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DHCPv6 prefix and delegation length unnecessarily limited
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Description

For DHCPv6 PD, the following commands exist:

set service dhcpv6-server shared-network-name <name> subnet <prefix> prefix-delegation prefix <pd-prefix> prefix-length <length>
set service dhcpv6-server shared-network-name <name> subnet <prefix> prefix-delegation prefix <pd-prefix> delegated-length <length>

The VyOS CLI limits the prefix-length from 32 to 64, and the delegated length from 32 to 96.

The underlying kea DHCPv6 server however does not have that limitation, it supports values from 1 to 128, as long as delegated-prefix is not smaller than the prefix length.

Why is this artificial limit introduced and can it be lifted. I have a situation where subnets use a /112 prefix, on which I can not configure SLAAC at the moment.

Details

Version
1.5-20260519
Is it a breaking change?
Perfectly compatible
Issue type
Unspecified (please specify)

Event Timeline

Obviously, I meant DHCPv6-PD, not SLAAC.

@WanWizard despite Kea's support for longer delegated prefix lengths, in my opinion the delegated prefix length should also be restricted to a maximum of /64. See https://datatracker.ietf.org/doc/html/rfc6177 for the best current practice regarding delegation of prefixes to end sites.

That may be your opinion, which is fine, as you clearly don't have a need for it. I do, and VyOS' python validation rule is the only thing stopping me.

I am dealing with a single /64 which needs to be split over lots of subnets, and I have no choice in the matter.