IPv6 connectivity failure from AS205100 to Fly.io Anycast network

General
1

Hello Fly.io Support,

IPv6 connections from the F3 Netze network (AS205100) to Fly.io are timing out.

Affected application:

  • Hostname: srv.treesy.com
  • Fly IPv6: 2a09:8280:1::c1:9a47:0
  • Source prefix: 2a0b:f4c0:58:1::/64
  • F3 Netze aggregate: 2a0b:f4c0::/40
  • Destination network: Fly.io AS40509

The DNS configuration is correct, and IPv4 connectivity to the application at 66.241.124.111 works normally.

This appears to affect Fly.io IPv6 generally from this source network, not only my application:

curl.exe -6 -I --connect-timeout 10 https://debug.fly.dev
curl: (28) Connection timed out after 10000 milliseconds

Other IPv6 destinations, including Google, are reachable from the same client.

A packet capture on the Freifunk router shows repeated TCP SYN packets being forwarded towards 2a09:8280:1::c1:9a47:0:443. The hop limit decreases from 63 to 62, confirming that the packets are forwarded upstream. No SYN-ACK or other response arrives.

Example timestamp: October 6, 2026, around 11:21 CEST.

Could you please check:

  • The return route from Fly.io/AS40509 to 2a0b:f4c0::/40 and specifically 2a0b:f4c0:58:1::/64
  • IPv6 peering or routing between AS40509 and AS205100
  • Whether traffic from this source prefix reaches a Fly.io edge

I can provide the complete packet capture and IPv6 traceroute if required.

Thank you.

2

hi, could you provide a traceroute (or mtr -rwbzo "LSD NABVW" 2a09:8280:1::c1:9a47:0)?

I tried to traceroute from our end and got a route well within the AS205100 network:

1859472c716738:/# mtr -rwbzo LSD\ NABVW 2a0b:f4c0:58:1::1
Start: 2026-10-06T16:34:01+0000
HOST: 1859472c716738                                                                                             Loss%   Snt Drop   Last   Avg  Best StDev  Wrst
  1. AS???         fdaa:3:752b:a7b:522:cd9c:9990:1 (fdaa:3:752b:a7b:522:cd9c:9990:1)                              0.0%    10    0    2.8   2.8   2.5   0.3   3.5
  2. AS???         fdaf:a7b:14d:: (fdaf:a7b:14d::)                                                                0.0%    10    0    0.7   1.0   0.7   0.7   2.9
  3. AS60068       2a02:6ea0:cf2d::1336 (2a02:6ea0:cf2d::1336)                                                    0.0%    10    0    0.7   0.8   0.6   0.2   1.4
  4. AS???         vl251.fra-itx7-core-2.cdn77.com (2a02:6ea0:1:6::52)                                            0.0%    10    0    1.0   1.2   1.0   0.1   1.3
  5. AS???         lwlcom.peering.cz (2001:7f8:7f::137)                                                           0.0%    10    0    1.5   1.9   1.4   1.1   5.0
  6. AS50629       2a00:c380:f001::d5 (2a00:c380:f001::d5)                                                        0.0%    10    0    1.4   1.8   1.4   1.0   4.8
  7. AS41047       2a0e:a6c0::100:66:1:2 (2a0e:a6c0::100:66:1:2)                                                  0.0%    10    0    5.8   6.1   5.7   0.6   7.6
  8. AS205100      ext.netshelter.fra.f3netze.de (2a0b:f4c0:400::)                                                0.0%    10    0    6.2  37.7   5.9  99.8 321.8
  9. AS205100      2a0b.f4c0.00e3.0000.0000.0000.0000.0001.rdns.f3netze.de (2a0b:f4c0:e3::1)                      0.0%    10    0   15.9  43.1  13.7  91.3 302.8
 10. AS205100      2a0b.f4c0.00cd.0000.0000.0000.0000.0001.rdns.f3netze.de (2a0b:f4c0:cd::1)                      0.0%    10    0   17.7  42.3  15.4  82.5 277.2
 11. AS205100      2a0b.f4c0.00b9.ffff.0000.0000.0000.0001.rdns.f3netze.de (2a0b:f4c0:b9:ffff::1)                 0.0%    10    0   27.3  43.9  16.0  72.1 248.7
 12. AS205100      2a0b.f4c0.0058.0000.0000.0000.0000.0001.rdns.f3netze.de (2a0b:f4c0:58::1)                     20.0%    10    2   24.1  22.6  17.9   5.1  31.8
 13. AS205100      2a0b.f4c0.0058.0000.65b5.8b49.cff2.a7b7.rdns.f3netze.de (2a0b:f4c0:58:0:65b5:8b49:cff2:a7b7)  10.0%    10    1   20.0  24.8  18.8   9.3  47.7
 14. AS???         ???                                                                                           100.0    10   10    0.0   0.0   0.0   0.0   0.0
3

This is the result:

root@my-router:~# mtr -rwbzo “LSD NABVW” 2a09:8280:1::c1:9a47:0
Start: 2026-10-06T20:52:05+0200
HOST: my-router Loss% Snt Drop Last Avg Best StDev Wrst

  1. AS205100 2a0b.f4c0.00b9.ffff.0000.0000.0000.0001.rdns.f3netze.de (2a0b:f4c0 :b9:ffff::1) 0.0% 10 0 1.5 2.0 1.4 0.5 3.0
  2. AS205100 2a0b.f4c0.00cd.0000.0000.0000.0000.0001.rdns.f3netze.de (2a0b:f4c0 :cd::1) 0.0% 10 0 36.3 26.7 3.8 17.3 51.3
  3. AS205100 2a0b.f4c0.00e3.0000.0000.0000.0000.0001.rdns.f3netze.de (2a0b:f4c0 :e3::1) 10.0% 10 1 32.8 30.0 7.2 11.8 45.7
  4. AS205100 2a0b:f4c0:100:1::1 (2a0b:f4c0:100:1::1) 10.0% 10 1 51.2 34.2 8.6 16.7 59.1
  5. AS47147 2a00:11c0:47:3::9a (2a00:11c0:47:3::9a) 0.0% 10 0 47.1 38.4 22.4 11.9 55.3
  6. AS1299 nug-b2-link.ip.twelve99.net (2001:2035:0:272d::1) 0.0% 10 0 49.6 37.0 13.2 16.5 52.6
  7. AS1299 ffm-bb1-link.ip.twelve99.net (2001:2034:a:199::slight_smile: 0.0% 10 0 59.4 53.9 26.7 16.5 73.7
  8. AS1299 ffm-b5-link.ip.twelve99.net (2001:2034:a:71::1) 0.0% 10 0 39.6 40.7 12.3 15.0 55.1
  9. AS??? ??? 100.0 10 10 0.0 0.0 0.0 0.0 0.0

This has been sent at 18:52 UTC from my internet-gateway.

4

thank you, we’re looking into it