On 02/26/2017 10:24 AM, Sander Steffann wrote:
2.3. Address Type Identification
The type of an IPv6 address is identified by the high-order
bits of the address, as follows:
Address type Binary prefix IPv6 notation
Section ------------ ------------- -------------
------- Unspecified 00...0 (128 bits) ::/128
2.4.2 Loopback 00...1 (128 bits) ::1/128
2.4.3 Multicast 11111111 ff00::/8
2.6 Link-Local unicast 1111111010 fe80::/10
2.4.6 Global Unicast (everything else)
I wonder if this table should explicitly call out ULAs, and
provide a reference to the corresponding section.
ULAs are not an address type, they are Global Unicast. Adding
them here might confuse people. And if we include ULAs then there
is lots more that we should include as well. So while I
understand your question, I think it would be better not to.
The "confusing" part is that, while globally unique, their scope is
not really global -- i.e., they are not meant to be globally
routable.
Indeed, globally unique vs globally routable. But if you go into this
then it's more complicated than it seems. Whether something is
routable and where are an operational choice. Companies choosing to
interconnect might route each other's ULA space, while some of my
RIPE NCC allocated space is not routed anywhere public. It's
difficult to give a fixed definition that doesn't take operational
stuff into account.
According to the definition of global scope in RFC4291, ULAs are not
really global. If they were, an ULA address should be able to uniquely
identify an interface in the whole (global) network. If anything, this
only happens "statistically".
In practice, sine 2001:db8::/16 is not routable, if your teaching a
course you'll probably use ULAs for a virtual lab. And since you copy
the same VMs to all attendees, they all end up using the same ULA
addresses. Hence their scope (within which an interface is uniquely
identified) will certainly not be global (multiple different interfaces
employ the same address at the same timeframe). :-)
Cheers,
--
Fernando Gont
SI6 Networks
e-mail: fgont(_at_)si6networks(_dot_)com
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