Cisco Cisco Prime Network 3.8 Dépliant
White Paper
All contents are Copyright © 1992–2007 Cisco Systems, Inc. All rights reserved. This document is Cisco Public Information.
Page 4 of 7
By default there are five kinds of information for a network element and, hence, polling cycles in a
group:
●
Status: Sets the polling rate for status-related information, such as device status (up/down),
port status, administrator status, and so on. The information is related to the operational
and administrative status of the network element. Default value of 60 seconds.
●
Configuration: Sets the polling rate for configuration-related information, such as Virtual
Circuit tables, scrambling, and so on. Default value of 360 seconds.
●
System: Sets the polling rate for system-related information, such as device name, device
location, and so on. Default value of 900 seconds.
●
Topology Layer 1 counters: Sets the polling rate of the topology process as an interval for
the Layer 1 counter. This is an ongoing process. Default value of 60 seconds.
●
Topology Layer 2 counters: Sets the polling rate of the topology process as an interval for
the Layer 2 counter. This process is available on demand. Default value of 60 seconds.
Each VNE uses so-called registrations to collect the different kinds of data from the associated
network element. Each registration specifies the commands to obtain a specific given item of data
and can be configured with a specific polling interval or logically associated with one of the polling
intervals on a per device/VNE basis.
Further, as multiple VNEs may use the same polling group, the intervals within the polling cycle
are randomized for each VNE. This means that, while the period between data collection
commands for a given polling interval will be the same for each VNE configured with the same
group, each VNE will actually be polling at different times. This “smoothes out” the load of the
management protocols on the network and reduces their impact.
See
Managing Polling Groups
in the Cisco ANA Administrator’s Guide for further information.
Smart Polling
Cisco ANA monitors and takes advantage of specific device change indicators, such as
configuration change notifications from traps, syslogs, or “Entity last change” MIB variables, which
trigger Cisco ANA to automatically invoke a new polling cycle. This capability supports a low-
frequency polling rate by default, while still identifying and reconciling changes quickly and so
keeping the VNE data current.
Management Protocol Optimizations
In network management, there are well-known trade-offs between the use of SNMP and
Telnet/SSH for monitoring and configuring network devices. SNMP has the advantage of being
designed for the purpose, with minimal overhead, simplicity, and wide adoption. SNMP has the
disadvantage that it is deployed over User Datagram Protocol (UDP), that SNMP agents are
typically low priority processes, and that implementations vary in quality and reliability with MIBs
having incomplete coverage and, on occasion, undesirable side effects.
Telnet/SSH has the advantages of being able to obtain any information, or effect any change,
available through the command-line interface (CLI) interface of a device, being session based, and
thus reliable, and having a higher degree of security, access control, and auditing capabilities
through TACACS. Some of these advantages also count against Telnet/SSH, though, so there is
no easy answer.