second ingress port in the set of ports coupling a switch of the first network;
• and
• in response to identifying the local address as the detector address in the ingress packet received from the second ingress port:
• identify a loop in the second network on the external VLAN;
• and
• disable transmission via the first ingress port.