Secondary IPv6 (2a07:a8c1::) unreachable — 100% packet loss from South Korea

Yongjun_K
14 hrs ago
2replies

Symptom
Since a few weeks ago, the secondary IPv6 anycast address (2a07:a8c1::)
has been 100% unreachable from my network in South Korea. Primary IPv6
(2a07:a8c0::) and both IPv4 anycast addresses (45.90.28.18, 45.90.30.18)
work perfectly with normal latency.

This causes real problems: any client application whose network stack
doesn't implement Happy Eyeballs properly (Unity-based games, winget,
some vendor updaters) gets stuck for several seconds to minutes per
connection attempt when it happens to pick the dead secondary IPv6
address, before eventually failing outright. Browsers are unaffected
since they race multiple addresses concurrently.

Diagnostics

C:\Users\yongj>ping 45.90.28.18
Pinging 45.90.28.18 with 32 bytes of data:
Reply from 45.90.28.18: bytes=32 time=35ms TTL=51
Reply from 45.90.28.18: bytes=32 time=41ms TTL=51
Reply from 45.90.28.18: bytes=32 time=35ms TTL=51
Reply from 45.90.28.18: bytes=32 time=36ms TTL=51
Ping statistics for 45.90.28.18:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 35ms, Maximum = 41ms, Average = 36ms
C:\Users\yongj>ping 2a07:a8c0::[PROFILE_ID]
Pinging 2a07:a8c0::[PROFILE_ID] with 32 bytes of data:
Reply from 2a07:a8c0::[PROFILE_ID]: time=37ms
Reply from 2a07:a8c0::[PROFILE_ID]: time=38ms
Reply from 2a07:a8c0::[PROFILE_ID]: time=37ms
Reply from 2a07:a8c0::[PROFILE_ID]: time=36ms
Ping statistics for 2a07:a8c0::[PROFILE_ID]:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 36ms, Maximum = 38ms, Average = 37ms
C:\Users\yongj>ping 45.90.30.18
Pinging 45.90.30.18 with 32 bytes of data:
Reply from 45.90.30.18: bytes=32 time=32ms TTL=51
Reply from 45.90.30.18: bytes=32 time=33ms TTL=51
Reply from 45.90.30.18: bytes=32 time=32ms TTL=51
Reply from 45.90.30.18: bytes=32 time=33ms TTL=51
Ping statistics for 45.90.30.18:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 32ms, Maximum = 33ms, Average = 32ms
C:\Users\yongj>ping 2a07:a8c1::[PROFILE_ID]
Pinging 2a07:a8c1::[PROFILE_ID] with 32 bytes of data:
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Ping statistics for 2a07:a8c1::[PROFILE_ID]:
    Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),
---
# From home network (LG U+ - AS17858)
PS C:\Users\yongj> tracert -6 2a07:a8c1::[PROFILE_ID]
Tracing route to dns2.nextdns.io [2a07:a8c1::[PROFILE_ID]]
over a maximum of 30 hops:
  1    <1 ms    <1 ms    <1 ms  fdab:d9c3:fb50:20::1
  2     1 ms     2 ms     1 ms  2406:5900:3:5def::1
  3     1 ms     1 ms     1 ms  2001:270:fb02:10:245:167:160:1
  4     1 ms     1 ms     1 ms  2001:270:fa02:1:213:2:68:1
  5     3 ms     4 ms     2 ms  2001:270:fb00:1:213:112:32:1
  6     2 ms     2 ms     2 ms  2001:270:fa00:1:213:114:36:1
  7     3 ms     2 ms     3 ms  2001:270:fb00:100:66:51:84:1
  8    28 ms    30 ms    29 ms  2001:270:fb00:100:65:115:36:2
  9     3 ms     *        *     2400:8800:f100::48
 10    63 ms    62 ms    62 ms  2401:95c0:13f4:1:103:98:72:211
 11    62 ms    61 ms    61 ms  2401:95c0:13f4:1:103:98:72:210
 12     *        *        *     Request timed out.
 13     *        *        *     Request timed out.
 14     *        *        *     Request timed out.
 15     *        *        *     Request timed out.
 16     *        *        *     Request timed out.
 17     *        *        *     Request timed out.
 18     *        *        *     Request timed out.
 19     *        *        *     Request timed out.
 20     *        *        *     Request timed out.
 21     *        *        *     Request timed out.
 22     *        *        *     Request timed out.
 23     *        *        *     Request timed out.
 24     *        *        *     Request timed out.
 25     *        *        *     Request timed out.
 26     *        *        *     Request timed out.
 27     *        *        *     Request timed out.
 28     *        *        *     Request timed out.
 29     *        *        *     Request timed out.
 30     *        *        *     Request timed out.
Trace complete.
---
# From mobile data (Korea Telecom - AS4766)
PS C:\Users\yongj> tracert -6 2a07:a8c1::[PROFILE_ID]
Tracing route to 2a07:a8c1::[PROFILE_ID] over a maximum of 30 hops
  1     4 ms     4 ms     2 ms  2001:e60:9569:4276::33
  2     *        *        *     Request timed out.
  3    33 ms    23 ms    24 ms  2001:e60:e050:5006:0:1:1201:e
  4    36 ms    28 ms    20 ms  2001:e60:e050:5005:10:59:0:3e
  5    25 ms    18 ms    24 ms  2001:e60:e050:5005:10:59:1:c1
  6     *        *        *     Request timed out.
  7    43 ms    25 ms    43 ms  2001:e60:e050:5008:10:59:16:26
  8    31 ms    25 ms    47 ms  2001:e60:e050:5008:10:59:17:4
  9    36 ms    30 ms    29 ms  2001:e60:e050:5008:10:59:17:203
 10    35 ms    24 ms    22 ms  2001:e60:e050:5008:10:59:17:11
 11    38 ms    18 ms    23 ms  2001:e60:e050:5008:10:59:18:46
 12    33 ms    36 ms    66 ms  2001:e60:e050:5008:172:24:235:1
 13    20 ms    19 ms    40 ms  2001:e60:e0ff:0:110:69:16:41
 14    38 ms    29 ms    34 ms  2001:e60:e0ff:0:110:69:18:ee
 15    33 ms    38 ms    24 ms  2400:36::350:20
 16    32 ms    28 ms    24 ms  2400::100:112:174:45:75
 17    38 ms    36 ms    33 ms  2400::100:112:174:91:2
 18    59 ms     *        *     2400:8800:1f03:1c::1
 19    95 ms    90 ms     *     2401:95c0:13f4:1:103:98:72:211
 20    90 ms    83 ms    93 ms  2401:95c0:13f4:1:103:98:72:210
 21     *        *        *     Request timed out.
 22     *        *        *     Request timed out.
 23     *        *        *     Request timed out.
 24     *        *        *     Request timed out.
 25     *        *        *     Request timed out.
 26     *        *        *     Request timed out.
 27     *        *        *     Request timed out.
 28     *        *        *     Request timed out.
 29     *        *        *     Request timed out.
 30     *        *        *     Request timed out.
Trace complete.

Same 2a07:a8c1:: unreachability confirmed again when tethered to a mobile carrier network (different AS, different physical path).

Environment
- OS: Windows 11 (build 26200)
- Networks tested: home fiber ISP (LG U+) + separate mobile carrier (KT) (both South Korea)
- Consistently reproducible for the past several weeks.

Related reports
This looks like the same class of issue reported here before:
- https://help.nextdns.io/t/q6y8g68/secondary-anycast-ipv6-timing-out
- https://help.nextdns.io/t/m1yppjv/ipv6-anycast-2a07a8c0-2a07a8c1-unreachable-from-verizon-fios-ewr-region

Could you check the routing/BGP advertisement for the secondary IPv6
anycast prefix toward South Korea? My NextDNS profile ID is available
on request — I'd rather not post it publicly. Happy to run
nextdns.io/diag or provide a traceroute if that helps narrow it down.

