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EXNET Fault Recovery and Redundancy
Overview
An EXNET system is self-healing with hardware failures involving a segment of the EXNET ring and an EXNET-ONE card. If a failure occurs, a node or ring segment is automatically bypassed as the EXNET port on the EXNET-ONE card is looped back.
There are no special hardware requirements to enable EXNET Fault Recovery. Configure the hardware as previously described in this document.
The EXNET cable is a fiber optic cable with separate cables for transmitting and receiving. During normal operation, the EXNET-ONE card receives packets from the ring through its EXNET Port A and transmits packets onto the ring through its EXNET Port B. In loopback mode, ring traffic is both received and transmitted through the same EXNET port. The two modes of operation are shown in EXNET-ONE Port Status.
Figure 5-10 EXNET-ONE Port Status
When an EXNET port is placed in loopback mode, the Fault Detect LEDs turn red and the host receives a Ring Status Report message indicating the status (normal or loopback) of both EXNET ports on the card.
An EXNET port cannot be placed in loopback mode by the host. To isolate a node from an CSP system, do one of the following:
1 Take the EXNET-ONE card out of service.
2 Power-down the node.
Normal Ring Operation shows the connection between nodes during normal operation. All nodes are receiving ring traffic on their EXNET A port and transmitting traffic on their EXNET B port.
During normal operation, the Signal Detect and Fault Detect LEDs are green.
Figure 5-11 Normal Ring Operation
Loopback Mode
Loopback Mode shows how EXNET ports on the EXNET-ONE card are put in loopback mode because of a failure in an EXNET ring segment.
• The EXNET ports connected to the failed ring segment (Node 1/EXNET A, Node 4/EXNET B) are placed in loopback mode.
• The traffic on the EXNET-ONE cards is both transmitted and received through one EXNET port.
• A ring connection is maintained between all nodes, and no calls are dropped.
This section describes what happens when a your system experiences a ring segment failure.
Ring Segment Failure illustrates the ring connection between nodes after the failure of a ring segment in a single ring configuration.
• The node that was connected to the failed segment at its EXNET A port loops back its EXNET A port.
• The node connected to the failed segment at its EXNET B port loops back its EXNET B port.
• A complete ring is maintained between all nodes.The host receives a Ring Status Report message from the affected nodes indicating that the affected EXNET ports are in loopback mode.
A redundant EXNET ring configuration has no effect if an EXNET ring segment fails on one of the rings. The affected ring self-heals and a complete loop is maintained on both rings.
Figure 5-13 Ring Segment Failure
This section describes what happens when your system experiences an EXNET-ONE card failure.
EXNET-ONE Card Failure – Single Ring shows the ring connection between nodes after the failure of an EXNET-ONE card in a single ring configuration.
• The node that was connected to the failed node’s EXNET A port loops back its EXNET B port.
• The node connected to the failed node’s EXNET B port loops back its EXNET A port.
• All calls on the failed node connected across the ring are purged.
• A ring connection is maintained between all remaining nodes. The host receives a Ring Status Report message from the adjacent nodes indicating that the affected EXNET ports are in loopback mode.
Figure 5-14 EXNET-ONE Card Failure – Single Ring
Important! If the EXNET-ONE card is reset, the EXNET ring resets when the node rejoins the ring.
If the Master Node fails in a non-redundant system, the EXNET ring resets and all inter-nodal connections are purged. To determine the Master Node, send a Ring Status Query to each node.
EXNET Card Failure – Redundant Ring shows the ring connection between nodes after the failure of an EXNET-ONE card in a redundant ring configuration.
Figure 5-15 EXNET Card Failure – Redundant Ring
• The node that was connected to the failed node’s EXNET A port (Node 2) loops back its EXNET B port on the affected ring
(Ring 1).
• The node that was connected to the failed node’s EXNET B port (Node 4) loops back its EXNET A port on the affected ring
(Ring 1).
• Traffic to and from Node 3 is routed through Ring 2. Traffic on other nodes is still carried on both rings. The host receives a Ring Status Report message from the adjacent nodes indicating that the affected EXNET ports are in loopback mode.
Important! In this scenario, there is no longer EXNET Redundancy for Node 3. If the EXNET-ONE card for Ring 2 fails, Node 3 is isolated from the CSP system and all inter-nodal connections involving Node 3 are dropped.