Jeff Vian wrote:
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).
This is partially incorrect, A PC does send to an IP address but the IP
address to MAC translation is done in the PC's TCP/IP stack. The IP
packet contains the MAC address which the PC must have before it can
send the TCP/IP packet anywhere. A layer 2 switch doesn't care about
an IP address (other than it's own for management). It's the ARP table
that has the translations for MAC to IP.
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.
See what's available is a bit ambigous but you are correct that the
arp entry last a _VERY_ short period of time.
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.
This is correct, a MAC address never traverses a router.
--
Linux Home Automation Neil Cherry ncherry@xxxxxxxxxxx
http://www.linuxha.com/ Main site
http://linuxha.blogspot.com/ My HA Blog
http://home.comcast.net/~ncherry/ Backup site
