Addressing plan
Subnet addressing plan
The current addressing plan (subject to change) is to attempt to
maintain an exact match between MITNET IPv4 subnet numbers and IPv6
subnet numbers:
Rule of thumb:
The MIT subnet 18.x/16 (where x is expressed in decimal)
corresponds to the IPv6 subnet 3ffe:1ce1:0:x::/64 (where x is
expressed in hexadecimal).
Don't forget to double-check the base conversion!
Subnets in 3ffe:1ce1:0:f000::/52 are currently being used for
miscellanous other usages (including tunnels and off-campus subnets).
One historical digression: folks who were around when chaosnet was still
active will remember that the first ipv4 subnets were based on the
numerical value of chaosnet network numbers (which were conventionally
expressed in octal..).
Address assignment within subnet
There are several options for address assignment:
Stateless address autoconfiguration
is probably the easiest,
and is suitable for mobile systems and mostly-client systems; your
system will send router solicitation messages to determine which
subnet it's on, and then form an address based on the 64-bit subnet
prefix and an EUI64 id, probably formed from one of its ethernet
addresses.
You'll end up with an address which looks like
3ffe:1ce1:0:bb:2a0:ccff:fe3d:86d
Manual configuration
Addresses in 3ffe:1ce1:0:x::0:/112 are reserved for
routers and v6-specific servers.
Addresses in 3ffe:1ce1:0:x::1:/112 are reserved for
addresses mapped 1:1 from a MITnet ipv4 address.
Rule of thumb:
The MITNET ipv4 address 18.x.y.z
can correspond to the IPv6 address 3ffe:1ce1:0:x::1:yz
(where yz, expressed in hexadecimal, is equal to y * 256 + z).