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Support for Multiple Primary Nodes to Associate With a Single Member Node in NetRef

 

Network node reference (NetRef) is an extension of the CTP adaptive port clocking. NetRef can be used to provide node level synchronization across a network. When NetRef is configured for primary or backup operation, the primary node sends clocking information to the backup node. The backup node uses an algorithm similar to that used for adaptive port clocking to control the local node clock so that it follows the clocking of the remote node. To operate in primary or backup mode, the remote primary node must be configured as a NetRef primary node with the IP address of the NetRef client configured. The backup node must be configured as a NetRef backup node with the IP address of the NetRef primary node configured. You can configure up to four primary modes, each of which can send their clocking information to a maximum of 10 slaves and the client node can receive clocking information from the configured primary nodes.

You can configure the four primary nodes using CTP Menu or the CTPView web server during Netref client configuration. As a result, a single client node can use the IP address of up to four primary nodes while you configure Netref client node settings.

Each primary node is assigned a priority during Netref client configuration. The primary node with the highest priority is assigned Priority 1, the second highest priority for the primary node is Priority 2, and so on. You cannot configure the priority of the primary nodes. The priorities assigned are unique for each primaries while configuring Netref client nodes. The client nodes synchronize their local clock with the clock of the highest priority primary node (Priority 1 primary node). After the highest priority primary goes down or when a problem occurs during the clock synchronization phase, the CTP device switches to its next highest priority primary (Priority 2 primary node). The client nodes synchronize their clock with the clock of Priority 2 primary node. The priorities of the primary nodes are also switched in the backend, after switching of the primary nodes takes place. In the case of flapping between the primaries, the primary (high priority) is retained or binding with the primary that contains a good clock quality is maintained.

When switching of the primaries takes place, an event of primary role change is logged into the syslog messages. The client node synchronization query provides the details of the primary node to which the client is locked and the details of the configured primary nodes along with their assigned priorities. You cannot configure the lowest priority primaries until its higher priority primaries are configured. Similarly, you cannot disable the highest priority primaries until its lower priority primaries are disabled.

When a node is configured as NetRef Primary, it starts generating the NetRef packets and send them to the client nodes. The client node accepts the packets from the highest priority primary node and the NetRef state of the client node is changed to wait state. If 16 sequenced packets are received by the client nodes, the NetRef state is changed from Wait state to Aggressive state. At this stage, if 8 packets are missed continuously, the NetRef state again moves back to the Wait state. These NetRef packets are processed and slope is calculated. Based on the slope, the clock of the client node is in synchronization with the primary node and the state changes to the Maintain state. The state changes from Maintain or Aggressive to Starvation when no NetRef packet is received in last 20 seconds. As soon as the node goes to Starvation state, switching of the primary takes place. The packets are processed by the client nodes to synchronize their clock with the next highest priority primary node. Flapping of the primaries occurs if you continuously “round robin” to each primary and wait for 20 seconds for an incoming NetRef packet.

The LED becomes red when NetRef is in Wait or Aggressive state. The LED is green when NetRef is in Maintain state. The switching of the primaries occurs as described in the following table:

Member Nodes

Assigned Priority

Assigned Priority After First Failure

Assigned Priority After Second Failure

Assigned Priority After Third Failure

Assigned Priority After Fourth Failure

Primary 1

1 (primary)

4

3

2

1 (primary)

Primary 2

2

1 (primary)

4

3

2

Primary 3

3

2

1 (primary)

4

3

Primary 4

4

3

1 (primary)

4

If all the four primary nodes goes down, the NetRef state remains in Starvation state and no switching will take place. When the NetRef state of the client node is Maintain and the primary goes down, the client node is unable to receive the packets within the last 20 seconds. Therefore, the NetRef state of the client node moves from Maintain state to Starvation state and switching takes place. When the NetRef state of the client node is Aggressive and the primary goes down, the client node is unable to receive the packets within the last 20 seconds. Therefore, the NetRef state of the client node transitions from Aggressive state to Starvation state and switching will take place.

When the NetRef state of the client node is in Wait state (waiting for NetRef packets from the primary node) and the primary node is disabled but the secondary primary nodes are sending NetRef packets to the client node, switching will take place.

Revert option is not supported; when the primary node comes up, the client node remains locked to the secondary primary node and does not become locked to the primary node.

Without multiple primary nodes support, when a node is configured as client, the node www_db string is

“23;1;0;0;0;0;0;0;0;0;0;5;1;5;1;5;1;5;1;5;1;;2|64|127.0.0.1/127.0.0.1/127.0.0.1/127.0.0.1/127.0.0.1/127.0.0.1/127.0.0.1/127.0.0.1/127.0.0.1/|0|255|;0;”

This www_db string is not different when multiple primary nodes are configured for a backup node. The first IP address in the www_db string contains a priority of 1, the second contains a priority of 2, and so on, as shown as follows:

“23;1;0;0;0;0;0;0;0;0;0;5;1;5;1;5;1;5;1;5;1;;2|64|10.216.118.73/10.216.118.86/10.216.118.90/10.216.118.88/127.0.0.1/127.0.0.1/127.0.0.1/127.0.0.1/127.0.0.1/|0|255|;0;” When node is configured as master, the node www_db string will remain same as it is there in the earlier releases.