Configuring Access Node Control Protocol on Cisco ASR 9000 Series Routers
Information About Configuring ANCP on Cisco ASR 9000 Series Routers
QC-91
Cisco ASR 9000 Series Aggregation Services Router Modular Quality of Service Configuration Guide
OL-23108-02
TCP creates a separate connection socket for each access node. Because access nodes are not identified
explicitly in ANCP messages, the TCP socket serves as the ANCP neighbor identifier for the ANCP
server.
Once the TCP connection between ANCP neighbors has been made, the ANCP adjacency protocol
establishes an ANCP session over that connection and negotiates ANCP capabilities. There is a single
ANCP session per ANCP neighbor. ANCP session information becomes a subset of the information of
a corresponding neighbor.
ANCP protocol supports dynamic neighbor detection so no configuration of access nodes is required.
ANCP neighbors can also be statically preconfigured on the ANCP server. In such a case, access nodes
are explicitly identified by their IDs, which then must match the sender-name field in the ANCP
adjacency protocol messages.
Neighbor Adjacency Timing
The adjacency timer defines the maximum delay between different stages of ANCP session
establishment and the period of ANCP keepalive.
ANCP adjacency lifetime is governed by the adjacency protocol. If synchronization with the peer access
node is lost (for example, if the adjacency dead timer expires), the ANCP server removes the adjacency,
and the underlying TCP connection is closed.
ANCP Messages
Two ANCP message types are processed by the ANCP server: Port Up and Port Down. Port Up messages
contain DSL rate information; Port Down messages indicate that the corresponding access line is no
longer available. DSL rate updates from Port Up messages are made available to the QoS subsystem.
Port Down messages are used to internally track the ANCP port state.
These messages can only be received by the server after the ANCP adjacency is established. However,
once a Port Up message is received, the DSL rate information it contains is considered valid indefinitely,
provided AN-port-to-interface mapping is configured for that port. It is stored in the AN port database
until it is overwritten by another Port Up message for this port or is cleared manually. The removal of
an adjacency or the reception of a Port Down message is reflected in the database for display and
troubleshooting purposes, but DSL rate information is not invalidated.
Port Mapping
AN ports are statically mapped to VLAN subinterfaces, referred to as AN-port-to-interface mapping.
This implies that there is at least one VLAN subinterface configured per subscriber line. There is no limit
to the number of interfaces that can be mapped to an AN port.
VLAN subinterfaces mapped to an AN port can be created or removed. When mapping is configured,
VLAN subinterfaces are referenced in the ANCP module by name. This name is used for notifications
of interface creation and deletion and provides the information that is used in updating the DSL rate.
An AN port database is maintained for all ports learned from Port Up messages. This database also
contains the AN-port-to-interface mapping database. If a Port Up message for an AN port arrives but no
interface is mapped to that port, the rate information is stored in the AN port database but not published.
When a mapping for that port is configured, the AN port database is scanned to identify any ANCP
messages that were received on this port prior to the mapping configuration. If there were, the known
rate is published.
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