ZyXEL Communications 4528F User Manual

XGS-4526/4528F/4728F User’s Guide

This chapter describes how the Switch gives a PPPoE termination server additional 
information that the server can use to identify and authenticate a PPPoE client.

A PPPoE Intermediate Agent (PPPoE IA) is deployed between a PPPoE server and 
PPPoE clients. It helps the PPPoE server identify and authenticate clients by adding 
subscriber line specific information to PPPoE discovery packets from clients on a 
per-port or per-port-per-VLAN basis before forwarding them to the PPPoE server.

If the PPPoE Intermediate Agent is enabled, the Switch adds a vendor-specific tag 
to PADI (PPPoE Active Discovery Initialization) and PADR (PPPoE Active Discovery 
Request) packets from PPPoE clients. This tag is defined in RFC 2516 and has the 
following format for this feature.

The Tag_Type is 0x0105 for vendor-specific tags, as defined in RFC 2516. The 
Tag_Len indicates the length of Value, i1 and i2. The Value is the 32-bit number 
0x00000DE9, which stands for the “ADSL Forum” IANA entry. i1 and i2 are PPPoE 
intermediate agent sub-options, which contain additional information about the 
PPPoE client. 

Table 95   PPPoE Intermediate Agent Vendor-specific Tag Format

Tag_Type

(0x0105)

Tag_Len

Value

i1

i2