当eth0断开连接时，UDP多播失败

当我在连接以太网电缆的Raspberry Pi 3上运行此片段时，它可以工作并在UDP多播上发送消息但是当以太网断开连接时会出现错误消息

import socket
from socket import IPPROTO_IPV6
import struct

PORT = 26000
ADDR = 'ff01::1' #IPV6 Multicast Address

addrInfo = socket.getaddrinfo(ADDR, None)[0]
mcast_sock = socket.socket(addrInfo[0], socket.SOCK_DGRAM)
mcast_sock.setsockopt(IPPROTO_IPV6, socket.IPV6_MULTICAST_HOPS, 1)
mcast_sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
mcast_sock.bind(('', PORT))

#Join Multicast grp.
group = socket.inet_pton(addrInfo[0], addrInfo[4][0])
mreq = group + struct.pack('@I', 0)
mcast_sock.setsockopt(IPPROTO_IPV6, socket.IPV6_JOIN_GROUP, mreq)

mcast_sock.sendto(b"Message", (ADDR, PORT))

仅Wlan0接口启动时出现错误消息

Traceback (most recent call last):
  File "test.py", line 20, in <module>
    mcast_sock.sendto(b"Message", (ADDR, PORT))
socket.error: [Errno 99] Cannot assign requested address

使用ifconfig：

eth0      Link encap:Ethernet  HWaddr b8:27:eb:13:e8:41
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:16716 errors:0 dropped:7224 overruns:0 frame:0
          TX packets:408 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:1017246 (993.4 KiB)  TX bytes:56739 (55.4 KiB)

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

wlan0     Link encap:Ethernet  HWaddr b8:27:eb:46:bd:14
          inet addr:10.90.128.72  Bcast:10.90.128.255  Mask:255.255.255.0
          inet6 addr: fe80::a4dd:c183:1f7a:5f43/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:58481 errors:0 dropped:41915 overruns:0 frame:0
          TX packets:5196 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:12027273 (11.4 MiB)  TX bytes:925411 (903.7 KiB)