IPv6 PD question - getting error "network mask too short prefix6"

[imk82]

Hi all,

a question for understanding how ISC DHCPv6 configuration is desired to work. What I want is to delegate /57 out of my /56 prefix to a downstream router. I try the following configuration (see screenshot as well):

Code Select Expand


Prefix Delegation Range
from: ::80:0000:0000:0000:0000
to: ::ff:ffff:ffff:ffff:ffff


But, this is not working, I get a "network mask too short prefix6" error message in the log if trying. On the other hand a:

Code Select Expand


Prefix Delegation Range
from: ::80:0000:0000:0000:0000
to: ::80:0000:0000:0000:0000


is accepted.

Has someone experience here and can explain the logic behind to me?

From my understanding, the first config is correct while the last is not.

Thanks and best regards
Robert

[dseven]

TL;DR - this (last post) might be worth a read: https://forum.opnsense.org/index.php?topic=31076.msg149989#msg149989

[stefan00]

Long answer short: Your second settings are correct.

If you're interested in the logic behind, read the post dseven mentioned above. This issue has never been resolved. ISCs dhcpd.conf.5 is simply a bit unclear about the correct configuration. OPNSenses UI help follows this, making it harder to understand.

In your case:

available network           ::/56
first available /57 prefix  ::/57
last available /57 prefix   ::80/57


So if you want to delegate the second /57 part of your network, ::80/57 is the only available available prefix it can delegate and choose from.

Hint: Think of the fields "from" and "to" as "first prefix block available" and "last prefix block available".

You only have one /57 delegatable prefix available. So ::80/57 are both start and end = "from" and "to".