Bulk Configuration of VLAN Ranges Using Agent-Circuit-Identifier Information Overview

Using bulk configuration to create S-VLAN IDs based on agent-circuit-identifier information is similar to the process of creating a bulk-configured VLAN range that is not based on agent-circuit-identifier information. However, when you issue the vlan bulk-config command with the svlan-range keyword to specify the S-VLAN ID range, you then specify the agent-circuit-identifier keyword instead of a VLAN ID range. This technique creates a unique type of S-VLAN range in which the agent-circuit-identifier information is used in place of the second tag.

The agent-circuit-identifier string is contained in the option 82 field of DHCP messages for DHCP traffic, or in the DSL Forum VSA 26-1 of PPPoE PADR and PADI packets for PPPoE traffic. The agent-circuit-identifier information identifies the subscriber’s access node and the DSL line on the access node. You can repeat the svlan-range and agent-circuit-identifier keywords to provide nonoverlapping VLAN subranges that reside within the VLAN range.

The following example configures a VLAN ID range made up of two subranges. The first subrange configures S-VLANs 200–250 and the second subrange configures S-VLANs 3000–3500. Both subranges configure the subscriber identification based on agent-circuit-identifier information.

host1(config)#interface gigabitEthernet 2/0 host1(config-if)#vlan bulk-config myAgent2BulkConfig svlan-range 200 250 agent-circuit-identifier svlan-range 3000 3500 agent-circuit-identifier

After you issue the vlan bulk-config command with the agent-circuit-identifier keyword, the router provisions the S-VLAN IDs in the specified bulk-configured VLAN range at the same time. The router does not dynamically create the VLAN subinterface until it receives incoming data traffic. The user information is generated from the incoming data traffic that contains the agent-circuit-identifier string.

Conceptually, a VLAN subinterface in this configuration has two attributes, an S-VLAN ID and an agent-circuit-identifier string. This is analogous to a regular S-VLAN that also has two attributes, an S-VLAN ID and a VLAN ID. However, the packet that the router receives is singly-tagged with only a VLAN ID. The use of the agent-circuit-identifier keyword in the vlan bulk-config command causes the router to further examine the packet and extract the agent-circuit-identifier string in order to generate the subscriber identification information.

In a DSL access network, subscriber information can be conveyed through either of the following methods:

For example, the following configurations uniquely identify subscribers by means of VLAN encapsulation:

The DSL Forum Technical Report (TR)-101—Migration to Ethernet-Based DSL Aggregation (April 2006) refers to the behavior of these configurations as the 1:1 forwarding model because there is a one-to-one correspondence between an individual subscriber and the VLAN encapsulation.

In contrast, the following configurations do not uniquely identify subscribers by means of VLAN encapsulation:

Instead, these configurations identify subscribers by means of the agent-circuit-identifier information present in DHCP and PPPoE control messages. DSL Forum TR-101 refers to the behavior of these configurations as the N:1 forwarding model because there is a many-to-one correspondence between subscribers and a VLAN.

Creating dynamic VLANs based on agent-circuit-identifier information enables you to manage subscribers in single-tagged or untagged N:1 configurations that do not use encapsulation to uniquely identify subscribers. In these configurations, the router intercepts the agent-circuit-identifier string from DHCP messages or from PPPoE PADR and PADI packets to build a unique subscriber interface.

For double-tagged 1:1 configurations, the router uses standard dynamic VLAN procedures to uniquely identify subscribers. In these configurations, the S-VLAN ID typically represents the DSLAM, and the VLAN ID represents the individual subscriber accessing the router through that DSLAM.

For configuration instructions, see Configuring Dynamic VLAN Subinterfaces Based on Agent Circuit Identifier Information.

Note: You must configure the DHCP local or external server to support the creation of dynamic subscriber interfaces that are based on the agent-circuit-id option (suboption 1) of the option 82 field in DHCP messages. See Configuring the DHCP Local Server or DHCP External Server Overview for information.

Related Documentation