Size of empty UDP and TCP packet?

Question

What is the size of an empty UDP datagram? And that of an empty TCP packet?

I can only find info about the MTU, but I want to know what is the \"base\" size of these

Answer 1

Himanshus answer is perfectly correct.

What might be misleading when looking at the structure of an Ethernet frame [see further reading], is that without payload the minimum size of an Ethernet frame would be 18 bytes: Dst Mac(6) + Src Mac(6) + Length (2) + Fcs(4), adding minimum size of IPv4 (20) and TCP (20) gives us a total of 58 bytes.

What has not been mentioned yet is that the minimum payload of an ethernet frame is 46 byte, so the 20+20 byte from the IPv4 an TCP are not enough payload! This means that 6 bytes have to be padded, thats where the total of 64 bytes is coming from.

18(min. Ethernet "header" fields) + 6(padding) + 20(IPv4) + 20(TCP) = 64 bytes

Hope this clears things up a little.

Further Reading:

• Ethernet_frame
• Ethernet