Chapter 28 PPPoE
GS1920 Series User’s Guide
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28.1.2.1 PPPoE Intermediate Agent Tag Format
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.
28.1.2.2 Sub-Option Format
There are two types of sub-option: “Agent Circuit ID Sub-option” and “Agent Remote ID Sub-
option”. They have the following formats.
The 1 in the first field identifies this as an Agent Circuit ID sub-option and 2 identifies this as an
Agent Remote ID sub-option. The next field specifies the length of the field. The Switch takes the
Circuit ID string you manually configure for a VLAN on a port as the highest priority and the Circuit
ID string for a port as the second priority. In addition, the Switch puts the PPPoE client’s MAC
address into the Agent Remote ID Sub-option if you do not specify any user-defined string.
Flexible Circuit ID Syntax with Identifier String and Variables
If you do not configure a Circuit ID string for a VLAN on a specific port or for a specific port, the
Switch adds the user-defined identifier string and variables into the Agent Circuit ID Sub-option.
The variables can be the slot ID of the PPPoE client, the port number of the PPPoE client and/or the
VLAN ID on the PPPoE packet.
The identifier-string, slot ID, port number and VLAN ID are separated from each other by a pound
key (#), semi-colon (;), period (.), comma (,), forward slash (/) or space. An Agent Circuit ID Sub-
Table 94 PPPoE Intermediate Agent Vendor-specific Tag Format
Tag_Type
(0x0105)
Tag_Len Value i1 i2
Table 95 PPPoE IA Circuit ID Sub-option Format: User-defined String
SubOpt Length Value
0x01
(1 byte)
N
(1 byte)
String
(63 bytes)
Table 96 PPPoE IA Remote ID Sub-option Format
SubOpt Length Value
0x02
(1 byte)
N
(1 byte)
MAC Address or String
(63 bytes)
