Tim wrote:
Wouldn't they also have to be co-relating IPs to MAC addresses? Surely
they couldn't just work by the MAC, alone?
For instance if my PC at 192.168.1.1 wants to do something with
192.168.1.2, all that goes out on the wire is the IP addresses, hoping
that something else figures out how to connect the two together, or
hoping that they're already directly connected together.
>From the manual (tiny bit of paper) that came with my simple switch, I
understood that it listened in on the traffic, worked out what IPs
belong to what MACs, and switched accordingly after a few initial
moments of discovering how the network was set up. If an IP or a MAC
changed for a device (just one, and not necessarily both), it'd need to
rethink things before it worked again.
I can't say what switch I have, it's a black box, in a dark spot in the
shelf. I can't see anything to identify it, just the blinking LEDs on
the front.
If I understand things correctly, for the local network, your
computer does the IP to MAC mapping. (Run arp to see it.) The
packet has the MAC address as part of it. For destinations that
need to use a gateway, it has the gateway MAC address. The other
thing to consider is that not all traffic has an IP address. This
is because TCP/IP is not the only network traffic possible on the
LAN. Other protocols use different identification.
What switches learn is what MAC address is on what port. This can
cause problems if you change connections, depending on how fast the
switch "learns" the new port. When you get beyond home-grade
equipment, you may be able to tell the switch not to automaticly
"learn" the new port. This prevents someone from "cloning" a MAC
address and hijacking traffic.
Mikkel
--
Do not meddle in the affairs of dragons,
for thou art crunchy and taste good with Ketchup!