can an access point connect through an access point?

[Jeff Vian]

On Mon, 2006-01-30 at 10:00 -0600, Mikkel L. Ellertson wrote:
> 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.
> 
A PC (or other device) sends packets to an IP address.  The switch maps
the IP to MAC to keep track of what is attached to each port and where
to send traffic.  A TCP packet does not contain MAC addressing (although
some protocols may).

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. 

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.

> Mikkel
> -- 
> 
>   Do not meddle in the affairs of dragons,
> for thou art crunchy and taste good with Ketchup!
>