{"id":8248,"date":"2019-10-30T11:15:45","date_gmt":"2019-10-30T11:15:45","guid":{"rendered":"https:\/\/rax-stg-wp-aws.com\/blogs\/packet-sniffers-and-how-to-protect-yourself-from-them\/"},"modified":"2026-11-03T19:29:31","modified_gmt":"2026-11-03T19:29:31","slug":"packet-sniffers-and-how-to-protect-yourself-from-them","status":"publish","type":"blogs","link":"https:\/\/www.rackspace.com\/en-gb\/blogs\/packet-sniffers-and-how-to-protect-yourself-from-them\/","title":{"rendered":"Packet sniffers and how to protect yourself from them"},"content":{"rendered":"<p><strong>Introduction<\/strong><\/p>\n<p>This post explores packet sniffers, which are a useful tool and a potential&nbsp;threat. It provides detailed information about packet sniffers, software used&nbsp;as packet sniffers, how sniffers work, types of sniffing, protocols vulnerable&nbsp;to sniffing, Wireshark\u00a9&nbsp;filters, threats of Address Resolution Protocol (ARP)&nbsp;poisoning, span port, and how to defend against packet sniffing.<\/p>\n<p><strong>What are packet sniffers?<\/strong><\/p>\n<p>A sniffer is a piece of software that captures network traffic and performs&nbsp;network analysis, traffic analysis, protocol analysis, sniffing, packet analysis,&nbsp;and so on. A packet sniffer is essentially a tool that aids in monitoring&nbsp;network traffic and troubleshooting a network. It works by capturing and&nbsp;analyzing packets of data that flow through a network. In some cases, a packet&nbsp;sniffer might be a dedicated hardware device.<\/p>\n<p>Sniffers capture, decode, and analyze network traffic and answer questions such&nbsp;as the following:<\/p>\n<ul>\n<li>Why is the network slow?<\/li>\n<li>What is the network traffic pattern?<\/li>\n<li>How is the traffic being shared between nodes?<\/li>\n<\/ul>\n<p><strong>Network analyzer&nbsp;<\/strong><\/p>\n<p>A network analyzer is a combination of hardware and software tools that can detect, decode, and&nbsp;manipulate traffic on the network. Network administrators use network analyzers to&nbsp;troubleshoot networking issues, but many hackers use them to gather vital&nbsp;information.<\/p>\n<p>Uses include:<\/p>\n<ul>\n<li>&nbsp; &nbsp; Passive sniffing (detection) &#8211; Difficult to detect<\/li>\n<li>&nbsp; &nbsp; Active sniffing (attack)<\/li>\n<\/ul>\n<p><strong>&nbsp;Common network analyzers&nbsp;<\/strong><\/p>\n<p>The following list contains some common analyzers:<\/p>\n<p>&#8211;&nbsp;&nbsp; &nbsp;Wireshark<br \/>\n&#8211;&nbsp;&nbsp; &nbsp;Ettercap\u00a9&nbsp;<br \/>\n&#8211;&nbsp;&nbsp; &nbsp;Dsniff\u00a9&nbsp;<br \/>\n&#8211;&nbsp;&nbsp; &nbsp;Tcpdump<br \/>\n&#8211;&nbsp;&nbsp; &nbsp;Etherpeak\u00a9&nbsp;<br \/>\n&#8211;&nbsp;&nbsp; &nbsp;Cain and Abel\u00a9&nbsp;<\/p>\n<p><strong>&nbsp;How a sniffer works<\/strong><\/p>\n<p>Data travels through a network in the form of packets. Packet-switched&nbsp;networks break down the data to transmit into several packets. They then&nbsp;reassemble these packets after all the data packets reach their intended&nbsp;destination.<\/p>\n<p>When you install a packet sniffer in the network, the sniffer intercepts the&nbsp;network traffic and captures the raw data packets. Subsequently, the packet&nbsp;sniffing software analyzes the captured data packet and presents the results to&nbsp;the network administrators in a user-friendly format so that they can interpret&nbsp;the data.<\/p>\n<p><img decoding=\"async\" src=\"\/wp-content\/uploads\/2026\/blog_article_images\/26628-body-Picture1_22.png\" alt=\"packet sniffer pic 1\" \/><\/p>\n<p><a href=\"https:\/\/www.eccouncil.org\/\"><em>Image Source<\/em><\/a>&nbsp;<\/p>\n<p><strong>&nbsp;Types of sniffing<\/strong><\/p>\n<p>There are two types of sniffing: passive and active.