I just ran the Broadcast Sender example on my Linux box and captured this header:
No. Time Source Destination Protocol Info
1 0.000000 192.168.1.6 255.255.255.255 UDP Source port: 59307 Destination port: 45454
Frame 1: 61 bytes on wire (488 bits), 61 bytes captured (488 bits)
Ethernet II, Src: Giga-Byt_c3:63:3f (1c:6f:65:c3:63:3f), Dst: Broadcast (ff:ff:ff:ff:ff:ff)
Internet Protocol, Src: 192.168.1.6 (192.168.1.6), Dst: 255.255.255.255 (255.255.255.255)
Version: 4
Header length: 20 bytes
Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00)
Total Length: 47
Identification: 0x0000 (0)
Flags: 0x02 (Don't Fragment)
Fragment offset: 0
Time to live: 64
Protocol: UDP (17)
Header checksum: 0x7910 [correct]
Source: 192.168.1.6 (192.168.1.6)
Destination: 255.255.255.255 (255.255.255.255)
User Datagram Protocol, Src Port: 59307 (59307), Dst Port: 45454 (45454)
Data (19 bytes)
0000 ff ff ff ff ff ff 1c 6f 65 c3 63 3f 08 00 45 00 .......oe.c?..E.
0010 00 2f 00 00 40 00 40 11 79 10 c0 a8 01 06 ff ff ./..@.@.y.......
0020 ff ff e7 ab b1 8e 00 1b c1 da 42 72 6f 61 64 63 ..........Broadc
0030 61 73 74 20 6d 65 73 73 61 67 65 20 31 ast message 1
No. Time Source Destination Protocol Info
1 0.000000 192.168.1.6 255.255.255.255 UDP Source port: 59307 Destination port: 45454
Frame 1: 61 bytes on wire (488 bits), 61 bytes captured (488 bits)
Ethernet II, Src: Giga-Byt_c3:63:3f (1c:6f:65:c3:63:3f), Dst: Broadcast (ff:ff:ff:ff:ff:ff)
Internet Protocol, Src: 192.168.1.6 (192.168.1.6), Dst: 255.255.255.255 (255.255.255.255)
Version: 4
Header length: 20 bytes
Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00)
Total Length: 47
Identification: 0x0000 (0)
Flags: 0x02 (Don't Fragment)
Fragment offset: 0
Time to live: 64
Protocol: UDP (17)
Header checksum: 0x7910 [correct]
Source: 192.168.1.6 (192.168.1.6)
Destination: 255.255.255.255 (255.255.255.255)
User Datagram Protocol, Src Port: 59307 (59307), Dst Port: 45454 (45454)
Data (19 bytes)
0000 ff ff ff ff ff ff 1c 6f 65 c3 63 3f 08 00 45 00 .......oe.c?..E.
0010 00 2f 00 00 40 00 40 11 79 10 c0 a8 01 06 ff ff ./..@.@.y.......
0020 ff ff e7 ab b1 8e 00 1b c1 da 42 72 6f 61 64 63 ..........Broadc
0030 61 73 74 20 6d 65 73 73 61 67 65 20 31 ast message 1
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As you can see the IP headers, which Qt has no direct influence over, do not contain the options field (lines 7/8 and second last byte on line 22 = 0x45).
Do you have a router/filter/firewall between sender and receiver that might be manipulating headers?
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