How to Use the Command "snoop" (with examples)

The “snoop” command is an effective utility in the SunOS operating system, serving as a network packet sniffer. Its primary use is to capture and analyze network traffic going through a specified network interface. As a SunOS equivalent of “tcpdump,” snoop offers similar functionality, allowing users to diagnose network issues, monitor traffic, and gain insights into the network’s health and activity.

Use case 1: Capture packets on a specific network interface

Code:

snoop -d e1000g0

Motivation:

When diagnosing network issues, it’s crucial to monitor the specific network interface involved. Capturing packets on a particular network interface can help network administrators or engineers identify and resolve issues related to network traffic, latency, or connectivity. By targeting a specific interface, you minimize unnecessary data capture from other interfaces, making the analysis more efficient and relevant.

Explanation:

• snoop: The main command to execute the network packet sniffing operation.
• -d: This flag specifies the network interface to monitor.
• e1000g0: Represents the name of the network interface from which packets will be captured, often used in systems with Ethernet connections.

Example Output:

Using device e1000g0 to capture packets.
   1   0.00000   host1 -> host2   ICMP Echo request (ping)
   2   0.00135   host2 -> host1   ICMP Echo reply (ping)
   3   0.02356   host3 -> host4   TCP 63172 > http [SYN]

Use case 2: Save captured packets in a file instead of displaying them

Code:

snoop -o path/to/file

Motivation:

Saving captured packets to a file allows for post-capture analysis, which is convenient when dealing with large amounts of data or in situations where capturing and analyzing data in real-time is impractical. Storing packet data is also essential for documenting and sharing findings with other team members or for future reference.

Explanation:

• snoop: Invokes the snoop utility.
• -o: This option specifies the output file where captured packets will be saved.
• path/to/file: The location and filename where the captured data will be stored.

Example Output:

Using device e1000g0 to capture packets.
Captured packets saved in file: /path/to/file

Use case 3: Display verbose protocol layer summary of packets from a file

Code:

snoop -V -i path/to/file

Motivation:

Verbose output is valuable when you require detailed insights into each packet’s protocol layers. It provides an in-depth summary, allowing you to dissect the communication structure and protocols, which is instrumental for understanding complex network behaviors or troubleshooting more intricate issues.

Explanation:

• snoop: The command used to analyze network traffic.
• -V: Stands for the verbose option, providing detailed protocol layer summaries.
• -i: Indicates input from a file.
• path/to/file: Specifies the saved capture file that should be analyzed.

Example Output:

   1   0.00000   host1 -> host2   IP  ------   84 bytes
       IP:   ----- IP Header -----
            Version = 4
            Header length = 20 bytes

Use case 4: Capture network packets that come from a hostname and go to a given port

Code:

snoop to port port from host hostname

Motivation:

Filtering packets based on both source hostname and destination port is particularly useful when diagnosing issues related to specific services or applications, as it narrows down the traffic to only those packets that are most relevant for the investigation.

Explanation:

• snoop: Executes the packet-sniffing process.
• to port: Denotes the destination port to filter packets.
• port: The specific port number that the packets are directed to.
• from host: Filters packets originating from a specified hostname.
• hostname: The source machine’s name that generates the packets.

Example Output:

   1   0.00000   hostname -> server   TCP 6379 > http
   2   0.00247   hostname -> server   TCP 6379 > http

Use case 5: Capture and show a hex-dump of network packets exchanged between two IP addresses

Code:

snoop -x0 -p4 ip1 ip2

Motivation:

Analyzing a hex-dump of network packets allows for a lower-level examination of data, which can sometimes unveil issues not apparent at higher abstraction levels. This method is especially beneficial when dealing with binary protocols or detecting malformations in packet headers.

Explanation:

• snoop: Starts the packet capture process.
• -x0: Option for providing a hex-dump from byte zero, ensuring full packet analysis.
• -p4: Tells snoop to show 4-byte wide data output, improving readability.
• ip1 ip2: Specifies the two IP addresses between which traffic should be captured.

Example Output:

   1   0.00000   ip1 -> ip2    IP
         0: 4500 003c 1c46 4000 4011 a6ec c0a8 0001    E..<.F@.@.......
       10: c0a8 00c7 0035 0035 0028 555b 396e 9128    ..5..5.([9n.(

Conclusion:

The “snoop” command in SunOS is an exceptionally versatile tool for network monitoring and analysis. Whether you’re troubleshooting network performance, analyzing traffic patterns, or ensuring security protocols are being followed, “snoop” provides the necessary functionality and flexibility through its various options to meet a wide array of network diagnostic needs.