&nbsp;<\/p>\n<p>Network administrators use passive sniffing on the hub used by the network to&nbsp;send traffic to all the ports. It only monitors packets sent by others and does&nbsp;not insert any additional data packets into the network traffic.<\/p>\n<p>Attackers use active sniffing to steal data from others. In a network that&nbsp;uses hubs to connect systems, all hosts on the network can see all the traffic,&nbsp;and therefore, an attacker can easily capture data packets.<\/p>\n<p><strong>&nbsp;What is Wireshark?<\/strong><\/p>\n<p>Formerly known as Ethereal, Wireshark is an open-source program with many free&nbsp;features that provides the following functionality:<\/p>\n<ul>\n<li>&nbsp; Helps you to decode over 750 protocols.<\/li>\n<li>&nbsp; Is compatible with many other sniffers.<\/li>\n<li>&nbsp; Has plenty of online resources available.<\/li>\n<li>&nbsp; Supports the command-line and GUI interfaces.<\/li>\n<li>&nbsp; Offers the TShark command-line interface that has the following three components:<\/li>\n<li>&nbsp; <strong>Editcap<\/strong>: Reads the captured packets from the infile and reads and writes&nbsp;the same capture files that are supported by Wireshark.<\/li>\n<li><strong>Mergecap<\/strong>: Combines multiple saved capture files into a single output file.<\/li>\n<li><strong>Text2pcap<\/strong>: Reads in an ASCII hex dump and writes the data described&nbsp;into a <em>pcap<\/em>&nbsp;or <em>pcapng<\/em>&nbsp;capture file.&nbsp; Text2pcap can read hex dumps with multiple packets in them and build a capture file of multiple packets.<\/li>\n<\/ul>\n<p><strong>&nbsp;Protocols vulnerable to sniffing<\/strong><\/p>\n<p>The following protocols are vulnerable to sniffing:<\/p>\n<ul>\n<li>&nbsp; &nbsp;HTTP<\/li>\n<li>&nbsp; &nbsp;Telnet<\/li>\n<li>&nbsp; &nbsp;rlogin<\/li>\n<li>&nbsp; &nbsp;POP<\/li>\n<li>&nbsp; &nbsp;IMAP<\/li>\n<li>&nbsp; &nbsp;SMTP and NNTP<\/li>\n<li>&nbsp; &nbsp;FTP<\/li>\n<\/ul>\n<p><strong>&nbsp;Users of network analyzers<\/strong><\/p>\n<p>The following roles use network analyzers:<\/p>\n<ul>\n<li>System administrators<\/li>\n<li>Understand system problems and performance<\/li>\n<li>Malicious individuals (intruders)<\/li>\n<li>Capture cleartext data<\/li>\n<li>Passively collect data on the following vulnerable protocols: FTP, POP3,<\/li>\n<li>IMAP, SMATP, rlogin, HTTP, and so on.<\/li>\n<li>Capture VoIP data<\/li>\n<li>Map the target network<\/li>\n<li>Discover traffic patterns<\/li>\n<li>Actively break into the network (backdoor techniques)<\/li>\n<\/ul>\n<p><strong>&nbsp;Filters<\/strong><\/p>\n<p>You can use filters to analyze captured data.<\/p>\n<p><img decoding=\"async\" src=\"\/wp-content\/uploads\/2026\/blog_article_images\/26628-body-Picture2_19.png\" alt=\"packet sniffer pic 2\" \/><\/p>\n<p><a href=\"https:\/\/www.wireshark.org\"><em>Image Source<\/em><\/a><\/p>\n<p>Sometimes, you can observe and record traffic traveling on a network, which&nbsp;might contain valuable information such as the following:<\/p>\n<ul>\n<li>&nbsp;Usernames and passwords<\/li>\n<li>&nbsp;Encrypted<\/li>\n<li>&nbsp;Unencrypted<\/li>\n<li>&nbsp;Email, web requests (and replies), data files, and so on.<\/li>\n<\/ul>\n<p><strong>&nbsp;&nbsp;Wireshark<\/strong><\/p>\n<p>Wireshark a is very popular network analyzer tool, which is used by network&nbsp;administrators to capture packets traversing through a network. Administrators&nbsp;mostly use it to identify network problems, but hackers also use it to decode&nbsp;secure information.