Enterasys Networks Security Router X-PeditionTM - Manual (Page 315)

Features
XSR User’s Guide 13-3
Figure 13-2 PPPoA Network Diagram
This implementation is restricted as follows:
• Maximum MTU of 1500 bytes
• ATM SVCs are not supported
• Frame Relay/ATM internetworking (per FRF.8) is not supported
• PPP coding transitions - switching the method (VC-multiplexed PPP to LLC-encapsulated
PPP and back) - are not supported
• PPP will not request the following LCP configuration options:
– Protocol Field Compression
– Field Check Sequence Alternatives
– Address-and-Control-Field-Compression
– Asynchronous-Control-Character-Map
PPP over Ethernet over ATM (Routed)
The XSR’s PPPoE option, as shown in Figure 13‐3 , encapsulates PPP PDUs in the form of Ethernet
frames which are encoded as bridged PDUs, as defined by RFC-2684. The router incorporates an
integrated PPPoE client which supports the features described below:
• PPPoE encapsulation according to RFC-2516
• PPPoE session management procedures according to RFC-2516
• Bridged Ethernet PDU (802.3) encapsulation according to RFC-2684
• Statically configured and negotiated IP addresses
• Although the XSR does not support bridging protocols and operations, since most ADSL
access concentrators support this encapsulation type the XSR implements the IP PDU
encapsulation portion of RFC-2684 as required to enable data traffic flows. Essentially, the
XSR implementation is an integrated PPPoE client supported over a router, not over a bridge
as specified in RFCs 2516 and 2684. PPPoE is invoked by the
encapsulation pppoe
command.
PC
PC
PHY
802.3
IP
1483
PPP
IP
ATM
ADSL
Access
Concentrator
Router / Modem with
integrated PPPoA client
PPPoA
Client DSL
ATM
SONET
ATM
DSLAM
Routed encapsulation
- LLC/SNAP
IP
Frwd
Local ethernet frames
Note: Your choosing the correct PPP encapsulation method depends on the Customer Premises
Equipment (CPE) support offered by your DSL provider.