3Com 5500-SI Configuration Manual page 686

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PPENDIX OM
IEEE802.1D (Legacy STP) and RSTP
The Switch 4200 is using legacy STP. STP (and RSTP) will reconfigure the network
to open the previously blocked link to Switch B. The STP reconfiguration will cause
all Switch forwarding databases (MAC address tables) to be fast aged (if using
RSTP, they will be flushed). If STP is enabled throughout the network, it will
reconfigure the network to ensure that no loops occur due to split aggregated
links.
If the Distributed Fabric has been configured to be the root bridge in the network
then this will encourage STP to maintain the traffic flow through the shortest
paths in the event of an Fabric Interconnect failure.
Resilient Links
The Switch 3300 will continue to send traffic down the active link to Switch A and
keep the link to Switch B in standby mode.
VLANs
As all VLANs will have been configured on all links, the traffic will still reach its
destination using the paths that remain open.
Router
Initially both Switches continue to route. Simultaneously the Switches attempt to
contact each other and carry out a process that determines which Switch will
become the Layer 3 router and which Switch will become the Layer 2 bridge. This
avoids the scenario of two different and independent routers operating with the
same identity.
Interconnect Recovery
When the interconnect recovers and starts to operate again, all links will
reconfigure themselves as they were before the failure, according to the protocols
used. The routing task will once again be shared between Switches A and B, using
the same IP address.