ip proxy-arp
How Does Proxy ARP Work?
Proxy ARP 是如何工作的？
Below is an example of how proxy ARP works:
下面这个例子说明了Proxy ARP 是如何工作的
Network Diagram
图表
The Host A (172.16.10.100) on Subnet A needs to send packets to Host D (172.16.20.200) on Subnet B. As shown in the diagram above, Host A has a /16 subnet mask. What this means is that Host A believes that it is directly connected to all of network 172.16.0.0. When Host A needs to communicate with any devices it believes are directly connected, it will send an ARP request to the destination. Therefore, when Host A needs to send a packet to Host D, Host A believes that Host D is directly connected, so it sends an ARP request to Host D.
这个主机A要发送数据包到主机D。图表显示主机A使用的是16位掩码。（注意这一点！）主机A相信目的网段是直接连接在172.16.0.0上的。于是主机A直接发送一个ARP请求给目的站点。
To reach Host D (172.16.20.200), Host A needs the MAC address of Host D.
Therefore, Host A broadcasts an ARP request on Subnet A, as below:
主机A 需要得到主机D的MAC地址，所以主机A广播ARP请求：
Sender's MAC Address
Sender's IP Address
Target MAC Address
Target IP Address
00-00-0c-94-36-aa
172.16.10.100
00-00-00-00-00-00
172.16.20.200
In above ARP request, Host A (172.16.10.100) is requesting that Host D (172.16.20.200) send its MAC address. The above ARP request packet is then encapsulated in an Ethernet frame with Host A's MAC address as the source address and a broadcast (FFFF.FFFF.FFFF) as the destination address. Since the ARP request is a broadcast, it reaches all the nodes in the Subnet A, including the router's e0 interface, but does not reach Host D. The broadcast will not reach Host D because routers, by default, do not forward broadcasts.
ARP请求里主机A将自己的MAC地址作为源地址 FFFF.FFFF.FFFF 做为目的地址进行广播。但是路由器的E0 口默认不支持转发广播。所以主机D不能响应这个ARP请求。
Since the router knows that the target address (172.16.20.200) is on another subnet and can reach Host D, it will reply with its own MAC address to Host A.
路由器知道主机D在其他子网，于是用自己的MAC地址来应答A
Sender's MAC Address
Sender's IP Address
Target MAC Address
Target IP Address
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