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=== Description (from pull-request) ===
It has come to my attention that there is a feature in LXD bridged NIC devices that will inherit the MTU of the parent device if not overriden using the `mtu` device property.
This issue existed in at least LXD 3.15, but only during hot-plug, as LXD used liblxc's MTU inheritance feature for boot time setup.
However in LXD 3.16 the boot-time and hot-plug device setup code was unified and this bug is now present also during boot-time setup.
From cac95d8390634ecdec6e16f2d0fdb70e3a979a1d Mon Sep 17 00:00:00 2001
From: Thomas Parrott <thomas.parr...@canonical.com>
Date: Wed, 14 Aug 2019 12:19:50 +0100
Subject: [PATCH 1/2] device/device/utils/network: Add support for MTU
inheriting from parent on bridged devices
If custom mtu setting is not supplied, and parent is supplied, then MTU is
inherited from parent device.
Signed-off-by: Thomas Parrott <thomas.parr...@canonical.com>
---
lxd/device/device_utils_network.go | 34 +++++++++++++++++++++++-------
1 file changed, 26 insertions(+), 8 deletions(-)
diff --git a/lxd/device/device_utils_network.go
b/lxd/device/device_utils_network.go
index 0596916789..dbf4c9501d 100644
--- a/lxd/device/device_utils_network.go
+++ b/lxd/device/device_utils_network.go
@@ -268,20 +268,22 @@ func NetworkAttachInterface(netName string, devName
string) error {
return nil
}
-// networkCreateVethPair creates and configures a veth pair. It accepts the
name of the host side
-// interface as a parameter and returns the peer interface name.
+// networkCreateVethPair creates and configures a veth pair. It will set the
hwaddr and mtu settings
+// in the supplied config to the newly created peer interface. If mtu is not
specified, but parent
+// is supplied in config, then the MTU of the new peer interface will inherit
the parent MTU.
+// Accepts the name of the host side interface as a parameter and returns the
peer interface name.
func networkCreateVethPair(hostName string, m config.Device) (string, error) {
peerName := NetworkRandomDevName("veth")
_, err := shared.RunCommand("ip", "link", "add", "dev", hostName,
"type", "veth", "peer", "name", peerName)
if err != nil {
- return "", fmt.Errorf("Failed to create the veth interfaces %s
and %s: %s", hostName, peerName, err)
+ return "", fmt.Errorf("Failed to create the veth interfaces %s
and %s: %v", hostName, peerName, err)
}
_, err = shared.RunCommand("ip", "link", "set", "dev", hostName, "up")
if err != nil {
NetworkRemoveInterface(hostName)
- return "", fmt.Errorf("Failed to bring up the veth interface
%s: %s", hostName, err)
+ return "", fmt.Errorf("Failed to bring up the veth interface
%s: %v", hostName, err)
}
// Set the MAC address on peer.
@@ -289,16 +291,32 @@ func networkCreateVethPair(hostName string, m
config.Device) (string, error) {
_, err := shared.RunCommand("ip", "link", "set", "dev",
peerName, "address", m["hwaddr"])
if err != nil {
NetworkRemoveInterface(peerName)
- return "", fmt.Errorf("Failed to set the MAC address:
%s", err)
+ return "", fmt.Errorf("Failed to set the MAC address:
%v", err)
}
}
- // Set the MTU on peer.
+ // Set the MTU on peer. If not specified and has parent, will inherit
MTU from parent.
if m["mtu"] != "" {
- _, err := shared.RunCommand("ip", "link", "set", "dev",
peerName, "mtu", m["mtu"])
+ MTU, err := strconv.ParseUint(m["mtu"], 10, 32)
+ if err != nil {
+ return "", fmt.Errorf("Invalid MTU specified: %v", err)
+
+ }
+
+ err = NetworkSetDevMTU(peerName, MTU)
+ if err != nil {
+ NetworkRemoveInterface(peerName)
+ return "", fmt.Errorf("Failed to set the MTU: %v", err)
+ }
+ } else if m["parent"] != "" {
+ parentMTU, err := NetworkGetDevMTU(m["parent"])
+ if err != nil {
+ return "", fmt.Errorf("Failed to get the parent MTU:
%v", err)
+ }
+ err = NetworkSetDevMTU(peerName, parentMTU)
if err != nil {
NetworkRemoveInterface(peerName)
- return "", fmt.Errorf("Failed to set the MTU: %s", err)
+ return "", fmt.Errorf("Failed to set the MTU: %v", err)
}
}
From 550878119d5dd253f65af0f74538d3d2ad1559f8 Mon Sep 17 00:00:00 2001
From: Thomas Parrott <thomas.parr...@canonical.com>
Date: Wed, 14 Aug 2019 12:20:45 +0100
Subject: [PATCH 2/2] test: Adds test for bridged parent MTU inheritance
Signed-off-by: Thomas Parrott <thomas.parr...@canonical.com>
---
test/suites/container_devices_nic_bridged.sh | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/test/suites/container_devices_nic_bridged.sh
b/test/suites/container_devices_nic_bridged.sh
index 7c1917f732..d531e7d9f0 100644
--- a/test/suites/container_devices_nic_bridged.sh
+++ b/test/suites/container_devices_nic_bridged.sh
@@ -257,6 +257,14 @@ test_container_devices_nic_bridged() {
false
fi
+ # Check that MTU is inherited from parent device when not specified on
device.
+ lxc network set "${brName}" bridge.mtu "1405"
+ lxc config device unset "${ctName}" eth0 mtu
+ if ! lxc exec "${ctName}" -- grep "1405" /sys/class/net/eth0/mtu ; then
+ echo "mtu not inherited from parent"
+ false
+ fi
+ lxc network unset "${brName}" bridge.mtu
# Add an external 3rd party route to the bridge interface and check that it
and the container
# routes remain when the network is reconfigured.
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