- Enterasys Security Router User's Guide

Features
13-4 Configuring ADSL
Figure 13-3 PPPoE Network Diagram
The limitations of this configuration are as follows:
• Maximum MTU of 1492 bytes
• ARP is not supported
• Other received bridged PDU types are silently discarded (802.4, 802.5, 802.6, FDDI)
• Does not send (PID type 0x00-01) and ignores received (PID type 0x00-01) LAN FCSs
• Spanning tree protocols are not supported
• Any received PDU which does not specify the XSR’s MAC address are silently discarded
• The access concentrator must be configured with bridging and ATM ILMI disabled
• ATM SVCs are not supported
Routed IP over ATM
The XSR’s Routed IP over ATM (IPoA) method, as shown in Figure 13-4, supports the following
subset of RFC-2684 as it relates to Routed IP PDUs:
• LLC encapsulated routed non-NLPID formatted IP version 4 PDUs over ATM PVCs
• Non-encapsulated routed IP v4 PDUs over ATM PVCs (virtual circuit multiplexing mode)
• Statically configured IP address
• IPoA is invoked by the
encapsulation ipoa command.
PC
PC
PHY
802.3
IP
1483
PPP
IP
ATM
ADSL
Access
Concentrator
Router / Modem with
integrated PPPoE client
PPPoE
Client
DSL
ATM
SONET
ATM
DSLAM
Bridge encapsulation
LLC/SNAP only
IP
Frwd
802.3
- no bridging PDUs
- no CRCs
- no ARP
- discard broadcast frames
- discard multi-cast frames
- discard PDUs without XSR’s MAC
Note: Your choosing the correct encapsulation method depends on the Customer Premises
Equipment (CPE) support offered by your DSL provider.