What Are Packet Sniffers and How Do They Work?

What Is a Packet Sniffer?

April 19, 2023

Sniffers are like a hidden camera that sits in the dark corner and gets everything that happens in the room. Then, the one who sets this surveillance receives this data - and figures out what to do next.

Sniffers are the application software, firmware, or hardware module that aims to gather the data sent from- and to the system of the entire network. They do not intrude into the data transfer, just copy the Internet packages they can reach. Not necessarily a malicious tool, sniffers can be of service to network administrators, Internet service providers, and security specialists. However, they are also a potential instrument of data and information thieves. Hardware sniffers can be (and sometimes are) embedded in routers, modems, and other types of nodes. Software sniffers can be installed on servers, intermediate devices, and endpoint computers.

How Sniffers Work?

To explain what a packet analyzer (another name for a sniffer) does, besides likening it to a road checkpoint, where all passing vehicles are inspected, we’ll have to explain how endpoints receive data in normal conditions without a sniffer involved.

Usually, a client receives and views only data intended for its IP address. However, within one network, much more data flows “past” each client. Therefore, unlike a usual spying program that only captures traffic related to the particular endpoint, a sniffer can log traffic from the whole network (or an available part of it,) thus being a much more encompassing tool.

Local wired shared-medium networks can roughly be divided into two groups, and the analyzers’ work specificity varies according to the networks' structure. Thus hub networks (where all traffic flows between all endpoints) are perfect for passive hard-to-detect sniffing, while switch networks that filter data (due to its massive amounts) require extra actions from the sniffer side. An analyzer needs to add more data to the traffic to monitor the whole data stream. Thus, it is much easier to detect such an active sniffer.

Monitoring overall network traffic requires the specific settings (promiscuous mode) of the network adapter of the sniffer-bearing device. Sniffers also vary in their ability to gather traffic and decode and analyze data. There are lots of settings in sniffers too. The analyzer operator can filter the packets to be analyzed by different criteria.

What Sniffers Are For?

Although modern data protection measures include such solutions as SSL-protected websites and Virtual Private Networks (VPN), sniffers do not become useless. Even encrypted data packets can provide analysts with enough information for certain administrative and security needs. For example, logging and analyzing traffic by network administrators can help detect and cut short untypical network activity. Just like that, watching street traffic can give you a notion about some road accident causing a traffic jam. Such a conclusion doesn’t require knowing who exactly drives the cars and who the passengers are. Depending on their functionality, packet sniffers can perform various actions:

• Analyze network issues;
• Track network penetration attempts;
• Detect unauthorized network usage;
• Debug network protocols and communications;
• Gather information on network and traffic for statistics;
• Define and isolate compromised endpoints;
• Identify suspicious content transferred over the network;
• Network applications performance troubleshooting, and other activities.

Unfortunately, spying and gathering users’ data and sensitive information with the subsequent attempt to sell or use it to harm is also possible sniffer employment. Sniffer usage can be both legal or illegal. In any jurisdiction, there is usually a way for security services, network administrators, and ISPs to use it legally. Also, a judge might issue a warrant for the police to use packet analyzers if there is a need to do it.

Can Sniffer Read My Data?

Yes and no. Theoretically, a sniffer can grant its users access to your data. But nowadays, since most websites and instant messengers use end-to-end encryption, the data contained in transferred packages remains inaccessible to the external eye. However, the data protection issue remains. First of all, not all websites have the needed level of encryption. To check whether a particular website has the required protection, look for HTTPS at the beginning of its address line. This abbreviation stands for Hyper Text Transfer Protocol Secure. If you notice that the website you are accessing employs an HTTP protocol – beware. You will not necessarily be spied upon there, but there will be a technical opportunity for that. You can learn more about the protection of client-to-server connections in our article on SSL certificates.

Also, note that website HTTPS protection only protects your data on that particular website. Your activity in-between protected websites (like the browsing history) can be monitored by sniffers. Moreover, sniffers have tools to decode certain types of encrypted packets. Therefore, the threat is still there.

How Can You Prevent Sniffing?

• Keep out from public wireless networks – they are the first candidate for a sniffer-driven man-in-the-middle attack device. You connect to a free wifi hotspot, and your traffic is already monitored before you even switch to safe encryption – that is a very plausible scenario.
• Use an antivirus solution. The sniffer is not a ghost – it exists on a certain device as a program (or as a piece of hardware, but that’s a different story). If you are a part of a network that is being “sniffed through” in a malicious manner, your computer is probably the vehicle for an involved sniffer. Thus, you need a tool to detect and remove the malicious program. GridinSoft Anti-Malware will do it in no time. If you already have this security program, its on-run protection won’t even allow malefactors to inject the malware. In this case, you install Anti-Malware intending to eliminate unexplained activity and launch the scan. The sniffer (if it is it) will be detected and removed.
• Avoid unprotected websites and messenger apps. It has been said that most websites are protected with encryption, and there is no easy way to crack such protection. There are some ways to do it, but they are beyond the capacities of a sniffer alone. However, if you share any data through websites without HTTPS or messaging applications without encryption, make no mistake: your data will be available in its original form if there is a sniffer nearby. Therefore, make sure you don’t roam unprotected parts of the Internet.

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