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38-2
Software Configuration Guide—Release 12.2(25)SG
OL-7659-03
Chapter38 Configuring NetFlow
Overview of NetFlow Statistics Collection
NetFlow exports flow information in UDP datagrams in one of two formats. The version 1 format was
the initial released version, and version 5 is a later enhancement to add Border Gateway Protocol (BGP)
autonomous system (AS) information and flow sequence numbers. In version 1 and version 5 format, the
datagram consists of a header and one or more flow records. The first field of the header contains the
version number of the export datagram.
This section contains the following subsections:
• Information Derived from Hardware, page 38-3
• Information Derived from Software, page 38-4
• Assigning the Input and Output Interface and AS Numbers, page 38-4
• Feature Interaction of Netflow Statistics with UBRL and Microflow Policing, page 38-5
• VLAN Statistics, page 38-5
NDE Versions
The Catalyst 4500 series switch supports NDE versions 1 and 5 for the captured statistics. NetFlow
aggregation requires NDE version 8.
Depending on the current flow mask, some fields in the flow records might not have values. Unsupported
fields contain a zero (0).
The following tables describe the supported fields for NDE version 5:
• Table 38-1—Version 5 header format
• Table 38-2—Version 5 flow record format
Table 38-1 NDE Version 5 Header Format
Bytes Content Description
0–1 version NetFlow export format version number
2–3 count Number of flows exported in this packet (1–30)
4–7 SysUptime Current time in milliseconds since router booted
8–11 unix_secs Current seconds since 0000 UTC 1970
12–15 unix_nsecs Residual nanoseconds since 0000 UTC 1970
16–19 flow_sequence Sequence counter of total flows seen
20–21 engine_type Type of flow switching engine
21–23 engine_id Slot number of the flow switching engine