On Mon, 2006-01-30 at 19:37, Jeff Vian wrote:
> >
> A PC (or other device) sends packets to an IP address.
If it sends them over ethernet, it sends it inside an ethernet
frame containing MAC addresses.
> The switch maps
> the IP to MAC to keep track of what is attached to each port and where
> to send traffic.
A switch doesn't need to know anything about TCP, although
managed ones have an interface for the management connection.
> A TCP packet does not contain MAC addressing (although
> some protocols may).
On a broadcast medium like ethernet, the packet must have
a destination MAC address. A point-to-point medium would
be different.
> ARP is a way for the local PC to see what is avialable, but if you check
> the ARP table on your PC it usually only remembers the MAC address for a
> very short time, thus the effect you describe above.
Arp is how the MAC address on the ethernet frame is managed and
matched to the destination IP. Switches just observe the MAC
when forwarding.
> Also, remember, MAC addressing is only valid on the local LAN. If it
> has to go through a router that cannot work. Those protocols that do
> use MAC addressing are local LAN protocols only.
But it needs to send to the router first with a MAC frame that
the switch will deliver to the right place.
--
Les Mikesell
lesmikesell@xxxxxxxxx
