cnp3-ebook/protocols/ethernet — English @ Weblate

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74 ../../protocols/ethernet.rst:334

	English the `identifier` of the root switch (`R`) 41/10000 · 41
75 ../../protocols/ethernet.rst:335

	English the `cost` of the shortest path between the switch that sent the `BPDU` and the root switch (`c`) 97/10000 · 97
76 ../../protocols/ethernet.rst:336

	English the `identifier` of the switch that sent the `BPDU` (`T`) 57/10000 · 57
77 ../../protocols/ethernet.rst:337

	English the number of the switch port over which the `BPDU` was sent (`p`) 66/10000 · 66
78 ../../protocols/ethernet.rst:339

	English We will use the notation `<R,c,T,p>` to represent a `BPDU` whose `root identifier` is `R`, `cost` is `c` and that was sent from the port `p` of switch `T`. The construction of the spanning tree depends on an ordering relationship among the `BPDUs`. This ordering relationship could be implemented by the Python function below. 327/10000 · 327
79 ../../protocols/ethernet.rst:350

	English In addition to the `identifier` discussed above, the network administrator can also configure a `cost` to be associated to each switch port. Usually, the `cost` of a port depends on its bandwidth and the [IEEE802.1d]_ standard recommends the values below. Of course, the network administrator may choose other values. We will use the notation `cost[p]` to indicate the cost associated to port `p` in this section. 413/10000 · 413
80 ../../protocols/ethernet.rst:353

	English Bandwidth 9/10000 · 9
81 ../../protocols/ethernet.rst:353

	English Cost 4/10000 · 4
82 ../../protocols/ethernet.rst:355

	English 10 Mbps 7/10000 · 7
83 ../../protocols/ethernet.rst:355

	English 2000000 7/10000 · 7
84 ../../protocols/ethernet.rst:356

	English 100 Mbps 8/10000 · 8
85 ../../protocols/ethernet.rst:356

	English 200000 6/10000 · 6
86 ../../protocols/ethernet.rst:357

	English 1 Gbps 6/10000 · 6
87 ../../protocols/ethernet.rst:357

	English 20000 5/10000 · 5
88 ../../protocols/ethernet.rst:358

	English 2000 4/10000 · 4
89 ../../protocols/ethernet.rst:359

	English 100 Gbps 8/10000 · 8
90 ../../protocols/ethernet.rst:359

	English 200 3/10000 · 3
91 ../../protocols/ethernet.rst:362

	English The `Spanning Tree Protocol` uses its own terminology that we illustrate in the figure above. A switch port can be in three different states : `Root`, `Designated` and `Blocked`. All the ports of the `root` switch are in the `Designated` state. The state of the ports on the other switches is determined based on the `BPDU` received on each port. 346/10000 · 346
92 ../../protocols/ethernet.rst:364

	English The `Spanning Tree Protocol` uses the ordering relationship to build the spanning tree. Each switch listens to `BPDUs` on its ports. When `BPDU = <R,c,T,p>` is received on port `q`, the switch computes the port's `root priority vector`: `V[q] = <R,c+cost[q],T,p,q>` , where `cost[q]` is the cost associated to the port over which the `BPDU` was received. The switch stores in a table the last `root priority vector` received on each port. The switch then compares its own `identifier` with the smallest `root identifier` stored in this table. If its own `identifier` is smaller, then the switch is the root of the spanning tree and is, by definition, at a distance `0` of the root. The `BPDU` of the switch is then `<R,0,R,p>`, where `R` is the switch `identifier` and `p` will be set to the port number over which the `BPDU` is sent. 834/10000 · 834
93 ../../protocols/ethernet.rst:366

	English Otherwise, the switch chooses the best priority vector from its table, `bv = <R,c+cost[q'],T,p,q'>`. The port `q'`, over which this best root priority vector was learned, is the switch port that is closest to the `root` switch. This port becomes the `Root` port of the switch. There is only one `Root` port per switch (except for the `Root` switches whose ports are all `Designated`). The switch can then compute its own `BPDU` as `BPDU = <R,c',S,p>` , where `R` is the `root identifier`, `c'` the cost of the best root priority vector, `S` the identifier of the switch and `p` will be replaced by the number of the port over which the `BPDU` will be sent. 656/10000 · 656

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