In a NAT situation, normally ICMP isn't forwarded, the router itself answers the PING (since it's what really "owns" the IP). Although in the case of multiple public IPs, a whole IP is often forwarded to a single machine behind the NAT (including ICMP traffic).
Protocol 41 isn't ICMP. Protocol 41 is IP protocol 41, ICMP is IP protocol 1. Many consumer grade routers don't have the capability of statically forwarding an IP protocol to an inside host. But typically they will forward the traffic if it's initiated from the inside. So if a box behind the actiontec generates an IP proto 41 packet going to the HE 6in4 server, the FW will set up a connection table entry for it which will forward return traffic. The trick is to keep this entry from timing out by keeping some sort of traffic flowing through 6in4. Easiest way to do this is to ping the HE gateway's IPv6 address every two minutes or so (depending on your connection table TTL on your router, which is often undocumented).
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Topic: Problem Setting up With Windows 7 (Read 5048 times)