Re: PCs with 2 IP addresses

Nathaniel Stitt (
Tue, 31 Oct 1995 15:31:20 -0800

>>This also brings up an interesting point for TCP/IP programming
>>in general: A single computer is *not* limited to having a single
>>active IP address! Software which assumes that there is only
>>a single address will encounter problems when that assumption is
>>violated. (I ran into the same problem in my own sofware!)

>This may sound like a stupid question but why would you NEED more than one
>IP address for any particular machine? What purpose does that serve?
>Bill Woodland
>Squeek on Undernet IRC channel #CU-SeeMe

You can have multiple IP addresses anytime you have 2 network cards
connected to separate networks. The purpose would be to access
resources on both networks at the same time, or to act as a router
between the two networks.

This may sound unusual, but consider this case: My PC contains an
ethernet card to connect to the LAN (the LAN is not connected to the
internet), I also have an ISDN modem which I use to connect to the
internet using PPP. This ISDN modem counts as the 2nd network card,
and is assigned a 2nd IP address on the machine. This 2nd IP address
is provided to me by my internet service provider. Even a regular
modem can count as a 2nd network card when using SLIP or PPP.

Cu-seeme works fine over the first network card (the LAN), but doesn't
work over the ISDN connection (the internet). I believe that cu-seeme
assumes that the first IP address it finds on the machine is the one
with internet connectivity, and it sends this address to the server.