Change downstream prefix delegations size from /62 to /64

I get a /56 prefix from my ISP which gets distributed to 16 /60 prefixes for 16 different VLANs.

At the other end of each VLAN is an OpenWRT router which takes the /60 prefix and further delegates it to /62 prefixes for more downstream routers (OpenWRT x86 VM running for dev and testing purposes).

So basically my setup is so :

pfSense (2001:db8:a:a000/56) >>> VLANs 1 - 16 >>> OpenWRT Router VLAN 1 (2001:db8:a:a010::/60) >> OpenWRT VM (2001:0db8:000a:a014::/62)

I want to change the PD size to /64 for anything down the OpenWRT R VLAN1, but couldn't find the appropriate place for it. Please help !!

(My setup is bonkers, I know already !)

Did you try lower "option ip6assign" on the downstream interface (assuming "lan") of "OpenWrt Router VLAN 1" ?

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Thanks @jow, it worked !

For anyone else visiting this post in the future :

Edit /etc/config/network

and add option ip6assign 64 to the end of the downstream interface :

config interface 'VLAN100'
        option ifname 'eth0.100'
        option proto 'static'
        option netmask ''
        option ip6prefix '2001:db8::/60'
        list ip6addr '2001:db8::/60'
        option ip6assign 64

@jow It works, but now the VLAN 100 Interface is assigning /64 blocks from every single upstream IPv6 block, not just the one specified under

list ip6addr '2001:db8::/60'

What to do ?

Try specifying „option ip6class VLAN100“ as well - this should restrict delegation to prefixes originating from the VLAN100 interface.

Another alternative would be editing /etc/config/dhcp and adding „option prefix_filter 2001:db8::/60„ in the „config dhcp” section for vlan100 downstream

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