It is recommended that the ping and mtr commands support the setting of packet size, which can be used to test whether the MTU settings of some nodes on the Internet are correct.

[moonteach]

1. The maximum MTU on the Internet is generally 1500 bytes. When a packet with the MTU of 1500 bytes enters AS12389, the packet is interrupted at the 15th hop.
   [root@linux]# mtr -s 1500 185.211.112.4 -zn -r -c 30 -f 8
   Start: 2026-04-03T10:07:09+0800
   HOST: hwint159-138-120-2 Loss% Snt Last Avg Best Wrst StDev
   AS??? ??? 100.0 30 0.0 0.0 0.0 0.0 0.0
   AS749 11.22.97.59 66.7% 30 2.0 3.3 1.7 12.1 3.1
   AS??? ??? 100.0 30 0.0 0.0 0.0 0.0 0.0
   AS??? 172.16.156.38 33.3% 30 1.9 2.2 1.9 3.1 0.3
   AS3491 3171363.218.165.141 0.0% 30 2.1 2.0 1.8 2.5 0.2
   AS3491 3171363.220.65.45 90.0% 30 161.0 161.2 161.0 161.4 0.2
   AS3491 3171363.220.196.23 66.7% 30 1150. 1121. 1035. 1224. 54.3
   AS12389 188.254.15.31 0.0% 30 230.1 199.8 196.6 230.1 7.2
   AS??? ??? 100.0 30 0.0 0.0 0.0 0.0 0.0

2. The packets with the MTU of 1496 bytes can pass through normally.
   [root@linux]# mtr -s 1496 185.211.112.4 -zn -r -c 30 -f 8
   Start: 2026-04-03T10:07:51+0800
   HOST: hwint159-138-120-2 Loss% Snt Last Avg Best Wrst StDev
   AS749 11.22.97.214 86.7% 30 2.4 3.4 2.2 6.8 2.2
   AS749 11.22.97.59 56.7% 30 1.7 5.1 1.7 20.1 6.4
   AS??? ??? 100.0 30 0.0 0.0 0.0 0.0 0.0
   AS??? 172.16.156.38 26.7% 30 1.9 2.0 1.7 2.2 0.1
   AS3491 3171363.218.165.141 0.0% 30 1.8 2.0 1.6 2.4 0.2
   AS3491 3171363.220.65.45 80.0% 30 161.2 161.3 161.2 161.4 0.1
   AS3491 3171363.220.196.23 96.7% 30 1148. 1148. 1148. 1148. 0.0
   AS12389 188.254.15.31 0.0% 30 197.0 199.3 196.6 219.6 5.1
   AS??? ??? 100.0 30 0.0 0.0 0.0 0.0 0.0
   AS205562 185.211.112.4 0.0% 30 204.8 205.1 204.7 213.1 1.5

   As a preliminary analysis, an MPLS network is located between hops 15 and 17. The MPLS network header is fixed at 4 bytes. When a packet with an MTU of 1500 bytes enters the MPLS network, the MPLS header of 4 bytes is added, and the MTU becomes 1504 bytes.
   However, the network between hops 15 and 17 does not consider the 4-byte MPLS header added to the packet, and therefore the interface MTU is still set to the default value of 1500 bytes.As a result, packets with an MTU of 1500 bytes cannot pass through these interfaces.
   These are the actual issues I have encountered, so I believe that adding the ability to set packet size to ping and mtr commands would be useful for troubleshooting network problems.