Ask HN: Linux based micro server for firewall

I'm fighting ipv6 issues with an older Sonicwall TZ100. I am longing for the days of setting up my firewall with iptables and am starting to think it's time to give this thing the boot. They want me to buy new hardware to support ipv6!

What micro server would people suggest for a firewall? I need at least 3 ethernets (WiFi, Wan, Lan) and would love four like the TZ100 has.