What Is Netflow?
NetFlow is a network protocol developed by Cisco Systems for collecting IP traffic information and monitoring network flow. It’s widely used for network traffic analysis and forms the basis for a variety of network management and security applications.
Here’s a brief overview of how NetFlow works:
Data Collection: NetFlow-enabled devices, like routers and switches, keep track of all IP packets passing through them. For each flow, which is a sequence of packets sharing the same source/destination IP addresses, ports, and protocol, the device records various pieces of information such as timestamps, packet and byte counts, source and destination IP addresses, port numbers, and the protocol type.
Flow Export: After collecting this data, the device periodically exports the flow records to a central collector, which is a server running NetFlow analysis software.
Data Analysis: The collected data can be analyzed to gain insights into network traffic patterns, bandwidth usage, and the types of traffic crossing the network. This information is Important for network performance management, traffic analysis, and security monitoring.
NetFlow is particularly useful for detecting irregularities in network traffic, which can indicate security threats like DDoS attacks or network breaches. It’s also used for capacity planning and ensuring that network resources are optimally utilized.
How To Enable Netflow on A Router.
To enable NetFlow on a router, you must use the following commands:
ip flow {ingress | egress}
This enables NetFlow on the interface and captures traffic that is being received or being transmitted by the interface.
ip flow-export destination ip-address udp-port
This is the IP address of the network device or server to which you want to send the NetFlow information and the number of the UDP port on which the network device or server is listening for this information. UDP port 9996 is commonly used for NetFlow.
ip flow-export version version
This specifies the version format that the export packet uses.
How To Configure Netflow.
HQ1(config)# interface Gi0/0
HQ1(config-if)# ip flow ingress
HQ1(config-if)# ip flow egress
HQ1(config-if)# exit
HQ1(config)# ip flow-export destination 172.16.20.84 9996
HQ1(config)# ip flow-export version 9
The figure above shows the configurations for NetFlow data capture and export to the NetFlow collector with IP address 172.16.20.84, where you can analyze the exported data.
Traffic that is received or transmitted by the GigabitEthernet 0/0 interface is captured using the ip flow command.
The captured NetFlow information is then sent to the collector with IP address 172.16.20.84 on UDP port 9996.
The ip flow-export version command shows that the export packet uses the version 9 format.
How to Verify Netflow Configuration on Cisco router.
You can use the show ip flow interface command to verify if NetFlow is enabled on an interface.
HQ1# show ip flow interface
GigabitEthernet0/0
ip flow ingress
ip flow egress
In the example, NetFlow is enabled in the ingress and egress directions on the GigabitEthernet0/0 interface.
Use the show ip flow export command to verify the status and statistics for NetFlow accounting data export.
HQ1# show ip flow export
Flow export v9 is enabled for main cache
Export source and destination details :
VRF ID : Default
Destination(1) 172.16.20.84 (9996)
Version 9 flow records
35 flows exported in 15 udp datagrams
In the example above, the configured destination for NetFlow export is 172.16.20.84 using UDP port 9996. The version of the configured flow export is 9.
In conclusion, NetFlow is a network protocol developed by Cisco for collecting IP traffic information. NetFlow is commonly used by network administrators to monitor and analyze network traffic, detect security threats, and optimize network performance. By capturing and analyzing data on IP traffic flows, NetFlow provides valuable insights into how network resources are being usedand helps in troubleshooting network issues.
