DHCP6 in San Carlos CA: NoAddrsAvail

[dentongentry]

For some time I have been using the Sonic Labs 6RD 6in4 tunnel to 208.201.234.221 as described in https://members.sonic.net/labs/ipv6tunnel/#

I tried turning on DHCP6, hoping that the rollout described in https://sonicstatus.com/2023/03/22/san- ... intenance/ had completed in San Carlos. I do get a DHCP6 response now, but it is NoAddrsAvail.

Running a sniffer on the WAN link of my router I see it send a Router Solicitation, and receive a Router Advertisement.

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14:59:57.336074 IP6 (hlim 255, next-header ICMPv6 (58) payload length: 16) fe80::a236:9fff:fe59:19b0 > ff02::2: [icmp6 sum ok] ICMP6, router solicitation, length 16
 source link-address option (1), length 8 (1): a0:36:9f:59:19:b0
   0x0000:  a036 9f59 19b0

14:59:57.339102 IP6 (class 0xc0, hlim 255, next-header ICMPv6 (58) payload length: 24) fe80::5e5e:abff:fed5:a1c0 > ff02::1: [icmp6 sum ok] ICMP6, router advertisement, length 24
hop limit 64, Flags [managed], pref medium, router lifetime 1800s, reachable time 0ms, retrans timer 0ms
 source link-address option (1), length 8 (1): 5c:5e:ab:d5:a1:c0
   0x0000:  5c5e abd5 a1c0

I see my router send a DHCP6 Solicit, and get NoAddrsAvail in response.

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14:59:58.303453 IP6 (hlim 1, next-header UDP (17) payload length: 76) fe80::a236:9fff:fe59:19b0.546 > ff02::1:2.547: [udp sum ok] dhcp6 solicit (xid=42fee3 (client-ID hwaddr/time type 1 time 656596109 a0369f5919b0) (IA_NA IAID:0 T1:0 T2:0) (elapsed-time 0) (option-request DNS-server DNS-search-list) (IA_PD IAID:0 T1:0 T2:0))

14:59:58.596270 IP6 (class 0xc0, hlim 255, next-header ICMPv6 (58) payload length: 32) 2001:5a8:0:7::66 > ff02::1:ff59:19b0: [icmp6 sum ok] ICMP6, neighbor solicitation, length 32, who has fe80::a236:9fff:fe59:19b0
 source link-address option (1), length 8 (1): 5c:5e:ab:d5:a1:c0
   0x0000:  5c5e abd5 a1c0

14:59:58.681985 IP6 (class 0xc0, hlim 64, next-header UDP (17) payload length: 204) fe80::5e5e:abff:fed5:a1c0.547 > fe80::a236:9fff:fe59:19b0.546: [udp sum ok] dhcp6 advertise (xid=42fee3 (client-ID hwaddr/time type 1 time 656596109 a0369f5919b0) (server-ID vid 0000058335633a35) (IA_NA IAID:0 T1:0 T2:0 (status-code NoAddrsAvail)) (IA_PD IAID:0 T1:10800 T2:17280 (IA_PD-prefix 2001:5a8:413a:a300::/56 pltime:21600 vltime:21600)) (DNS-server 2001:5a8::11 2001:5a8::33))

I next see my router send a DHCP6 Request, and get another NoAddrsAvail. My router then tries sending Solicit a couple more times.

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14:59:59.313152 IP6 (hlim 1, next-header UDP (17) payload length: 141) fe80::a236:9fff:fe59:19b0.546 > ff02::1:2.547: [udp sum ok] dhcp6 request (xid=675ea (client-ID hwaddr/time type 1 time 656596109 a0369f5919b0) (server-ID vid 0000058335633a35) (IA_NA IAID:0 T1:0 T2:0 (status-code NoAddrsAvail)) (elapsed-time 0) (option-request DNS-server DNS-search-list) (IA_PD IAID:0 T1:0 T2:0 (IA_PD-prefix 2001:5a8:413a:a300::/56 pltime:21600 vltime:21600)))

14:59:59.405494 IP6 (class 0xc0, hlim 64, next-header UDP (17) payload length: 204) fe80::5e5e:abff:fed5:a1c0.547 > fe80::a236:9fff:fe59:19b0.546: [udp sum ok] dhcp6 reply (xid=675ea (client-ID hwaddr/time type 1 time 656596109 a0369f5919b0) (server-ID vid 0000058335633a35) (IA_NA IAID:0 T1:0 T2:0 (status-code NoAddrsAvail)) (IA_PD IAID:0 T1:10800 T2:17280 (IA_PD-prefix 2001:5a8:413a:a300::/56 pltime:21600 vltime:21600)) (DNS-server 2001:5a8::11 2001:5a8::33))

14:59:59.750227 IP6 (hlim 1, next-header UDP (17) payload length: 60) fe80::a236:9fff:fe59:19b0.546 > ff02::1:2.547: [udp sum ok] dhcp6 solicit (xid=a2b6aa (client-ID hwaddr/time type 1 time 656596109 a0369f5919b0) (IA_NA IAID:0 T1:0 T2:0) (elapsed-time 0) (option-request DNS-server DNS-search-list))

15:00:00.884813 IP6 (hlim 1, next-header UDP (17) payload length: 60) fe80::a236:9fff:fe59:19b0.546 > ff02::1:2.547: [udp sum ok] dhcp6 solicit (xid=a2b6aa (client-ID hwaddr/time type 1 time 656596109 a0369f5919b0) (IA_NA IAID:0 T1:0 T2:0) (elapsed-time 123) (option-request DNS-server DNS-search-list))

[msiegen]

Hi dentongentry,

In your packet capture your router is soliciting two kinds of IPv6 address, an IA_NA and an IA_PD. IA_NA is a single address for the router itself to use and IA_PD is a delegated prefix that the router can subdivide and assign to downstream subnets on your home LAN.

Sonic only supports IA_PD, and that part of the response looks successful as you got a /56. The NoAddrsAvail error is for the IA_NA and is expected.

You may be able to reconfigure your router to not request an IA_NA, and avoid the error. More importantly, make sure the router is assigning a /64 out of the IA_PD downstream to your LAN. The router can then use its LAN address to reach the outside world, so there's no need for a separate IA_NA address.

[dentongentry]

Thank you, and for the benefit of anyone finding this in the future: this all worked. I configured my router to not request an address for itself and to only request a delegated prefix. I set the LAN interface to follow the prefix assigned to the WAN, so the devices within the home use the first delegated prefix.

The router itself doesn't currently get an IPv6 address for its own use, but this isn't terribly concerning to me. I think I could configure it to make an address for itself as the ::1 address of one of the prefixes, but have no pressing need to do so right now.