Ryota Ozaki <ozaki-r%netbsd.org@localhost> writes: > I have questions about the Proxy ARP feature. > > arp(8) has two options: "pub" and "pub proxy". > What's the different between them and what > are expected behaviors of them? Besides the use case Christos mentioned, the other one is when you have an Ethernet with a subnet, and one host you have some link to another host that you'd like to also be addressed within the subnet. Consider 10.0.0.0/8, with a host 10.0.0.20, and another computer without an ethernet but with a SLIP or PPP link to 10.0.0.20, that you want to be 10.0.0.21. On 10.0.0.20, you would publish a proxy arp entry for 10.0.0.21, using 10.0.0.20's ethernet address. This would be "pub", to cause replies to be sent to queries (normally queries are processed without looking at the arp cache, but only your addresses, I think). And "proxy", so that 10.0.0.20 would not use it. Sometimes this would be done for dialup hosts, especially homegrown ad hoc to one's computer at campus. This setup does not require a proxy arp daemon, because there are small numbers of non-changing entries. Besides "why don't you plug .21 into the Ethernet", the other question is "why don't you allocate a subnet for the PPP link and run a routing protocol", and the answer was usually "I dno't have any subnets to allocate" or "it's too hard to make it work".
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