Unable to send unicast messages in ad-hoc mode with new iPad models

Question

AlixPry OP

Created Jun ’21

Replies 3

Boosts 0

Participants 2

Hi, I have this problem. I attach a simple project in order that you can replicate this issue.

The simple project is in this link

Instructions:

Put in ad-hoc mode your Mac, create a network and launch in a shell server_udp.py
Launch socket-test project in a new iPad, for example A2230 (MY2V2TY/A) model with iOS 14.5.1 (or 14.6)
Run in another shell of the Mac ifconfig command and write the ip (something like 169.254. ...) on the Destination IP in the socket-test app in the iPad
Select an interface (for example en0), press Init and then Send. In the console of XCode, iPad prints that it sends 4 bytes, but nothing happens in the server_udp.py (in fact there is a print when it receives something).

If you try the same procedure with old iPad model or in AP mode, everything works fine!

I have also an update: after you follow all the instructions, try to do this:

disassociate Mac from ad-hoc network
riassociate from the list of airport (iPad continues to be in ad-hoc)
Select an interface, press Init and then Send. In the console of XCode, iPad prints that it sends 4 bytes, AND finally in the server_udp.py happens the magic.

Why if I create the ad-hoc network on my Mac first, iPad cannot send packets?

Thanks in advance

Boost

Answer 1

Systems Engineer OP

Apple

Jun ’21

Launch socket-test project in a new iPad, for example A2230 (MY2V2TY/A) model with iOS 14.5.1 (or 14.6) iPad prints that it sends 4 bytes, but nothing happens in the server_udp.py (in fact there is a print when it receives something).

It looks like you are wanting to send broadcast packets onto a network:


sockt = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
...
int opt = 1;
int ret = setsockopt(sockt, SOL_SOCKET, SO_BROADCAST, (char *) &opt, sizeof(opt));

Make sure to check the update to the Local Network Privacy FAQ-3 post here. Sending and receiving a UDP Broadcast via BSD sockets now requires the Multicast Entitlement.

Matt Eaton
DTS Engineering, CoreOS
meaton3@apple.com

0

Answer 2

AlixPry OP

Jun ’21

The link is ok now!

0

Answer 3

AlixPry OP

Jun ’21

Even if I comment that lines, I still have the same problem with unicast data.

0