3Com PS Hub 40, User Manual

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What are Resilient Links?
You can make the network more robust by adding resilience to it.
When a link fails all communication between equipment on each side
of the link is lost. To ensure important communication is not lost, the
network needs to be reinstated immediately which could be very
inconvenient for the network manager. If a spare link was configured
to automatically pick up when the broken link failed, the network
would appear to function normally to the user. At worst, a few packets
would be corrupted or lost.
This is the concept of resilience. One link is on standby (called the
standby link) waiting to take over if another link (called the main link)
fails. This pair is called a resilient link pair . The resilient link ports can be
on different hubs in the stack, and any network devices can be at the
other ends of the links.
When the network is in use, the stack that has been used to set up the
resilient link pair, monitors the state of both the main link and the
standby link. If the main link fails, the standby link becomes active.
You can use the Resilient Links page to view the status of the links.
If you have an SNMP network management application, you can
configure the hub to send
traps (messages) to the SNMP network
management application, if the states of the links change.
Resilient Link Pairs
To set up a resilient link pair, you need to manage the stack that both
links in the pair are connected to. The number of resilient link pairs you
can set up is only restricted by the number of ports you have in the
stack.
When you set up the resilient link pair, you need to specify the ports
that the main link and standby link are connected to.
Load Balancing does not move ports that are part of a resilient link pair.