ip communications infrastructure

To ensure the reliability of the network, to solve the single point of failure, the need to introduce redundant topology.

In a redundant topology, loop appears.

Loop problems caused by:

1) duplicate copy of the frame;

2) Unstable MAC address table of the switch;

3) broadcast storm.

Solution to the broadcast storm: Spanning Tree Protocol.

Spanning Tree Protocol can automatically find and eliminate redundant network topology loops.

1) The algorithm enables SPA redundant ports to "a blocked state";

2) only one link in the network to take effect;

3) When the entry into force of the link fails, it will be in a "blocked" the port reopened in order to ensure the reliability of the network.

STP-related concepts:

1）桥ID（Bridge ID）=Bridge Priority + MAC

2) Port ID (Port ID) = Port Priority + Port No

3) the root bridge

4) non-root bridge

5) the root port

6) the specified port

7) blocked ports

8) Root path cost

9）Forwording Blocking BPDU

1, the bridge ID

Switch bridge ID will become the bridge with

Bridge priority MAC address of the bridge

2 6 bytes

Bridge priority range: 0 to 65535; Default: 32768 (0x8000)

First, determine the priority of the bridge, the lowest priority will be the bridge with the bridge;

Switches or bridges if the same bridge priority, the bridge MAC address comparison, with the lowest MAC address will become with the bridge.

2, Port ID (with port participation in elections)

Port priority port number

1 byte 1 byte

Port priority range: 0 to 255; Default: 128 (0x80)

The smaller the port priority value, the higher the priority;

If the same port priority, the lower the number, the higher the priority.

3, the root path cost (cost)

Chain bandwidth costs

10G 2

1000M 4

100M 19

10M 100

STP rules:

1) Each network has only one root bridge;

2) Each non-root bridge has only one root port;

3) Each chain has one and only one designated port;

4) All the ports on the root bridge are designated ports;

5) root ports and designated ports are Forwading;

6) blocked port Blocking.

STP workflow:

The first step: to elect a root bridge;

The second step: to elect a root port on each non-root bridge;

The third step: to elect a designated port on each segment;

Step four: blocking non-root, with the designated ports.

STP port states:

Blocking-- obstruction

Listening-- monitor

Learning-- learning

Forwarding-- forward

Disabled (off) - disabled