684 APPENDIX D: 3COM XRN

How a Failure affects

the Distributed Fabric

This section provides supplementary information on how the Distributed Fabric
and traffic flow is affected by failure of an Fabric Interconnect and of a unit in the
Distributed Fabric.
Loss of a Switch within
the XRN Distributed
Fabric
When a Switch unit in the Distributed Fabric fails, assuming you have followed the
recommendations in “Important Considerations and Recommendations” on
page 676, your traffic flow should continue through your network.
The way the network reacts depends upon which features are configured on
which links. For example, Figure 186 shows an XRN network where all the edge
devices are connected to the Distributed Fabric using a range of supported
features, some of which are legacy features.
Figure186 XRN Network reaction on Distributed Fabric unit failure
Should Switch A fail, the network will react in the following way:
LACP (IEEE 802.3ad) and Legacy Aggregated Links
The Switch 4400 and Switch 4300 Aggregated Links will reroute all traffic down
the link connected to Switch B.
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.
Switch4400 units
XRNDistributed Fabric
802.3ad
AggregatedLink
ResilientLink
StandbyLink
ActiveLink
SwitchB
STP/RSTPenabled
X
Switch4200
Switch3300
SwitchA
Legacy
AggregatedLink
Switch4300
UnitFailure