Cisco WS-SUP32-GE-3B Software Configuration Guide - Page 771

Flow Masks, Catalyst Supervisor Engine 32 PISA Cisco IOS Software Configuration Guide, Release 12.2ZY

Page 771 highlights

Chapter 47 Configuring NetFlow Understanding NetFlow Flow Masks These sections describe NetFlow on the PFC3B in more detail: • Flow Masks, page 47-3 • Flow Mask Conflicts, page 47-4 A flow is a unidirectional stream of packets between a given source and a given destination. A flow mask specifies the fields in the incoming packet that NetFlow uses to identify the flow. NetFlow gathers statistics for each flow defined by the flow mask. The PFC3B supports the following flow masks: • source-only-A less-specific flow mask. The PFC3B maintains one entry for each source IP address. Statistics for all flows from a given source IP address aggregate into this entry. • destination-A less-specific flow mask. The PFC3B maintains one entry for each destination IP address. Statistics for all flows to a given destination IP address aggregate into this entry. • destination-source-A more-specific flow mask. The PFC3B maintains one entry for each source and destination IP address pair. Statistics for all flows between the same source IP address and destination IP address aggregate into this entry. • destination-source-interface-A more-specific flow mask. Adds the source VLAN SNMP ifIndex to the information in the destination-source flow mask. • full-A more-specific flow mask. The PFC3B creates and maintains a separate table entry for each IP flow. A full entry includes the source IP address, destination IP address, protocol, and protocol ports. • full-interface-The most-specific flow mask. Adds the source VLAN SNMP ifIndex to the information in the full-flow mask. The flow mask determines the granularity of the statistics gathered, which controls the size of the NetFlow table. The less-specific flow masks result in fewer entries in the NetFlow table and the most-specific flow masks result in the most NetFlow entries. For example, if the flow mask is set to source-only, the NetFlow table contains only one entry per source IP address. The statistics for all flows from a given source are accumulated in the one entry. However, if the flow mask is configured as full, the NetFlow table contains one entry per full flow. Many entries may exist per source IP address, so the NetFlow table can become very large. See the "NetFlow Configuration Guidelines and Restrictions" section on page 47-5 for information about NetFlow table capacity. OL-11439-03 Catalyst Supervisor Engine 32 PISA Cisco IOS Software Configuration Guide, Release 12.2ZY 47-3

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47-3
Catalyst Supervisor Engine 32 PISA Cisco IOS Software Configuration Guide, Release 12.2ZY
OL-11439-03
Chapter 47
Configuring NetFlow
Understanding NetFlow
These sections describe NetFlow on the PFC3B in more detail:
Flow Masks, page 47-3
Flow Mask Conflicts, page 47-4
Flow Masks
A flow is a unidirectional stream of packets between a given source and a given destination. A flow mask
specifies the fields in the incoming packet that NetFlow uses to identify the flow. NetFlow gathers
statistics for each flow defined by the flow mask.
The PFC3B supports the following flow masks:
source-only—A less-specific flow mask. The PFC3B maintains one entry for each source IP
address. Statistics for all flows from a given source IP address aggregate into this entry.
destination—A less-specific flow mask. The PFC3B maintains one entry for each destination IP
address. Statistics for all flows to a given destination IP address aggregate into this entry.
destination-source—A more-specific flow mask. The PFC3B maintains one entry for each source
and destination IP address pair. Statistics for all flows between the same source IP address and
destination IP address aggregate into this entry.
destination-source-interface—A more-specific flow mask. Adds the source VLAN SNMP ifIndex to
the information in the destination-source flow mask.
full—A more-specific flow mask. The PFC3B creates and maintains a separate table entry for each
IP flow. A full entry includes the source IP address, destination IP address, protocol, and protocol
ports.
full-interface—The most-specific flow mask. Adds the source VLAN SNMP ifIndex to the
information in the full-flow mask.
The flow mask determines the granularity of the statistics gathered, which controls the size of the
NetFlow table. The less-specific flow masks result in fewer entries in the NetFlow table and the
most-specific flow masks result in the most NetFlow entries.
For example, if the flow mask is set to source-only, the NetFlow table contains only one entry per source
IP address. The statistics for all flows from a given source are accumulated in the one entry. However, if
the flow mask is configured as full, the NetFlow table contains one entry per full flow. Many entries may
exist per source IP address, so the NetFlow table can become very large. See the
“NetFlow Configuration
Guidelines and Restrictions” section on page 47-5
for information about NetFlow table capacity.