How to switch to another network card when the current network card can not connect to the broker with paho mqtt library

[okyihu]

there are 4 network ports on my circuit board (running the embedded linux system), how to switch to another network card when the current network cann't connect to the broker with paho mqtt API ? thanks for helping.

[icraggs]

The 1.4 branch has an update to allow this. You can take a look at the paho_c_sub and paho_c_pub samples to see how this works.

If you invoke paho_c_pub like this:

 paho_c_pub x -A sds -v

it will display a list of interfaces and addresses:

Interface name "lo0" family 0 addresses: 
	IPv4 127.0.0.1
	IPv6 ::1
	IPv6 fe80::1

Interface name "en0" family 0 addresses: 
	IPv6 fe80::81:8c3c:5d27:34f7
	IPv6 2002:3394:b915:0:4e8:d264:2b4f:fb10
	IPv6 2002:3394:b915:0:297b:2435:7003:4898
	IPv4 192.168.178.20

Interface name "awdl0" family 0 addresses: 
	IPv6 fe80::84a:6ff:fe18:e6d3

Interface name "llw0" family 0 addresses: 
	IPv6 fe80::84a:6ff:fe18:e6d3

Interface name "utun0" family 0 addresses: 
	IPv6 fe80::94cd:2fe6:5b7c:db09

Interface name "utun1" family 0 addresses: 
	IPv6 fe80::f0e8:9e61:7169:fa82

Interface name "utun2" family 0 addresses: 
	IPv6 fe80::ce81:b1c:bd2c:69e

You can use the interface name or an address to select the interface to use.