UDP reference

You have to remember diferences between TCP and UDP. Here's a quick definition of UDP:

UDP is the User Datagram Protocol. It is used to send individual packets across an IP network, in an unreliable fashion. This means that successful, error-free delivery of a message is not guaranteed.

So remember that UDP is not reliable but it's fast! Examples of protocols that use UDP are TFTP, DNS (it can use TCP too!), DHCP, SNMP, RCP, NFS.

If you're really interested in its standard and how it's defined, you should definitely read the RCF doc here:

RFC 768 - User Datagram Protocol


And finally a couple of jokes:

"A UDP packet walks into a bar, no one acknowledges him.
A TCP packet walks into a bar twice because no one acknowledged him the first time."

"The best thing about UDP jokes is i don’t care if you get it or not."

Understanding Spanning Tree Protocol

If you ever studied CCNA, I bet you had troubles understanding Spanning Tree Protocol (IEEE 802.1D). I know I did! Here's an explanation of it so you can clear your doubts.

1 - Basic concepts

Spanning Tree Protocol (STP) is a OSI layer 2 protocol (Data Link).

Its function is to deal with loops presence due to redundant links existence. This protocol grants switches the ability to enable or disable automatically the connection links guaranteeing a loop-free topology.