Rebuilding the Blog and Resolving the Issue of Only TCP Communication Becoming Unreachable from Starlink to ConoHa VPS
Hello, I'm Munou.
It's been a while since the last update. Actually, some articles from late 2025 got blown away, and here we are now.
Codex
Recently, I started using Codex, and the development experience was so good that I've gotten completely hooked.
So, I re-architected the blog using Codex, moving away from Lume CMS, which I had been dissatisfied with for a long time.
It's good that I can write in SSG's Markdown, but since I was mostly updating from the browser, I realized there was no point in specifically writing with my usual editor, vim.
Image-related issues were particularly problematic, making me reluctant to update the blog easily...
The code is published here, but it's full of bugs right now.
GitHub - haturatu/alleycat: cms
It seems like maintenance could be resumed, so I started maintaining it again. And surprisingly, when I replied to someone on Reddit looking for a fork, it turned out to be someone who had already opened an issue on my repository.
The world is a small place, isn't it?
Network becomes unreachable to ConoHa VPS
Then, a problem suddenly occurred.
It seems that a Path MTU Black hole was occurring. It was truly strange; things requiring UDP communication like WireGuard, and DNS servers, were reachable, but all TCP-based communications like SSH and HTTP were failing.
Since ConoHa VPS itself is hosted on FreeBSD, I looked into it and found information that the problem could be solved by normalizing packets using the scrub function of the packet filter (pf), so I configured it as follows.
set skip on lo
set block-policy drop
exsrv1 = dummy
insrv1 = dummy
insrv2 = dummy
wireguard_clients="{ dummy, dummy, dummy }"
wanint="vtnet0"
wg_ports="{51820}"
scrub in on $wanint all random-id max-mss 1360
scrub out on $wanint all random-id max-mss 1360
~~~With this, both upstream and downstream are normalized, and the packet segment size becomes 1360.
Mysterious Point
As a possible cause for this, there was speculation that Starlink's CGNAT might be faulty.
$ mtr -T -P 443 -n -r -c 2 163.44.113.145
Start: 2026-02-24T00:13:53+0900
HOST: thepassenger Loss% Snt Last Avg Best Wrst StDev
1.|-- 192.168.1.1 0.0% 2 1.4 1.5 1.4 1.6 0.1
2.|-- 100.64.0.1 0.0% 2 19.3 19.4 19.3 19.4 0.1
3.|-- 172.16.251.26 0.0% 2 20.1 23.4 20.1 26.8 4.8
4.|-- ??? 100.0 2 0.0 0.0 0.0 0.0 0.0
5.|-- 206.224.70.186 0.0% 2 25.9 22.3 18.8 25.9 5.0
206.224.70.182
6.|-- 210.171.225.229 0.0% 2 23.0 22.7 22.4 23.0 0.4
7.|-- ??? 100.0 2 0.0 0.0 0.0 0.0 0.0
8.|-- 172.71.208.15 0.0% 2 24.9 23.1 21.3 24.9 2.5
162.159.109.42
9.|-- 172.71.4.38 0.0% 2 21.9 23.3 21.9 24.8 2.1
172.64.212.62
10.|-- 172.71.4.35 0.0% 2 63.3 43.8 24.2 63.3 27.7
172.70.221.227
11.|-- ??? 100.0 2 0.0 0.0 0.0 0.0 0.0
12.|-- 172.70.165.3 0.0% 2 44.7 39.8 35.0 44.7 6.9
13.|-- 150.95.7.204 0.0% 2 33.4 34.0 33.4 34.6 0.8
14.|-- 150.95.7.139 0.0% 2 39.2 50.3 39.2 61.4 15.7
15.|-- 150.95.7.147 0.0% 2 36.6 37.2 36.6 37.9 0.9
16.|-- 163.44.113.145 0.0% 2 34.2 35.8 34.2 37.5 2.3$ tracepath -n -m 30 163.44.113.145
1?: [LOCALHOST] pmtu 1500
1: 192.168.1.1 1.347ms
1: 192.168.1.1 1.293ms
2: 100.64.0.1 53.580ms asymm 3
3: 172.16.251.26 37.025ms
4: 206.224.70.208 34.552ms (incomplete router returned corrupted data) asymm 7
5: 206.224.70.184 37.307ms
6: 210.171.225.229 34.518ms
7: No response
8: 172.71.4.43 34.303ms
9: 162.159.109.87 39.922ms
10: 162.159.109.55 33.535ms
11: No response
12: 172.70.165.3 56.395ms asymm 11
13: 150.95.7.204 46.647ms asymm 10
14: 150.95.7.139 66.797ms asymm 11
15: 150.95.7.147 46.542ms asymm 12
16: No response
17: No response
18: No responseOriginally, even though the default packet size for Starlink and my network environment was 1500, I had the impression that TCP communication handled things appropriately, but I couldn't understand why this suddenly occurred this month between ConoHa VPS <-> Starlink.
If Starlink's original CGNAT was faulty, it wouldn't be strange for the problem to have occurred much earlier, but it's such a mysterious phenomenon that I've been feeling uneasy about it.