Protocol Data Units

Question 1

What is a PDU?

Answer 1

PDU = Protocol Data Unit.
This is a unit of information that is sent by a protocol at an OSI layer.
For example, a switch is operating on an Ethernet PDU.
Another example, TCP or UDP PDU = TCP segment or UDP datagram.

Question 2

What is MTU?

Answer 2

MTU = Maximum Transmission Unit.

The maximum size of an IP packet to send across a network without requiring fragmentation.

Question 3

What is the downside of fragmentation?

Answer 3

Fragmentation slows things down. Losing a fragment can also lose an entire packet.