Date: Mon, 16 Mar 2009 18:36:09 +0100 From: Martin <nakal@web.de> To: stable@freebsd.org Subject: IPv6 gif(4) MTU: manpage vs src inconsistency? Message-ID: <20090316183609.2b948933@zelda.local>
next in thread | raw e-mail | index | archive | help
Hi, it seems I have trouble to reach some websites using IPv6 through a gif tunnel. Most websites work, except for these two: www.freebsd.org www.kame.net I've searched for problems and it seems, I cannot send ping packets larger than 1232 from the host behind my router. That's why I wanted to decrease the MTU on gif from 1280 to 1240, as the manpage gif(4) suggests: "If the outer protocol is IPv6, path MTU discovery for encapsulated packets may affect communication over the interface. The first bigger-than- pmtu packet may be lost. To avoid the problem, you may want to set the interface MTU for gif to 1240 or smaller, when the outer header is IPv6 and the inner header is IPv4." And I tried it: # ifconfig gif0 mtu 1240 ifconfig: ioctl (set mtu): Invalid argument It does not work, because in source, you can find: if_gif.h: #define GIF_MTU (1280) /* Default MTU */ #define GIF_MTU_MIN (1280) /* Minimum MTU */ #define GIF_MTU_MAX (8192) /* Maximum MTU */ What now? One of the values is wrong, in my opinion. I still don't know the exact cause of the IPv6 website problems. Is there anyone who has a solution for this? I can access ALL WEBSITES from my router directly that has configured the gif tunnel. But all hosts that use the router for default route cannot access the two websites. I have also no issues with traffic to IRC server and so on. I've just found these two hosts that are "different" somehow. This is confusing. Router configuration: tun0: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> metric 0 mtu 1492 inet xx.xx.xx.xx --> yy.yy.yy.yy netmask 0xffffffff Opened by PID 433 gif0: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> metric 0 mtu 1280 tunnel inet xx.xx.xx.xx --> 192.88.99.1 inet6 2002:xxxx:xxxx::1 prefixlen 64 Host behind the router that chokes on the two websites: re0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500 options=389b<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,VLAN_HWCSUM,WOL_UCAST,WOL_MCAST,WOL_MAGIC> ether zz:zz:zz:zz:zz:zz inet6 fe80::zzzz:zzzz:zzzz:zzzz%re0 prefixlen 64 scopeid 0x1 inet 192.168.0.12 netmask 0xffffff00 broadcast 192.168.0.255 inet6 fde2:zzzz:zzzz:zzzz:zzzz:zzzz:zzzz:zzzz prefixlen 64 autoconf inet6 2002:xxxx:xxxx:1:zzzz:zzzz:zzzz:zzzz prefixlen 64 autoconf media: Ethernet autoselect (100baseTX <full-duplex>) status: active -- Martin
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20090316183609.2b948933>