Bug: inconsistent VTEP device MAC address in Ubuntu 22.04

[luc99hen]

I use netlink to create a vxlan device and get the created device MAC address directly afterwards. However I found that the MAC address get from netlink is different from ip link show

After further digging, I found that the interval is important. When I add a interval after creating, the MAC address is correct.
The test script is as following. Notice that time.Sleep(time.Second*10) makes a difference.

import (
        "fmt"
        "log"
        "net"
        "time"

        "github.com/vishvananda/netlink"
)

func main() {
        vxlanName := "vxlan0"
        vxlanID := 10
        vtepIP := "10.0.0.1"

        // Set up the VXLAN link attributes
        vxlan := &netlink.Vxlan{
                LinkAttrs: netlink.LinkAttrs{
                        Name: vxlanName,
                },
                VxlanId:      vxlanID,
                VtepDevIndex: 0, // Index 0 represents no specific interface bound for VTEP, adjust as necessary
                SrcAddr:      net.ParseIP(vtepIP),
                Port:         4789, // Default VXLAN UDP port
        }

        // Create the VXLAN link
        if err := netlink.LinkAdd(vxlan); err != nil {
                log.Fatalf("Failed to create VXLAN link: %v", err)
        }

        // !!!! This line makes a difference 
        time.Sleep(time.Second*10)

        // Get the link by name
        link, err := netlink.LinkByName(vxlanName)
        if err != nil {
                log.Fatalf("Failed to get VXLAN link: %v", err)
        }

        // Get the MAC address
        mac := link.Attrs().HardwareAddr
        fmt.Printf("MAC address of %s: %s\n", vxlanName, mac)
}

I am testing in Ubuntu 22.04, kernel 5.15 with netlink v1.1.0

[luc99hen]

Now I can confirm that this systemd udev configuration MACAddressPolicy=persistentis the cause of the inconsistency.
When I remove /usr/lib/systemd/network/99-default.link this problem is solved.

I think this may be caused by the race of udev and kernel.

netlink may need to wait udev finishing initializing before performing following task in specific systemd version.