Vc Split Scenarios - Nokia 7210 Configuration Manual

7210 SAS-M, T, R6, R12, Mxp, Sx, S Basic System
Configuration Guide

5.8 VC Split Scenarios

A VC split can occur as a result of the following failures in a VC:
In the event of single stacking link failure in a VC, all nodes including the active and
standby CPM-IMM nodes can continue to communicate with each other. There is no
impact on the control plane and no services are lost because an alternate path exists
around the point of failure. Services on all the IMM-only nodes continue to forward
traffic; however, there might be an impact to the switching throughput as the stacking
port bandwidth reduces by half.
Similarly, in the event of a single node failure in a VC, the VC can continue to operate
with the active CPM-IMM node (or the standby CPM-IMM node if the active failed).
There is no impact to the control plane or services and services on all the IMM
continue to forward traffic. However, services provisioned on the failed node are lost
and there might be an impact to the switching throughput as the stacking port
bandwidth reduces by half.
If a double failure occurs, because two links fail, or two nodes fail, or a link and a node
fail, the VC will have two islands of nodes/cards. One of these islands needs to own
the VC. To decide which island of nodes will own the VC and continue normal
functions, the following occurs:
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• A power cycle may be required if the role is changed from a CPM-IMM node to
an IMM-only node.
• a single stacking link failure
• a single node failure
• a double failure consisting of two failed links, two failed nodes fail, or a failed link
and a failed node
• If an island has only IMM-only nodes, they all reboot.
• If one of the islands has both active and standby CPM-IMM nodes, nothing
happens to the nodes in that island. They continue to work as normal and
services configured on these nodes continue to operate in the VC without
impact. The nodes on the second island reboot.
• If one of the islands has the active CPM-IMM node and the other has the standby
CPM-IMM node, the island with the greater number of nodes continues to be
functional in the VC and all the nodes in the other island reboot. If software
determines that the island with the active CPM-IMM is also the island with the
greater number of nodes, that island continues normal operation while the nodes
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