According to the Cocoa Packet Analyzer website:
Cocoa Packet Analyzer is a native Mac OS X implementation of a network protocol analyzer and packet sniffer. CPA supports the industry-standard PCAP packet capture format for reading, capturing and writing packet trace files.
- Basic packet capturing (libPCAP/ tcpdump filter expressions can be used).
- Analyze, display and filter packet trace files.
- Supports PCAP packet capture format.
- Quicklook plugin included – it is basic but at least you can get an overview over packet trace files in finder.
- Intel 64-bit CPU support.