Supported Platforms
Related Documentation
ANCP Topology Discovery and Traffic Monitoring Overview
This topic describes ANCP as a means to monitor and modify subscriber traffic in the access network.
Access Node Control Protocol (ANCP) acts as a control plane between a service-oriented Layer 3 edge device and a Layer 2 access node. The access nodes—ANCP neighbors—are network devices that terminate access loops from subscribers; for DSL access loops, the access node is a DSL access multiplexer (DSLAM). Queuing and scheduling mechanisms for subscriber traffic must avoid congestion within the access network while contending with multiple flows and distinct CoS requirements. These mechanisms require the edge device—a router acting as a broadband network gateway (BNG), often also called a network access server (NAS)—to provide information about the access network and subscriber traffic.
ANCP always reports upstream and downstream traffic rates to AAA and only downstream traffic rates to CoS. By default, ANCP reports net data rates, that is, the portion of the total data rate that can be used to transmit user information. You can enable CoS to more accurately shape subscriber traffic by configuring ANCP to adjust the net data rate by a fixed percentage for each line type. This adjusted or calculated rate is the net data rate reduced by the amount of technology overhead incurred by each DSL line type. The result is a closer approximation of the rate of subscriber data traffic.
You can monitor ANCP events and operations by including the traceoptions statement at the [edit protocols ancp] hierarchy level.
ANCP is supported on VLAN over Ethernet and VLAN demux over aggregated Ethernet interfaces.
ANCP was developed as an extension of RFC 3292, General Switch Management Protocol (GSMP) V3, but is now defined in RFC 6320, Protocol for Access Node Control Mechanism in Broadband Networks.
Topology Discovery
The router uses topology discovery to collect information from the access node. The information includes the following:
- Topology of the access network
- DSL line state
- Actual upstream and downstream net data rates of a synchronized DSL link
- Maximum attainable upstream and downstream net data rates
- Interleaving delay
Subscriber Services
The router receives the service profile for the subscribers from a RADIUS server. Most of the services are enforced by the router itself. The router shapes the aggregate egress traffic to subscribers based on the local loop throughput reported by the DSLAM. This traffic shaping optimizes traffic flow while avoiding traffic drops in the access node.
Some service attributes, such as interleaving delay and multicast channel information, are enforced at the access node. ANCP provides the line configuration mechanism that the edge device can use to pass the line configuration on to the access nodes. Typically, multiple profiles are provisioned on the access node. The router instructs the access node which profile to use for a given subscriber.
Subscribers typically receive some combination of voice, data, and video services. Each service can be provisioned on a VLAN. A subscriber might receive only a single service over a single VLAN configured on a logical interface. A group of VLANs carrying services to a subscriber is an interface set. Subscribers are identified based on the unique access loop circuit identifier that is configured on the access node through which they receive traffic. You must configure ANCP to associate this identifier with the logical interface or interface set. When ANCP receives a port management message from an access node, it uses the access loop circuit identifier contained in the message to determine which logical interface or interface set corresponds to the subscriber.
 | Note: The ANCP access loop circuit identifier is equivalent to the agent circuit ID used in DHCP and PPPoE packets to identify the DSLAM interface from which subscriber requests are initiated. |
ANCP Interfaces and Access Loop Circuit Identifiers
You can configure a logical interface by specifying the interface name at the [edit protocols ancp interfaces] hierarchy level. Include the access-identifier statement when you do so to associate the access loop circuit identifier with the interface. You can configure an interface set by including the interface-set statement at the [edit protocols ancp interfaces] hierarchy level. Associate the access loop circuit identifier with the interface set by including the access-identifier statement at the [edit protocols ancp interfaces interface-set interface-set-name] hierarchy level.
The access loop circuit identifier is typically unique across the network; no two interfaces across multiple neighbors (access nodes) share the same identifier. However, in some networks, the identifier might be unique only for a given neighbor. In this case you must associate each identifier with the node’s IP address to disambiguate identifiers that are duplicated within the network. To do so, include the neighbor ip-address statement with the access-identifier statement for both interfaces and interface sets.
| Note: ANCP support is limited to traffic shaping when the identifiers are unique only within an access node (and therefore duplicate identifiers can be present in the network). ANCP support for RADIUS authentication and accounting requires that the identifiers be unique across the network. The DHCP and PPPoE processes are not aware of the access node IP addresses and consequently cannot distinguish between duplicate identifiers. This situation prevents the AAA services framework from correlating a DHCP or PPPoE client session with an access line for RADIUS authentication and accounting. |
 | Best Practice: We recommend that you configure each access loop circuit identifier to be unique across the network. |
Some access nodes might not be running the current IETF implementation of ANCP. Instead, they run an earlier version. You can enable ANCP to operate in backwards-compatible mode with all neighbors by including the pre-ietf-mode statement at the [edit protocols ancp] hierarchy level.
You can control how many discovery table entries are accepted from any neighbor by including the maximum-discovery-table-entries statement at the [edit protocols ancp] hierarchy level.
ANCP Neighbors
ANCP exchanges adjacency messages with neighbors. If an adjacency message is not received from a neighbor within the expected period, then the neighbor is considered to be down and is disconnected. You can adjust how long ANCP waits for adjacency messages from all neighbors by including the adjacency-timer statement at the [edit protocols ancp] hierarchy level. The interval between adjacency messages is automatically set to one-third the value of the adjacency timer.
ANCP can monitor and shape traffic only for access nodes that are configured as ANCP neighbors. Neighbors can establish TCP connections with the router. Include the neighbor statement at the [edit protocols ancp] hierarchy level to configure an access node as an ANCP neighbor.
You can also configure parameters for a specific neighbor that override global or default configurations by including any of the following statements at the [edit protocols ancp neighbor ip-address] hierarchy level:
- adjacency-timer—Adjust the interval between adjacency messages exchanged with this neighbor.
- ietf-mode—Prevent ANCP from operating in a backwards-compatible mode for this neighbor; for neighbors that use the current IETF implementation of ANCP.
- maximum-discovery-table-entries—Specify how many discovery table entries are accepted from this neighbor.
- pre-ietf-mode—Enable ANCP to operate in a backwards-compatible mode for this neighbor; for neighbors that use the original IETF implementation of ANCP rather than the current implementation.
