> have to confess ignorance . . . I have no idea what protocol 41 provides or allows.
As liquorice says, IP protocol 41 is a mechanism that allows the transmission of IPv6 packets over IPv4-only networks, onwards to an IPv6-speaking far-end network, which could be the entire IPv6 Internet. IP protocol41 thus allows IPv6 traffic to be carried over networks that contain routers that don’t understand IPv6 addresses by simply hiding it.
IPv6 packets are just sent straight inside an IPv4 packet with just an IPv4 header, and nothing else at all, not even a UTP header. It’s a very basic non-encrypted tunnel.
I unfortunately
have to use proto41 when my Firebricks are conversing with AA during 3G-failover mode, because the 4G/3G carrier networks that AA uses to connect me on Three to AA
do not speak IPv6 yet. IPv6 is always ‘coming soon’ - their excuses to AA. For me this means the cost of 20 extra bytes wasted per IPv6 packet, wastage in the form of the initial IPv4 packet and which I had to allow for with a reduced IPv6 MTU, which is a damned nuisance. The AA routers for example and my FB2700 just add/subtract the proto41 IPv4 header according to static config (without the addition of some further autoconfig to provide the dest address needed), and, given that address, it all simply works. It all has to be about the most basic IPv6-‘in/over’-IPv4 transition mechanism there is.
The
dest IPv4 address will be that of a preset partnering router, which is parked on the boundary between an IPv4 network and an IPv6+4 network. That router will peel off the IPv4 protocol 41 headers leaving a straight IPv6 packet which is then sent on its way to the IPv6 dest address contained in the packet.
There are a ridiculously huge number of such translation or ‘transition’ mechanisms, all with confusingly similar sounding names; need a program to pick out the prepositions used in the name and turn the whole thing into an English explanation. Other transition mechanisms have various more sophisticated tricks, such as being able to automatically work out what are the values of destination IP address from stuff encoded in the packets somewhere. They may feature more or less auto config/zeroconfig and may or may not be more flexible/more restricted in their addressing capabilities which might be a good/bad thing.