Yongjun_K
13 hrs ago
Reported - view

Follow-up:

One thing worth calling out explicitly from the two traceroutes I
posted above: they converge at the exact same hop before dying.

LG U+ (home): hop 11/12 → 2401:95c0:13f4:1:103:98:72:210 / ...211
KT mobile: hop 19/20 → 2401:95c0:13f4:1:103:98:72:210 / ...211 (same IP)

Two completely unrelated Korean ASes hit the identical IP and then
both die at the exact same point past it. That strongly suggests the
break isn't at either ISP individually, but somewhere in a shared
upstream transit/peering path beyond that hop — possibly wherever
that IP block hands off toward the secondary anycast prefix.

I also ran the official diag tool for more detail:


Welcome to NextDNS network diagnostic tool.
This tool will capture latency and routing information regarding
the connectivity of your network with NextDNS.
The source code of this tool is available at https://github.com/nextdns/diag
Do you want to continue? (press enter to accept)
Testing IPv6 connectivity
  available: true
Fetching https://test.nextdns.io
  status: ok
  client: 122.47.166.130
  protocol: DOH
  dest IP: 45.90.28.18
  server: zepto-tyo-1
Fetching PoP name for ultra low latency primary IPv4 (ipv4.dns1.nextdns.io)
  vultr-sel: 4.115ms
Fetching PoP name for ultra low latency secondary IPv4 (ipv4.dns2.nextdns.io)
  vultr-tyo: 33.082ms
Fetching PoP name for anycast primary IPv4 (45.90.28.0)
  zepto-tyo: 35.782ms
Fetching PoP name for anycast secondary IPv4 (45.90.30.0)
  vultr-tyo: 38.729ms
Fetching PoP name for ultra low latency primary IPv6 (ipv6.dns1.nextdns.io)
  vultr-sel: 5.366ms
Fetching PoP name for ultra low latency secondary IPv6 (ipv6.dns2.nextdns.io)
  vultr-tyo: 33.942ms
Fetching PoP name for anycast primary IPv6 (2a07:a8c0::)
  zepto-hkg: 41.993ms
Fetching PoP name for anycast secondary IPv6 (2a07:a8c1::)
Fetch error: Get "https://dns.nextdns.io/info": dial tcp [2a07:a8c1::]:443: connectex: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond.
Pinging PoPs
  vultr-sel (IPv6): 3.633ms
  vultr-sel: 3.886ms
  vultr-tyo (IPv6): 32.607ms
  zepto-hkg (IPv6): 37.519ms
  anexia-hkg (IPv6): 39.587ms
  zepto-tpe (IPv6): 59.059ms
  zepto-tyo (IPv6): 140.667ms
  vultr-tyo: 32.095ms
  zepto-tyo: 34.347ms
  anexia-hkg: 39.568ms
  hostinginside-tpe: 55.341ms
  zepto-hkg: 63.182ms
  zepto-tpe: 80.529ms
  premiumrdp-mnl: 99.33ms
  lightnode-mnl: 128.667ms
Traceroute for ultra low latency primary IPv4 (141.164.63.208)
    2 122.47.166.129    1ms   *     *
    3 10.245.167.161    2ms   2ms   1ms
    4  1.213.100.197    2ms   1ms   1ms
    5  1.213.113.173    9ms  32ms   8ms
    6    100.68.2.78    1ms   1ms   1ms
    7   100.68.84.94    2ms   3ms   2ms
    8   100.68.89.50    2ms   3ms   3ms
    9 211.234.118.38    *     4ms   3ms
   10 203.246.164.210    8ms   9ms  11ms
   11  121.78.63.150    4ms   4ms   4ms
   12                   *     *     *
   13                   *     *     *
   14                   *     *     *
