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packet to the PPPoE server.
6. PPPoEIA intercepts PPPoE discovery frames from the client and inserts a unique line
identifier (circuit-id/remote-id) using the PPPoE Vendor-Specific tag (0x0105) to PADR
(PPPoE Active Discovery Request) packets. The PPPoE IA forwards these packets to the
PPPoE server after the insertion.
7. The PPPoE server generates a unique session ID for the session and sends the session ID to
the PPPoE client through a PADS packet. If no error occurs, the session will
established and PPPoE moves on to the Session stage.
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.
Table 1 PPPoE Intermediate Agent Vendor-specific Tag Format
Tag_Type
Tag_Len
(0x0105)
The Tag_Type is 0x0105 for vendor-specific tags, as defined in RFC 2516. The Tag_Len
indicates the length of Value, #1 and #2. The Value is the 32-bit number 0x00000DE9, which
stands for the "ADSL Forum" IANA entry. #1 and #2 are PPPoE intermediate agent sub-options,
which contain additional information about the PPPoE client.
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.
Table 2PPPoE IA Circuit ID Sub-option Format: User-defined String
SubOpt
Length
0x01
N
(1 byte)
(1 byte)
SubOpt
Length
0x02
N
(1 byte)
(1 byte)
The 0x01 in the first field identifies this as an Agent Circuit ID sub-option and 0x02 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 system variables can be the host name of the access node (Switch), the port number
Value
String
(64 bytes)
Table 3PPPoE IA Remote ID Sub-option Format
MAC Address or String
(64 bytes)
188
#1
Value
Value
thus be
#2
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