Tested OK on Xenial with Pike UCA:
16: gre_sys@NONE: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 65000 qdisc pfifo_fast
master ovs-system state UNKNOWN mode DEFAULT group default qlen 1000
link/ether 56:5c:6e:19:f5:4b brd ff:ff:ff:ff:ff:ff
However testing on artful currently blocked pending resolution of bug 1743746
which prevents an increase in the MTU of the gre devices.
** Tags removed: verification-pike-needed
** Tags added: verification-pike-done
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gre_sys set to default 1472 when using path_mtu > 1500 with ovs 2.8.x
Status in Ubuntu Cloud Archive:
Status in Ubuntu Cloud Archive pike series:
Status in Ubuntu Cloud Archive queens series:
Status in neutron:
Status in linux package in Ubuntu:
Status in openvswitch package in Ubuntu:
Status in linux source package in Artful:
Status in openvswitch source package in Artful:
Status in linux source package in Bionic:
Status in openvswitch source package in Bionic:
OpenStack Clouds using GRE overlay tunnels with > 1500 MTU's will observe
packet fragmentation/networking issues for traffic in overlay networks.
Deploy OpenStack Pike (xenial + pike UCA or artful)
Create tenant networks using GRE segmentation
Instance networking will be broken/slow
gre_sys devices will be set to mtu=1472 on hypervisor hosts.
Minimal; the fix to OVS works around an issue for GRE tunnel port setup via
rtnetlink by performing a second request once the gre device is setup to set
the MTU to a high value (65000).
[Original Bug Report]
Pike neutron 11.0.2-0ubuntu1.1~cloud0
Jumbo frames setttings per:
global_physnet_mtu = 9000
path_mtu = 9000
gre_sys MTU is 1472
Instances with MTUs > 1500 fail to communicate across GRE
ifconfig gre_sys MTU 9000
Note: When ovs rebuilds tunnels, such as on a restart, gre_sys MTU is set
back to default 1472.
Note: downgrading from OVS 2.8.0 to 2.6.1 resolves the issue.
With Ocata or Pike and OVS 2.6.x
gre_sys MTU defaults to 65490
It remains at 65490 through restarts.
This may be related to some combination of the following changes in OVS which
seem to imply MTUs must be set in the ovs database for tunnel interfaces and
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