2012年11月29日 · You are creating the socket as socket(AF_INET, SOCK_DGRAM, 0); meaning that it's a datagram (=UDP, typically) socket, so the network stack will automatically include IP header & UDP headers, etc. But since you are trying to create your own IP and UDP headers you must create a raw socket, then send the packet (and also calculate the checksum as ...

The size of a UDP header is 8 bytes. This means an IP packet with an empty UDP datagram as payload takes at least 28 (IPv4) or 48 (IPv6) bytes, but may take more bytes. Also note that in the case of Ethernet, the IP packet will additionally be wrapped in a MAC packet (14 byte header + 4 byte CRC) which will be embedded in an Ethernet frame (8 ...

2016年12月30日 · The UDP header length field is the length of the UDP header plus the UDP data. It is indeed redundant since this length can be calculated from the IP header total length field where the UDP datagram length is the IP total length minus the IP header length.

2012年2月16日 · If you are going for a fixed header, you assume that the first X bytes of every UDP message are metadata. You pick the X and it never changes per message. The recipient then knows to read X bytes as the header and all the rest as a message.

2018年6月4日 · UDP: Size of Ethernet frame - 24 Bytes Size of IPv4 Header (without any options) - 20 bytes Size of UDP header - 8 bytes. Total size of an Ethernet Frame carrying an IP Packet with an empty UDP Datagram - 24 + 20 + 8 = 52 bytes. EDIT: the above incorrectly states the ethernet frame bytes as 24B. It's instead 18 (or 22 for VLAN-tagged ethernet).

2008年12月11日 · The UDP header itself specifies only the protocol port number. Thus, to verify the destination, UDP on the sending machine computes a checksum that covers the destination IP address as well as the UDP datagram. The pseudo-header is not transmitted with the UDP datagram, nor is it included in the length."

2014年7月22日 · The packet like you said, has the "payload" which is the data itself it needs to transfer (usually the user's data), the "header" contains various things depending on the protocol you are using, for example UDP contains just simple things in the header like Destination and Source IP/PORT, TCP on the other end contains more things like the sequence number of the …

The application will run on a LAN (not internet). I've been assuming that if my MTU is 1500 then thats how big a UDP payload can be, but I'm not sure if the UDP header is meant to fit within that too. I'm suspecting that if I send a UDP packet with a 1500 byte payload and the machine MTU is 1500 bytes will it end up sending two packets?

The UDP header has a datagram length field that is 16 bits, meaning that that the largest theoretical UDP datagram is 65,535, but that can never be reached because UDP is encapsulated inside an IP packet, which has a theoretical overall maximum length of 65,535 (the same) but you must subtract the IP and UDP headers from that size to figure the ...

2020年4月11日 · IP header contains the total length of the IP packet; Important: UDP header is fixed 8 Bytes => no meaning to make the header bigger for a constant; TCP header can vary with options; If you're looking for the reason why UDP includes the data and TCP doesn't, you can check in the draft of each RFC specification.