About this interactive
From the lesson's frame comparison:
- **Ethernet** covers Layer 1 and Layer 2. Its header has a six-byte destination and a six-byte source MAC address, because many devices can share the link.
- **HDLC and PPP** are Layer 2 only, carried here over a T1 serial line. With two routers on a point-to-point link there is no one else to address: the address field is one byte, and there is no source address. Both also name the protocol they carry: PPP in its protocol field, Cisco's HDLC in a proprietary type field.
- Both ends of the serial link must use the same encapsulation, or the line protocol stays down. HDLC is the default on Cisco serial interfaces.
The video says HDLC's address is all ones. That is PPP's (0xFF); Cisco's HDLC uses 0x0F for unicast and 0x8F for broadcast.
What you'll learn
- Tell an Ethernet frame from an HDLC or PPP frame by its addressing, its header size and the link it runs on
- Explain why the two ends of a serial link need the same Layer 2 encapsulation, and that HDLC is the Cisco default
Aligned to
Cisco CCNA
1.1
Explain the role and function of network components
1.3
Compare physical interface and cabling types
Key terms
- Ethernet Frame
- The Layer 2 data unit used on Ethernet networks, containing a preamble, source and destination MAC addresses, an EtherType field identifying the Layer 3 protocol, a payload (typically an IP packet), and a 4-byte FCS for error detection. Switches use the MAC addresses in Ethernet frames to make forwarding decisions.
- High-Level Data Link Control
HDLC
- A bit-oriented synchronous data link layer protocol used for point-to-point WAN connections, providing framing, flow control, and error detection. Cisco's proprietary version of HDLC is the default encapsulation on Cisco serial interfaces and adds a protocol type field absent from the ISO standard.
- Point-to-Point Protocol
PPP
- A data link protocol used to establish a direct connection between two nodes.
- Serial Interface
- A router interface used to connect WAN links such as T1 lines, typically configured with a WAN encapsulation protocol like PPP or HDLC.
- MAC Address
- A 48-bit hardware address assigned to a network interface and written as six hexadecimal octets, such as 00:1A:2B:3C:4D:5E. It identifies a device uniquely on a local network segment, and switches forward frames by looking it up in their MAC address table.
Topics
Wan
Hdlc
Ppp
Ethernet
Layer 2
Serial Links
Interactive
Streak Sort
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