On Wed, May 17, 2017 at 1:14 PM, Dimitri John Ledkov <launch...@surgut.co.uk > wrote:
> I'm very naive, so please bear with me if this is a silly question. As > far as I can tell the existing MTU setting in networkd will apply to > both ipv4 and ipv6 simultaniously. Are you arguing that you want > specific control of MTU and use different values for ipv4 and ipv6? > Yes AFAICT, the MTUBytes field which is a link property, applies to the device itself. IPv6 has a separate *protocol* level MTU where it is used to fragment IPv6 packets so they can be tunneled (among other things) over IPv4. There's also a specific IPv6 MTU setting to prevent IPv6 packets from being to small (I think 1280 is the minimum MTU allowable for IPv6 packets. Subsequently, the kernel has *two* MTUs, Device (ethernet, ppp, etc) and IPv6 protocal device: /sys/class/net/<interface>/mtu ipv6: /proc/sys/net/ipv6/conf/<interface>/mtu Would it not be sufficient to set the appropriatly-lowest/highest common > denominator value for MTU? > It is not. In the case that you want to use 9000 MTU on an ipv6 address, one needs to ensure that the MTU of the underlying device is raised from the default to 9000 otherwise the V6 MTU means nothing. In some cases you want to raise the MTU of the underlying device, but *not* raise the MTU of the IPV6 this is a tunneling case: eth0 mtu 9000 ipv6 mtu 1480 So, yes, we want independent control over v4 and v6 MTU. Note, the upstream discussions (IMHO) punt the problem to Router Advertisements; however what does remain is that we currently have this control with ifupdown (with some help of pre/post scripts). I had a start at getting this working in networkd, however I wasn't able to achieve the independent control > > -- > You received this bug notification because you are subscribed to the bug > report. > https://bugs.launchpad.net/bugs/1671951 > > Title: > networkd should allow configuring IPV6 MTU > > To manage notifications about this bug go to: > https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/ > 1671951/+subscriptions > -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1671951 Title: networkd should allow configuring IPV6 MTU To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1671951/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
