H3C Technologies H3C S3100 Series Switches - Manual (Page 192)

Operation Manual – MSTP
H3C S3100-52P Ethernet Switch
Chapter 1 MSTP Configuration
1-17
Link failures in a network result in the spanning tree recalculation and spanning tree
structure change. As the newly calculated configuration BPDUs cannot be advertised
across the entire network immediately when the new spanning trees are calculated,
temporary loops may occur if the new root ports and designated ports begin to forward
packets immediately.
This problem can be solved by adopting a state transition mechanism. With this
mechanism, newly selected root ports and designated ports undergo an intermediate
state before they begin to forward packets. That is, it costs these ports a period
(specified by the forward delay parameter) for them to turn to the forwarding state. In
the period, the newly calculated configuration BPDUs are advertised across the entire
network.
z
The hello time parameter is used for testing link failures.
A switch regularly sends hello packets to other switches at the interval specified by the
hello time parameter to test whether the links fail.
z
The max age parameter is used to judge whether or not a configuration BPDU
times out. The configuration BPDUs which time out will be discarded.
I. Configuration procedure
Table 1-11 Configure MSTP time-related parameters
Operation Command Description
Enter system view system-view —
Configure the forward
delay parameter
stp timer
forward-delay
centiseconds
Required
The forward delay parameter
defaults to 1,500 centiseconds
(namely, 15 seconds).
Configure the hello time
parameter stp timer hello
centiseconds
Required
The hello time parameter
defaults to 200 centiseconds
(namely, 2 seconds).
Configure the max age
parameter stp timer max-age
centiseconds
Required
The max age parameter
defaults to 2,000 centiseconds
(namely, 20 seconds).
All switches in a switched network adopt the three time-related parameters configured
on the CIST root bridge.