two interfaces one subnet
Patrick W. Gilmore
patrick at ianai.net
Mon May 11 22:01:01 CDT 2009
On May 11, 2009, at 8:04 PM, Ben Scott wrote:
> On Mon, May 11, 2009 at 6:01 PM, Patrick W. Gilmore
> <patrick at ianai.net> wrote:
>> It doesn't matter which physical interface transmits the packet.
> Well, in the general sense, I suppose not. The computer can put
> whatever it wants in an Ethernet frame, and as long as it's valid for
> the receiving system, it will work.
The OP asked for an RFC showing why this is forbidden. It is not. It
works fine. I stated many times that several implementations deny
your ability to do this, but the "rules" permit it just fine.
>> Another example: Imagine a web server with two uplinks in _different_
>> subnets running Quagga.
> That's a different scenario entirely. Diverse routes work fine
> because all the intermediate routers work the same way I describe
> above: They don't care where the packet came from, they don't know
> about "connections", they just forward packets to the destination.
Do you even read your own posts? Specifically:
On May 11, 2009, at 5:40 PM, Ben Scott wrote:
> Either way, if
> the packet *from* X was addressed *to* B but the response comes back
> from *A*, then host X is going to drop the packet as
The receiving host X does not care (or even know) if A and B are in
the same prefix. Intermediate systems have nothing to do with it as
they do not touch the source IP address in the packet. (We are
obviously ignoring NAT/PAT, etc.) So if it works with "diverse
routes", it works without diverse routes.
In other words, you contradicted yourself. Don't worry, you are in
good company in this thread. The OP alone did that 4 times by my
count, and I stopped reading his posts because he did it so often.
To summarize: Two physical interfaces on one machine in the same
prefix is allowed. There is no RFC against it - just the opposite.
So quit arguing over "but my $THING doesn't support it properly" or
"but it will break $SOMETHING" or whatever your favorite hang-up is.
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