Suffit de ping la passerelle et de soustraire la valeur au ping vers le serveur distant et ça donne le ping en câblé.
Exemple
--- 1.0.0.1 ping statistics ---
4 packets transmitted, 4 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 7.490/7.600/7.758/0.103 ms
--- 10.1.1.1 ping statistics ---
4 packets transmitted, 4 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 1.906/2.594/2.960/0.414 ms
7.6 - 2.594 = 5.006
Ça fait 5 ms de ping vers 1.0.0.1 en câblé