Hirschmann GREYHOUND GRS1020 - Page 501

Redundancy
12.3
Spanning Tree
161
UM Config GRS
Release
8.0 09/2019
Max Age and Diameter
The “Max Age” and “Diameter” values largely determine the maximum expansion of a Spanning
Tree network.
Diameter
The number of connections between the devices in the network that are furthest removed from
each other is known as the network diameter.
Figure 34: Definition of diameter
The network diameter that can be achieved in the network is MaxAge-1.
In the state on delivery, MaxAge = 20 and the maximum diameter that can be achieved = 19. When
you set the maximum value of 40 for MaxAge, the maximum diameter that can be achieved = 39.
MaxAge
Every STP-BPDU contains a “MessageAge” counter. When a bridge is passed through, the counter
increases by 1.
Before forwarding a STP-BPDU, the bridge compares the “MessageAge” counter with the
“MaxAge” value specified in the device:
 When MessageAge < MaxAge, the bridge forwards the STP-BPDU to the next bridge.
 When MessageAge = MaxAge, the bridge discards the STP-BPDU.
Figure 35: Transmission of an STP-BPDU depending on MaxAge
1
Diameter = 7
23 45 67
Root-Bridge
Message
Age= 0
MaxAge= 5
Root-Bridge
Message
Age= 1
Message
Age= 2
Message
Age= 3
Message
Age= 4
Message
Age= 5
Message
Age= 5