I am using a fast ethernet of 100 Mbps, whose frame size is less than 1500 bytes (1472 bytes for payload as per my textbook). In that, I was able to send and receive a UDP packet of message size 65507 bytes, which means the packet size was 65507 + 20 (IP Header) + 8 (UDP Header) = 65535.

If the frame's payload size itself is maximum of 1472 bytes (as per my textbook), how can the packet size of IP be greater than that which here is 65535?

I used sender code as

char buffer[100000];
for (int i = 1; i < 100000; i++)
{
    int len = send (socket_id, buffer, i);
    printf("%d\n", len);
}

Receiver code as

while (len = recv (socket_id, buffer, 100000))
{
     printf("%d\n". len);
}

I observed that send returns -1 on i > 65507 and recv prints or receives a packet of maximum of length 65507.