What is the size of udp packets if I send 0 payload data in c#?

c# header udp packet udpclient
Syaiful Nizam Yahya picture Syaiful Nizam Yahya · Nov 18, 2010 · Viewed 64.1k times · Source

I have figured out the maximum data before fragmentation between 2 endpoints using udp is 1472(other endpoints may vary). This states that mtu is 1500bytes and header overhead per packet is 28bytes. Is it safe to assume that if I send 0 bytes data (payload), the actual data being transferred is 28bytes? I am doing some benchmark, so it is crucial for me to know, what happens in the channel.

Answer

dtb picture dtb · Nov 18, 2010

  • The MTU is the maximum size of an IP packet that can be transmitted without fragmentation.

    IPv4 mandates a path MTU of at least 576 bytes, IPv6 of at least 1280 bytes.

    Ethernet has an MTU of 1500 bytes.

  • An IP packet is composed of two parts: the packet header and the payload.

    The size of an IPv4 header is at least 20 bytes, the size of an IPv6 header at least 40 bytes.

    The payload of an IP packet is typically a TCP segment or a UDP datagram.

  • A UDP datagram consists of a UDP header and the transported data.

    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 byte preamble sequence). This adds 26 bytes of data to the IP packet, but doesn't count against the MTU.

So you cannot assume that a UDP datagram will cause a specific number of bytes to be transmitted.

Related questions

Parsing CSV files in C#, with header

Is there a default/official/recommended way to parse CSV files in C#? I don't want to roll my own parser. Also, I've seen instances of people using ODBC/OLE DB to read CSV via the Text driver, and a …

Read More
Add custom header in HttpWebRequest

I need to add some custom headers to the HttpWebRequest object. How can I add Custom Header to HttpWebRequest object in Windows Phone 7.

Read More
Cannot set some HTTP headers when using System.Net.WebRequest

When I try to add a HTTP header key/value pair on a WebRequest object, I get the following exception: This header must be modified using the appropriate property I've tried adding new values to the Headers collection by using …

Read More