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

When the router receives the ARP Request, if it finds that the destination IP address of the query is in a different subnet, the router will act as the ARP of the agent, answer instead, and tell the querier the MAC address it wants to do.

If an ARP request is sent from a host on one network to another host on the same network segment but not on the same physical network, the device that connects them with the proxy ARP function can answer the request, a process called proxy ARP (Proxy ARP).

The proxy ARP function shields the fact that separate physical networks are available to users as if they were on the same physical network.

Proxy ARP is divided into ordinary proxy ARP and local proxy ARP. The application scenarios of the two are different:

The application environment of ordinary proxy ARP is that the hosts that want to communicate with each other are connected to different layer 3 interfaces of the device, and these hosts are not in the same broadcast domain.

The application environment of the local agent ARP is that the hosts that want to interwork are connected to the same layer 3 interface of the device, and these hosts are not in the same broadcast domain.

Lab environment description:

Create VLAN 2 and VLAN 3 ip 2 ip addresses on R1 are 172.16.0.1 fastethernet2/0 and VLAN 3 ip addresses are 172.16.1.1 fastethernet2/0 and fastethernet2/1 opening layer 2 ports of R1, which are divided into VLAN 2 (fastethernet2/0) and VLAN 3 (fastethernet2/1) respectively.

PC1 and PC are assigned IP addresses 172.16.0.2 and 172.16.1.2, respectively, with a 16-bit mask and no gateway address. Because if it is a 24-bit mask and the gateway address is not configured, the packet will not be sent.

You can see Proxy ARP is enable. The proxy arp function is on by default (cisco), and the H3C device using dis proxy-arp interface vlan 2meme H3C is off by default.

The proxy arp function of VLAN 2 is enabled, 172.16.0.2 (no gateway) can ping 172.16.1.2 arp function is turned off, 172.16.0.2 (no gateway) cannot ping 172.16.1.2

VLAN 3 is the same.

Note two points: the IP address mask of PC is 16 bits, which makes PC think that it is on the same network segment, and that PC does not need to configure a gateway address.

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