WAN encapsulation:
- Leased Line: PPP, HDLC
- Packet Switching – Frame Relay, X.25, ATM
- Circuit Switching – PPP, HDLC
- Metro Ethernet – Ethernet
- Broadband – PPPoE, PPPoA, Ethernet
HDLC – Cisco’s default point to point encapsulation for circuit switched and dedicated circuits
PPP – Router to Router or host to network over synchronous or asynchronous circuits
Frame Relay – Switched data link layer protocol handles multiple virtual circuits. Successor to X.25
ATM – International standard for cell relay. Uses fixed 53 byte cell switched technology. Allows processing in hardware.
Broadband – PPPoE and PPPoA (256kbps to 24Mbps), provide transmission over the PSTN. Cable Ethernet, data over cable TV infrastructure, 3-30Mbps.
Metro Ethernet – Point to point and multipoint. Ethernet over dark fibre, SONET/SDH, RPR.
Overview of PPP
PPP supports 2 types of Physical Interfaces
Asynchronous Serial: POTS dialup
Synchronous Serial: ISDN or leased lines
Link Control Protocol (LLP) is used to negotiate and setup control options on the WAN link.
3 Phases of PPP Session Establishment
- Link Establishment: Each PP device sends LCP packets to configure and test the data link. If a configuration option is not included in an LCP packet the default value is assumed.
- Authentication: If used, authentication takes place before the network layer protocol phase. PAP and CHAP are supported.
- Network Layer Protocol: PPP devices send NCP packets to choose and configure the protocol for example IP.
PAP: Passwords are sent i clear text with no protection from playback/replay attacks.
CHAP: Uses 3 way handshake at the stat of the link and periodically thereafter to verify identity of the remote node.
Configuring and Verifying PPP
Enable PPP on an interface
Enable Authentication:
- Configure router hostname
- Configure username/password
- PAP/CHAP
PPP summary
There are two components of PPP;
LCP negotiates the connection
NCP encapsulates the traffic
by 