I had this issue: ping6 from a machine in the XLS Hosting network to a machine which has a IPv6 adres in the SURFnet AS didn't work. A tcpdump showed that traffic from surfnet to xls hosting did work, but the reverse didn't. I did disable my firewall but that wasn't the issue. I did report this issue to XLS Hosting and they were able to resolve it. This is what they told me: Translated message: The problem is located at Surfnet itself, but it's not clear to me how and what. If our uploink resets the BGP-session to surfnet that it'll work for some time. Eventually it will break again. That's not something in our control. Please contact Surfnet about this and ask them what happens. Original message (in dutch): Het probleem zit eigenlijk bij Surfnet zelf, maar het is me onduidelijk hoe en wat. Als onze uplink naar surfnet de BGP-sessie reset, gaat het weer werken. Maar na verloop van tijd lijkt het dan weer stuk te gaan. Dit is iets waar wij eigenlijk helemaal geen controle over hebben. Je zou het zelf eens bij Surfnet kunnen navragen wat daar gebeurt. More info: NIC Handle: DVE3-SIXXS IPv4 and IPv6 trace information from the machine in the network of XLS Hosting: root@server4:~# tracepath nlams05.sixxs.net 1: vps20031.xlshosting.net 0.171ms pmtu 1500 1: gw-v123.xl-is.net 10.121ms 1: gw-v123.xl-is.net 0.335ms 2: rt-eu01-v2.xl-is.net 7.041ms 3: surfnet.sara1.nl-ix.net 0.893ms asymm 4 4: AE2.500.JNR01.Asd001A.surf.net 0.877ms asymm 5 5: V1131.sw4.amsterdam1.surf.net 1.167ms 6: sixxs.surfnet.nl 0.931ms reached Resume: pmtu 1500 hops 6 back 59 root@server4:~# tracepath nlams05.sixxs.net 1: vps20031.xlshosting.net 0.114ms pmtu 1500 1: gw-v123.xl-is.net 0.356ms 1: gw-v123.xl-is.net 0.340ms 2: rt-eu01-v2.xl-is.net 0.564ms 3: surfnet.sara1.nl-ix.net 0.803ms asymm 4 4: AE2.500.JNR01.Asd001A.surf.net 0.876ms asymm 5 5: V1131.sw4.amsterdam1.surf.net 1.096ms 6: sixxs.surfnet.nl 0.931ms reached Resume: pmtu 1500 hops 6 back 59