HP procurve 8100fl series Management And Configuration Manual page 130

Spanning-Tree Operation
802.1s Multiple Spanning Tree Protocol (MSTP)
Note on Path Cost
9-14
Plan individual regions based on VLAN groupings. That is, plan on all
■
MSTP switches in a given region supporting the same set of VLANs. Within
each region, determine the VLAN membership for each spanning-tree
instance. (Each instance represents a single forwarding path for all VLANs
in that instance.)
■ There is one logical spanning-tree path through the following:
• Any inter-regional links
• Any IST or MST instance within a region
• Any legacy (802.1D or 802.1w) switch or group of switches. (Where
multiple paths exist between an MST region and a legacy switch,
expect the CST to block all but one such path.)
Determine the root bridge and root port for each instance.
■
■ Determine the designated bridge and designated port for each LAN seg­
ment.
■ Determine which VLANs to assign to each instance, and use port trunks
with 802.1Q VLAN tagging where separate links for separate VLANs would
result in a blocked link preventing communication between nodes on the
same VLAN. (Refer to "MSTP Operation with 802.1Q VLANs" on page
9-10.)
Identify the edge ports connected to end nodes and enable the edge-port
■
setting for these ports. Leave the edge-port setting disabled for ports
connected to another switch, a bridge, or a hub.
RSTP and MSTP implement a greater range of path-costs and new default path-
cost values to account for higher network speeds. These values are different
than the values defined by 802.1D STP as shown below.
Port Type 802.1D STP Path Cost
10 Mbps 100
100 Mbps 10
1 Gbps 5
Because the maximum value for the path-cost allowed by 802.1D STP is 65535,
devices running that version of spanning tree cannot be configured to match
the values defined by MSTP, at least for 10 Mbps and 100 Mbps ports. In LANs
where there is a mix of devices running 802.1D STP, RSTP, and/or MSTP, you
should reconfigure the devices so the path-costs match for ports with the same
network speeds.
RSTP and MSTP Path Cost
2 000 000
200 000
20 000