<\/p>\n<p>The following image shows a Wireshark screen:<\/p>\n<p><img decoding=\"async\" src=\"\/wp-content\/uploads\/2026\/blog_article_images\/26628-body-Picture3_12.png\" alt=\"packet sniffer pic 3\" \/><\/p>\n<p><a href=\"https:\/\/www.wireshark.org\"><em>Image Source<\/em><\/a>&nbsp;<\/p>\n<p><strong>&nbsp;Example \u2013 A nmap port scan:<\/strong><\/p>\n<ul>\n<li>&nbsp; &nbsp; Target host: 10.0.0.1 &#8211;&nbsp;Start Wireshark<\/li>\n<li>&nbsp; &nbsp; Source host: 10.0.0.2 or the attacker&#8217;s computer&nbsp; \u2013 Perform a TCP-connect scan: `nmap \u2013sT &lt;target host&gt;`<\/li>\n<li>&nbsp; &nbsp; View results<\/li>\n<\/ul>\n<p><strong>Example \u2013 A web connection:&nbsp;<\/strong><\/p>\n<ul>\n<li>Target host: 10.0.0.1 &#8211;&nbsp;Start Wireshark<\/li>\n<li>Source host: 10.0.0.2<\/li>\n<li>Open web browser: Type any website name<\/li>\n<li>View results<\/li>\n<\/ul>\n<p><strong>&nbsp;Example \u2013 An FTP connection:&nbsp;<\/strong><\/p>\n<ul>\n<li>Target host: 10.0.0.1&nbsp;\u2013&nbsp;Start Wireshark<\/li>\n<li>&nbsp;Source host: 10.0.0.2&nbsp;\u2013 Use the ftp client: <em>ftp &lt;target host&gt;<\/em><\/li>\n<li>View results<\/li>\n<\/ul>\n<p><strong>&nbsp;Man-in-the-middle&nbsp;<\/strong><\/p>\n<p>The man-in-the-middle is a common attack tactic.&nbsp;In a switched environment, a host receives only the following:<\/p>\n<ul>\n<li>&nbsp; Traffic destined for itself<\/li>\n<li>&nbsp; Broadcast traffic<\/li>\n<\/ul>\n<p>The host cannot see traffic between other hosts. The man-in-the-middle attack&nbsp;enables you to insert yourself as an (undetected) intermediary between&nbsp;communicating hosts.<\/p>\n<p><strong>&nbsp;What is ARP poisoning?<\/strong><\/p>\n<p>Address Resolution Protocol (ARP) poisoning is when an attacker sends falsified ARP messages over a local&nbsp;area network (LAN) to link an attacker\u2019s MAC address with an IP address of a&nbsp;legitimate computer or a server on the network. After the attacker\u2019s media access control (MAC) address&nbsp;is linked to an authentic IP address, the attacker can receive any messages<br \/>\ndirected to the legitimate MAC address. As a result, the attacker can intercept,&nbsp;modify, or block communications to the legitimate MAC address.<\/p>\n<p>Attackers look for the following opportunities to use ARP poisoning:<\/p>\n<ul>\n<li>&nbsp; Sensitive, unencrypted communications &#8211; &nbsp;Web requests or replies, email, FTP, or HTTP<\/li>\n<li>&nbsp; Weakly-encrypted communications&nbsp; &#8211; &nbsp;Old versions of SSH or RDC<\/li>\n<\/ul>\n<p><strong>&nbsp;&nbsp;&nbsp;ARP poisoning &nbsp;countermeasures<\/strong><\/p>\n<p>Dynamic ARP inspection in Cisco\u00a9 systems helps to prevent man-in-the-middle&nbsp;attacks by not relaying invalid or gratuitous ARP replies to other ports in the&nbsp;same VLAN. Dynamic ARP inspection intercepts all ARP requests and all replies&nbsp;on untrusted ports. Each intercepted packet is verified for valid IP-to-MAC&nbsp;bindings via DHCP snooping. Denied ARP packets are either dropped or logged by&nbsp;the switch for auditing when ARP poisoning attacks are stopped. Incoming ARP&nbsp;packets on the trusted ports are not inspected. Dynamic ARP inspection can also&nbsp;rate-limit ARP requests from client ports to minimize port scanning mechanisms.<\/p>\n<p><strong>&nbsp;How to defend against sniffing<\/strong><\/p>\n<p>Use the following techniques and best practices to protect yourself from<br \/>\nsniffing attacks:<\/p>\n<ul>\n<li>&nbsp; Restrict the physical access to the network media to ensure that a packet&nbsp; sniffer cannot be installed.