[pve-devel] [PATCH docs/manager/qemu-server v3 0/3] Make VirtIO network devices inherit MTU from bridge by default

Stefan Hanreich s.hanreich at proxmox.com
Thu Jul 17 19:50:09 CEST 2025


The current default behavior for VirtIO network devices is to default to 1500
MTU, unless otherwise specified. This is inconvenient in cases where the MTU is
not the default value (e.g. for VXLAN VNets or bridges with jumbo frames).
Containers already inherit the MTU of the bridge, if not set, so change the
behavior of VMs to be more in line with containers. This also makes using
non-standard MTUs more convenient and less error-prone since users do not have
to remember setting the MTU everytime they configure a network device on such a
brige.

Changes from v2:
* rebase on top of re-formatted code
* fix tests with new qemu version

Changes from v1:
* better document this behavior
* show better hints in the UI
* improve test case

qemu-server:

Stefan Hanreich (1):
  net: automatically set host_mtu to bridge mtu for virtio netdevs

 src/PVE/QemuServer.pm                  | 30 ++++++++++++++------------
 src/PVE/QemuServer/Network.pm          |  3 ++-
 src/test/cfg2cmd/netdev_vxlan.conf     |  7 ++++++
 src/test/cfg2cmd/netdev_vxlan.conf.cmd | 28 ++++++++++++++++++++++++
 src/test/run_config2command_tests.pl   |  6 ++++++
 5 files changed, 59 insertions(+), 15 deletions(-)
 create mode 100644 src/test/cfg2cmd/netdev_vxlan.conf
 create mode 100644 src/test/cfg2cmd/netdev_vxlan.conf.cmd


pve-manager:

Stefan Hanreich (1):
  qemu: network: adjust MTU emptyText to match new default behavior

 www/manager6/qemu/NetworkEdit.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)


pve-docs:

Stefan Hanreich (1):
  qm: document new default behavior for mtu setting

 qm.adoc | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)


Summary over all repositories:
  7 files changed, 63 insertions(+), 20 deletions(-)

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