Re: GID clarifications

! From: Vivek Kashyap <[email protected]>
 
! Yes, the port's GUID is the manufacturer assigned EUI-64 id for the port. It 
is
! probably better to use the IBA term 'portGUID'.

yes, it seems to be sufficient to just reword GUID to something like
"portGUID(EUI-64)".

Note that there is slight ambiguity in the way GID0 is defined in 4.1.1 of
the spec; which is why I dont prefer changing the wording to "GID0" in the rfc.

<snip>
"...This GID is referred to as GID index 0 and is formed by techniques 3(a)
and 3(b) described below."
^^^
 
3(a) talks about how GID0 is formed with default-prefix(fe80)::EUI64
3(b) talks about how GID0 is formed with subnet-prefix::EUI64
3(c) talks about GIDs 1 and above.

So its better to leave the "IB subnet prefix" part of the GID definition in
the rfc(9.1.1) and just reword "GUID" to "portGUID(EUI-64)". That way an
endpoint does provide the GID0 formed with IB subnet prefix when available.
If the IB subnet prefix also happens to be the default-prefix, that's life.

As far as RECOMMENDED vs. MUST, going by the IETF standards, RECOMMENDED is
compelling enough for implementors to follow it blindly, still leaving room
for some clever implementations.

<snip>
3. SHOULD   This word, or the adjective "RECOMMENDED", mean that there
   may exist valid reasons in particular circumstances to ignore a
   particular item, but the full implications must be understood and
   carefully weighed before choosing a different course.

thx,
~Ajoy

! 
! Vivek
! 
! On Wed, 3 Dec 2003, Kanoj Sarcar wrote:
! 
! > Vivek Kashyap wrote:
! > >
! > > Kanoj,
! > >
! > > The port's GUID is it's EUI-64 identifier. A GID, in turn can be formed 
using this GUID, the CA's GUID or some other value. Any GID is unique in the IB 
fabric however only by using the port's GUID/EUI-64 identifier can one uniquely 
identify the port. The other GID's, as noted, can be applied to other ports too 
- though not concurrently. The GID formed using the EUI-64 identifier is the 
'GID at index 0'. I've made note of your comment and can clarify further as 
needed.
! > >
! > > wrt, using only GID at index 0 as in the MAC address, there have been 
proponents of using the other GIDs (non EUI-64 GID).
! > >
! > > Vivek
! >
! > Vivek,
! >
! > Per IBA 1.1 section 4.1 EUI-64 subsection and 4.1.1 item 2, manufacturer 
assigned and
! > SM assigned values are required to be EUI-64 compliant (they differ only in 
u/l bits).
! > Thus, all GIDs contain an EUI-64 in the lower 64 bits; thus saying "GUID is 
its EUI-64
! > identifier" might be confusing. Saying "GUID using manufacturer assigned 
EUI-64 identifier"
! > or better "GID index 0" removes all confusion. I think we agree on the 
intent, I just
! > want to make sure if you use the term GUID, you do specifically define what 
you mean
! > by it.
! >
! > Regarding MUST vs RECOMMENDED, is it worthwhile reconsidering given that
! >
! > 1. SM assigned GIDs are not that popular (anymore?)
! > 2. it allows determination of sender's ipoib address, thus allowing 
(receiver side)
! > implementations to be dlpiv2 conformant?
! >
! > Thanks.
! >
! > Kanoj
! >
! >
! >
! > > --
! > > Vivek Kashyap
! > > Linux Technology Center, IBM
! > > [email protected]
! > > [email protected]
! > > Ph: 503 578 3422 T/L: 775 3422
! > >
! > >     Kanoj Sarcar <[email protected]>
! > >     Sent by: [email protected]
! > >
! > >     12/02/2003 03:54 PM
! > >     Please respond to Kanoj.Sarcar
! > >
! > > Hi,
! > >
! > > It seems that certain parts of the
! > > draft-ietf-ipoib-ip-over-infiniband-05.txt draft might
! > > require clarification. For this discussion, please refer to
! > >
! > > 1. section 9.1 Link Information says:
! > > "The GID, if formed using the GUID, can be used to unambiguously
! > > identify an endpoint."
! > >
! > > 2. section 9.1.1 Link Layer Address/Hardware Address, part c) says:
! > > "It is RECOMMENDED that the GID formed by the combination of the
! > > IB subnet prefix and the port's GUID be included in the
! > > link-layer/hardware address."
! > >
! > > Can comment #2 be safely taken to mean that GID index 0 is
! > > being RECOMMENDED? Port GUID seems somewhat ambiguous, since I
! > > am not sure (after reading IBA 1.1 section 4.1) whether the
! > > term GUID refers only to the manufacturer assigned value that appears
! > > in lower 64 bits of GID index 0, or whether it also includes
! > > lower 64 bits of SM assigned GIDs at higher indices. If GID index 0
! > > was really intended, the comment should explicitly state so to prevent
! > > confusion.
! > >
! > > Also, to make things simple, is it reasonable to REQUIRE implementations
! > > to always use GID index 0 (maybe this depends on whether existing
! > > implementations all use GID0 only)? The reason this might be
! > > interesting is that when a node receives a packet without a GRH
! > > (whereby it already knows the sender's LID and QPN), it can possibly
! > > reverse lookup the sender's LID to identify the sender's GID index
! > > 0 and concatenate the sender's QPN to figure out the sender's link
! > > address. Thus, a receiver can always figure out the sender's address,
! > > even when a GRH is not present. This would be similar to ethernet,
! > > where a receiver can always determine a sender's address, and thus
! > > is more DLPIv2 (unitdata_indication) friendly.
! > >
! > > Regarding comment #1, what does "unambiguously identify an endpoint"
! > > mean? GIDs are unique in the subnet; and if an IP link contains
! > > members in multiple IBA subnets, the subnet prefixes will disambiguate
! > > which endport is being referred.
! > >
! > > Thanks.
! > >
! > > Kanoj
! > >
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! >
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! 
! __
! 
! Vivek Kashyap
! Linux Technology Center, IBM
! 
! 
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