# US 10,320,692 B2 · Ethernet loopback detection and service traffic blocking > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,320,692 B2 - Document ID: US10320692B2 - Status: Granted - Kind: B2 - Application number: 14/483,949 - Filed: 2014-09-11 - Published: 2016-03-17 - Granted: 2019-06-11 - Earliest claimed: 2014-09-11 - Assignees: Fujitsu Limited - Applicants: Fujitsu Limited - Inventors: Stephen John Unger; Frank Schumeg - Web page: https://patentgrep.com/patent/US10320692B2 ## CPC - H04L 47/32: by discarding or delaying data units, e.g. packets or frames - H04L 12/462: {LAN interconnection over a bridge based backbone} - H04L 12/4625: {Single bridge functionality, e.g. connection of two networks over a single bridge} - H04L 45/74: Address processing for routing - H04L 12/4641: {Virtual LANs, VLANs, e.g. virtual private networks [VPN] (LAN interconnection over a bridge based backbone H04L12/462; encapsulation techniques H04L12/4633; routing of packets H04L45/00; packet switches H04L49/00; virtual private networks for security H04L63/0272)} - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) ## Abstract A method and system for Ethernet loopback detection snoops an egress frame at a UNI-N edge device and records at least one source field of the egress frame, such as a MAC address or a VLAN tag. Ingress frames at the UNI-N edge device are monitored for having the same value in the source field as the egress frame. When an ingress frame has the same source field value as the egress frame, the ingress frame is identified as a loopback frame and is dropped at the UNI-N edge device. ## Claims ### Claim 1 A method for Ethernet loopback detection, the method comprising: snooping an egress frame at a network element, wherein the network element is an edge device of a user network interface in a service provider network, the network element coupled to a customer network at the user network interface; storing a first media access controller (MAC) address from a first source field of the egress frame; monitoring an ingress frame received from the customer network, wherein a second MAC address in the first source field of the ingress frame is compared with the first MAC address in the first source field of the egress frame; and when the second MAC address matches the first MAC address, dropping the ingress frame. ### Claim 2 (depends on 1) The method of claim 1, further comprising: counting down a first aging time after snooping the egress frame; and after the first aging time has elapsed, deleting the first MAC address. ### Claim 3 (depends on 1) The method of claim 1, wherein the first egress frame is chosen at random. ### Claim 4 (depends on 1) The method of claim 1, wherein the monitoring the ingress frame is performed for each ingress frame received from the customer network. ### Claim 5 (depends on 1) The method of claim 1, wherein the service provider network implements a connection oriented Ethernet serving the customer network. ### Claim 6 (depends on 5) The method of claim 5, further comprising: storing a first virtual local area network (VLAN) tag from a second source field of the egress frame; wherein monitoring the ingress frame received from the customer network includes comparing a second VLAN tag in the second source field of the ingress frame with the first VLAN tag; and when the second VLAN tag matches the first VLAN tag, dropping the ingress frame. ### Claim 7 (depends on 6) The method of claim 6, further comprising: counting down a second first aging time after snooping the egress frame; and after the second aging time has elapsed, deleting the first VLAN tag. ### Claim 8 A network element for Ethernet loopback detection, the network element comprising: a processor; non-transitory computer readable memory media accessible to the processor, wherein the network element is an edge device of a user network interface in a service provider network, the network element coupled to a customer network at the user network interface, and wherein the memory media store processor-executable instructions, the instructions, when executed by the processor, cause the processor to: snoop an egress frame intended for the customer network; store a first media access controller (MAC) address from a first source field of the egress frame; monitor an ingress frame received from the customer network, wherein a second MAC address in the first source field of the ingress frame is compared with the first MAC address in the first source field of the egress frame; and when the second MAC address matches the first MAC address, drop the ingress frame. ### Claim 9 (depends on 8) The network element of claim 8, further comprising instructions executable to: countdown a first aging time after storing the egress frame; and after the first aging time has elapsed, delete the first MAC address. ### Claim 10 (depends on 8) The network element of claim 8, wherein the instructions to snoop the egress frame include instructions to: select the first egress frame at random. ### Claim 11 (depends on 8) The network element of claim 8, wherein the instructions to monitor the ingress frame are performed for each ingress frame received from the customer network. ### Claim 12 (depends on 8) The network element of claim 8, wherein the service provider network implements a connection oriented Ethernet serving the customer network. ### Claim 13 (depends on 12) The network element of claim 12, further comprising instructions executable to: store a first virtual local area network (VLAN) tag from a second source field of the egress frame; wherein the instructions to monitor the ingress frame received from the customer network include instructions to compare a second VLAN tag in the second source field of the ingress frame with the first VLAN tag; and when the second VLAN tag matches the first VLAN tag, drop the ingress frame. ### Claim 14 (depends on 13) The network element of claim 13, further comprising instructions executable to: countdown a second aging time after storing the egress frame; and after the second aging time has elapsed, delete the first VLAN tag.