Native IPv6 from Elisa FTTH
Thursday, September 25. 2025
My beloved ISP whom I love to hate has finally ... after all the two decades of waiting ... in Their infinite wisdom ... decided to grant us mere humans, humble payers of their monthly bills a native IPv6.
This is easily a day I thought would never happen. Like ever.
Eight years ago, when I was living in Stockholm, I had proper and good IPv6. There is a blog post of that with title Com Hem offering IPv6 via DHCPv6 to its customers.
By this post, I don't want to judge ongoing work nor say anything negative. This is just a heads-up. Something is about to happen. Everything isn't like it should be, but I have had patience this far. I can wait a bit longer.
Current Status
Here is a list of my observations as of 25th Sep 2025:
- There is no SLAAC yet. Delivery is via DHCPv6.
- One, as in a single, IPv6-address per DHCP-client host ID. I don't know how many addresses would I be able to extract. IPv6 has a "few" of them.
- No Prefix Delegation. 1 IPv6, no more. Not possible to run a LAN at this point.
- No default gateway in the DHCPv6 options. DNS ok. Connectivity to Internet is not there yet.
- No ISP firewall. Example: outgoing SMTP to TCP/25 egresses ok.
- Incoming IPv6 ok.
I'm sure many of these things will change to better and improve even during upcoming weeks and months.
Overcoming the obstacle: Figuring out a default gateway
Oh, did I mention there is no default gateway? That's a blocker!
Good thing is, that there is a gateway and it does route your IPv6-traffic as you'd expect. Getting the address is bit tricky and ISP doesn't announce it. (Credit: mijutu)
Running:
tcpdump -i eth0 -vv 'udp and (port 546 or port 547)'
while flipping the interface down&up will reveal something like this:
21:40:50.541022
IP6 (class 0xc0, hlim 255, next-header UDP (17) payload length: 144)
fe80::12e8:78ff:fe23:5401.dhcpv6-server > my-precious-box.dhcpv6-client:
[udp sum ok] dhcp6 advertise
That long porridge of a line is split up for clarity. The good bit is fe80::12e8:78ff:fe23:5401.dhcpv6-server. Now I have the link-local address of the DHCPv6-server. What would be the odds, it would also route my traffic if asked nicely?
ip -6 route add default via fe80::12e8:78ff:fe23:5401 dev eth0
Testing the Thing
Oh yes! My typical IPv6-test of ping -6 -c 5 ftp.funet.fi will yield:
PING ftp.funet.fi (2001:708:10:8::2) 56 data bytes
64 bytes from ipv6.ftp.funet.fi (2001:708:10:8::2): icmp_seq=1 ttl=60 time=5.42 ms
64 bytes from ipv6.ftp.funet.fi (2001:708:10:8::2): icmp_seq=2 ttl=60 time=5.34 ms
64 bytes from ipv6.ftp.funet.fi (2001:708:10:8::2): icmp_seq=3 ttl=60 time=5.29 ms
64 bytes from ipv6.ftp.funet.fi (2001:708:10:8::2): icmp_seq=4 ttl=60 time=5.31 ms
64 bytes from ipv6.ftp.funet.fi (2001:708:10:8::2): icmp_seq=5 ttl=60 time=5.39 ms
Outgoing SSH/HTTP/whatever works ok. Incoming SSH and HTTPS work ok. Everything works! Test-ipv6.com result:
Cloudflare Speedtest result:
This is very flaky. I ran it from Linux console over X11.
Also, the typical Speedtest.net, which I'd typically run, won't support IPv6 at all.
Finally
I'm so excited! I can not wait for Elisa's project to complete
eqez on :
Since Elisa currently doesn't grant standard DHCPv6 Prefix Delegation (PD) but provides a prefix via SLAAC, you can use UniFi's Single Network feature to map that single prefix directly to your primary LAN:
WAN Settings (Internet 1):
IPv6 Connection: Set to SLAAC.
Delegation Type: Select Single Network (instead of Prefix Delegation).
LAN Settings (Networks -> Default):
IPv6 Interface Type: Set to Prefix Delegation.
Prefix Delegation Interface: Select Internet 1.
Prefix Delegation ID: Leave on Auto.
By selecting Single Network on the WAN interface, UniFi takes the single /64 prefix received from Elisa and attaches it directly to your primary LAN segment. Your local clients will immediately receive native public 2001:... addresses via SLAAC. This only works for a single network/VLAN because only one /64 is advertised, but it gives you a fully functional, native IPv6 setup for your main network.