ipv6 notes

secrets of IPv6 prefix delegation on Comcast's business service

A /56 is allocated to the cable modem, but only the first /59 (0) is routed initially. The next one (xx20::/59) may be allocated, perhaps to wifi. Each delegation establishes a route for a new /59 subnet. By requesting all possible delegations, one can force the whole /56 to be routed. But, more importantly, performing a release before renew avoids changing the SLA (/59 subnet) number(s):

release dhcpv6-pd interface eth1
renew   dhcpv6-pd interface eth1

The relevant fragment of configuration for Ubiquiti's Edgerouter, reformatted for brevity:

interfaces {
    ethernet eth0 { ... }
    ethernet eth1 {
        address 10.1.10.100/16
        address 2603:3024:90c:9e00::2/60
        /* omitted firewall, ipv6 stanzas */
        ip { enable-proxy-arp }
        dhcpv6-pd {
            pd 0 {
                interface eth0 {
                    host-address ::6
                    no-dns
                    prefix-id :1
                    service slaac
                }
                interface eth2 {
                    host-address ::2
                    no-dns
                    prefix-id :2
                    service slaac
                }
                prefix-length /59
            }
            pd 1 { prefix-length /59 }
            pd 2 { prefix-length /59 }
            pd 3 { prefix-length /59 }
            pd 4 { prefix-length /59 }
            pd 5 { prefix-length /59 }
            pd 6 { prefix-length /59 }
            pd 7 { prefix-length /59 }
            rapid-commit disable
        }
    }
}

Thanks for these articles: prefix notes, based on prefix exhaustion by John Burwell.