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In This Chapter
This chapter provides information to configure Cflowd.
Topics in this chapter include:
Cflowd Overview
Cflowd is a tool used to sample IPv4, IPv6, MPLS, and Ethernet traffic data flows through a router. Cflowd enables traffic sampling and analysis by ISPs and network engineers to support capacity planning, trends analysis, and characterization of workloads in a network service provider environment.
Cflowd is also useful for traffic engineering, network planning and analysis, network monitoring, developing user profiles, data warehousing and mining, as well as security-related investigations. Collected information can be viewed several ways such as in port, AS, or network matrices, and pure flow structures. The amount of data stored depends on the cflowd configurations.
Cflowd maintains a list of data flows through a router. A flow is a uni-directional traffic stream defined by several characteristics such as source and destination IP addresses, source and destination ports, inbound interface, IP protocol and TOS bits.
When a router receives a packet for which it currently does not have a flow entry, a flow structure is initialized to maintain state information regarding that flow, such as the number of bytes exchanged, IP addresses, port numbers, AS numbers, etc. Each subsequent packet matching the same parameters of the flow contribute to the byte and packet count of the flow until the flow is terminated and exported to a collector for storage.
Figure 26 depicts the basic operation of the cflowd feature. This sample flow is only used to describe the basic steps that are performed. It is not intended to specify implementation.
Figure 26: Basic Cflowd Steps
When a flow is exported from the cache, the collected data is sent to an external collector which maintains an accumulation of historical data flows that network operators can use to analyze traffic patterns.
Data is exported in one of the following formats:
Figure 27 depicts Version 5, Version 8, Version 9, and Version 10 flow processing.
Figure 27: V5, V8, V9, V10, and Flow Processing
As the entries within the aggregate matrices are aged out, they are accumulated to be sent to the external flow collector in Version 8 format.
The sample rate and cache size are configurable values. The cache size default is 64K flow entries.
A flow terminates when one of the following conditions is met:
When the user executes a clear cflowd command.
Version 8
There are several different aggregate flow types including:
V8 is an aggregated export format. As individual flows are aged out of the raw flow cache, the data is added to the aggregate flow cache for each configured aggregate type. Each of these aggregate flows are also aged in a manner similar to the method the active flow cache entries are aged. When an aggregate flow is aged out, it is sent to the external collector in the V8 record format.
Version 9
The Version 9 format is a more flexible format and allows for different templates or sets of cflowd data to be sent based on the type of traffic being sampled and the template set configured.
Version 9 is interoperable with RFC 3954, Cisco Systems NetFlow Services Export Version 9.
Version 10
Version 10 is a new format and protocol that inter-operates with the specifications from the IETF as the IP Flow Information Export (IPFIX) standard. Like Version 9, the version 10 format uses templates to allow for different data elements regarding a flow that is to be exported and to handle different type of data flows such as IPv4, IPv6, and MPLS.
Version 10 is interoperable with RFC 5150 and 5102.
Cflowd Filter Matching
In the filter-matching process, normally, every packet is matched against filter (access list) criteria to determine acceptability. With cflowd, only the first packet of a flow is checked. If the first packet is forwarded, an entry is added to the cflowd cache. Subsequent packets in the same flow are then forwarded without needing to be matched against the complete set of filters. Specific performance varies depending on the number and complexity of the filters.
Cflowd Configuration Process Overview
Figure 28 displays the process to configure Cflowd parameters.
Figure 28: Cflowd Configuration and Implementation Flow
There are three modes in which cflowd can be enabled to sample traffic on a given interface:
Configuration Notes
The following cflowd components must be configured for cflowd to be operational: