masud62 this is something Messi, I just got out of this problem, and not to good, but, let me help you throu this hell....
First you goanna config the card you connect to the local net, and config like any other device, like 192.158.100.25 or something, this is the one you will use to connect via web, and connection your extensions from inside. This is easy because is in the setup of the issabel.
Then you need to go in the command terminal, the black screen with the white letters and config the second card with commands of Linux ( google it), depend the dsitribution is the command, after you config the IP of the second card, (note: in the most case the troncal supplier give you the IP you need to config in this card, the gateway, and the IP of the troncal server.) You need to make a static route, this will tell issabel that when try to reach the troncal address are going you use the 2card, this is know like "static route", google it, and specific the distribution of the Linux, because the command change. And config the troncal like is in the tutorials,
Hope this will help you
