MTU/Path_MTU/blackholeについて、ここに記述してください。 

perl -e "print 'packettoolongyaithuji6reeNab4XahChaeRah1diej4' x 180" > payload.bin
curl  -v -s http://icmpcheck.popcount.org/icmp --data @payload.bin

*   Trying 139.162.188.91...
* Connected to icmpcheck.popcount.org (139.162.188.91) port 80 (#0)
> POST /icmp HTTP/1.1
> Host: icmpcheck.popcount.org
> User-Agent: curl/7.47.0
> Accept: */*
> Content-Length: 8100
> Content-Type: application/x-www-form-urlencoded
> Expect: 100-continue
> 
< HTTP/1.1 100 Continue
* We are completely uploaded and fine
< HTTP/1.1 200 OK
< Date: Thu, 28 Feb 2019 05:15:01 GMT
< Content-Type: text/plain; charset=utf-8
< Connection: close
< Transfer-Encoding: chunked
< 
{"msg1": "Upload complete", "mtu":1500, "lost_segs":0, "retrans_segs":0, "total_retrans_segs":0, "reord_segs":3, "snd_mss":1400, "rcv_mss":853}
* Closing connection 0