Q-in-Q Ethernet rings

Abstract

A resilient virtual Ethernet ring has nodes interconnected by working and protection paths. Each node has a set of VLAN IDs (VIDs) for tagging traffic entering the ring by identifying the ingress node and whether the traffic is on the working or protection path. MAC addresses are learned in one direction around the ring. A port aliasing module records in a forwarding table a port direction opposite to a learned port direction. Each node can also cross-connect working and protection paths. If a span fails, the two nodes immediately on either side of the failure are cross-connected to fold the ring working-path traffic is cross-connected onto the protection path at the first of the two nodes and is then cross-connected back onto the working path at the second of the two nodes so that traffic always ingresses and egresses the ring from the working path.

1 . A method of routing frame-based traffic over a resilient virtual ring having a working path and a protection path, the method comprising steps of:
 selecting one of the working path and the protection path to carry the traffic, the protection path being different from the working path;   defining, for each node of the ring, a plurality of unique ring tags, the plurality of unique ring tags uniquely identifying the corresponding node and the selected one of the working path and the protection path to carry the traffic; and   tagging frames entering the virtual ring with one of the plurality of unique ring tags to uniquely identify both the node that has tagged the frames and the selected one of the working path and the protection path.   
     
     
         2 . The method as claimed in  claim 1  wherein the ring tags further identify which one of two opposing directions around the ring that the frames are being carried. 
     
     
         3 . The method as claimed in  claim 2  wherein the frame-based traffic comprises Ethernet frames and wherein the step of defining the plurality of unique ring tags comprises defining a plurality of VLAN IDs (VIDs) for each node of the ring to identify the two opposing directions for both the working and protection paths. 
     
     
         4 . The method as claimed in  claim 3  wherein the step of tagging frames entering the virtual ring comprises assigning one of the VIDs associated with the working path to the traffic entering the ring using Q-in-Q VLAN stacking. 
     
     
         5 . The method as claimed in  claim 1  further comprising steps of:
 monitoring traffic arriving at each node; and 
 discarding traffic that is tagged with the ring tag assigned by that same node when the traffic first entered the ring. 
 
     
     
         6 . The method as claimed in  claim 1  further comprising steps of:
 monitoring a destination MAC address of a packet arriving at a node to determine whether the node has already learned an off-ring path to the destination MAC address; 
 causing the packet to egress the node if the off-ring path to the destination MAC address has already been learned; and 
 stripping the ring tag when the packet egresses the node. 
 
     
     
         7 . The method as claimed in  claim 1  further comprising steps of:
 enabling nodes on the ring to learn off-ring paths to MAC addresses by observing traffic that is inserted onto the ring using standard bridging; 
 learning on-ring paths to MAC addresses by observing traffic received over the working path from other nodes on the ring; and 
 recording in the respective forwarding tables a port direction for each learned MAC address for on-ring paths, the port direction recorded being opposite to an actual port direction detected by the node, thereby preserving the unidirectionality of the working ring path. 
 
     
     
         8 . The method as claimed in  claim 1  further comprising steps of:
 detecting a span failure between two nodes in the ring; and 
 cross-connecting the working and protection paths at the two nodes to isolate the span failure by folding the ring such that traffic on the working path is cross-connected onto the protection path at a first one of the two nodes and then the traffic is cross-connected back onto the working path at the second one of the two nodes whereby traffic can only ingress or egress the ring from the working path. 
 
     
     
         9 . The method as claimed in  claim 1  further comprising steps of:
 sending traffic in opposite directions on both the working and protection paths; 
 sending Connectivity Fault Management (CFM) heartbeats; and 
 enabling a destination node on the ring to select traffic based on characteristics of the CFM heartbeats received at the destination node. 
 
     
     
         10 . The method as claimed in  claim 2  further comprising self-discovery steps of:
 randomly selecting a potentially usable ring tag at each node being initialized; 
 sending the potentially usable ring tag around the ring in an attempt to ping oneself whereupon one of the other nodes in the ring may strip the potentially usable ring tag from the ring if the potentially usable ring tag is recognized by one of the other nodes as a ring tag already in use; 
 seizing the potentially usable ring tag as an owned ring tag if the ring tag returns to the node being initialized; and 
 repeating the steps of randomly selecting, sending and seizing until the node being initialized has pinged itself a number of times to acquire the ring tags. 
 
     
     
         11 . A resilient virtual ring for routing frame-based traffic, the resilient virtual ring comprising:
 a working path;   a protection path, the protection path being different from the working path; and   a plurality of nodes, the plurality of nodes being interconnected by the working path and the protection path, wherein each node is associated with a plurality of ring tags for uniquely tagging traffic entering the resilient virtual ring, the ring tags identifying both the node that tagged the traffic and one of the working path and the protection path to carry the traffic.   
     
     
         12 . The ring as claimed in  claim 11  wherein the ring tags further identify which one of two opposing directions around the ring that the traffic is being carried. 
     
     
         13 . The ring as claimed in  claim 11  wherein the ring tags are VLAN IDs (VIDs) for uniquely tagging Ethernet frames in the ring. 
     
     
         14 . The ring as claimed in  claim 11  wherein each node comprises:
 a forwarding table for recording learned MAC addresses; and 
 a port aliasing module for receiving learned MAC addresses and for recording in the forwarding table a port direction that is opposite to an actual port direction detected by the node, thereby preserving the unidirectionality of the working path. 
 
     
     
         15 . The ring as claimed in  claim 11  wherein each node comprises a cross-connect for cross-connecting the working path to the protection path to thus enable ring folding in response to a failure in the working path. 
     
     
         16 . The ring as claimed in  claim 11  wherein the ring tags comprise two VIDs per ring per node to thus enable Emulated LAN (ELAN). 
     
     
         17 . The ring as claimed in  claim 11  wherein the ring tags comprise four VIDs per ring for Source Specific Multicast (SSM). 
     
     
         18 . The ring as claimed in  claim 11  wherein the ring tags comprise two VIDs per ring for Source Specific Broadcast (SSB).