(usagi-users 02090) Different types of tunnels

[Yaniv Kaul <ykaul@xxxxxxxxxxxxxx>]

Hi,

I'm trying to understand what are the different types of tunnels 
available, to get IPv6 over IPv4. I found zillion terms and RFCs, not 
sure what matches what.
To make things happier, I'm working on multiple operating systems 
(Linux, with and without USAGI; Solaris 9; Nokia IPSO 3.7; Win XP SP1, 
Cisco IOS 12.2).
Here's what I got so far, I'd be happy to get corrections/comments. [One 
that I already know of, is that some of those tunneling techniques are 
considered deprecated.]
Here goes:

1. Automatic, using 'compatible' address (::w.x.y.z):  Seems supported 
in Linux, if using IPV6_AUTOTUNNEL="yes" in /etc/sysconfig/network .
Does it refer to RFC2893? If so, I'm not sure I understand it 
completely, as the RFC seems to suggest a multicast IPv4 environment is 
required.
2. Manual, using 'compatible' address on the link local (fe80::w.x.y.z). 
Seems supported in Linux, using 
/etc/sysconfig/network-scripts/ifcfg-sitX, where X>0.
Is this RFC 2529? Seems like Solaris supports it, and it only (although 
RFC 2893 was written by a SUN dude). Is this a '6 over 4' tunnel?
3. Manual 2? - addresses are fe80::a.b.c.d.w.x.y.z, where w.x.y.z is the 
IPv4 source, and a.b.c.d is the IPv4 destination. Seen only on Nokia 
IPSO. Referred to as '6 in 4' tunnels.
4. '6 to 4'. RFC 3056. 2002:w.x.y.z::/48 . Supported on Linux (with 
USAGI), XP SP1, Cisco IOS, Nokia IPSO. Didn't work for me on the USAGI - 
put IPV6TO4INIT in /etc/sysconfig/network-scripts/ifcfg-eth0, nothing 
happened. I assume it's a misconfiguration on my side, though.
5. ISATAP - fe80::5fe:w.x.y.z . XP SP1, experimental on USAGI.

Issues:
- Not sure if Cisco supports 1 or 2, as it seems there's a mixup between 
the two.
- Can anyone tell me what 'sit' stands for (as in "/sbin/ip tunnel add 
sit1 mode SIT...") ?
- Can anyone tell me what is "6 in 4", what is "6 to 4" ? I assume "6 
over 4" is RFC 3056.
- Anyone knows how to configure Nokia's "6 in 4" in Linux (item 3) ?
- Does the use of 'compatible' addresses implies the use of RFC 2893? I 
think there's 'compatible' tunnel, which I could not find defined 
exactly (for example, Cisco supports it, but does not support RFC 2529) 
and there's RFC 2893.

Sorry for all the mixup, hope someone can shed some light on this, or 
refer me to an ultimate source...

TIA,
Y.