3Com 7750 Series, Справочник по командам

Страница: 279 / 1177

3Com Switch 7750 Series
Command Reference Guide – MSTP Chapter 1 MSTP Configuration Commands
1-29
1.1.27 stp max-hops
Syntax
stp max-hops hops
undo stp max-hops
View
System view
Parameter
hops : Maximum hops to be set. This argument ranges from 1 to 40. The default
maximum hops value of an MST region is 20.
Description
Use the stp max-hops command to set the maximum hops for the MST region the
current switch belongs to.
Use the undo stp max-hops command to revert to the default maximum hops.
The maximum hops values configured on the region roots of the CIST and MSTI in an
MST region limit the size of the MST region.
A configuration BPDU contains a field that maintains the remaining hops of the
configuration BPDU. And a switch discards the configuration BPDUs whose remaining
hops are 0. After a configuration BPDU reaches a root bridge of a spanning tree in a
MST region, the value of the remaining hops field in the configuration BPDU is
decreased by 1 every time the configuration BPDU passes a switch. Such a
mechanism disables the switches that are beyond the maximum hops from
participating in spanning tree generation, and thus limits the size of an MST region.
With such a mechanism, the maximum hops configured on the switch operating as the
root bridge of the CIST or an MSTI in a MST region becomes the network diameter of
the spanning tree, which limits the size of the spanning tree in the current MST region.
The switches that are not root bridges in the MST region adopt the maximum hops
settings of their root bridges.
Example
# Set the maximum hops of the current MST region to 35.
<3Com> system-view
System View: return to User View with Ctrl+Z.
[3Com] stp max-hops 35