Re: dhcpcd and routing of ipv6 prefixes

[Roy Marples <roy%marples.name@localhost>]

On 2016-06-14 19:43, Rhialto wrote:
> On Tue 14 Jun 2016 at 09:24:07 +0100, Roy Marples wrote:
> > On 13/06/2016 19:16, Rhialto wrote:
> > > On Mon 13 Jun 2016 at 20:14:51 +0200, Gert Doering wrote:
> > >> Hi,
> > >>
> > >> On Mon, Jun 13, 2016 at 08:08:25PM +0200, Rhialto wrote:
> > >>> On Mon 13 Jun 2016 at 12:50:09 +0100, Roy Marples wrote:
> > >>>>
> > >>>> On 12/06/2016 20:37, Rhialto wrote:
> > >>>>> re0: adding address 2001:984:4b2a:fc::1/62
> > >>>>> re0: pltime 3600 seconds, vltime 7200 seconds
> > >>>>> if_addaddress6: Invalid argument
> > >>>>
>
> > 	# get a /64 and assign it to re0
> > 	ia_pd 2 re0/0
> >
> > That is wrong, at least in the trunk version.
> > An SLA of zero without specifying the prefix length now just takes the
> > prefix as is and assigns it to one interface. What you want is this.
> >
> > 	# Try and make a /64, otherwise take what we're given.
> > 	# (delegated prefix length + interface index) <= 64
> > 	ia_pd 2 re0
> >
> > or
> >
> > 	# Try and make a /64, otherwise take what we're given.
> > 	# interface index could be >2 which fails when handed a /62.
> > 	ia_pd 2 re0/1
>
> I'm going to try this one:
>
> re1: delegated prefix 2001:984:4b2a:fc::/62
> re0: adding address 2001:984:4b2a:fd::1/64
> re0: acquired 600226.750768155, now 600226.752412916, diff 0.001644761
> re0: adj pltime 3600 seconds, vltime 7200 seconds
> re0: adding route to 2001:984:4b2a:fd::/64
>
> it now assigns a /64 addres (but a different one!) and the error 
> message is
> gone. So I'm going to try the next one with a sla_id of 0 instead:
>
> > or
> >
> > 	# Force a /64.
> > 	# We could use an SLA of 0 here, but it's more clear to use >0.
> > 	ia_pd 2 re0/1/64
>   	ia_pd 2 re0/0/64
>
> re1: delegated prefix 2001:984:4b2a:fc::/62
> re0: adding address 2001:984:4b2a:fc::1/64
> re0: acquired 600583.885924426, now 600583.887089799, diff 0.001165373
> re0: adj pltime 3600 seconds, vltime 7200 seconds
> re0: adding route to 2001:984:4b2a:fc::/64
>
> and also no error message. I think I'll stay with this one for now.

Good that it's fixed!
Hopefully you can re-test the faulty config if once I fix it problem 
(sadly i ran out of time today).

> > Comments on how to improve dhcpcd.conf(5) to reflect this are welcome 
> > :)
>
> I've been staring a long time at the various ids that are around.
> A short glossary of them, including their range of values, their 
> default
> value, and in which context they must be unique, would be welcome.
>
>     "sla_id is an integer which must be unique inside the iaid and is 
> added
>     to the prefix which must fit inside prefix_len less the length of 
> the
>     delegated prefix."
>
> could probably be clearer as something like
>
>     "sla_id (site-level aggregation identifier) is a small integer 
> which
>     must be unique inside the iaid and if omitted defaults to the
>     interface index. The delegated prefix is zero-padded to the
>     prefix_len, and then the sla_id is added. This must fit within the
>     padding, i.e. the prefix as delegated must not change. Otherwise
>     XYZ happens. This new prefix is used to form addresses."
>
> It isn't clear to me what happens for instance if the delegated prefix
> is already 64 bits, the sla_id is 1 (requiring 1 bit) and a total 
> prefix
> length of 64 is requested. Does something get truncated?

dhcpcd will refuse to delegate from the prefix because 64 (delegated 
length) + 1 (sla id in bits) + 64 is greater than /128.

>     "The interface index is a small integer, assigned by the operating
>     system, identifying each interface, and is essentially equivalent 
> to
>     the interface's name."
>
> How do I see the interface index anyway? ifconfig doesn't seem to show
> it.
>
> I see that https://tools.ietf.org/html/rfc3315 has a nice glossary, I
> suppose descriptions of duid, ia, iaid could also be borrowed from 
> there.
>
>     "The duid (DHCP Unique Identifier) is an identification of a DHCP
>     participant; each DHCP client and server have exactly one DUID."
>
> Some typos I noticed in the manual:
>
>      hostname name
>              Sends hostname to the DHCP server so it can be registered 
> in DNS.
>              If hostname is an empty string then the current system 
> hostname
>              is sent.  If hostname is a FQDN (ie, contains a .) then it 
> will
>              be encoded as such.
>
> several `hostname's should be `name'.

http://roy.marples.name/projects/dhcpcd/info/e1a9ac90521b5537

>      ia_na [iaid [/ address]]
>              Request a DHCPv6 Normal Address for iaid.  iaid defaults 
> to the
>              iaid option as described above.  You can request more than 
> one
>              ia_na by specifying a unique iaid for each one.

> what does `address' do? Is it the same/similar as `suffix' in ia_pd?

It literally requests the address you specify.
IA_NA addresses don't have a prefix as such and will always use a /128.

>     ia_pd ...
> 	    In this case prefix_len is increased to the highest multiple
> 	    of 8 that can accommodate the sla_id.
>
> should that be the lowest multiple of 8? (This might actually answer my
> question about too-long sla_ids above)

I think highest is correct?
Anyone else think othewise?

Thanks

Roy