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Speed problems and other problems too
Authored by: paulio on Aug 25, '03 11:57:53AM

The IP address problem is more common then you might think. I've seen this before a number of times. I've seen this on campus networks as well as household cable modems. Here is the situation:

Two machines are behind a cable modem/DSL. (There is no router or airport in this simple example.) Both machines get IP addresses from the ISP like 111.222.333.xxx and 111.222.444.xxx. For whatever reason, the netmask is 255.255.255.0. Note that with this netmask these IP addresses are not in the same subnet.

The machines can't see each other in the server browser because rendezvous works only for machines in the same subnet, but one machine can share files with the other machine as long as you type in the IP address manually.

The problem is that large file transfers are slow. The reason is that the machines are on different subnets so they cannot communicate directly, even though they are physically on the same local network. The packets must go from the first machine over the local network, then out the cable modem to the internet, then back in the cablem modem into the local network, to the second machine.

This is really slow. File transfers that should take minutes take hours.

Try doing a Retrospect backup like this (which _can_ see the other machine for some reason, dispite the IP address problems) and it will take forever.

This situation with a Retrospect backup over a metered connection where internet access is paid for by the byte and you could have a financial disaster.



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