Using native OS X NAT with VirtualBox

bootpd.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>bootp_enabled</key>
    <true/>
    <key>detect_other_dhcp_server</key>
    <integer>1</integer>
    <key>dhcp_enabled</key>
    <array>
        <string>vboxnet0</string>
    </array>
    <key>reply_threshold_seconds</key>
    <integer>0</integer>
    <key>Subnets</key>
    <array>
        <dict>
            <key>allocate</key>
            <true/>
            <key>lease_max</key>
            <integer>86400</integer>
            <key>lease_min</key>
            <integer>86400</integer>
            <key>name</key>
            <string>10.0.69</string>
            <key>net_address</key>
            <string>10.0.69.0</string>
            <key>net_mask</key>
            <string>255.255.255.0</string>
            <key>net_range</key>
            <array>
                <string>10.0.69.50</string>
                <string>10.0.69.254</string>
            </array>
        </dict>
    </array>
</dict>
</plist>

enable.sh

sudo /bin/launchctl load -w /System/Library/LaunchDaemons/bootps.plist
sudo /usr/libexec/PlistBuddy -c 'add :ProgramArguments:3 string -e' /System/Library/LaunchDaemons/com.apple.pfctl.plist

nat-pf.rules

nat on en0 proto {tcp, udp, icmp} from 10.0.69.0/24 to any -> (en0)
nat on en1 proto {tcp, udp, icmp} from 10.0.69.0/24 to any -> (en1)
pass from {lo0, 10.0.69.0/24} to any keep state

sysctl.conf

net.inet.ip.forwarding=1