ZyXEL Communications MES3500-24F 用户手册

MES3500-24/24F 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. 

There are two types of sub-option: “Agent Circuit ID Sub-option” and “Agent Remote ID Sub-
option”. They have the following formats.

 

PPPoE Intermediate Agent Vendor-specific Tag Format

Tag_Type

(0x0105)

Tag_Len

Value

i1

i2

PPPoE IA Circuit ID Sub-option Format: User-defined String

SubOpt

Length

Value

0x01

(1 byte)

N

(1 byte)

String

(63 bytes)