Re: Proxy ARP

[christos%astron.com@localhost (Christos Zoulas)]

In article <rmiy4a8ylag.fsf%fnord.ir.bbn.com@localhost>,
Greg Troxel  <gdt%ir.bbn.com@localhost> wrote:
>-=-=-=-=-=-
>
>
>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.

That is correct. This is another use case and pppd does this (sets SIN_PROXY)
in sys-bsd.c

>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".

Or I want to be in the same broadcast domain with my cable box
because cable providers are using that to figure out if I am
allowed to stream to my device or not.

christos