OpenBSD and DHCPv6 PD

[neilehodges]

Someday Comcast will support native IPv6 where I'll be living, and I'd love to take advantage of it.  I can't seem to figure out how I would set rtadvd and a DHCPv6 PD client up, though.  I've posted on a few BSD forums, but they don't seem to have any information either.

My router currently is using DHCPv6 for some hosts, but has SLAAC configured (again, with rtadvd) for most.  How would I go about getting DHCPv6 PD working in the future on OpenBSD?

[neilehodges]

Will Comcast be using DHCPv6 PD or be handing out static prefixes?  Does anybody know the long-term path?

[jimb]

I believe they will be using DHCPv6 PD. 

As for setting it up, you'd have to read the man pages and maybe the RFCs.  :P

[kriteknetworks]

I believe they will be using DHCPv6 PD. 

Hey jimb...what leads you to believe this?

[jimb]

I believe they will be using DHCPv6 PD.  

Hey jimb...what leads you to believe this?

Mostly skuttlebutt on the Comcast IPv6 trial forum site.

[Midnight]

Someday Comcast will support native IPv6 where I'll be living, and I'd love to take advantage of it.  I can't seem to figure out how I would set rtadvd and a DHCPv6 PD client up, though.  I've posted on a few BSD forums, but they don't seem to have any information either.

My router currently is using DHCPv6 for some hosts, but has SLAAC configured (again, with rtadvd) for most.  How would I go about getting DHCPv6 PD working in the future on OpenBSD?

Hi.

I know this thread is over a year old now...but I too am wondering about essentially the same exact thing.  I want to know if anyone has any information about how Comcast is implementing native dual stack on consumer cable connections.  I know when you turn on IPv6 forwarding, that automatically disables ra_accept so that cannot be used on the WAN interface.  But I hear like you mentioned that they plan to use DHCPv6 to give the customer the IPv6 address and some other info for a delegated subnet.  Does OpenBSD 5.1 have a working DHCPv6 client/server?

[Midnight]

Hi everyone...

I just managed to get a delegated prefix working on my OpenBSD router using the isc-dhclient software package I installed (the default included dhclient does NOT support IPv6 at all it appears).

There are a couple of things:

1)  The isc-dhclient package does NOT include a dhclient-script of it's own so I was forced to work off the already included one in OpenBSD 5.1.  Ironically this version has subroutines in it specifically for IPv6.  However they clearly do not work, especially when attempting to work in Prefix Delegation mode.  I tweaked the script to figure out how it worked and eventually found it was getting it's information via temporary environment variables and depending on what's set when it's called, it attempts to configure the system accordingly.  So I watched the behavior of #sudo /usr/local/sbin/dhclient -d -6 -P -D LL -N vr0 -sf /root/dhclient-script until I found the information that was necessary to provision an IPv6 address on the WAN interface and then modified the script some to provision the delegated prefix obtained via dhclient -6 -P mode.

Here's where the deficiencies remain to be solved.

2)  There was never any mention of DNS server IPs...ok fine I can continue to work off the IPv4 ones for now, no biggie.

3)  But worse than that was the IPv6 default route was never configured, and I quickly realized it was because such information is simply NOT supplied via DHCPv6 because if you read the RFCs it's meant to be obtained via a standard IPv6 Router Advertisement, which....

4)  ...can't be done!!! because my router is configured for forwarding which if you also read the RFCs means net.inet6.ip6.accept_rtadv=0 has to be disabled!!!  So wait, how is this supposed to work?  If you take the link local IPv6 address of the DHCPv6 server and manually configure it as your default route, then magically your delegated subnet suddenly works.

So my question is...does anyone know how to force net.inet6.ip6.accept_rtadv=1 to enabled and still be able to enable forwarding of IPv6 in the kernel?  Or is there a way to leave forwarding enabled and still somehow extract the information that would otherwise be obtained automatically via the kernel and manually configure it via a script of some kind?

I am willing to post my modifications to the dhclient-script from OpenBSD 5.1 in case anyone is interested in seeing how I got it to sort of work, and maybe refine what I started.

Midnight

[passport123]

Since Comcast was mentioned, I thought I'd add some more info.

With Comcast IPv6 dual stack, you need to do the following:

• use rtsol to request a router advertisement.   This step will set up a default route for IPv6
• use DHCP6 to request IA_NA and IA_PD.  This step will give you a /128 IPv6 address (typically in the 2001:558/31 address range).   You will get a prefix delegation (PD) in the 2601::/28 range.   The PD will be /64.  If your DHCP6 client can provide PD Hints to the DHCP6 server, you can "hint" for a /60 and receive it.

Here's a diagram that explains it a bit further. 




Here's the message thread for that image:
http://www.dslreports.com/forum/r28960304-


OpenBSD does not yet allow a box to request router advertisements and also forward packets.   As a result, I've switched to FreeBSD which, since version 9, has allowed this configuration ability.   These release notes:

https://www.freebsd.org/releases/9.0R/relnotes-detailed.html#AEN1395

explain the change to comply with RFC6204.  (Scroll down a bit in the release notes until you see the section starting with "More specific explanations of the changes are as follows," and then start reading.)


Hope this helps.