DHCPv6 Confirm in DOCSIS networks

[Ole Trøan]

Tore,

> My cable provider just got included me in their IPv6 pilot. One of the
> first things I noticed when testing (using a computer directly attached
> to the cable modem) was that DHCPv6 Confirm messages went unanswered.
> The first time I connected went fast, while all subsequent connections
> (e.g. after resuming from suspend) was slow, as the Confirm request had
> to time out before information from the cached lease was used.
> 
> I understood from my provider that the likely cause was that their Cisco
> CNR DHCPv6 server did not support DHCPv6 Confirm, and they also pointed
> me to the following UNH-IOL document, which says «Transmission of DHCPv6
> Confirm message is not expected on a DOCSIS WAN network»:
> 
> https://www.iol.unh.edu/services/testing/ipv6/grouptest/white_papers/CPE_IPv6_Test_Event_Whitepaper.pdf

that's not quite what the document says.

> This strikes me as rather strange - as far as I can tell, the DHCPv6
> client has no way of determining if the Ethernet interface is running on
> is connected to a DOCSIS modem or something else, so I don't see how it
> could possibly selectively disable the use of Confirm in the case of DOCSIS.
> 
> Does anyone have more information on why DHCPv6 Confirm wouldn't be
> expected and supported in DOCSIS networks? (Does it work in Comcast's
> network?)

I'm probably at fault for why Confirm is a bit of an ugly duckling in access network, by stating in RFC3633 that Confirm isn't used for IA_PD (Renew is used instead). we're changing that with http://tools.ietf.org/html/draft-troan-dhc-dhcpv6-stateful-issues-00

in any case, CNR handles Confirm and when you only use IA_NA as you do, using Confirm is perfectly fine.

cheers,
Ole