isoc.org/DS (alg 13, id 2371): No response was received until the UDP payload size was decreased, indicating that the server might be attempting to send a payload that exceeds the path maximum transmission unit (PMTU) size. See RFC 6891, Sec. 6.2.6. (199.19.57.1, UDP_-_EDNS0_4096_D_KN)
isoc.org/DS (alg 13, id 2371): No response was received until the UDP payload size was decreased, indicating that the server might be attempting to send a payload that exceeds the path maximum transmission unit (PMTU) size. See RFC 6891, Sec. 6.2.6. (199.19.57.1, UDP_-_EDNS0_4096_D_KN)
isoc.org/DS has warnings; select the "Denial of existence" DNSSEC option to see them.