On Thu, 11 May 2017 21:10:11 +0200 Fredrik Markström <fredrik.markstrom@xxxxxxxxx> wrote: > On Thu, May 11, 2017 at 6:01 PM, Stephen Hemminger > <stephen@xxxxxxxxxxxxxxxxxx> wrote: > > On Thu, 11 May 2017 15:46:27 +0200 > > Fredrik Markstrom <fredrik.markstrom@xxxxxxxxx> wrote: > > > >> From: Fredrik Markström <fredrik.markstrom@xxxxxxxxx> > >> > >> is_skb_forwardable() currently checks if the packet size is <= mtu of > >> the receiving interface. This is not consistent with most of the hardware > >> ethernet drivers that happily receives packets larger then MTU. > > > > Wrong. > > What is "Wrong" ? I was initially skeptical to implement this patch, > since it feels odd to have different MTU:s set on the two sides of a > link. After consulting some IP people and the RFC:s I kind of changed > my mind and thought I'd give it a shot. In the RFCs I couldn't find > anything that defined when and when not a received packet should be > dropped. > > > > > Hardware interfaces are free to drop any packet greater than MTU (actually MTU + VLAN). > > The actual limit is a function of the hardware. Some hardware can only limit by > > power of 2; some can only limit frames larger than 1500; some have no limiting at all. > > Agreed. The purpose of these patches is to be able to configure an > veth interface to mimic these different behaviors. Non of the Ethernet > interfaces I have access to drops packets due to them being larger > then the configured MTU like veth does. > > Being able to mimic real Ethernet hardware is useful when > consolidating hardware using containers/namespaces. > > In a reply to a comment from David Miller in my previous version of > the patch I attached the example below to demonstrate the case in > detail. > > This works with all ethernet hardware setups I have access to: > Why not just use an iptables rule to enforce what ever semantic you want?
