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When that's done, exit the VirtualBox preferences and open the Virtual Machine network settings.
Adapter 1 should be on the NAT network. This is the interface that will be able to reach the Internet through the host. You won't have to do anything special; the guest will use the correct interface automatically.
Adapter 2 should be connected to vboxnet0, where it will get an IP address in the range you specified in the last dialog box above. This will be the interface the host uses to browse the guest, and the IP address Avalon will be configured with.
Adapter 2 should be on the NAT network. This is the interface that will be able to reach the Internet through the host. You won't have to do anything special; the guest will use the correct interface automatically.
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After you complete the configuration and boot the system, run ifconfig on the guest and look at the IP address of interface en0 to know what IP address to use from the host to contact the guest.