IPv6 elusive problem of PD configuration

[timur-davletshin]

On some occasions PD is not configured, just IPv6 address of WAN interface. As a result no IPv6 addresses are configured on client machines.

OpenWrt 25.12 RC3 (AX3200 and x86 were tested). Earlier releases were affected too. Hard to reproduce. Works 9 out 10 as intended.

/etc/config/network:

config interface 'loopback'
	option device 'lo'
	option proto 'static'
	option ipaddr '127.0.0.1'
	option netmask '255.0.0.0'

config globals 'globals'
	option ula_prefix 'fdaf:XXXX:XXXX::/48'
	option dhcp_default_duid '0004d19c3e412df74f56a1c77f1a6fd56f97'
	option packet_steering '1'

config device
	option name 'br-lan'
	option type 'bridge'
	list ports 'lan1'
	list ports 'lan2'
	list ports 'lan3'

config interface 'lan'
	option device 'br-lan'
	option proto 'static'
	option ipaddr '192.168.1.254'
	option netmask '255.255.255.0'
	option ip6assign '60'
	option ip6hint '10'

config interface 'wan'
	option proto 'pppoe'
	option device 'wan'
	option username 'EDITED'
	option password 'EDITED'
	option ipv6 '1'

config interface 'wan6'
	option proto 'dhcpv6'
	option device '@wan'
	option reqaddress 'try'
	option reqprefix 'auto'
	option norelease '1'

Tcpdump capture:

PD was configured:

14:30:29.426512 IP6 (flowlabel 0x63207, hlim 1, next-header UDP (17) payload length: 111) fe80::XXXX:XXXX:XXXX:3fe4.546 > ff02::1:2.547: [udp sum ok] dhcp6 solicit (xid=4ed8a4 (elapsed-time 0) (option-request SIP-servers-domain SIP-servers-address DNS-server DNS-search-list SNTP-servers NTP-server opt_67 opt_103 opt_82) (client-ID uuid d19c3e412df74f56a1c77f1a6fd56f97) (reconfigure-accept) (Client-FQDN) (IA_NA IAID:943556677 T1:0 T2:0) (IA_PD IAID:1 T1:0 T2:0))
14:30:29.437299 IP6 (hlim 255, next-header UDP (17) payload length: 185) fe80::XXXX:XXXX:XXXX:ecf3.547 > fe80::XXXX:XXXX:XXXX:3fe4.546: [udp sum ok] dhcp6 advertise (xid=4ed8a4 (client-ID uuid d19c3e412df74f56a1c77f1a6fd56f97) (server-ID hwaddr/time type 1 time 746747274 c8b6d35fa6bd) (preference 255) (IA_NA IAID:943556677 T1:0 T2:0 (status-code NoAddrsAvail)) (IA_PD IAID:1 T1:86400 T2:138240 (IA_PD-prefix 2a00:XXXX:XXXX:XX00::/56 pltime:172800 vltime:259200) (status-code Success)) (DNS-server 2a01:XXX:XXX::1:2 2a01:XXX:XXX::1:3))
14:30:29.437787 IP6 (flowlabel 0x63207, hlim 1, next-header UDP (17) payload length: 140) fe80::XXXX:XXXX:XXXX:3fe4.546 > ff02::1:2.547: [udp sum ok] dhcp6 request (xid=72f418 (elapsed-time 0) (option-request SIP-servers-domain SIP-servers-address DNS-server DNS-search-list SNTP-servers NTP-server opt_67 opt_103) (client-ID uuid d19c3e412df74f56a1c77f1a6fd56f97) (server-ID hwaddr/time type 1 time 746747274 c8b6d35fa6bd) (reconfigure-accept) (Client-FQDN) (IA_PD IAID:1 T1:0 T2:0 (IA_PD-prefix 2a00:XXXX:XXXX:XX00::/56 pltime:172800 vltime:259200)))
14:30:29.449532 IP6 (hlim 255, next-header UDP (17) payload length: 180) fe80::XXXX:XXXX:XXXX:ecf3.547 > fe80::XXXX:XXXX:XXXX:3fe4.546: [udp sum ok] dhcp6 reply (xid=72f418 (client-ID uuid d19c3e412df74f56a1c77f1a6fd56f97) (server-ID hwaddr/time type 1 time 746747274 c8b6d35fa6bd) (IA_NA IAID:943556677 T1:0 T2:0 (status-code NoAddrsAvail)) (IA_PD IAID:1 T1:86400 T2:138240 (IA_PD-prefix 2a00:XXXX:XXXX:XX00::/56 pltime:172800 vltime:259200) (status-code Success)) (DNS-server 2a01:XXX:XXX::1:2 2a01:XXX:XXX::1:3))

