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

Owen DeLong <owen@delong.com> Fri, 13 November 2015 17:46 UTC

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From: Owen DeLong <owen@delong.com>
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Date: Fri, 13 Nov 2015 09:43:03 -0800
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References: <8D175A1F-B1AE-44B4-838E-1C853B6C937D@cisco.com> <CAKD1Yr15C-uoxUw0kgWO-d=LmUK8qWGLS7vt+22W+k8xXtDY+g@mail.gmail.com> <2134F8430051B64F815C691A62D9831832F393F1@XCH-BLV-504.nw.nos.boeing.com> <2134F8430051B64F815C691A62D9831832F3941D@XCH-BLV-504.nw.nos.boeing.com> <563811DF.9020603@gmail.com> <2134F8430051B64F815C691A62D9831832F394F7@XCH-BLV-504.nw.nos.boeing.com> <563821EB.3040508@gmail.com> <2134F8430051B64F815C691A62D9831832F39A09@XCH-BLV-504.nw.nos.boeing.com> <56392B6D.8030703@gmail.com> <2134F8430051B64F815C691A62D9831832F3A88F@XCH-BLV-504.nw.nos.boeing.com> <2134F8430051B64F815C691A62D9831832F3A97F@XCH-BLV-504.nw.nos.boeing.com> <CAHDzDLBG8xZxUFsAuN-7WuruZcULF1QAS_ch=gD5rGQMZfskow@mail.gmail.com> <2134F8430051B64F815C691A62D9831832F3E8B0@XCH-BLV-504.nw.nos.boeing.com> <CAJE_bqd-1x5EJ=rkebiBFdNds6so5+iNGftiUf+MUu9P1up1bA@mail.gmail.com> <CAKD1Yr1X8UzQ58FeG6PYG9L1MyibV0J-JpcS2hxwzCdV=HizXg@mail.gmail.com> <ad0e90cf5f74407fa5338a7b6130bd1a@XCH-RTP-005.cisco.co! m> <5645DE07.3050605@gmail.com> <6f8ba1d9357b4cf786df990ebe09c965@XCH-RTP-005.cisco.com>
To: "Hemant Singh (shemant)" <shemant@cisco.com>
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Subject: Re: [v6ops] DAD again [was: draft-ietf-v6ops-host-addr-availability discussion]
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> On Nov 13, 2015, at 05:58 , Hemant Singh (shemant) <shemant@cisco.com> wrote:
> 
> 
> -----Original Message-----
> From: v6ops [mailto:v6ops-bounces@ietf.org] On Behalf Of Alexandre Petrescu
> Sent: Friday, November 13, 2015 7:57 AM
> To: v6ops@ietf.org
> Subject: Re: [v6ops] DAD again [was: draft-ietf-v6ops-host-addr-availability discussion]
> 
> 
>> One wouldnt care about DAD on loopback interface, because it's not noise on a wire, and it's not time consuming.
> 
> So how will you deal with a duplicate IPv6 address configured on a loopback interface?  As I said in my example, a router is using the IPv6 address on a loopback interface to source packets and a duplicate is detected - the network breaks down.
> 

How is it possible to have a duplicate address on a loopback interface?

If you assign an address to a loopback interface, the address is present on the interface. If you attempt to assign it there again, it should be a no-op.

To the best of my knowledge, it is impossible to assign the same address to the same interface twice.

The duplicate address case applies when two systems on the same link have the same address. Since there is never more than one system on a loopback link by definition, it seems to me that the scenario you propose is impossible by definition.

Owen

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