Short version: Fred agrees that LISP is "not really achieving
a true locator/identifier split.". He also
thinks that "the LISP acronym itself seems a bit
misleading". I think it is very misleading.
We discuss the meaning of "EID" and whether
such addresses - or any global unicast address -
identifies a host or just an interface on a host.
Hi Fred,
Thanks for your reply, in which you wrote:
> As I have said many times here on the list, what LISP
> is calling "EID" is nothing more and nothing less than
> an IP address.
Yes - all hosts and all routers except ITRs treat them the same as
any other global unicast IP address. ITRs have a special algorithm
for handling packets whose destination address matches an EID prefix.
> IP addresses are assigned to interfaces; hence, they name an end
> system *interface* and not the end system itself.
A host may have multiple interfaces, but no two hosts share the same
interface. So if a global unicast address IP address identifies an
interface, it is also true to say that as a result of this, this IP
address also identifies a host. (This is not counting anycast, of
course.)
> Moreover, these LISP EIDs are routable within a certain scope; even
> if that scope is only node-local.
I am not quite sure what you mean by "node-local" in the context of
routing packets.
A packet whose destination address is a LISP EID is perfectly
routable anywhere in the world, assuming there are one or more Proxy
Tunnel routers advertising the "coarse" prefix which covers this EID
address. (In Ivip, it is DITRs advertising Mapped Address Blocks -
MABs.) All the routers except ITRs use the existing algorithm they
use for all other packets with global unicast destination addresses.
ITRs use a second algorithm. For a full description, please see:
Re: [rrg] LEIDs, SPI & ordinary IP addresses as both IDs & Locs
http://www.ietf.org/mail-archive/web/rrg/current/msg06082.html
> Conversely, a true identifier (like a HIP HIT) is not routable
> within any scope.
Yes, a HIP HIT is purely an Identifier.
> So, I have to agree that LISP is not really achieving
> a true locator/identifier split.
OK - thanks for this.
> The LISP EID IMHO would be more accurately renamed as "Endpoint
> Interface iDentifier", and the LISP acronym itself seems a bit
> misleading. ["iDentifeir" typo corrected.]
Since a group of completely different architectures (Core-Edge
Elimination) do, as the central element of their architecture,
implement the "Locator / Identifier Separation" naming model (which
predates "LISP) I regard LISP's current name as being completely
misleading and a source of difficulty for anyone trying to understand
the "LISP" architecture, or the entire scalable routing field.
To call what is currently known as a "LISP EID" address as:
Endpoint Interface iDentifier
wouldn't make much sense to me, since this description also fits any
global unicast address which a host is using, or any other address
such as an RFC 1918 or RFC 4193 ULA address which also identifies a
host interface, and therefore also a host.
In Ivip, I chose the term "Scalable PI" (SPI) address for the new
"edge" subset of the global unicast address space which can scalably
provide provider-independent address space to end-user networks for
the purposes of portability, multihoming, inbound TE and mobility. I
don't have a particular term for the remainder, which remains as
"core" space, according to the meaning of "Core-Edge Separation".
Since Ivip doesn't slice up SPI space into prefixes, there's no such
thing as an SPI prefix - other than a Mapped Address Block, which is
the DFZ-advertised prefix covering a block of SPI space. I use a
term first used by Bill Herrin - "micronet" - to refer to the integer
number of contiguous IPv4 addresses or IPv6 /64s which all have the
same mapping.
I think the terms LISP, EID and RLOC are confusing. "Proxy Tunnel
Router" is a poor term too, since it doesn't proxy for anything.
The term "LISP" (Locator Identity Separation Protocol) is really
muddying the waters and I think the field and the "LISP" architecture
would be much better off if it had a new name.
Perhaps I will refer to it as:
"the architecture which, ideally, would be formerly known as LISP"
- Robin
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