   15 141.164.63.208    3ms   3ms   4ms
Traceroute for ultra low latency secondary IPv4 (167.179.109.118)
    2                   *     *     *
    3 10.245.167.157    2ms   1ms   1ms
    4   1.208.100.93    2ms   1ms   1ms
    5  1.213.113.173    2ms   3ms   3ms
    6                   *     *     *
    7    100.65.51.5    2ms   2ms   2ms
    8  100.67.55.134   31ms  31ms  31ms
    9  100.67.58.146   31ms  31ms  31ms
   10 210.171.225.160   39ms  39ms  42ms
   11     10.71.3.26   32ms  33ms  32ms
   12    10.71.0.226   32ms  31ms  32ms
   13   66.42.47.184   32ms  31ms  32ms
   14 167.179.109.118   31ms  31ms  31ms
Traceroute for anycast primary IPv4 (45.90.28.0)
    2                   *     *     *
    3 10.245.167.161    2ms   1ms   2ms
    4  1.213.100.197    2ms   1ms   2ms
    5  1.208.113.173    3ms  11ms  10ms
    6                   *     *     *
    7    100.66.52.9    2ms   2ms   1ms
    8  100.65.115.38    3ms   3ms   3ms
    9  129.250.8.217   29ms  28ms  28ms
   10  129.250.6.102   28ms  28ms  29ms
   11   129.250.7.78    *    35ms   *
   12   129.250.7.14   36ms  40ms  36ms
   13   61.120.145.2   39ms  38ms  38ms
   14   84.17.33.105   33ms  34ms  34ms
   15 199.119.64.143   33ms  34ms  35ms
   16 103.170.232.11   33ms  34ms  35ms
   17     45.90.28.0   34ms  35ms  34ms
Traceroute for anycast secondary IPv4 (45.90.30.0)
    2                   *     *     *
    3 10.245.167.161    2ms   1ms   1ms
    4     1.213.2.69    2ms   3ms   3ms
    5   1.208.112.33    2ms   3ms   3ms
    6                   *     *     *
    7    100.65.52.1    4ms   3ms   3ms
    8  100.67.55.138   33ms  33ms  32ms
    9  100.67.58.130   36ms  36ms  33ms
   10 210.171.225.160   64ms  55ms  52ms
   11     10.71.3.26   33ms  45ms  32ms
   12    10.71.0.226   32ms  31ms  31ms
   13   66.42.47.184   33ms  31ms  31ms
   14     45.90.30.0   33ms  33ms  33ms
Traceroute for ultra low latency primary IPv6 (2401:c080:1c01:ff9:5400:3ff:fe77:e880)
    2 2406:5900:3:5def::1    2ms   2ms   1ms
    3 2001:270:fb02:10:245:167:160:1    2ms   2ms   1ms
    4 2001:270:fb02:1:213:100:196:1    2ms   1ms   1ms
    5 2001:270:fb00:1:208:113:172:1    2ms   3ms   3ms
    6 2001:270:fb00:1:213:145:4:2    3ms   3ms   3ms
    7 2001:270:e:115:89:254:192:1    3ms   2ms   3ms
    8 2400::100:112:174:9:2d    2ms   3ms   3ms
    9 2400::100:112:174:9:be    3ms   3ms   3ms
   10 2400:16::101:119    3ms   3ms   3ms
   11 2401:2700:8::6    4ms   3ms   3ms
   12 2401:2700::29a    5ms   4ms   5ms
   13 2001:19f0:fc00::a54:22a   16ms  20ms  30ms
   14 2001:19f0:fc00::a54:12    3ms   3ms   3ms
   15 2401:c080:1c00:ae::33    4ms   4ms   4ms
   16 2401:c080:1c01:ff9:5400:3ff:fe77:e880    4ms   4ms   4ms
Traceroute for ultra low latency secondary IPv6 (2001:19f0:7001:5e19:5400:2ff:fec8:7b5a)
    2 2406:5900:3:5def::1    2ms   2ms   1ms
    3 2001:270:fa02:10:245:167:156:1    2ms   1ms   1ms
    4 2001:270:fa02:1:208:3:188:1    1ms   1ms   1ms
    5 2001:270:fa00:1:208:112:32:1   14ms   7ms   7ms
