Hello,

I connected my laptop to a router with two different interfaces (eth1
and wlan0).

ARP proxy is not enabled:
# cat /proc/sys/net/ipv4/conf/eth1/proxy_arp
0
# cat /proc/sys/net/ipv4/conf/wlan0/proxy_arp
0

After some time, network-manager starts to answer to ARP request for the
same IP address with replies containing different MAC addresses,
triggering a duplicated IP address. For example, using wireshark to
capture packets:


78  1101.899731  AdbBroad_bf:13:01  Broadcast  ARP  42  Who has
192.168.0.13?  Tell 192.168.0.254
Frame 78: 42 bytes on wire (336 bits), 42 bytes captured (336 bits) on
interface 0
Ethernet II, Src: AdbBroad_bf:13:01 (dc:0b:1a:xx:xx:xx), Dst: Broadcast
(ff:ff:ff:ff:ff:ff)
Address Resolution Protocol (request)

79  1101.899764  LiteonTe_bb:69:c9  AdbBroad_bf:13:01  ARP  42
192.168.0.13 is at 40:f0:2f:xx:xx:xx
Frame 79: 42 bytes on wire (336 bits), 42 bytes captured (336 bits) on
interface 0
Ethernet II, Src: LiteonTe_bb:69:c9 (40:f0:2f:xx:xx:xx), Dst:
AdbBroad_bf:13:01 (dc:0b:1a:xx:xx:xx)
Address Resolution Protocol (reply)

80  1101.898347  AdbBroad_bf:13:01  Broadcast  ARP  60  Who has
192.168.0.13?  Tell 192.168.0.254
Frame 80: 60 bytes on wire (480 bits), 60 bytes captured (480 bits) on
interface 1
Ethernet II, Src: AdbBroad_bf:13:01 (dc:0b:1a:xx:xx:xx), Dst: Broadcast
(ff:ff:ff:ff:ff:ff)
Address Resolution Protocol (request)

81  1101.898380  RealtekS_53:44:58  AdbBroad_bf:13:01  ARP  42
192.168.0.13 is at 00:e0:4c:xx:xx:xx
Frame 81: 42 bytes on wire (336 bits), 42 bytes captured (336 bits) on
interface 1
Ethernet II, Src: RealtekS_53:44:58 (00:e0:4c:xx:xx:xx), Dst:
AdbBroad_bf:13:01 (dc:0b:1a:xx:xx:xx)
[Duplicate IP address detected for 192.168.0.13 (00:e0:4c:xx:xx:xx) -
also in use by 40:f0:2f:xx:xx:xx (frame 79)]
Address Resolution Protocol (reply)


I expect that network-manager answers to ARP request for the same IP
address with the same MAC address.