No PD was configured, just IPv6 address:

14:33:39.523538 IP6 (flowlabel 0x63207, hlim 1, next-header UDP (17) payload length: 111) fe80::XXXX:XXXX:XXXX:3fe4.546 > ff02::1:2.547: [udp sum ok] dhcp6 solicit (xid=b788b7 (elapsed-time 0) (option-request SIP-servers-domain SIP-servers-address DNS-server DNS-search-list SNTP-servers NTP-server opt_67 opt_103 opt_82) (client-ID uuid d19c3e412df74f56a1c77f1a6fd56f97) (reconfigure-accept) (Client-FQDN) (IA_NA IAID:943556677 T1:0 T2:0) (IA_PD IAID:1 T1:0 T2:0))
14:33:39.530563 IP6 (hlim 255, next-header UDP (17) payload length: 185) fe80::XXXX:XXXX:XXXX:ecf3.547 > fe80::XXXX:XXXX:XXXX:3fe4.546: [udp sum ok] dhcp6 advertise (xid=b788b7 (client-ID uuid d19c3e412df74f56a1c77f1a6fd56f97) (server-ID hwaddr/time type 1 time 746747274 c8b6d35fa6bd) (preference 255) (IA_NA IAID:943556677 T1:0 T2:0 (status-code NoAddrsAvail)) (IA_PD IAID:1 T1:86400 T2:138240 (IA_PD-prefix 2a00:XXXX:XXXX:XX00::/56 pltime:172800 vltime:259200) (status-code Success)) (DNS-server 2a01:XXX:XXX::1:2 2a01:XXX:XXX::1:3))
14:33:39.530988 IP6 (flowlabel 0x63207, hlim 1, next-header UDP (17) payload length: 140) fe80::XXXX:XXXX:XXXX:3fe4.546 > ff02::1:2.547: [udp sum ok] dhcp6 request (xid=600036 (elapsed-time 0) (option-request SIP-servers-domain SIP-servers-address DNS-server DNS-search-list SNTP-servers NTP-server opt_67 opt_103) (client-ID uuid d19c3e412df74f56a1c77f1a6fd56f97) (server-ID hwaddr/time type 1 time 746747274 c8b6d35fa6bd) (reconfigure-accept) (Client-FQDN) (IA_PD IAID:1 T1:0 T2:0 (IA_PD-prefix 2a00:XXXX:XXXX:XX00::/56 pltime:172800 vltime:259200)))
14:33:39.539737 IP6 (hlim 255, next-header UDP (17) payload length: 180) fe80::XXXX:XXXX:XXXX:ecf3.547 > fe80::XXXX:XXXX:XXXX:3fe4.546: [udp sum ok] dhcp6 reply (xid=600036 (client-ID uuid d19c3e412df74f56a1c77f1a6fd56f97) (server-ID hwaddr/time type 1 time 746747274 c8b6d35fa6bd) (IA_NA IAID:943556677 T1:0 T2:0 (status-code NoAddrsAvail)) (IA_PD IAID:1 T1:86400 T2:138240 (IA_PD-prefix 2a00:XXXX:XXXX:XX00::/56 pltime:172800 vltime:259200) (status-code Success)) (DNS-server 2a01:XXX:XXX::1:2 2a01:XXX:XXX::1:3))

It looks nearly identical to me. Probably I missed something.

[systemcrash]

They're identical....

[timur-davletshin]

They're identical....

That's the point. Problem is not in ISP, but in the way OpenWrt processes it. There are timing differences between messages, that could be the clue...

[systemcrash]

It's not a problem of timing, at least not in the client sense. A transaction can complete as quickly or not as it does, and succeed. It's not impossible that there are multiple upstream servers, and 1/10 times you draw the short straw. I've seen that before.

When you manage to capture this failing transaction, you can send an email to my commit address and we can take a look at it.

It's inconvenient, but you can run a tcpdump capturing as you have done (to a file) on wan only DHCPv6 traffic, including ICMPv6 RA and RS, so that the one time it fails, you manage to get it.