Subject: [tcpm] 793bis: proposed multihoming clarification from 1122

From: Wesley Eddy <[email-masked]>
Date: Wed, 28 Sep 2016 12:11:55 -0400

A couple of places in RFC 1122 discuss TCP behavior for source address 
selection on multihomed hosts.

Section 4.2.4.4 has non-requirements language in the implementation 
section that nebulously says "the networking software will choose an 
appropriate local IP address".  The actual requirements-language "MUST" 
on how this works is in 4.2.3.7 that describes what happens more explicitly.

In 793bis, my proposal is to condense material from these 2 different 
sections together more clearly, into:

          For an active OPEN call, a specified "local IP address"
          parameter will be used for opening the connection.  If the
          parameter is unspecified, TCP MUST ask the IP layer to select
          a local IP address before sending the (first) SYN.  See the
          function GET_SRCADDR() in Section 3.3.4.3 of RFC1122.

I think that's basically just an editorial change, but wanted to make 
sure the WG sees it.  My plan is to include this (or whatever improved 
version the WG suggests) in the next revision of 793bis.

Any feedback is appreciated.

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From: Joe Touch <[email-masked]>
Date: Wed, 28 Sep 2016 09:57:55 -0700

Hi, Wes,

Do we also need language that says that if the parameter IS specified,
it MUST NOT be overwritten (e.g., by the process below)?

I'm not sure if anyone does this, but I'm increasingly seeing
implementation discussions where developers do virtually anything that
isn't explicitly prohibited.

Joe

On 9/28/2016 9:11 AM, Wesley Eddy wrote:
> appropriate local IP address".  The actual requirements-language
> "MUST" on how this works is in 4.2.3.7 that describes what happens
> more explicitly.
>
> _______________________________________________
> tcpm mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/tcpm

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From: Wesley Eddy <[email-masked]>
Date: Wed, 28 Sep 2016 13:10:57 -0400

We could change "will be used" to "MUST be used".

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From: Joe Touch <[email-masked]>
Date: Wed, 28 Sep 2016 10:20:03 -0700

Yes - that does it. ;-)