Advanced Traffic Management Guide K/KA/KB.15.15

Path cost parameter values
RSTP and MSTP Path CostPort Type
2,000,00010Mbps
200,000100 Mbps
20,0001Gbps
2,00010Gbps
Cisco switches reduce the path costs on aggregated links. For example on the 3750 switch, the
path cost on an etherchannel group with two gigabit links is 10,000. One gigabit link is 20,000.
HP Switches do not reduce path cost on aggregated links.
Equipment and software versions
Tables 37 and 38 list equipment and specified software version for each switch in this scenario.
It’s a good practice to download the latest software for each switch that will participate in MSTP.
Table 37 HP equipment S/W version
S/W VersionHP Equipment
K.12.30 or greaterHP Switch 8200zl
K.12.02 or greaterHP Switch 5400zl
L.10.24 or greaterHP Switch 4202vl-48G
T.12.03 or greaterHP Switch 2900-48G
N.10.09 or greaterHP Switch 2810-48G
M.10.30 or greaterHP Switch 3400cl-48G
Table 38 Cisco equipment S/W version
S/W VersionCisco Equipment
IOS 12.2(25)SED3550
IOS 12.2(25)SEC23750
Configuration checklist
• Upgrade all switches to the latest software version.
• Ensure that the MST configuration on all switches match exactly. The name,
revision, and instance VLAN mappings must be identical on all switches
participating in MSTP.
• Configure all trunks on Cisco switches as 802.1Q (dot1q) trunks.
• Be sure to configure all edge ports. If you don’t, you will see a lot of topology
changes. In this configuration no edge ports are configured.
• All backbone ports (switch to switch links) must be members of all VLANs to
insure your network supports all of the forwarding paths necessary for the
desired connectivity. All ports connecting one switch to another within a region
and one switch to another between regions should be configured as members
of all VLANs configured in the region.
• Never connect LAGs before they’re configured. This will create loops in your
network and cause an unstable environment.
Introduction 379