Netflow vs. PCAP (Packet Capture)
Making the Most of NetFlow and PCAP Files for Threat Detection
Netflow & PCAPs Compared
NetFlow and PCAP are two different ways to capture and analyze network traffic, each with its own strengths. NetFlow is a metadata-based format developed by Cisco that summarizes network flows — for example, which IPs communicated, when, how much data was transferred, and over which ports and protocols. It provides a lightweight, scalable view of network activity that’s ideal for long-term monitoring and anomaly detection across large environments.
In contrast, PCAP (Packet Capture) records the full contents of every network packet, including headers and payloads. This offers deep visibility and forensic-level detail, which is crucial when analyzing attacks, malware behavior, or protocol anomalies. However, PCAP files are much larger, more resource-intensive to capture and analyze, and often require more storage and expertise to use effectively. NetFlow, while lighter and easier to scale, doesn’t capture actual content — so it can miss subtle or content-based threats that PCAP would reveal.
Challenges in Analyzing NetFlow Logs:
| No data below layer 3 |
Description: There is no visibility into protocols below the IP layer, such as Ethernet, ARP, STP, CDP, 802.1Q (VLANs), and others. Consequences: Low-layer discovery and mapping techniques, address spoofing, poisoning, and many types of man-in-the-middle attacks cannot be detected. |
| No data above layer 4 |
Description: There is no visibility into the application layer for critical protocols like DNS, DHCP, HTTP, TLS/SSL, SMB, LDAP, LLMNR, mDNS, NetBIOS, and others. Consequences: Application layer mapping and enumeration, masquerading, and many forms of injection and exploitation techniques cannot be detected. |
| No inspection of packet payload (Deep Packet Inspection - DPI) |
Description: Only metadata about connections is logged, while the actual data within the packets is largely discarded. Consequences: Signature and application layer fingerprinting capabilities, detection of application methods and actions, as well as stream reassembly and file extraction, are impossible. |
| No native name resolution available |
Description: Netflow does not resolve native DNS traffic to provide reliable and real-time entity names. Consequences: Investigating incidents without reliable and real-time name resolution is very difficult and prone to various identification errors. |
| Connection direction can be unreliable |
Description: Network connections will often appear reversed, causing clients to appear as servers and vice versa. Consequences: Higher rate of false positives when analyzing behaviors and activities for anomalies. |
| Connection duplicates exist in the data by design |
Description: Netflow aggregation strategies cause each connection to appear multiple times if the duration exceeds 1 minute (this duration can sometimes be extended). Consequences: Profiling entity behavior based on session duration, data upload, and data download is impossible, as this data is either unreliable or difficult to reconstruct. |
| Does not detect network tunnels |
Description: Netflow does not check for tunneling protocols that encapsulate other complete data packets using different communication protocols (e.g., VXLAN, IP-in-IP, GRE, SSTP, L2TP, PPTP, etc.). Consequences: Many forms of data transfer (such as exfiltration and collection), as well as command and control sessions that hide within legitimate protocols, cannot be detected. |
Free Online Security Analysis of Your Netflow or PCAP files:
Your Netflow and PCAP files can be used to to discover malicious activity, security vulnerabilities and other interesting network events:
