Re: IP routing with remote DNS, but server & client on same subnet - how?

On Oct 16, 4:34 pm, Stefan Monnier <monn...@xxxxxxxxxxxxxxxx> wrote:
Thanks! I like this theory (well, maybe to you it is a fact!) -- so
tonight I will try pulling the ethernet cable out of the cable modem
while a file transfer from my website is underway. If all stays on my
local network and no traffic out through the ISP, then the file
transfer (staying within the Linksys router) should be uninterrupted.

It may work. It may also fail because disconnecting the modem may force PPP
to take down the connection and interface and hence remove the external IP
and potentially remove the corresponding iptables rules as well, depending
on how the scripts work. It'll probably work, tho.

Another way to look at it is to run a tcpdump on the WAN side and look at
the packets that go through.

Stefan

Here are my experiments. Tell me if it makes sense:

1. With the cable modem plugged in, I surfed to my website www.foodomain.net
(which is a server on my home network)
2. I surfed to a link to a large document (32Meg)
3. *Before* clicking on the link, I unplugged the cable modem
(disconnecting from the internet)
4. I clicked on the file link -- and it timed out, server
unreachable.

Next experiment:

1. With the cable modem plugged in, I surfed to my website www.foodomain.net
2. I surfed to a link to a large document (32Meg)
3. I *first* clicked on the link, then during the file transfer, I
unplugged the cable modem
4. The file transfer completed successfully!

So, from this I deduce that the internet connection is required only
for DNS -- but after that the actual routing of packets from the
server and the client (all within my home network) do not involve the
internet connect -- and stays off my ISP's network.

Does this sound right? If so, then the transport layer is already
very optimized and knows enough to stay within its own subnet if it
can. This is excellent, if correct.

Thanks,
Randy

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