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

"Hemant Singh (shemant)" <shemant@cisco.com> Sun, 15 November 2015 12:25 UTC

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From: "Hemant Singh (shemant)" <shemant@cisco.com>
To: "Templin, Fred L" <Fred.L.Templin@boeing.com>, "Mukom Akong T." <mukom.tamon@gmail.com>
Thread-Topic: [v6ops] DAD again [was: draft-ietf-v6ops-host-addr-availability discussion]
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Date: Sun, 15 Nov 2015 12:25:35 +0000
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Cc: "v6ops@ietf.org" <v6ops@ietf.org>
Subject: Re: [v6ops] DAD again [was: draft-ietf-v6ops-host-addr-availability discussion]
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Fred,

Sorry for the delay.  I am catching up with the original thread.   Please see below.

>From: v6ops [mailto:v6ops-bounces@ietf.org] On Behalf Of Templin, Fred L
>Sent: Monday, November 09, 2015 3:00 PM
>To: Mukom Akong T.
>Cc: v6ops@ietf.org
>Subject: Re: [v6ops] DAD again [was: draft-ietf-v6ops-host-addr-availability discussion]


>>'N' sends a DHCPv6 PD Solicit over the WAN interface
>>and receives a prefix delegation 'P'. 'N' can now assign prefix 'P' to either the
>>loopback interface or the LAN interface, but MUST NOT assign 'P' to the WAN
>>interface.

>This is correct, since this WAN interface would have already gotten legitimate non-link-local addresses by other means.

There is another reason.  The prefix delegation (PD) RFC in RFC3633 says

[the requesting router MUST NOT assign any delegated prefixes or subnets from the delegated prefix(es) to the link through which it received the DHCP message from the delegating router.]

The reason RFC3633 has such a restriction is because if it were possible, then the WAN IPv6 global address is on-link to the northbound SP router.   The delegated prefix in P is supposed to be not on-link on the WAN.   Thus if a loopback (lo) interface is configured with an IPv6 address from prefix P, the  IPv6 address is not on-link and thus the lo interface does not initiate DAD for the address.

However, if an address is configured on the lo interface manually and the address is not using an address from a DHCPv6 PD, what transpires?   The intent of the admin is to configure an address which is not on-link to the directly connected network.   The only other case is if the directly connected network includes a node who manually assigned its IPv6 address (or is broken) and the address happens to match the address on the lo interface - now DAD is needed.   

Hemant