Sending UDP datagram without fragmentation

I want to send broadcast message to all peers in my local network. Message is a 32 bit integer. I can be sure, that message will not me fragmented, right? There will be two options: - peer will receive whole message at once - peer will not receive message at all

Going further, 4 bytes is maximum size of data, that can be sent in 开发者_如何学Cone UDP datagram? I use Ethernet based network in 99%.

IPv4 specifies a minimum supported MTU of 576 bytes, including the IP header. Your 4 byte UDP payload will result in an IP packet far smaller than this, so you need not fear fragmentation.

Furthermore, your desired outcome - "peer will receive whole message at once or peer will not receive message at all" is always how UDP works, even in the presence of fragmentation. If a fragment doesn't arrive, your app won't recieve the packet at all.

The rules for UDP are "The packet may arrive out-of-order, duplicated, or not at all. If the packet does arrive, it will be the whole packet and error-free.". ("Error-free" is obviously only true within the modest limits of the IP checksum).

Ethernet packets can be up to around 1500 bytes (and that's not counting jumbo frames). If you send broadcast messages with a payload of only 4 bytes, they shouldn't get fragmented at all. Fragmentation should only occur when the packet is larger than the Maximum Transmission Unit (so about 1500 bytes over Ethernet).