dhcpcd-discuss

On 10/07/2014 12:10, Andrew Cooks wrote:
> Hi Roy
>
> On Thu, Jul 10, 2014 at 5:35 PM, Roy Marples <roy@xxxxxxxxxxxx> wrote:
> > For IPv4 there is only ever one address. For IPv6, well, there are 
> > quite a
> > few!
>
> Oh. Having multiple IPv4 addresses is common enough, but I didn't
> realise that dhcp can only assign one and that dhcpv6 is different.
>
> > DHCPv6 reasons have the suffix of 6
> > BOUND6, REBIND6, REBOOT6, etc. They generally mirror the IPv4 reasons.
> > In this instance, the addresses are held within IA options as an array
> > dhcp6_ia_na1_ia_addr1=addr1
> > dhcp6_ia_na1_ia_addr2=addr2
> > dhcp6_ia_na2_ia_addr1=addr3
> > dhcp6_ia_ta1_ia_addr1=addr4
> > dhcp6_ia_pd1_ia_prefix1=prefix4
> >
> > Basically, each IA type can have more than one IAID assigned - for 
> > example
> > one interface required for whatever reason two addresses, you could 
> > set two
> > IAIDS.
> > On the other hand, for your one IAID the server might want to hand you 
> > two
> > addresses as well. The above format allows for this.
> >
> > For IPv6 Router Advertisements, there is just the ROUTERADVERT reason
> > in this instance, all the current valid addresses from all routers are 
> > an
> > array
> > ra1_prefix=address
> > ra2_prefix=address
>
> Thanks. I think part of the problem is that I've been using Router
> Advertisement (with radvd) and don't understand the relationship
> between RA and DHCPv6 properly yet. I'll have to configure another
> VLAN with DHCPv6 and without RA for more tests.

An RA typically has a O and M bits.
O means get Other information only via DHCPv6, such as DNS setup.
M means get an Address and Other information via DHCPv6.
No bits set generally means there is no DHCPv6 server on the network
The RA can also send a prefix (like subnet) and if it's a router 
(default route) or not.

For dhcpcd, we only initiate DHCPv6 by default if the M or O bits are 
set.
You can force DHCPv6 without an RA though.

> The second part that I don't understand yet is whether it's not
> feasible to track all RA-assigned addresses or not dhpcd's concern
> what those addresses are.

dhcpcd does track these if you set ipv6ra_own in dhcpcd.conf, otherwise 
it won't.

> > For the dhcpcd-dbus and dhcpcd-ui projects we only look at the 1st NA
> > address.
>
> I wasn't aware of dhcpcd-dbus, so I'll definitely have a look. Does
> either dhcpcd-dbus or dhcpcd-ui track enough state to be able to
> report changes to RA-assigned addresses?

If dhcpcd is controlling RA then yes.

> > Others whilst may exist, typically they won't in real world usage. If 
> > they
> > do, the chances are you won't be running a GUI on the device itself, 
> > web
> > front end maybe.
>
> The device I'm working on has both an LCD display and a web interface.
> One part of the use case is to report the new address to the user when
> a cable is plugged in. So, while the user can go nuts with address
> assignment, we'd still like to report something sensible. We report
> only the first IPv4 address and first global scope IPv6 address
> through the event mechanism, but the complete list is in a menu if the
> user needs to see all of them.
>
> Since dhcpcd made everything so elegantly simple with link detection,
> static addresses and ip4ll, I was hoping that IPv6 RA could be
> similar. If not, I'll create a little script to track all RA assigned
> addresses, but I think that state should be kept out of the
> applications, if possible.
>
> Thanks for the great software and the help!

You're welcome :)

Thanks

Roy