Subject: [Ips] New thought for draft-ietf-ips-iscsi-impl-guide-00.txt

From: William Studenmund <[email-masked]>
Date: Wed, 3 Aug 2005 13:31:07 -0700

One thing I've remembered I wanted to note is that initiators should 
prepare themselves for DNS names showing up multiple times in 
SendTargets discovery.

The reason for this is that a TargetAddress value does not indicate if 
a DNS address is IPv4 or IPv6. It is possible for a DNS name to map to 
both an A and AAAA record.

If the target's configuration explicitly indicates IPv4 vs IPv6, it is 
possible to have different portals on the v4 and v6 addresses for a DNS 
name. It is also possible for the different portals to report the same 
DNS name and also be in different portal groups. In this case, the TPGT 
reported for each would differ.

Take care,

Bill
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From: "Mallikarjun C." <[email-masked]>
Date: Tue, 09 Aug 2005 14:24:47 -0700

Bill,

Sorry, I was traveling part of last week, and all of this week.

You raise an interesting question, and I think clarifying this in the 
Implementer's guide could be useful.

Is it reasonable to require that whenever one DNS name maps to multiple 
IP addresses (v4 or v6), targets must return the specific IP address(es) 
the TPG can be reached on (not the DNS name), except when the TPG can be 
reached via all IP addresses (v4 & v6) that the DNS name resolves to?

Thanks.

Mallikarjun

Mallikarjun Chadalapaka
Networked Storage Architecture
StorageWorks Division
Hewlett-Packard MS 5668
Roseville CA 95747
cbm [at] rose.hp.com

William Studenmund wrote:
> The reason for this is that a TargetAddress value does not indicate if a 
> DNS address is IPv4 or IPv6. It is possible for a DNS name to map to 
> ------------------------------------------------------------------------
>

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From: William Studenmund <[email-masked]>
Date: Tue, 9 Aug 2005 17:43:39 -0700

On Aug 9, 2005, at 2:24 PM, Mallikarjun C. wrote:

> Is it reasonable to require that whenever one DNS name maps to 
> multiple IP addresses (v4 or v6), targets must return the specific IP 
> address(es) the TPG can be reached on (not the DNS name), except when 
> the TPG can be reached via all IP addresses (v4 & v6) that the DNS 
> name resolves to?

As a target implementer, I'd rather not do that. However what you 
describe makes a lot of sense and would probably be a clean thing to 
do. I'd rather not do it, but it could be easier than the pain 
initiators would see.

Oh, I'd restrict the requirement to portals (TargetAddress entries) on 
the same TCP port; if a TCP port number is served by only one IP 
address family (v4 or v6), no restriction seems needed. Changing the 
port number makes differing TargetAddresses look different, so the 
initiators should be able to handle that situation. Also, I'd phrase it 
that the TPG is the same for all IP addresses. Rather than reaching a 
TPG, you're reaching a portal that is in a TPG.

As a nit, I think I'd phrase this as requiring that portals that are 
configured to use a common DNS name MUST all use the same TPGT for any 
given target. If a common DNS name is configured for portals that 
belong to different TPGs, the target MUST report the resolved IP 
addresses rather than the DNS names.

Hmmm... That's still wordy and mushy.

What I'm trying to get to is that the target only needs to look at 
portals that are configured to use the same DNS name, it doesn't have 
to look up a DNS name and then try and find out what portals all map to 
the returned addresses. Having to do DNS lookups on all hostnames and 
then having to sift through all the returned records would be a mess.

So the algorithm I have in mind is that the target scans all the (text) 
host names. For each host name, if all the portals are members of the 
same TPG, then the DNS name can be returned. Otherwise the numeric 
addresses have to be returned. Note that since the TPGs are strictly 
defined per-node, this calculation could get interesting. :-)

Next question, is it ok for the target to return multiple identical 
TargetAddress entries? This would only happen if it's ok to use a DNS 
name and we have both a v4 and v6 portal. I think it'd be easier for 
targets to permit this, and it could also serve as an indication to 
initiators that there really are multiple portals present.

Any input from initiator folks? How much would/will this issue confuse 
your discovery systems?

Take care,

Bill

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From: William Studenmund <[email-masked]>
Date: Wed, 10 Aug 2005 11:37:46 -0700

On Aug 9, 2005, at 5:43 PM, William Studenmund wrote:

> initiators should be able to handle that situation. Also, I'd phrase 
> it that the TPG is the same for all IP addresses. Rather than reaching 
> a TPG, you're reaching a portal that is in a TPG.

I'm sorry I wasn't able to make the IETF in Paris. But I had an idea 
after reading David's minutes. If we are going to extend SendTargets 
discovery to cover other transports, like IB, then we could perhaps 
also extend the discovery to be explicit about which IP transport (v4 
or v6) to use. Thus the ambiguity will be gone.

Take care,

Bill