> A caveat to running multiple IPs on one card is that their is 
> much more CPU usage as the NIC goes into PROMISCIOUS mode 
> which means that every packet is passed up the stack for 
> processing.  So if you are on a busy network you can get ALOT
> of packets and that can really slow down your system.

This does not sound correct.  Promiscuous mode is not necessary to
have more than on IP address on an ethernet hardware interface.  In
fact, the only change necessary (other than the software, of course)
is for the same interface to answer ARP requests for more than one
IP address; in fact it should ARP for all of the IP addresses it 
hosts.

ARP, of course, is the Address Resolution Protocol whereby other
computers on the network can discover the hardware address associated
with a given IP address.  The hardware (MAC, or ethernet) address is
a 48-bit number unique to each ethernet device.  These MAC addresses
are discovered via broadcast using ARP.

You would use promiscuous mode on your ethernet card if you were 
running a packet sniffer or some other network monitoring software.

Everything runs slowly on very busy non-switched networks anyway...

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Jim Ockers (ockers@ockers.net)                     Ask me about Linux!
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