Stenographer is a full-packet-capture utility for buffering packets to disk for intrusion detection and incident response purposes. It provides a high-performance implementation of NIC-to-disk packet writing, handles deleting those files as disk fills up, and provides methods for reading back specific sets of packets quickly and easily.
It is designed to:
It is designed to:
- Write packets to disk, very quickly (~10Gbps on multi-core, multi-disk machines)
- Store as much history as it can (managing disk usage, storing longer durations when traffic slows, then deleting the oldest packets when it hits disk limits)
- Read a very small percentage (<1%) of packets from disk based on analyst needs
- Complex packet processing (TCP stream reassembly, etc)
- It’s fast because it doesn’t do this. Even with the very minimal, single-pass processing of packets we do, processing ~1Gbps for indexing alone can take >75% of a single core.
- Processing the data by reading it back from disk also doesn’t work: see next bullet point.
- Reading back large amounts of packets (> 1% of packets written)
- The key concept here is that disk reads compete with disk writes… you can write at 90% of disk speed, but that only gives you 10% of your disk’s time for reading. Also, we’re writing highly sequential data, which disks are very good at doing quickly, and generally reading back sparse data with lots of seeks, which disks do slowly.