单臂路由与三层交换技术
我们如何实现不同vlan之间的通信：
- 单臂路由技术：二层交换机+路由器
- 三层交换技术：三层交换机
一、单臂路由技术
单臂路由（router-on-a-stick）是指在路由器的一个接口上通过配置子接口（或“逻辑接口”，并不存在真正物理接口）的方式，实现原来相互隔离的不同VLAN（虚拟局域网）之间的互联互通。
二、使用实例
代码如下（示例）：
LSW5
The device is running!
<Huawei>undo terminal monitor
Info: Current terminal monitor is off.
<Huawei>sys
Enter system view, return user view with Ctrl+Z.
[Huawei]sysname LSW5
[LSW5]vlan bat 2 3
Info: This operation may take a few seconds. Please wait for a moment...done.
[LSW5]int e0/0/1
[LSW5-Ethernet0/0/1]port link-type trunk
[LSW5-Ethernet0/0/1]port trunk allow-pass vlan all
[LSW5-Ethernet0/0/1]int e0/0/2
[LSW5-Ethernet0/0/2]port link-type access
[LSW5-Ethernet0/0/2]port default vlan 2
[LSW5-Ethernet0/0/2]int e0/0/3
[LSW5-Ethernet0/0/3]port link-type access
[LSW5-Ethernet0/0/3]port default vlan 3
R2
代码如下（示例）：
The device is running!
<Huawei>undo terminal monitor
Info: Current terminal monitor is off.
<Huawei>sys
Enter system view, return user view with Ctrl+Z.
[Huawei]sysname R2
[R2]int e0/0/0
[R2-Ethernet0/0/0]undo shutdown
Info: Interface Ethernet0/0/0 is not shutdown.
[R2-Ethernet0/0/0.2]int e0/0/0.1
[R2-Ethernet0/0/0.1]vlan-type dot1q 2 default
[R2-Ethernet0/0/0.1]ip add 192.168.2.1 24
[R2-Ethernet0/0/0.1]int e0/0/0.2
[R2-Ethernet0/0/0.2]vlan-type dot1q 3 default
[R2-Ethernet0/0/0.2]ip add 192.168.3.1 24
[R2-Ethernet0/0/0.1]q
通讯结果：
PC>ping 192.168.3.10
Ping 192.168.3.10: 32 data bytes, Press Ctrl_C to break
From 192.168.3.10: bytes=32 seq=1 ttl=127 time=125 ms
From 192.168.3.10: bytes=32 seq=2 ttl=127 time=78 ms
From 192.168.3.10: bytes=32 seq=3 ttl=127 time=78 ms
From 192.168.3.10: bytes=32 seq=4 ttl=127 time=78 ms
From 192.168.3.10: bytes=32 seq=5 ttl=127 time=78 ms
--- 192.168.3.10 ping statistics ---
5 packet(s) transmitted
5 packet(s) received
0.00% packet loss
round-trip min/avg/max = 78/87/125 ms
PC>ping 192.168.2.10
Ping 192.168.2.10: 32 data bytes, Press Ctrl_C to break
From 192.168.2.10: bytes=32 seq=1 ttl=127 time=78 ms
From 192.168.2.10: bytes=32 seq=2 ttl=127 time=94 ms
From 192.168.2.10: bytes=32 seq=3 ttl=127 time=78 ms
From 192.168.2.10: bytes=32 seq=4 ttl=127 time=78 ms
From 192.168.2.10: bytes=32 seq=5 ttl=127 time=94 ms
--- 192.168.2.10 ping statistics ---
5 packet(s) transmitted
5 packet(s) received
0.00% packet loss
round-trip min/avg/max = 78/84/94 ms
该处使用的url网络请求的数据。
二、三层交换技术
三层交换（也称多层交换技术，或 IP 交换技术）是相对于传统交换概念而提出的。众所周知，传统的交换技术是在 OSI 网络标准模型中的第二层 —— 数据链路层进行操作的，而三层交换技术是在网络模型中的第三层实现了数据包的高速转发。简单地说，三层交换技术就是：二层交换技术＋三层转发技术。
使用实例
代码如下（示例）
The device is running!
<Huawei>undo terminal monitor
Info: Current terminal monitor is off.
<Huawei>sys
Enter system view, return user view with Ctrl+Z.
[Huawei]sysname LSW1
[LSW1]vlan bat 2 3
Info: This operation may take a few seconds. Please wait for a moment...done.
[LSW1]int g0/0/1
[LSW1-GigabitEthernet0/0/1]port link-type access
[LSW1-GigabitEthernet0/0/1]port default vlan 2
[LSW1-GigabitEthernet0/0/1]int g0/0/2
[LSW1-GigabitEthernet0/0/2]port link-type access
[LSW1-GigabitEthernet0/0/2]port default vlan 3
[LSW1-GigabitEthernet0/0/2]q
[LSW1]int vlan 2
[LSW1-Vlanif2]ip add 192.168.2.1 24
[LSW1-Vlanif2]int vlan 3
[LSW1-Vlanif3]ip add 192.168.3.1 24
[LSW1-Vlanif3]q
通信结果：
PC>ping 192.168.3.10
Ping 192.168.3.10: 32 data bytes, Press Ctrl_C to break
From 192.168.3.10: bytes=32 seq=1 ttl=127 time=94 ms
From 192.168.3.10: bytes=32 seq=2 ttl=127 time=47 ms
From 192.168.3.10: bytes=32 seq=3 ttl=127 time=46 ms
From 192.168.3.10: bytes=32 seq=4 ttl=127 time=32 ms
From 192.168.3.10: bytes=32 seq=5 ttl=127 time=47 ms
--- 192.168.3.10 ping statistics ---
5 packet(s) transmitted
5 packet(s) received
0.00% packet loss
round-trip min/avg/max = 32/53/94 ms
PC>ping 192.168.2.10
Ping 192.168.2.10: 32 data bytes, Press Ctrl_C to break
From 192.168.2.10: bytes=32 seq=1 ttl=127 time=31 ms
From 192.168.2.10: bytes=32 seq=2 ttl=127 time=47 ms
From 192.168.2.10: bytes=32 seq=3 ttl=127 time=47 ms
From 192.168.2.10: bytes=32 seq=4 ttl=127 time=46 ms
From 192.168.2.10: bytes=32 seq=5 ttl=127 time=47 ms
--- 192.168.2.10 ping statistics ---
5 packet(s) transmitted
5 packet(s) received
0.00% packet loss
round-trip min/avg/max = 31/43/47 ms
总结
单臂路由技术：当只有二层交换机时，又要实现不同vlan间通信时，需要用到单臂路由技术。
三层交换技术：三层交换机可配置vlanif接口，通过vlanif接口可配置ip地址，成为不同vlan对应的网关，从而实现不同vlan间路由。
三层交换的出现，解决了局域网中网段划分之后，网段中子网必须依赖路由器进行管理的局面，从而缓解了由于路由器负担过重而造成的网络瓶颈问题。