dhclient6, IA_PD hints, Comcast, and a "pd hint"

Steven Carr sjcarr at gmail.com
Fri Aug 23 02:12:47 UTC 2013

So the client wouldn't get a /60 subnet mask, you'd need to subnet and
route the /60 into (16) individual /64s. All IPv6 LANs that end
clients live on should be /64.


On 23 August 2013 01:26, Troy Telford <ttelford.groups at gmail.com> wrote:
> I'm using ISC dhclient 4.2.4
> Comcast has rolled out native IPv6 in my area.
> By default, Comcast assigns a /64 prefix to users. I'm not too happy about
> this, as I have a few subnets I'd like to keep separated, and you can't do
> that with a /64 from what I understand.
> According to the thread at:
> http://forums.comcast.com/t5/Home-Networking-Router-WiFi/IPv6-prefix-size-and-home-routing/td-p/1495933
> Comcast will provide a /60 if the DHCP client requests it in IA_PD. (I'm
> less familiar with the details of what that actually means, so bear with
> me).
> The instructions given by Comcast are for Cisco iOS, and are something along
> the lines of:
> interface GigabitEthernet0/0
> description Comcast Public
> ipv6 address dhcp
> ipv6 enable
> ipv6 dhcp client pd hint ::/60
> ipv6 dhcp client pd prefix-from-Comcast
> ipv6 traffic-filter ipv6_inbound in
> The same thread has working configurations for wide-dhcpv6-client (the
> bottom of the thread), where the prefix size is set by:
> id-assoc pd 1 {
>    prefix ::/60 infinity
> I've been unable to find any documentation that describes how to configure
> ISC dhclient to request a prefix size of /60.  (I can only find references
> to 'dhclient -6 -P ethxyz' - which results in a /64 being assigned.
> Does anybody know how to configure dhclient to request a /60 instead of
> letting the server use its default of /64?
> It'd be nice to know and have documented (and easy to find), as Comcast is
> in the process of deploying IPv6 across their network. I'm sure I'm not the
> only or last person who will ask to be able to subnet my IPv6 network.
> Thanks.
> --
> Troy Telford
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> dhcp-users at lists.isc.org
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