HP Cisco Nexus 5000 Cisco Nexus 5000 Series Switch CLI Software Configuration - Page 197

Information About Rapid PVST+ Bridge Priority Value Bridge Priority Value The bridge priority is a 4-bit value when the extended system ID is enabled. Note In Cisco NX-OS, the extended system ID is always enabled; you cannot be disable the extended system ID. Related Topics • Configuring the Rapid PVST+ Bridge Priority of a VLAN, page 170 Extended System ID A 12-bit extended system ID field is part of the bridge ID. Figure 20: Bridge ID with Extended System ID The switches always use the 12-bit extended system ID. Combined with the bridge ID, the system ID extension functions as the unique identifier for a VLAN. Table 14: Bridge Priority Value and Extended System ID with the Extended System ID Enabled Bridge Priority Value Extended System ID (Set Equal to the VLAN ID) Bit Bit Bit Bit Bit Bit Bit Bit 9 Bit 8 Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 16 15 14 13 12 11 10 32768 16384 8192 4096 2048 1024 512 256 128 64 32 16 8 4 2 1 STP MAC Address Allocation Note Extended system ID and MAC address reduction is always enabled on the software. With MAC address reduction enabled on any switch, you should also enable MAC address reduction on all other connected switches to avoid undesirable root bridge election and spanning tree topology issues. When MAC address reduction is enabled, the root bridge priority becomes a multiple of 4096 plus the VLAN ID. You can only specify a switch bridge ID (used by the spanning tree algorithm to determine the identity of the root bridge, the lowest being preferred) as a multiple of 4096. Only the following values are possible: •0 • 4096 • 8192 • 12288 OL-16597-01 Cisco Nexus 5000 Series Switch CLI Software Configuration Guide 151