With more than one project on the same network, there are connection conflicts

[PeteKnight]

The Arduino shields don’t have a fixed MAC address, you specify it yourself in the code.

Take a look at these threads for info on configuring the MAC address:

MAC address help

I am using 2 ethernet shields and they both show up with the same MAC address, I have tried to change one with no luck. these are the lines I added to the sketch to change the address. byte mac[] = {0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED}; IPAddress ip(192, 168, 1, 19); Blynk.begin(auth, mac, ip);

[SOLVED] Blynk.begin woes

Regarding MAC: Please consult Arduino_Ethernet_Manual example for all parameters. We will change this part a bit - so mac will be auto-generated.

You said earlier that you were using MQTT, but there’s no MQTT code in the sample you posted. Can you share your full code?

Pete.