Let’s explore the Spanning Tree Protocol BPDU format.

Bridges exchange BPDUs encapsulated into Ethernet frames. There are two types of BPDUs:

  • Configuration BPDU

Spanning Tree BPDU format : what does it look like in an Ethernet Frame?

Let’s see how a BPDU fits into an Ethernet frame. We should know that STP needs the LLC sub-layer because LLC acts as a transport protocol for STP. So in a STP frame, you’ll find LLC.

If you recall from the Ethernet post, the IEEE 802.3 Ethernet frame with LLC sub-layer is composed of:

  • IEEE 802.2 LLC
  • IEEE 802.3 MAC

copyright Networkinglessons.wordpress.com

In the Data field of the Ethernet frame lays the BPDU. The BPDU format is as follows:


© CCIE Practical Studies, Vol II

So When STP process kicks in, it gives its BPDU to the Ethernet protocol which encapsulates the BPDU into an Ethernet frame, in the Data field.

Categories: CCNP Collaboration

Keyboard Banger

Keyboard Banger is a network engineer from Africa. He has been working in network support and administration since 2008. He started writing study notes about certification exams and technology topics a couple of years ago. When he's not writing articles, he can be found wandering on technical forums.


Leave a Reply

Your email address will not be published. Required fields are marked *