Chapter 6: Configuring DSL Access with PPPoA

PPPoA is defined in RFC 2364 as PPP over AAL5.

PPPoA Types

Three types of PPPoA are available:

• Virtual circuit multiplexed PPP over AAL5 (AAL5MUX) (RFC 2364)
• LLC encapsulated PPP over AAL5 (AAL5SNAP) (RFC 2364) (default)
• Cisco PPP over ATM (PPPoA) (Cisco proprietary)

VC-Multiplexed PPP over AAL5

Provides a separate virtual circuit for each routed protocol to be transported.

Configuration:

interface ATM0/0
 no ip address
 dsl operating-mode auto
 pvc 8/35
  encapsulation aal5mux ppp Virtual-Template1
!
interface Virtual-Template1
 encapsulation ppp
 ip address negotiated
 ppp authentication chap
 ...

LLC Encapsulated PPP over AAL5

Provides a single virtual circuit for all higher-layer protocols.

AAL5SNAP is the default method.

An LLC header is inserted at the beginning of the PDU.

The LLC header contains the following information:

• Destination Service Access Point (DSAP) - Set to 0xFE for SNAP
• Source Service Access Point (SSAP) - Set to 0xFE for SNAP
• Frame Type (Control) - 0x03 (unnumbered)

Configured with encapsulation aal5snap.

Cisco PPPoA

Allows for multiple PVCs on multiple subinterfaces.

Cisco equipment is required end-to-end.

Configured with encapsulation ciscoppp.