criu

Mac-VLAN

Mac-VLAN is a Linux network driver that allows creating multiple virtual interfaces with unique MAC addresses on top of a single physical interface. These virtual interfaces act as standalone devices on the network, each with its own IP and MAC address.

Checkpoint and Restore of Mac-VLAN

CRIU identifies Mac-VLAN interfaces by monitoring netlink messages (specifically RTM_NEWLINK) and inspecting their attributes.

1. Checkpointing

During a dump, CRIU extracts the following attributes for each Mac-VLAN device:

Parent Interface: The physical device (or “upper” link) that the Mac-VLAN is built upon (identified via IFLA_LINK).
Mode: The specific Mac-VLAN operational mode (e.g., bridge, private, vepa, passthru), extracted from IFLA_MACVLAN_MODE.
Flags: Any additional configuration flags associated with the interface (IFLA_MACVLAN_FLAGS).
MAC Address: The unique hardware address of the virtual interface.

2. Restoration

To recreate a Mac-VLAN interface exactly as it was, CRIU performs the following:

Link Creation: It sends an RTM_NEWLINK netlink message with the kind set to "macvlan", specifying the original mode and the link to the parent device.
Index Preservation: To ensure that any application sockets bound to the interface index remain valid, CRIU uses the IFLA_NEW_IFINDEX attribute. This allows CRIU to request the exact same interface index that the device possessed before the checkpoint. (This kernel feature was originally developed specifically to support CRIU).
Namespace Migration: Once created, the interface is moved into the target network namespace for the restored process.

External Interface Mapping

Since the parent physical interface may have a different name or index on the destination host during migration, CRIU provides the --external option to map these dependencies:

# Example mapping of an internal macvlan interface to a host physical interface
criu restore --external macvlan[eth0]:phys0 ...

This tells CRIU that the Mac-VLAN interface which was originally attached to eth0 should now be attached to the physical interface phys0 on the current host.