On Fri, 31 Mar 2000, Bill Freeman wrote:
> Can any of the truly IP.aware comment on the scheme below?
I don't know if I qualify for that, but I can comment on the scheme. :-)
> IIUC, it is perfectly possible to have two separate subnets on the same
> ethernet.
Yes. An IP "subnet" operates above the level of the actual network hardware
(at "layer three", if you're into OSI). You can have multiple IP subnets on a
single physical network, and you can have a single IP subnet that spans
multiple physical networks.
> It's just that a pair of machines on separate subnets can't directly
> communicate.
Correct. The network interface will receive all the traffic for both IP
subnets, but the IP code in the kernel will discard anything not for that
machine's address(es).
> There needs to be a router (or should I be saying gateway) ...
The terms "gateway" and "router" are pretty much synonymous for this
application. When one talks of a "gateway", one usually means the specific
router that connects your local subnet to other subnets (often the Internet at
large). The term "default gateway" means the router which gets packets that
the local machine doesn't otherwise know where to send.
> ... between the subnets to let them talk, and the packets will pass on the
> ether twice: once from source to router; once from router to destination.
Correct.
> Certainly the router that routes between the two subnets could have two
> net.cards on the same ether, but it may even be possible to have two
> logical interfaces, each with their own IP address and netmask, run
> through a single physical card (nothing in the hardware to stop it).
Correct. Most good OSes (read: Linux but not Win9X) allow you to assign
multiple IP addresses to a single network interface. The Linux kernel calls
this "IP aliasing". You can even use Linux to connect the two subnets
together using a single interface and the kernel's built-in routing support
(called "IP forwarding").
--
Ben Scott <[EMAIL PROTECTED]>
| Linux: Something better then MS-Windows, for free! http://www.linux.com |
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