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RE: To DAD or not to DAD?

"Hemant Singh (shemant)" <shemant@cisco.com> Sat, 28 February 2015 11:59 UTC

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From: "Hemant Singh (shemant)" <shemant@cisco.com>
To: Erik Nordmark <nordmark@acm.org>, Hesham Soliman <hesham@elevatemobile.com>, "6man@ietf.org" <6man@ietf.org>
Subject: RE: To DAD or not to DAD?
Thread-Topic: To DAD or not to DAD?
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Date: Sat, 28 Feb 2015 11:59:30 +0000
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References: <54E4EC1A.3080303@acm.org> <D10B6C10.5B347%hesham@elevatemobile.com> <54E61297.5020507@acm.org> <D10CC6F8.5B508%hesham@elevatemobile.com> <54E7B4C0.3020907@acm.org> <D10EA52E.5B5C1%hesham@elevatemobile.com> <54F17DC7.20806@acm.org>
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Specifically for a cable modem, I had contacted Andrew privately.   My comment to him for draft-yourtchenko-6man-dad-issues-00 and cable modem is included below between squared braces.

[There is this text in your document

"Similarly, a DSL or cable modem whose line status is invisible to IP
   stack either within the modem or to a host connected on the Ethernet
   side, also renders the DAD ineffective - the delay before the
   connectivity is established can be much longer than any DAD wait."

Remove cable modem from the above paragraph.  Cable standards mandate each time the RF interface of the modem bounces, the modem initiates DAD; so does RFC 4862.  Also, any cable modem resets its LAN interface if the modem's RF interface bounces.  This is also mandated in cable standards.]

Hemant

-----Original Message-----
From: ipv6 [mailto:ipv6-bounces@ietf.org] On Behalf Of Erik Nordmark
Sent: Saturday, February 28, 2015 3:35 AM
To: Hesham Soliman; Erik Nordmark; 6man@ietf.org
Subject: Re: To DAD or not to DAD?


Protocols are supposed to be robust against packet loss. The fact that a modem or the spanning tree protocol can cause outages for an tens of seconds should just be a particular loss pattern meaning that things should recover after the connectivity is back.

RS didn't do that, but now we have resilient-rs.

But I don't think it is useful to have some more fine-grained view of different flavors of "link up" means. Do do that one would need to add something to the IEEE 802 set of protocols, get the Ethernet device drivers to implement that new thing, and then make the DAD code use it.
Still, after that effort, it would only handle the STP case and not the modem case (AFAICT). In the modem case the local link in the house is up. But that Ethernet doesn't know that it is being bridged over a modem to some other devices; that bridging logic is layered on top of the Ethernet port behavior.

    Erik


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