Subject: [Ipoverib] GID clarifications

From: Kanoj Sarcar <[email-masked]>
Date: Tue, 02 Dec 2003 15:54:06 -0800

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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---

From: "Randy Presuhn" <[email-masked]>
Date: Wed, 3 Dec 2003 11:33:11 -0800

Hi -

> From: "Kanoj Sarcar" <[email-masked]>
> To: <[email-masked]>
> Sent: Tuesday, December 02, 2003 3:54 PM
> Subject: [Ipoverib] GID clarifications
...
> which endport is being referred.
...

I guess the logical conclusion is that this is incompatible with any
kind of NAT, or management from outside of a NAT-ed network.
(This may well be a feature rather than a bug, but I wanted to be
sure.)

Randy

---

From: "bill" <[email-masked]>
Date: Wed, 3 Dec 2003 14:06:49 -0800

I don't think this is the case - NAT is completely contained within
Layer 3.  It does not do any layer 2 munging as far as I can tell.  I
believe the comment was in relationship to IB subnets (you have to be
very careful - as they only differ by a letter)

Kanoj correct me if I am wrong

Bill

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf
Of Randy Presuhn
Sent: Wednesday, December 03, 2003 11:33 AM
To: [email-masked]
Subject: Re: [Ipoverib] GID clarifications

Hi -

...

...

I guess the logical conclusion is that this is incompatible with any
kind of NAT, or management from outside of a NAT-ed network. (This may
well be a feature rather than a bug, but I wanted to be
sure.)

Randy

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---

From: "Randy Presuhn" <[email-masked]>
Date: Wed, 3 Dec 2003 14:27:37 -0800

Hi -

...
...

Thanks for the clarification.  I'm happy as long as whatever
shows up in the MIB is sufficiently unique to prevent confusion.
For example, consider what could happen when mutiple
enterprises outsource their network management to the
same provider.  The management systems need to be able to
tell whether a given idententifier refers to the same or different
systems, particularly if the relationships between the enterprises
potentially involve shared facilities.

Randy

---

From: Kanoj Sarcar <[email-masked]>
Date: Wed, 03 Dec 2003 15:04:55 -0800

> shows up in the MIB is sufficiently unique to prevent confusion.

"Sufficiently unique" seems to be the key point here. If you consider any
GID of any endport in one IBA subnet, or in a set of IBA subnets
all connected by IBA routers, the GID is guaranteed to uniquely
identify the endport (which is what I pointed out originally). 
 
> potentially involve shared facilities.

If the provider is managing two unconnected sets of IBA subnets
(simple example would be a single IBA subnet for A, and a single
IBA subnet for B, not connected to each other), then two different
endports might have the same GID; ie, by looking at the GID, you 
could not decide whether it referred to the endport in A or in B.
This is true in general, but if everyone decided to always used
GID index 0, then all GIDs are guaranteed to be unique (I think I
see what the intent of the statement in the draft was).

As Bill pointed out, NAT probably does not look at macaddress/GID
to make this differentiation. If you believe you have some protocol
or system that needs to differentiate based on the IPoIB macaddress/GID,
you should bring it up to the list; it will add weight to the 
argument that everyone must be required to (as opposed to recommended 
to) use GID index 0.

Thanks. 

Kanoj

---

From: "Randy Presuhn" <[email-masked]>
Date: Wed, 3 Dec 2003 15:40:20 -0800

Hi -

> To: "Randy Presuhn" <[email-masked]>
> Cc: <[email-masked]>
> Sent: Wednesday, December 03, 2003 3:04 PM

...
> could not decide whether it referred to the endport in A or in B.

Now, thinking about a management system that only knows what
it can see through MIBs: how can it know whether A and B are
connected or not?  What happens if they start out unconnected,
and later, due to, for example, a corporate merger, they become
connected?  How do we guarantee that the identifiers for A and B
are unique?  If they are not guaranteed to be unique, does it matter?

> see what the intent of the statement in the draft was).

This sounds like a safer way to go, but I'm obviously an IB neophyte.

> argument that everyone must be required to (as opposed to recommended

Based on Bill's clarification, I am no longer concerned about NAT.
I am only asking about how the WG intends to manage this stuff
when the identifiers are not globally unique.

Randy