NAME

proxyarpd, proxytab − proxy ARP daemon

SYNOPSIS

/usr/etc/proxyarpd [ ifname [ configfile ] ]

DESCRIPTION

proxyarpd is used for hosts which does not understand sub-netmask in a subnetted environment. 

In the case that a host which does not understand sub-netmask wants to communicate with any host on the other physical network, the first host believes all host on the network can reach directly, and try to transmit physical data frame to the destination host instead of the gateway to reach it.  Before the transmission, the host broadcasts ARP request to know the hardware address of the destination.  But the destination host is on the other physical network, and it cannot receive the broadcasted request.  They cannot communicate in this way. 

A proxyarpd daemon responds to these ARP requests with the hardware address of the gateway host, not the destination host on the other physical network.  The sender host believes the hardware address as the receiver’s and transmit the frame.  The frame will be received by the gateway and transported correctly, and the communication will be succeeded. 

When an ifname is specified, proxyarpd will act only on the specified interface.  Without any ifname, it will act on all the interfaces shown in the configuration file.

If the configfile is specified, it is used as the configuration file, while /etc/proxytab is the default configuration file. 

Each line in the configuration file must be contain the information as follows:

interface  network  netmask  gateway

interface
Specify the interface name. If the proxyarpd boots with ifname, only the lines whose interface is same as it will be used.

network
The network address or the host address in dot notation, which proxyarpd will responds for it. 

netmask
The sub-netmask for network. A proxyarpd do AND operation with each bit between the address contained in ARP request and netmask, and responds only if the result is the same value with network. Use 255.255.255.255 as the netmask for the host address, network.

gateway
The address of the gateway host to reach the destination host. It must be on the network connected by the interface. The special gateway ‘−’ means that proxyarpd should not responds on this network. It is used to describe the exception for local network. The exception entry must be appeared first.

A # indicates the beginning of a comment. 

FILES

/etc/proxytab
/dev/bpf∗

SEE ALSO

bpf(4)

BUGS

If the proxyarpd responds to the ARP request for the host which really exists on the physical network, the destination host may write a warning message to the console:

duplicate IP address!! sent from ethernet address ... 

NEWS-OSRelease 4.2.1R