Shulou(Shulou.com)06/01 Report--

The basic concept of STP includes the BID (bridge ID) of the switch. Port ID. Port cost. Port status. Port role.

The port priority of the current port can be changed by executing stp port priority. Can directly affect whether the port will be elected as the designated port.

Modify the default port cost calculation method by using the stp pathcost-standard command

Stp pathcost-standard (do1d-1998/dol1t/legacy)

To configure path expense values for different ports, you can execute STP cost separately

STP election process:

1. Electing the root bridge

two。 Non-root switch elects root port

3. Each line elects a designated port

4. Blocking non-root, non-designated port

The root bridge, root port, designated port and blocking port are all selected according to the following rules. The smaller the better.

All this information is available in BPDU.

Comparison rules:

1.bridge ID: priority (default 32768) + MAC address

2.Cost path cost: calculated according to the proportion of interface bandwidth

3.port ID: priority (default 128) + port number

Root Bridge Election:

1. Select the root bridge: each switch assumes that it is the root, sends BPUD messages to each other, and then runs for the root bridge by comparing the rules.

two。 Select the root port: each switch selects the root port (the optimal path) according to the cost of receiving the BPDU sent by the root bridge. The switch receives the cumulative cost and the forwarding does not accumulate.

3. Select a designated port: each link selects a designated port according to the comparison rules, and each link must have a designated port.

4. Select blocking port: in addition to the root port, designated port, the rest is blocking port

STP port role:

Root port: root port, the nearest port from the switch to the root bridge

The non-root switch has one and only one RP port, and the root switch has no RP (root port) port

The upstream corresponding port of the network segment where the RP port is located must be the DP (designated port) port.

When a switch determines all port roles, it must first determine the RP port role, and determine the ports of other roles.

Designated port: the port that advertises BPDU in a network segment is a designated port, and there is only one DP port in each network segment. Copy the traffic forwarded to the root bridge

ALternate port: the AP port is the second-best path from the current switch to the root switch and is the backup port of the switch RP port

Backup port: a BP port is called a backup port when an interface receives its own better BPDU from another interface of the bridge itself. BP provides backups for DP and is always in the discarding state.

Computing port role: in the calculation process, first determine the root bridge, and then RP.DP. And other port roles.

During the calculation, the topology information in BPDU is compared in turn, such as BID (bridge ID) and Pathcost (port cost). Specify bridge ID and portID (port ID). The smaller the value, the better.

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