User manual
FL SWITCH MM HS
5-24
PHOENIX CONTACT 6874_en_09
5.2.5.9 Modifying the Protocol Timer
It may be necessary to modify the protocol timer if, e.g., there are more than ten active
Spanning Tree components in a single network. You can also attempt to reduce the
reconfiguration times by modifying the timer. However, care should be taken in order to
prevent unstable networks.
Please note that the protocol times are specified by the root switch and that they are
distributed to all devices via BPDU. It is therefore only necessary to modify the values in
the root switch. If the root switch fails, the timer values of another active STP switch (i.e.,
the new root switch) will be valid for the entire network segment. Please remember this
during component configuration.
Specifying the Timer Values (STP and RSTP)
– Maximum number of active Spanning Tree components along the path beginning at
the root switch (please refer to the following two example illustrations):
= (MaxAge/2) - Hello Time + 1
– 2 x (Forward Delay - 1 s) ≥ MaxAge
– MaxAge ≥ 2 × (Hello Time + 1 s)
The value ((MaxAge/2) - Hello Time) for a ring topology corresponds to the maximum
number of components with active Spanning Tree.
Figure 5-18 Example 1 for the "relevant path"
Modifying the protocol timer may result in unstable networks.
LNK
MODE
1
2
X1
LNK
MODE
1
2
X2
LNK
MODE
1
2
X3
LNK
MODE
1
2
X4
US1
US2
Fail
Reset
MODE
ACT
100
FD
FL SWITCH MM HS
Ord. No.28 32 32 6
MAC
Address
LNK
MODE
1
2
X1
LNK
MODE
1
2
X2
LNK
MODE
1
2
X3
LNK
MODE
1
2
X4
US1
US2
Fail
Reset
MODE
ACT
100
FD
FL SWITCH MM HS
Ord. No.28 32 32 6
MAC
Address
FL SWITCH MCS 16TX
Ord.No. 28 32 70 0
MAC
Address
1357
2468
9
11
13
15
10
12
14
16
91610 11 12 13 14 15
18234567
MODE
ACT
100
FD
US1 US2
FAIL
X19
V.24
X17
US1 GND US2 GND
X18
R1 R2
FL SWITCH MCS 16TX
Ord.No. 28 32 70 0
MAC
Address
1357
2468
9
11
13
15
10
12
14
16
91610 11 12 13 14 15
18234567
MODE
ACT
100
FD
US1 US2
FAIL
X19
V.24
X17
US1 GND US2 GND
X18
R1 R2
FL SWITCH MCS 16TX
Ord.No. 28 32 70 0
MAC
Address
1357
2468
9
11
13
15
10
12
14
16
91610 11 12 13 14 15
18234567
MODE
ACT
100
FD
US1 US2
FAIL
X19
V.24
X17
US1 GND US2 GND
X18
R1 R2
Relevant path for
timer value settings
Inactive link