Re: [lwip-users] IPv6 MTU vs IPv4 MTU

[Raphael Zulliger]

Thanks for your replies.

I'd like to stress again that both, the mentioned Ubuntu and a Windows 10 system respect different MTUs for IPv4 and IPv6 in my case, as shown by Wireshark. I.e. Sending UDP frames, it behaves like this:
 - IPv4: Frames are being fragmented starting from 1473 Bytes (which makes sense, as MTU=1500 - 20B (Ipv4 header) - 8B (UDP header) = 1472)
 - IPv6: Frames are being fragmented starting from 1433 Bytes (MTU=1480 (because the router advertisement sets it up like this - which seems  to be default in our case) - 40B (Ipv6 header) - 8B (UDP header) = 1432)

How shall we proceed?

On 06.09.2017 05:24, Joel Cunningham wrote:

Sent from my iPad

On Sep 4, 2017, at 13:48, "address@hidden" <address@hidden> wrote:

Raphael Zulliger wrote:

What do you think? Have I found a bug and shall I open a bug report or

am I wrong?

I'm not really sure. After all, the MTU is what a network can send. Having a different MTU for IPv4 and IPv6 doesn't make much sense to me?

Looks like one of the differences is minimum supported MTU of 1280 for IPv6 versus 576 for IPv4.

Also, the change in fragmentation (routers can't fragment with IPv6) could result in the host device lowering it's MTU to accommodate a link with lower MTU. IPv4 could continue with the higher MTU since the link with smaller MTU could just fragment

http://tcpipguide.com/free/t_IPv6DatagramSizeMaximumTransmissionUnitMTUFragment.htm

Joel

_______________________________________________
lwip-users mailing list
address@hidden
https://lists.nongnu.org/mailman/listinfo/lwip-users