On Sat, 23 Feb 2008 09:17:14 -0800 (PST) [EMAIL PROTECTED] wrote:
> http://bugzilla.kernel.org/show_bug.cgi?id=10073 > > Summary: Just-small-enough packets in tunnels are silently eaten > Product: Networking > Version: 2.5 > KernelVersion: 2.6.23 (mainline), 2.6.25-rc2 (mainline), 2.6.18-6-amd64 > (Debian > Platform: All > OS/Version: Linux > Tree: Mainline > Status: NEW > Severity: normal > Priority: P1 > Component: IPV6 > AssignedTo: [EMAIL PROTECTED] > ReportedBy: [EMAIL PROTECTED] > > > Hi, > > This has been broken for quite a while, but I haven't gotten around to debug > it > until now. > > I have an IPv6-in-IPv4 tunnel between two points, both with MTU 1500 on the > regular v4 network. (I've verified that I can indeed send 1500-byte packets > and > fragments over IPv4 from the two points.) By default, Linux assigns MTU 1480 > to > this tunnel. > > However, if I try to ping -s 5000 from one side of the tunnel to the other, I > get > first "Packet too big, mtu=1480" and then on the next packet (when the machine > tries to send 1480-byte fragments) "Packet too big, mtu=1472". After that, the > packet goes through. > > However, in some cases it seems I do not seem to get the "Packet too big" ICMP > at all. In particular, if I change to a GRE tunnel (where the default MTU is > 1476), and send in 1476-byte packets, they are just eaten. They clearly go > into > the GRE tunnel (according to tcpdump), but no IPv4 packets ever go out on the > other side, and no ICMPs are sent back. (There's no iptables rules on the > router in question, nor any relevant sysctl settings except that IPv6 > forwarding is of course turned on.) If I lower MTU on the interfaces to 1468, > everything seems to work just fine. (I cannot change the MTU of a regular ipip > tunnel, so it's impossible for me to check whether a lower MTU would have > fixed > the issues for those as well, but it seems reasonable.) > > Any idea where the extra eight bytes go? Is there some inner layer of > encapsulation in the kernel (adding eight bytes internally) that I've missed? > -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
