http://www.cisco.com/warp/public/473/spanning_tree1.swf
我见过的最好的FLASH,翻译下其中的文字(双语对照)
1.
Consider the example in winch there are bridges:
Bridge A
Bridge B
Bridge C
3个网桥作为范例：
网桥A 网桥B 网桥C
2.
Each bridge has a connection with the other bridges.
每个网桥与其他网桥有一个连接线路。
3.
At the bootup,all of the bridges think of themselves as the Root
Bridge.
在引导启动阶段，所有的网桥把自己看作根网桥（Root Bridge）。
4.
Assume that the first step is that Bridge C sends the BPDU to Bridges A and B,announcing that Bridge C is the Root,with the Root ID of 32768.00-00-00-00-00-02.
Note that Bridge B's Root ID will change from 03 to 02.Also note that Bridge A's Root ID will not change.
设想第一步网桥C发送BPDU到网桥A和B，宣布网桥C是根Root，Root ID是32768.00-00-00-00-00-02。
网桥B的Root ID将从03改为02。网桥A的Root ID 将不会改动。
5.
Considering that Bridge B's Bridge ID is greater than the Root ID it seens in the BPDU,Bridge B accepts that Bridge C is root.
Bridge A still considers itself as the Root as its Bridge ID is less than the Root ID it seens in the BPDU.Bridge C still thinks of itself as the Root.
鉴于网桥B的网桥ID比在BPDU中的网桥ID高，网桥B认为网桥C作为root。
网桥A一直认为它自己是Root，因为它的网桥ID比BPDU中的Root ID 小。网桥C一直认为它自己是Root。
6.
Assume that the next step is for Bridge A to send BPDUs towards Bridge B and C announcing itself as the Root.
Note the change in B and C's Root IDs to 01.Bridge A's Root ID is 372768.00-00-00-00-00-01.
下一步网桥A向网桥B和C发送BPDU，宣布自己是Root.
改变网桥B和C的Root ID记录为01。网桥A的Root ID 为 372768.00-00-00-00-00-01.
7.
All bridges are now is agreement that Bridge A is the Root
Bridge.
所有的网桥现在一致认为网桥A为 Root Bridge。
8.
Every non-root bridge must select one Root port.A bridge's root port is the port closest to the Root bridge.
Non-root Bridges elect their respective root port based on the Root path Cose,which is the cumulative cost of all links to the root bridge.
每个非根网桥（non-root bridge）必须选择一个根端口。A网桥的根端口（ root port）离根网桥最近。
非根网桥基于根路径代价（ Root path Cose）选择它们各自的根端口，即到根网桥的所有连接的累积代价（cost）。
9.
Assuming that all links between the bridges have the same speed(say 100 Mbps with a cost of 19,according to the IEEE),Bridge B and Bridge C elect their Root ports.
假设所有网桥间的链路有相同的速度（依照IEEE100 Mbps代价为19），网桥B和C选择他们的根端口。
10.
Election of Designated ports
Ports providing the least path cost from the segment to the root are elected as designated ports.
选举制定的端口
选择从网段到根有最少路径代价的端口作为制定端口。
11.
The bridge containing the designated port for a given segment is referred to as the designated bridge for that segment.
在特定网段含有指定端口的网桥被认为是该网段segment的指定网桥。
12.
there are three segments:
segment 1
segment 2
segment 3
Since the ports on Bridge A are directly connected to the Root
Bridge,these ports become the designated ports for Segment 1 and Sement 2.
这里有三个网段：网段1 网段2 网段3
网桥A上的端口直接连接根网桥，这些端口成为了网段1和2的指定端口。
13.
Sement3
The path cost to the root bridge is the same for Bridge B and Bridge C.The tie breaker is the lower bridge ID of Bridge C.
网段3
网桥A和网桥C到根网桥的路径代价相同。 平局决胜制tie breaker降低了网桥C的网桥ID。
14.
Since the bridge ID of Bridge C is less than the bridge ID of Bridge B,the designated port for Segment 3 becomes port 1/2 of Bridge C.
网桥C的网桥ID小于网桥B的，网段B的指定端口变为网桥C的1/2端口。
15.
Root port and the designated ports go into the forwarding states.
根端口和制定端口进入转发状态(Forwarding state)
16.
Ports that are neither the root ports nor the designated ports,in other words ports that are non-designated ports,go to the blocking state.
既不是根端口也不是标记端口，而是未指定端口进入阻塞状态(Blocking state）。
17.
At this point Spanning tree has fully converged.
这时生成树成功聚合。
18.
Bridge C has a better BPDU than Bridge B.Bridge C continues to send BPDUs advertising its superiority over Bridge B.
As long as Bridge B continues to receive these Superior BPDUs on port 1/2,the port remains in the Blocking mode.
网桥C比网桥B有较好的BPDU 。 网桥C继续发送BPDU广告它的优越性超过网桥B。
在网桥B继续在端口1/2接收这些上级BPDU时，端口保持阻塞模式。
19.
For any reason if Bridge B fails to receive these BPDUs for max age time,which is 20 seconds by default,it would start to transition to the forwarding mode.
Most of the Spanning Tree Algorithm(STA) failures occur due to the excessive loss of BPDUs causing the blocked ports to transition to forwarding mode.
由于一些原因，如果网桥B失败的在最大老化时间Max Age Time （默认20秒）接收到这些BPDU。它将开始改变转发模式。
大多的生成树算法(STA)失败发生由于过多的丢失BPDU导致阻塞端口转换为转发模式。
20.
Spanning Tree Failure
The blocked port has gone into fowarding mode and the Spanning Tree Failure occurred.
生成树失败
阻塞端口进入转发模式，生成树失败发生。
21.
一些由于丢失BPDU引起阻塞端口进入转发模式的情形：
双方配合不当Duplex Mismatch
单项链路Unidirectional Link
包破坏Packet Corruption
资源错误Resource Errors
速端口（Portfast）配置错误Portfast Configuration Error
难使用的生成树协议STP参数调整和直径（网络拓扑中末端站点任意2个连接之间网桥最大数量2－7）流出Awkward STP Parameter Tuning and Diameter Issues
软件错误Software Errors
关于上述情形详细资料请继续阅读相关文档
学习下英语 :)
11. referred to as vbl.称为,被认为是
19. due to adv.由于, 应归于
