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In Release 12.1(EA1 and later, Catalyst 3550 switches support the 802.1T spanning-tree extensions.
Some of the bits previously used for the switch priority are now used as the VLAN identifier. The result
is that fewer MAC addresses are reserved for the switch, and a larger range of VLAN IDs can be
supported, all while maintaining the uniqueness of the bridge ID. As shown in Table 15-1, the two bytes
previously used for the switch priority are reallocated into a 4-bit priority value and a 12-bit extended
system ID value equal to the VLAN ID. In earlier releases, the switch priority is a 16-bit value.
就是说 两个字节的 BID 的优先级设置,总共16个bit,其中
4个bit表示的是原先的 priority 优先级,另外12位表示的是vlan,
左边的四位表示的是优先级,右面的12位表示的是vlan信息,
所以最低步进值是 0001 0000 0000 0000 = 4096 了。。。
是这样吗?
当然这句话也重要。
Spanning tree uses the extended system ID, the switch priority, and the allocated spanning-tree MAC
address to make the bridge ID unique for each VLAN。
就是说利用4位的 优先级,以及 12位的 vlan 信息,以及剩下的 6*8 =48位的 mac 地址,给出每个vlan的每个switch的
唯一的 BID。
[ 本帖最后由 kentchoi 于 2008-12-8 09:28 编辑 ] |
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