Re: [v6ops] DAD again [was: draft-ietf-v6ops-host-addr-availability discussion]

"Hemant Singh (shemant)" <shemant@cisco.com> Fri, 13 November 2015 23:44 UTC

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From: "Hemant Singh (shemant)" <shemant@cisco.com>
To: Owen DeLong <owen@delong.com>
Thread-Topic: [v6ops] DAD again [was: draft-ietf-v6ops-host-addr-availability discussion]
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Subject: Re: [v6ops] DAD again [was: draft-ietf-v6ops-host-addr-availability discussion]
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-----Original Message-----
From: Owen DeLong [mailto:owen@delong.com] 
Sent: Friday, November 13, 2015 6:16 PM
To: Hemant Singh (shemant)
Cc: Alexandre Petrescu; v6ops@ietf.org
Subject: Re: [v6ops] DAD again [was: draft-ietf-v6ops-host-addr-availability discussion]


>A LO interface may, but does not need to perform DAD as far as I am concerned. Sure, if it’s convenient for the coders, the performance impact is negligible and it keeps code paths consistent reducing >the potential for bugs.

Please reply to my comment where I said if the lo does not perform DAD, then the lo does not have to join the all-nodes and the solicited-node multicast addresses.   One has to look at the comprehensive picture.   A NA signaling a DAD dup is destined to the all-nodes multicast destination - but the lo interface has disabled DAD.   So why join the all-nodes address or the solicited-node multicast address?  If the interface is also not initiating nor replying to any address resolution, there is not ND operation required on this lo interface.

>However, that does not mean that those addresses don’t need to work with ND correctly as it may well be that application A binds to one address on LO and communicates with an entirely different >address also on LO to carry out transactions with application B. As a result, A will need to be able to discover the link layer address for B, effectively.

No.  The lo interface forwards a packet to the outbound interface which performs any ND address resolution. 

>Arguably, ND isn’t necessary since the LO binding should take care of this, but most operating systems don’t bother to special case this as the effort offers little reward and substantial complexity.

Please note IPv6 ND and DAD are interface-scoped.   An OS has to confirm to interface-specific IPv6 DAD and ND properties. 

Hemant