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CDD-880 Multi Receiver Router
Appendix E
BPDUs are ranked in order as follows:
1. Lowest Root bridge ID
2. Lowest Root path cost
3. Lowest sender bridge ID
4. Lowest sender port number
The CDD-880 also follows this ranking. Tweaking STP/RSTP parameters allows for the election of
which port to use first.
E.2
Operational Examples
Figure E-1 shows a potential intended use for Port Diversity. The core network has physical path
redundancy including redundant Ethernet switches. As per the ranking order explained
previously, Port Diversity allows the CDD-880 to choose the physical path based first on physical
link state, and then via BPDU information provided by the switches' STP/RSTP processes. The
CDD-880 can react to a failure of any of the numbered links (identified in the figure as L1
through L5) as needed. Management Traffic (GE MGMT#x) and Data Traffic (GE ST #x) subnets
exist on the same physical port, but care must be taken in the routing core to keep the traffic
isolated at the subnet level.
Within the STP/RSTP domain, one bridge will be the Root bridge. The switch with the lowest
priority (0-61440 in increments of 4096) is elected as Root. By default, the switches will have a
priority of 32768; if all switches have the same priority, then the switch with the lower base
MAC Address is elected as the Root.
Figure E-1. Port Diversity Example #1
E–2
MN-CDD880
Revision 2
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