442 APPENDIX D: 3COM XRN
Legacy STP (IEEE802.1D) and RSTP (IEEE 802.1w)
The Switch 4200 is using legacy STP. STP 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).
Resilient Links
The Switch 3300 is using resilient links, which should be set up at the 3300 end of
the link. The Switch 3300 will detect the unit failure and activate the link to Switch
B
VLANs
Any VLANs will not be affected by unit failure.
Router
Switch B will continue to do all the routing. As it was routing prior to Switch A’s
failure there will be no change of the router identity, that is, the router interface IP
addresses will not change. The router interface MAC addresses may change but
this will have no visible impact on your network. Any MAC address change is
propogated to your network by the issuing of gratuitous ARP messages.
Switch A Recovery
When Switch A 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.
Loss of the Fabric
Interconnect
When an interconnect fails between two Switches in the Distributed Fabric,
assuming you have STP/RSTP and LACP enabled as recommended in
“Important
Considerations and Recommendations” on page 434, your traffic flow should
continue through your network.
Figure 115 XRN Network reaction on Fabric Interconnect failure
In Figure 115, if the interconnect fails, the network will react in the following way:
Switch 4400 units
XRN Distributed Fabric
802.3ad
Aggregated Link
Resilient Link
Standby Link
Active Link
STP/RSTP enabled
X
Switch 4200
Switch 3300
Legacy
Aggregated Link
Switch 4300
Interconnect Failure
Switch A
Switch B
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