Flow When A Link Breaks - Dell PowerConnect B-RX Configuration Manual

14
Ring initialization for shared interfaces
Port 2/1 on Ring 1's master node is the primary interface of the master node. The primary
interface forwards an RHP packet on the ring. Since all the interfaces on Ring 1 are regular ports,
the RHP packet is forwarded to all the interfaces until it reaches Port 2/2, the secondary interface
of the master node. Port 2/2 then blocks the packet to complete the process.
On Ring 2, Port 3/1, is the primary interface of the master node. It sends an RHP packet on the
ring. Since all ports on S4 are regular ports, the RHP packet is forwarded on those interfaces.
When the packet reaches S2, the receiving interface is a tunnel port. The port compares the
packet's priority to its priority. Since the packet's priority is the same as the tunnel port's priority,
the packet is forwarded up the link shared by Rings 1 and 2.
When the RHP packet reaches the interface on node S2 shared by Rings 1 and 2, the packet is
forwarded since its priority is less than the interface's priority. The packet continues to be
forwarded to node S1 until it reaches the tunnel port on S1. That tunnel port determines that the
RHP packet's priority is equal to the port's priority and forwards the packet. The RHP packet is
forwarded to the remaining interfaces on Ring 2 until it reaches port 3/2, the secondary interface
of the master node. Port 3/2 then blocks the packet to prevent a loop.
When the RHP packet from Ring 2 reached S2, it was also forwarded from S2 to S3 on Ring 1 since
the port on S2 has a higher priority than the RHP packet. The packets is forwarded around Ring 1
until it reaches port 2/2, Ring 1's the secondary port. The RHP packet is then blocked by that port.

Flow when a link breaks

If the link between shared interfaces breaks (Figure 73), the secondary interface on Ring 1's
master node changes to a preforwarding state. The RHP packet sent by port 3/1 on Ring 2 is
forwarded through the interfaces on S4, then to S2. The packet is then forwarded through S2 to S3,
but not from S2 to S1 since the link between the two nodes is not available. When the packet
reaches Ring 1's master node, the packet is forwarded through the secondary interface since it is
currently in a preforwarding state. A secondary interface in preforwarding mode ignores any RHP
packet that is not from its ring. The secondary interface changes to blocking mode only when the
RHP packet forwarded by its primary interface is returned.
402 BigIron RX Series Configuration Guide
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