BigIron RX Series Configuration Guide 40753-1001986-01Ring initialization for shared interfaces 14node, the packet is forwarded through the secondary interface since it is currently in apreforwarding state. A secondary interface in preforwarding mode ignores any RHP packet that isnot from its ring. The secondary interface changes to blocking mode only when the RHP packetforwarded by its primary interface is returned.The packet then continues around Ring 1, through the interfaces on S1 to Ring 2 until it reachesRing 2’s master node. Port 3/2, the secondary interface on Ring 2 changes to blocking mode sinceit received its own packet, then blocks the packet to prevent a loop.NOTEOn the ring member node, the primary and secondary interface is not only decided by theconfiguration, but also decide by the RHP flow from the ring master. The primary and secondaryinterface may not be swapped even if the configuration changes and there is an active ring masterin the topology. If there is no active ring master in the topology, then the running configuration of theinterface on the member node will follow what was configured.Selection of master nodeAllowing MRP rings to share interfaces limits the nodes that can be designated as the master node.Any node on an MRP ring that does not have a shared interface can be designated as the ring’smaster node. However, if all nodes on the ring have shared interfaces, nodes that do not havetunnel ports can be designated as the master node of that ring. If none of the nodes meet thesecriteria, you must change the rings’ priorities by reconfiguring the rings’ ID.In Figure 72, any of the nodes on Ring 1, even S1 or S2, can be a master node since none of itsinterfaces are tunnel ports. However in Ring 2, neither S1 nor S2 can be a master node since thesenodes contain tunnel ports.RHP processing in rings with shared interfacesInterfaces on an MRP ring have one of the following states:• Preforwarding (PF) – All ring interfaces are in this state when you enable MRP.• Forwarding (F) – An interface changes from Preforwarding to Forwarding when the port’spreforwarding time expires.• Blocking (B) – The interface cannot forward data. Only the secondary interface on the Masternode can be Blocking.The primary interface of the master node initiates the RHP packets and sends it on the ring. Whenthe packet reaches an interface, MRP checks to see if the receiving interface is a regular port or atunnel port.If the port is a regular port, the RHP packet is forwarded to the next interface. Forwarding of thepacket continues on the ring until the secondary interface of the master node receives the packetand blocks it.If the port is a tunnel port, MRP checks the priority of the RHP packet and compares it to thepriority of the tunnel port:• If the RHP packet’s priority is less than or equal to the interface’s priority, the packet isforwarded through that interface.• If the priority of the RHP packet is greater than the priority of the interface, the RHP packet isdropped.
