user manual

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Cisco Active Network Abstraction Fault Management User Guide, Version 3.6 Service Pack 1
OL-14284-01
Chapter 3 Cisco ANA Event Correlation and Suppression
Correlation Flows
This method is usually applicable for problems in the network layer and above (OSI network model) that
might be caused due to a problem upstream or downstream. An example is an OSPF Neighbor Down
event caused by a link-down problem in an upstream router. Another important distinction between
Cisco ANA PathTracer and the correlation flow is that the correlation flow may run on an historical
snapshot of the network.
DC Model Correlation Cache
The DC model correlation cache represents the network as it was before an event occurred or during a
specific time frame by enabling the DC cache to be stored.
A flow of packets occurs on the virtual network, as part of correlation of all DCs, from one VNE to a
destination VNE while simulating the virtual network state of a past moment in time, and these packets
are forwarded via the message processing mechanism from one DC to another DC according to the rules
of the flow. If there are active DCs, and if there is a change in the DC’s property value or if a DC was
removed, all the DC properties that are marked as cache-based will be stored in the DC model cache for
a configurable period of time as defined in the registry and these property values can be restored.
The DC model cache implements this so that the VNE holds cache information for each flow related to
a DC (for example, routing entries or bridge entries) and for forwarding tables, so when a VNE needs to
reflect its DC model, as it was at some point of time in the past, the VNE will be able to do so based on
the cached information it keeps. The DC Property mechanism stores the related data of each property
(when cache management is enabled) for a configurable period of time. The default is 10 minutes. The
cache can be enabled or disabled in the registry (by default it is enabled).
The cached data (the data that is old according to the configured value in the registry) is periodically
cleaned up, in order to maintain the latest valid VNE cache information. This includes old property
values and also previously removed DCs, so that removed DCs are kept in a cache only for the defined
amount of time. The Cache Manager Component of the DA repeatedly (the period of time is defined in
the registry) sends itself a cleanup message in order to initiate a cleanup of the old property values, and
all of the DCs that were removed outside of the defined period. So after 10 minutes all the DC properties
with a timeout are automatically cleared.
Using Weights
In cases where there are multiple potential root causes along the same service path, Cisco ANA enables
the user to define a priority scheme (weight) which can determine the actual root cause.
The correlation system will use the following information to identify more precisely the root-cause
alarm:
• weight: >=0 The correlation flow will collect the alarm, but will not stop.
The correlation mechanism will choose the alarm with the highest weight as the root cause for the alarm
that triggered the correlation by flow.
Correlating TCA
TCAs participate in the correlation mechanism, and can correlate or be correlated to other alarms.