On 2016-02-01, LÉVAI Dániel <[email protected]> wrote:
> obsd @ 2016-01-31T17:49:04 +0100:
>> On 31-01-16 17:13, LÉVAI Dániel wrote:
> [...]
>> >So turns out, that if I request anything other than sla_id 0 or 1, I get
>> >another subnet, but with a /72 prefix. Also, using:
>> >ia_pd 1 re1/1 athn0/2 athn1/3
>> >... resulted in the same subnet/prefix sent to me, for all interfaces.
>> >
>> >For some reason I had to increment the sla_ids by 4 to get another
>> >subnet. So:
>> >ia_pd 1 re1/1 athn0/4 athn1/8
>> >... actually worked, and got three different subnets, but all came with
>> >a /72 prefix. And for some other reason, none of my devices (Linux,
>> >Android, Chromecast...) would accept a /72 address advertised, so
>> >although they all got a reply for their rtsol, they ignored it...
>
>
>> A /72 should not work (and indeed does not work as you found out)! The
>> smallest subnet (with the exception of a /127 /128) is /64. Your ISP is
>> doing The Wrong Thing (tm). Instead your ISP should provide you with a /56
>> (for 256 subnets) or, even better, with a /48, where you would have 65536
>> subnets. The latter is the preferred standard although some ISP's do not
>> understand the sheer size of IPv6, and therefore think that they are wasting
>> space handing out /48's. NANOG is full of discussions about this.
>>
>> See
>> http://serverfault.com/questions/426183/how-does-ipv6-subnetting-work-and-how-does-it-differ-from-ipv4-subnetting
>> for example.
>
> Interesting. I even tried to specifically request a prefix with
> ia_pd 1/::/64 [...]
> ... but alas it didn't make any difference.
>
> Could it be that this is the error of dhcpcd's implementation of the
> request, and not the ISP's? Before I try the customer services, I just
> want to make sure this is not PEBKAC.
I think the ISP are probably only handing out one /64, and while I'm
not sure how dhcpcd copes in that situation (you could ask on the dhcpcd
mailing list), it's probably doing the best it can under the conditions
(but not good enough for SLAAC).
Our tcpdump(8) doesn't decode dhcpv6 but if you use e.g. wireshark
you'll see something like this in the ISP's reply,
# tshark -i pppoe1 -V port 546 or port 547
[...]
Identity Association for Prefix Delegation
Option: Identity Association for Prefix Delegation (25)
Length: 41
Value: 00000002ffffffffffffffff001a0019ffffffffffffffff...
IAID: 00000002
T1: infinity
T2: infinity
IA Prefix
Option: IA Prefix (26)
Length: 25
Value: ffffffffffffffff302a0280117003000000000000000000...
Preferred lifetime: infinity
Valid lifetime: infinity
Prefix length: 48
Prefix address: 2a02:8011:7003::
And in your case I think it will probably have "Prefix length: 64".
If so, I'd start by asking the ISP if they can configure things to
let you have a /48 or /56.
