I'm seeing a problem with ipv6 that started 2-3 days ago. This is in Phoenix area.

IPv6 stopped working. When I started troubleshooting I narrowed the problem to DHCPv6.

My router sends DHCPv6 Solicit. Cox/Spectrum network answers with DHCPv6 Advertise (IA_NA address and IA_PD prefix). My router then sends DHCPv6 Request for that same offer. I do not receive a DHCPv6 Reply to those Requests.

It appears that the cox/spectrum DHCPv6 server isn't working, but I cannot confirm if it's the cox dhcp server or some other issue. I can confirm that I never get a reply to my DHCPv6 request.

I put a TAP in the network between my router and the cox network to confirm. Here is a sample conversation. I can provide the full pcap to cox support or we can re-create the problem live with the TAP in place.

Capture: inline tap between customer WAN Ethernet and fiber handoff
Time zone: America/Phoenix (MST)
Date: 2026-09-27
Wireshark filter: udp.port == 546 || udp.port == 547

Parties on this link
Customer router (my WAN): fe80::de0e:96ff:fe55:c710 UDP 546
DHCPv6 server (cox side): fe80::1a4a:6fff:fefa:e747 UDP 547
All-DHCP-servers multicast: ff02::1:2

Expected four-message exchange (RFC 3315)
1. Client Solicit
2. Server Advertise
3. Client Request (asks to use the offered address and prefix)
4. Server Reply (confirms the lease so the client can use IPv6)
What this capture shows: steps 1–3. Step 4 is not present after Request.

Sample starting at 19:02:27 (one full attempt)

1) 19:02:27.284 SOLICIT (customer → multicast)
fe80::de0e:96ff:fe55:c710.546 → ff02::1:2.547
dhcp6 solicit xid=bfffbf
Client-ID: MAC dc:0e:96:55:c7:10
Asking for: IA_NA (WAN address) and IA_PD (prefix)
Meaning: my router is looking for a DHCPv6 server.

2) 19:02:27.293 ADVERTISE (server → customer) ~9 ms later
fe80::1a4a:6fff:fefa:e747.547 → fe80::de0e:96ff:fe55:c710.546
dhcp6 advertise xid=bfffbf (same transaction as the Solicit)
Server-ID MAC: 00:50:56:b2:45:3b
Offered IA_NA: 2600:8800:ff04:3d0:7998:108a:791f:f5b4 (preferred/valid xxxxs)
Offered IA_PD: 2600:8800:1aa0:76::/64 (preferred/valid xxxxs)
DNS: 2001:578:3f::30 , 2001:578:3f:1::30
Meaning: a server on your network received the Solicit and offered
an address and a prefix. This packet reached my WAN.

3) 19:02:28.223 SOLICIT (customer retry, new xid=fdfff6)
Same as (1). Server Advertises again at 19:02:28.232 with the same
IA_NA and IA_PD (xid=fdfff6).

4) 19:02:28.235 REQUEST (customer → multicast)
fe80::de0e:96ff:fe55:c710.546 → ff02::1:2.547
dhcp6 request xid=fbeab6
Includes your Server-ID (00:50:56:b2:45:3b)
Requests the exact IA_NA and IA_PD from the Advertise
Meaning: my router accepted the offer and is asking to bind that
address and prefix. This is the message that needs a Reply.

5) 19:02:29.255 through 19:04:55.376 REQUEST retransmissions
Same Request contents, new xid each time, typical backoff
(~1s, 2s, 4s, 8s, 15s, 30s, …). Nine Requests in this attempt.
In this capture: no DHCPv6 Reply matching those Request xids.

Missing after (4) and (5)
DHCPv6 Reply from fe80::1a4a:6fff:fefa:e747:547
to fe80::de0e:96ff:fe55:c710:546
with the Request xid, confirming IA_NA and IA_PD.
Without that Reply, my router cannot install IPv6 (no WAN address,
no delegated prefix).

Same capture, Reply does occur — but only for Release

6) 19:04:55.656 RELEASE (customer → multicast)
dhcp6 release xid=ffebef
Same IA_NA and IA_PD as above

7) 19:04:55.746 REPLY (server → customer) ~90 ms later
dhcp6 reply xid=ffebef status-code Success
Meaning: Replies from this server do reach my WAN. I am not
receiving a Reply when the message is Request.

The 19:05:07 Solicit starts the same pattern again (Advertise, then
Request, no Reply in the remainder of the file).

What I need from IP/DHCPv6

Please check whether a DHCPv6 Reply to these Requests is sent on this
fiber/PON session. Filter: udp.port == 546 || udp.port == 547
times 19:02:27–19:05:08 MST 2026-09-27

Welcome to the Cox Community

Speed decrease after 5-8 mins (1-2Mbps)

KevinM2

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