I have 2 ip tested, but have no response

I have test loopback address "127.0.0.1"

>> echoudp('on',4012)

u = udp('127.0.0.1',4012);

fopen(u);

fwrite(u,65:74);

A = fread(u,10)

A =

65

66

67

68

69

70

71

72

73

74

>>

This is good!

I have 2 IP, first(192.168.1.6), second(192.168.1.30) ◀ This is USB 2 RJ45

So, I have on 2 matlab window, test following

i)

echoudp('on',4012)

u = udp('192.168.1.30',4012);

fopen(u);

A = fread(u,10)

ii)

echoudp('on',4013)

u = udp('192.168.1.6',4013);

fopen(u);

fwrite(u,1:10);

But, fread have no data!

A=[ ]

absolutely fwrite first, and then fread!