Appreciate the kernel team has been pretty busy the last few months; is
there an ETA on when this fix might make it into the 4.13 kernels? I
know we've pushed the HWE kernel version forward for xenial - so any
OpenStack deployments using HWE with GRE tunnels will hit this problem.
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4.13: unable to increase MTU configuration for GRE devices
Status in linux package in Ubuntu:
Status in linux source package in Artful:
Status in linux source package in Bionic:
GRE overlay networks can't carry traffic with MTU > 1500
sudo add-apt-repository cloud-archive:pike
sudo apt update
sudo apt install openvswitch-switch
sudo ovs-vsctl add-br br-tun
sudo ovs-vsctl add-port br-tun gre0 -- set interface gre0 type=gre
gre_sys device will be configured with MTU 1472.
sudo ip link set gre_sys mtu 65000
will fail with EINVAL.
Under Linux 4.13 its not possible to configure GRE tunnel devices with
a MTU larger than 1500; this impacts on Open vSwitch (which creates
tunnel devices for GRE overlay networking) and the ip tools.
The kernel will error with:
gre_sys: Invalid MTU 65000 requested, hw max 1500
The side effect of this is that if overlay networks are configured
with high MTUs, the gre devices fragment the packets and networking is
This is resolved as part of the upcoming 4.15 kernel under:
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