Re: subnets & 2 NICS in a mashine
On Thursday 09 November 2000 13:06, robert_wilhelm_land wrote:
> Does ipfowarding relate on something special compiled into the kernel
> or do I need a certain package?
Yes and Yes. Read the howto documents on IP-Masquerading and IP-Chains.
Then re-read them, then meditate and pray for understanding; it's hard if you
don't REALLY know networking well.
> Generaly I seemed to have
> misunderstood that IP packets are _not_ sent to a certain ethernet
> card but are rather propagated within the subnet?
> Simple example:
> A server with two NIC's (each NIC connected via ethernet to a client)
> wants to send data to only one client. This server should know by
> looking into /etc/hosts which IP number the client has assigned to and
> may not be pertubed by another client within the same subnet.
> Could you help me in this special example?
>
Okay, this I know about:
On an ethernet network every packet of information that is transmitted by a
computer is visible to all NICs on the network. For a NIC to actually accept
a packet for it's machine, the packet must be addressed to that NIC's MAC
address (the ethernet driver translates IPs to MACS when transmitting
packets), or the nic must be in "promisquious mode", which allows it to
accept all packets (special case used to sniff packets).
It seems you think of packets traveling around on your network as if they
were a road; the data hops in a car, pulls out of it's driveway, drives down
the street and pulls into another driveway, then gets out and knocks on the
door of the recipient.
A kind of wierd analogy might be like this: You're talking on a two-way
radio (HAM, walkie-talkie, etc..), where only one person can talk at any
given time. Each person is allowed 30 seconds maximum of talk time before
they must pause and let someone else talk if they want. When someone starts
tallking, they say "I want to talk to Fred." and then they start talking.
Not being interrested in what is being told to fred, everyone else ignores
what is being said until they hear the phrase "I want to talk to...".
That's kind of what's going on on the physical side of the network (wire,
NICs). Hope that helps your understanding.
--
Did you know that if you play a Windows 2000 cd backwards, you
will hear the voice of Satan?
That's nothing! If you play it forward, it'll install Windows 2000.
Reply to: