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User Guide for Cisco Security Manager 4.4
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Chapter 59 Configuring Router Interfaces
PVCs on Cisco IOS Routers

Understanding OAM

The Operation, Administration, and Maintenance (OAM) feature provides fault management and
performance management for ATM and is based on the standard defined in ITU recommendation I.610.
OAM detects network connectivity failures on a PVC and reacts by bringing down the PVC. Without
OAM, a PVC would remain up after network connectivity is lost. In such a situation, routing table entries
would continue to point to the PVC, resulting in lost packets.
Security Manager enables the use of F5 OAM, which operates at the virtual circuit (VC) level. To detect
a failure along the PVC path on an end-device, such as a Cisco IOS router, OAM uses the following cells:
• Loopback cells—At regular intervals, routers configured for OAM send loopback cells which must
be looped in the network. This looping point can be the machine at the end of the PVC (end-to-end
loopback cells) or a device on the path (segment loopback cells). A failure occurs when the loopback
cell fails to return to its point of origin.
• Continuity Check (CC) cells—CC cells are sent regularly by routers configured for OAM to check
the integrity of the link. CC cells can be sent either end-to-end or confined to a particular segment
of the PVC. Activation and deactivation cells are used to initiate and suspend continuity checking.
Any connectivity failures are reported in special SNMP notifications.
• Alarm Indication Signal (AIS) cells—In the event of a failure at the physical layer, AIS cells are
sent to downstream devices to report a virtual connection failure at the ATM layer. The PVC moves
to the down state after a defined number of AIS cells are received and does not come up again until
a defined interval passes without additional AIS cells.
• Remote Detection Indication (RDI) cells—When AIS cells are sent to warn downstream devices of
a connectivity failure, RDI cells are sent upstream in response as a control and feedback mechanism
for the network.
AIS/RDI cells are sent using the same VPI/VCI as the user cells on the affected PVC until the failure is
resolved.
Related Topics
•Understanding ATM Management Protocols, page 59-48
•PVCs on Cisco IOS Routers, page 59-46
•Defining OAM Management on ATM PVCs, page 59-53
Defining ATM PVCs
You define an ATM permanent virtual circuit (PVC) by selecting an ATM interface and then defining the
following settings:
•The PVC ID.
•The type of encapsulation to use.
•Whether ILMI management is enabled on this PVC.
•Whether Inverse ARP (InARP) is used to learn the IP addresses of the destination devices.
•Options related to PPP over Ethernet (PPPoE) and PPP over ATM (PPPoA).
•Quality-of-service settings, such as traffic shaping.
•Static IP address mappings in place of InARP.