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HackerBlaster
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DHCPv6 Problem

Thu Apr 12, 2012 5:15 pm

Hi. I am relatively new at this. That's not to say I don't know what DHCP stands for, I am an experienced software engineer, however I'm new to networking. I have the following simple setup:

DHCP server (Enterprise Linux 5.5) connected to my OS X Lion Laptop. I have no problems acquiring IPv4, domain, DNS, etc. I however cannot get DHCPv6 to work. Here is a dump of my dhcp6s.conf file:

interface eth0 {
server-preference 255;
renew-time 60;
rebind-time 90;
prefer-life-time 130;
valid-life-time 200;
allow rapid-commit;
option dns_servers dead:face:dead:beef::1 sub.domain.example;
link AAA {
range dead:face:dead:beef::1000 to dead:face:dead:beef::ffff/64;
prefix dead:face:dead:beef::/64;
};
};


In OS X Settings I have Configure IPv4: Off; Configure IPv6: Automatically,

What am I doing wrong? I feel like I've faithfully followed online tutorials. Any help will be greatly appreciated.

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jdsilva
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Re: DHCPv6 Problem

Thu Apr 12, 2012 5:24 pm

The "Automatic" setting in OS X refers to IPv6 SLAAC and not DHCP. This mean the OSX host will use the IPv6 Neighbour Discovery protocol to listen for "Router Advertisements" (that are supposed to come from the gateway(s) for the link) and use those to autoconfigure themselves with an IPv6 Global address. In those router advertisements you can set the "managed-config" flag, which tells the hosts to use DHCP instead of SLAAC.

So having never done this before, I would think that you needs a device to send RAs onto the link with the managed-config flag set before your host will even try to use DHCP.

HackerBlaster
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Re: DHCPv6 Problem

Thu Apr 12, 2012 5:39 pm

A device to send RAs? What software would I need to send those RAs? Could they be sent by the DHCPv6 server I'm using?

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jdsilva
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Re: DHCPv6 Problem

Thu Apr 12, 2012 9:02 pm

I don't know. Let's see what we can find.

Starting with the RFC for DHCPv6:

Section 3, http://www.ietf.org/rfc/rfc3315.txt
IPv6 Stateless Address Autoconfiguration [17] specifies procedures by
which a node may autoconfigure addresses based on router
advertisements [13], and the use of a valid lifetime to support
renumbering of addresses on the Internet. In addition, the protocol
interaction by which a node begins stateless or stateful
autoconfiguration is specified. DHCP is one vehicle to perform
stateful autoconfiguration. Compatibility with stateless address
autoconfiguration is a design requirement of DHCP.

IPv6 Neighbor Discovery [13] is the node discovery protocol in IPv6
which replaces and enhances functions of ARP [14]. To understand
IPv6 and stateless address autoconfiguration, it is strongly
recommended that implementors understand IPv6 Neighbor Discovery.


Right... So my theory is correct by RFC standards. A host should configure itself according to how the RAs tell it to configure itself.

http://www.ietf.org/rfc/rfc2461.txt

Page 10
Router Advertisements (and per-prefix flags) allow routers to inform
hosts how to perform Address Autoconfiguration. For example, routers
can specify whether hosts should use stateful (DHCPv6) and/or
autonomous (stateless) address configuration. The exact semantics
and usage of the address configuration-related information is
specified in [ADDRCONF].


Page 18
M 1-bit "Managed address configuration" flag. When
set, hosts use the administered (stateful) protocol
for address autoconfiguration in addition to any
addresses autoconfigured using stateless address
autoconfiguration. The use of this flag is
described in [ADDRCONF].


Cool! I love it when I guess correctly! :)

So, back to the problem at hand... I don't see anything in the dhcpv6s.conf man page that says you can set the M flag in RAs (or make it send RAs period). I think you need a real router capable of doing that function. I'll poke around bit more and see what I can see.

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raven
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Re: DHCPv6 Problem

Fri Apr 13, 2012 9:04 am

Found that on another forum:

Quick testing shows that when "Automatic" is used for the IPv6
setting, OS X will correctly look at the A, M, and O flags of an IPv6
RA and make use of DHCPv6 when instructed to.
http://ccie20728.wordpress.com/

'

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