    6 2001:270:fa00:100:65:15:44:1    2ms   3ms   1ms
    7 2001:270:fa00:100:65:52:68:1    3ms   3ms   3ms
    8 2001:270:fa00:100:65:115:100:2   38ms  20ms  21ms
    9                   *     *     *
   10 2400:8800:1f11:37::1    *    32ms   *
   11 2400:8800:1f11:37::2    *    49ms  32ms
   12 2001:19f0:fc00::a47:f6   33ms  33ms  33ms
   13 2001:19f0:fc00::a47:302   33ms  33ms  33ms
   14 2001:19f0:7000:4c6::33   31ms  31ms  31ms
   15 2001:19f0:7001:5e19:5400:2ff:fec8:7b5a   32ms  32ms  32ms
Traceroute for anycast primary IPv6 (2a07:a8c0::)
    2 2406:5900:3:5def::1    2ms   2ms   1ms
    3 2001:270:fa02:10:245:167:156:1    1ms   1ms   1ms
    4 2001:270:fa02:1:208:3:188:1    2ms   1ms   1ms
    5 2001:270:fa00:1:208:112:32:1    2ms   2ms   3ms
    6 2001:270:fa00:100:65:15:12:1    2ms   1ms   1ms
    7 2001:270:fa00:100:65:52:76:1    3ms   2ms   3ms
    8 2001:270:fd00:1:213:105:108:2    3ms   3ms   3ms
    9 2001:270:fa00:61:42:202:92:2   37ms  37ms  36ms
   10 2001:270:fa00:100:67:30:84:2   37ms  38ms  37ms
   11 2001:de8:7::6:68:3   37ms  37ms  36ms
   12 2a02:6ea0:2:1190:5235::6   39ms  38ms  38ms
   13 2a0b:4342:64::167   38ms  37ms  37ms
   14 2407:b9c0:f000:104::50   37ms  38ms  38ms
   15    2a07:a8c0::   39ms  39ms  39ms
Traceroute for anycast secondary IPv6 (2a07:a8c1::)
    2 2406:5900:3:5def::1    2ms   1ms   1ms
    3 2001:270:fa02:10:245:167:156:1    1ms   1ms   1ms
    4 2001:270:fb02:1:208:100:92:1    1ms   1ms   1ms
    5 2001:270:fa00:1:213:113:172:1    3ms   2ms   3ms
    6 2001:270:fa00:100:65:15:0:1    1ms   3ms   1ms
    7 2001:270:fa00:100:65:51:12:1   20ms  26ms   2ms
    8 2001:270:fa00:100:65:115:100:2    2ms   3ms   3ms
    9                   *     *     *
   10                   *     *     *
   11 2401:95c0:13f4:1:103:98:72:210   63ms  63ms  63ms
   12                   *     *     *
   13                   *     *     *
   14                   *     *     *
   15                   *     *     *
   16                   *     *     *
   17                   *     *     *
   18                   *     *     *
   19                   *     *     *
   20                   *     *     *
   21                   *     *     *
   22                   *     *     *
   23                   *     *     *
   24                   *     *     *
   25                   *     *     *
   26                   *     *     *
   27                   *     *     *
   28                   *     *     *
   29                   *     *     *
   30                   *     *     *
Do you want to send this report? [Y/n]:

Might be useful if you're checking with whichever upstream sits
behind 2401:95c0:13f4:1:103:98:72:210/211.

- NextDNs
- 11 hrs ago
- Reported - view
Please send the diag as dm

Content aside

11 hrs agoLast active
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Secondary IPv6 (2a07:a8c1::) unreachable — 100% packet loss from South Korea

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