三个交换机分别为S1、S2、S3，两台PC分别为PCA和PCB，如果两台主机都属于同一个VLAN，要想实现主机之间的互通，三台交换机上需要怎么配置，用H3C

在这种情况下，需要在三个交换机上进行以下配置：

1. 创建VLAN，并将两台主机分配到该VLAN中：

<S1> system-view
[S1] vlan 10
[S1-vlan10] quit
[S1] interface GigabitEthernet 1/0/1
[S1-GigabitEthernet1/0/1] port link-type access
[S1-GigabitEthernet1/0/1] port default vlan 10
[S1-GigabitEthernet1/0/1] quit

<S2> system-view
[S2] vlan 10
[S2-vlan10] quit
[S2] interface GigabitEthernet 1/0/1
[S2-GigabitEthernet1/0/1] port link-type access
[S2-GigabitEthernet1/0/1] port default vlan 10
[S2-GigabitEthernet1/0/1] quit

<S3> system-view
[S3] vlan 10
[S3-vlan10] quit
[S3] interface GigabitEthernet 1/0/1
[S3-GigabitEthernet1/0/1] port link-type access
[S3-GigabitEthernet1/0/1] port default vlan 10
[S3-GigabitEthernet1/0/1] quit

2. 配置交换机之间的链路：

<S1> system-view
[S1] interface GigabitEthernet 1/0/2
[S1-GigabitEthernet1/0/2] port link-type trunk
[S1-GigabitEthernet1/0/2] port trunk allow-pass vlan 10
[S1-GigabitEthernet1/0/2] quit

<S1> interface GigabitEthernet 1/0/3
[S1-GigabitEthernet1/0/3] port link-type trunk
[S1-GigabitEthernet1/0/3] port trunk allow-pass vlan 10
[S1-GigabitEthernet1/0/3] quit

<S2> system-view
[S2] interface GigabitEthernet 1/0/2
[S2-GigabitEthernet1/0/2] port link-type trunk
[S2-GigabitEthernet1/0/2] port trunk allow-pass vlan 10
[S2-GigabitEthernet1/0/2] quit

<S2> interface GigabitEthernet 1/0/3
[S2-GigabitEthernet1/0/3] port link-type trunk
[S2-GigabitEthernet1/0/3] port trunk allow-pass vlan 10
[S2-GigabitEthernet1/0/3] quit

<S3> system-view
[S3] interface GigabitEthernet 1/0/2
[S3-GigabitEthernet1/0/2] port link-type trunk
[S3-GigabitEthernet1/0/2] port trunk allow-pass vlan 10
[S3-GigabitEthernet1/0/2] quit

<S3> interface GigabitEthernet 1/0/3
[S3-GigabitEthernet1/0/3] port link-type trunk
[S3-GigabitEthernet1/0/3] port trunk allow-pass vlan 10
[S3-GigabitEthernet1/0/3] quit

这样，三个交换机之间的链路就配置好了，两台主机也都分配到了同一个VLAN中，它们之间就可以互相通信了。