IPv6-PD DHCP device assignment issues?

Installing and Using OpenWrt
1

I am looking for some assistance in tracking down what seems to be an anomily in the IPv6 DHCP device assignment.

A little background: Having a sole available provider that had no intention of moving to IPv6 in my lifetime, I removed most IP6 capabilities from my mvebu Snapshot builds. Don't work, don't care sort of thing. Well, I just made my first X86-64 build, and obviously, I couldn't sysupgrade, so starting with defaults, I rebuilt my network, massaged my backup and restored my 'shinit, SSL keys, and package configs. Apparently everything works from what I can see.

Then I noticed that the LuCi Overview screen tells me my new provider delegates a /56 IPv6, and I set about accommodating it into my network.

3 of my most recent devices come back with both GUA/LUA addresses that I can at least ping6 successfully, so to all intents and purposes, "it all works".

Here is my problem. 1 IPv6 address (both GUA and LUA) follows my expectation that the ip6 addressing assignment is based on the dhcp static v4 IP octet 4 in the IPv6 address assignment, but for some reason the other two IPv6 lease assignments do not. As well, I cannot understand how the dhcpv6.script and dhcpv6.sh scripts parse these odd hostnames from my /etc/config/dhcp.

Here is my /etc/config/dhcp:

Summary 
config dnsmasq
	option domainneeded '1'
	option localise_queries '1'
	option rebind_protection '0'
	option local '/lan/'
	option domain 'lan'
	option expandhosts '1'
	option authoritative '1'
	option readethers '1'
	option leasefile '/tmp/dhcp.leases'
	option localservice '1'
	option noresolv '1'
	option localuse '1'
	option confdir '/tmp/dnsmasq.d'
	option sequential_ip '1'
	option cachesize '0'
	list server '127.0.0.53'

config dhcp 'lan'
	option interface 'lan'
	option leasetime '12h'
	option dhcpv4 'server'
	option dhcpv6 'server'
	option ra 'server'
	list ra_flags 'managed-config'
	list ra_flags 'other-config'
	option ra_slaac '1'
	option start '2'
	option limit '39'

config dhcp 'wan'
	option interface 'wan'
	option ignore '1'

config odhcpd 'odhcpd'
	option maindhcp '0'
	option leasefile '/tmp/hosts/odhcpd'
	option leasetrigger '/usr/sbin/odhcpd-update'
	option loglevel '4'

config host
	option name 'HP-Elite-Network-Monitor'
	option ip '10.10.1.100'
	option mac 'redacted'
	option leasetime 'infinite'
	option dns '1'

config domain
	option ip '10.10.1.100'
	option name 'HP-Elite-Network-Monitor'

config host
	option name 'HP-OfficeJet-3830'
	list mac 'redacted'
	option ip '10.10.1.110'
	option leasetime 'infinite'
	option dns '1'

config domain
	option name 'HP-OfficeJet-3830'
	option ip '10.10.1.110'

config host
	option name 'Apple-iPad-Air2'
	option ip '10.10.1.115'
	option mac 'redacted'
	option leasetime 'infinite'
	option dns '1'

config domain
	option name 'Apple-iPad-Air2'
	option ip '10.10.1.115'

config host
	option name 'BBPB'
	option ip '10.10.1.120'
	option mac 'redacted'
	option leasetime 'infinite'
	option dns '1'

config domain
	option name 'BBPB'
	option ip '10.10.1.120'

config host
	option name 'Media-Box'
	option ip '10.10.1.125'
	option mac 'redacted'
	option leasetime 'infinite'
	option dns '1'

config domain
	option name 'Media-Box'
	option ip '10.10.1.125'

config host
	option name 'Vostro-7620-Buildroot'
	option ip '10.10.1.240'
	option mac 'redacted'
	option leasetime 'infinite'
	option dns '1'

config domain
	option name 'Vostro-7620-BuildRoot'
	option ip '10.10.1.240'

config host
	option name 'Vostro-7620-ETH'
	option ip '10.10.1.241'
	list mac 'redacted'
	option leasetime 'infinite'
	option dns '1'

config domain
	option name 'Vostro-7620-ETH'
	option ip '10.10.1.241'

config host
	option name 'UniFi-AP-Lite'
	option ip '10.10.1.245'
	option mac 'redacted'
	option leasetime 'infinite'
	option dns '1'

config domain
	option name 'UniFi-AP-Lite'
	option ip '10.10.1.245'

config host
	option name 'Netgear-GS308T'
	option ip '10.10.1.250'
	option mac 'redacted'
	option leasetime 'infinite'
	option dns '1'

config domain
	option name 'Netgear-GS308T'
	option ip '10.10.1.250

and my /var/hosts/odhcpd

Summary 
2xx5:5xx8:xxf7:3200::115	Apple-iPad-Air2
fd23:781d:e3cc::115	Apple-iPad-Air2
# br-lan 0001000123d4064becadb86edd74 0 Apple-iPad-Air2 1705764248 115 128 2xx5:5xx8:xxf7:3200::115/128 fd23:781d:e3cc::115/128

2xx5:5xx8:xxf7:3200::23e	HP-OfficeJet-3830-AIO
fd23:781d:e3cc::23e	HP-OfficeJet-3830-AIO
# br-lan 00030001c8d9d25010d9 2 HP-OfficeJet-3830-AIO 1705764248 23e 128 2xx5:5xx8:xxf7:3200::23e/128 fd23:781d:e3cc::23e/128

2xx5:5xx8:xxf7:3200::26a	Vostro-7620
fd23:781d:e3cc::26a	Vostro-7620
# br-lan 0004d87e2e268dedc9c2e1bf71e06cdbda57 6cbc577e Vostro-7620 1705764248 26a 128 2xx5:5xx8:xxf7:3200::26a/128 fd23:781d:e3cc::26a/128

Am I missing something here? Or is this just nothing to be concerned about, situation normal?

2

Yes.

This assumption is incorrect, there is nothing special about "octet 4", nor any relation to the IPv4 assignments at all. If you want to set IPv6 addresses, you need to configure duid and hostid in addition to your desired IPv4 settings (/etc/config/dhcp) - and keep in mind that (e.g.) android and SLAAC behave completely different…

1 Like
3

SLAAC means that the client on its own (usually at random) chooses the last 64 bits of its IP attached to the announced /64 prefix. The router has no control of that IP choice. Android always uses SLAAC, it intentionally does not support DHCPv6.

If the network offers both methods, Windows will take both an DHCPv6 and a random SLAAC, and periodically rotate to new SLAAC for privacy reasons.