Why does Facebook spoof the source IP address of the hop before this server? They spoof the source IP address that is performing the traceroute. 66.220.156.68 --- 7 FACEBOOK-IN.ear1.Atlanta2.Level3.net (4.16.185.58) 51.736 ms 51.678 ms 52.075 ms 8 ae2.bb01.atl1.tfbnw.net (74.119.78.214) 51.636 ms 51.584 ms 51.720 ms 9 be36.bb01.frc3.tfbnw.net (31.13.26.199) 58.669 ms ae4.bb05.frc3.tfbnw.net (31.13.27.129) 61.085 ms ae16.bb06.frc3.tfbnw.net (74.119.76.117) 59.731 ms 10 ae5.bb04.iad3.tfbnw.net (31.13.26.57) 111.338 ms ae7.bb04.iad3.tfbnw.net (31.13.31.245) 110.007 ms 110.015 ms 11 ae9.dr07.ash3.tfbnw.net (31.13.29.29) 68.692 ms ae10.dr08.ash2.tfbnw.net (31.13.28.207) 67.846 ms ae12.dr08.ash3.tfbnw.net (31.13.29.191) 68.629 ms 12 * * * 13 * * * 14 8.25.38.1 (8.25.38.1) 68.571 ms 68.718 ms 68.132 ms 15 edge-star-mini-shv-07-ash4.facebook.com (66.220.156.68) 67.903 ms 67.752 ms 68.071 ms --- Hop 14 is the source ip of the traceroute which is forged. This essentially makes hop 14 reply using the same ip for src and dst. Sam