I have a (none automatic) 6to4 tunnel on my system. Normally I can connect to ipv6 systems: ping www.google.com Pingen naar www.l.google.com [2a00:1450:8003::67] van 2001:xxxx:xxxxx::8001 met 32 bytes aan gegevens: Antwoord van 2a00:1450:8003::67: tijd=21 ms Antwoord van 2a00:1450:8003::67: tijd=21 ms Antwoord van 2a00:1450:8003::67: tijd=22 ms Antwoord van 2a00:1450:8003::67: tijd=22 ms When I connect to my workplace through vpn the ping above uses an ipv4 address ping www.google.com Pingen naar www.l.google.com [209.85.229.104] met 32 bytes aan gegevens: Antwoord van 209.85.229.104: bytes=32 tijd=23 ms TTL=55 Antwoord van 209.85.229.104: bytes=32 tijd=23 ms TTL=55 Antwoord van 209.85.229.104: bytes=32 tijd=23 ms TTL=55 Antwoord van 209.85.229.104: bytes=32 tijd=22 ms TTL=55 ping -6 still works (but with the ipv6 address that is returned by the dns server at my workplace). If I change the DNS of my netwerk connction to the DNS server at my workplace also works. nslookup from a (windows 2008) server at my work gives: nslookup www.google.nl Niet-bindend antwoord: Naam: www.l.google.com Addresses: 2a00:1450:8006::68 209.85.229.104 209.85.229.99 209.85.229.147 Aliases: www.google.com nslookup with the DNS server of my ISP (addresses can change with each call) Niet-bindend antwoord: Naam: www.l.google.com Addresses: 2a00:1450:8003::69 66.102.13.147 66.102.13.99 66.102.13.106 66.102.13.103 66.102.13.104 66.102.13.105 Aliases: www.google.com When the VPN is disconnected, everything is working again. I tried looking up addresses from my own program. If I try a call of getaddrinfo with PF_UNSPEC I only get ipv4 addresses for www.google.com. If I add the hint AI_ALL I do get both the ipv6 and ipv4 addresses.