ESP32 Forum

Greetings,

I am using both ethernet and wifi in the current project. Does setting the default net_if to one of the two before each time socket connect is called force the socket to be bound with the specific net_if? Assume the target ip address is in an ip section of neither net_ifs and and ip_v4 routing picks the default net_if.

Bests
Wang

I haven't tried it, but I think you just need to specify the IP address of the interface you want to bind to.

nopnop2002 wrote: ↑

Thu Sep 19, 2024 4:16 am

I haven't tried it, but I think you just need to specify the IP address of the interface you want to bind to.

Code: Select all

SOCKET s = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

sockaddr_in localaddr = {0};
localaddr.sin_family = AF_INET;
// for WiFi
localaddr.sin_addr.s_addr = inet_addr("192.168.10.103");
// for Ethernet
//localaddr.sin_addr.s_addr = inet_addr("192.168.10.104");
bind(s, (sockaddr*)&localaddr, sizeof(localaddr));

Thanks a lot for the reply. Not quite familiar with lwip stuff, is bind() only used for a server socket to listen to connection requests on specific netif or can it also be used for a client socket to select a specific netif for reaching the target server? In my case, I am attempting to force a client socket to use specific netif for reaching the server. Appreciative for any further hints.

bind is used for a server socket to listen to connection requests.

If you want to force client sockets to use a specific netif to reach the server, this sample is just the right fit.

https://github.com/espressif/esp-idf/tr ... _multi_net

The example shows different ways to do it. One is in fact to bind() the (client) socket to an interface's IP address before connecting.

The example is clearly the right way to go. Really appreciate the help form both of you!