<\/li>\n<li>&nbsp;Use encryption to protect confidential information.<\/li>\n<li>&nbsp;Permanently add the MAC address of the gateway to the ARP cache.<\/li>\n<li>&nbsp;Use static IP addresses and static ARP tables to prevent attackers from&nbsp;adding spoofed ARP entries for their machines to the network.<\/li>\n<li>Turn off network identification broadcasts, and if possible, restrict the network to authorized users in order to protect the network from being&nbsp;discovered with sniffing tools.<\/li>\n<li>Use the IPv6 instead of the IPv4 protocol.<\/li>\n<li>Use encrypted sessions such as Secure Shell (`ssh`) instead of Telnet.<\/li>\n<li>Use Secure Copy (`scp`) instead of a file transfer protocol (`ftp`).<\/li>\n<li>Use Secure Socket Layer (SSL) for email connections.<\/li>\n<\/ul>\n<p><strong>Conclusion<\/strong><\/p>\n<p>These days, many attacks happen through packet sniffing. Packet sniffers are&nbsp;placed in cyber cafes and on open wifi in restaurants, hotels, and public&nbsp;places. You can protect your data with a little caution. You should never use&nbsp;open wifi and should stop using open text protocols like ftp, http, IMAP, Telnet,&nbsp;and SNMP V1 and V2. You must install SSL certificates in your websites, use&nbsp;Secure File Transfer Protocol (`<em>sftp<\/em>`) instead of `<em>ftp<\/em>`, and use SSH instead of&nbsp;telnet. You should use SNMP V3 and opt for the strongest encryption.<br \/>\n&nbsp;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Packet sniffers and how to protect yourself from them<\/p>\n","protected":false},"author":2,"featured_media":8250,"menu_order":0,"comment_status":"open","ping_status":"open","template":"","format":"standard","meta":{"content-type":"","nid":"26628","content_type":"blog","created_by":"10130","authored_on":"2024-02-20T12:15:45+00:00","field_article_industries":"","tag_category":"Technical","field_blog_author_text":"by Prasuram Jaishwal, Network Security Engineer, Rackspace Technology","seo_description":"Delve into packet sniffers\u2014a useful tool and potential threat. Understand their mechanisms, vulnerabilities, and defense strategies.\r\n","field_featured_image":"","insights_image":"\/wp-content\/uploads\/2026\/blog_technical_images\/26628-insights_image-security-technical-blog-1-insights.jpg","field_partners":"","rxt_platforms":"Multicloud Security","product":"Rackspace Security Essentials","publisheddate":"2019-10-30T11:15:45","rxt_solutions":"Security","opengraph_tag":"","x_tag":"","teaser_flag":"Technical Blog","seo_titile":"Understanding, Threats, and Defense Mechanisms | Rackspace Technology","field_topics":"","field_slug":"packet-sniffers-and-how-you-protect-yourself","footnotes":""},"categories":[178],"tags":[204],"class_list":["post-8248","blogs","type-blogs","status-publish","format-standard","has-post-thumbnail","hentry","category-blog","tag-technical"],"_links":{"self":[{"href":"https:\/\/www.rackspace.com\/en-gb\/wp-json\/wp\/v2\/blogs\/8248","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.rackspace.com\/en-gb\/wp-json\/wp\/v2\/blogs"}],"about":[{"href":"https:\/\/www.rackspace.com\/en-gb\/wp-json\/wp\/v2\/types\/blogs"}],"author":[{"embeddable":true,"href":"https:\/\/www.rackspace.com\/en-gb\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.rackspace.com\/en-gb\/wp-json\/wp\/v2\/comments?post=8248"}],"version-history":[{"count":3,"href":"https:\/\/www.rackspace.com\/en-gb\/wp-json\/wp\/v2\/blogs\/8248\/revisions"}],"predecessor-version":[{"id":9988,"href":"https:\/\/www.rackspace.com\/en-gb\/wp-json\/wp\/v2\/blogs\/8248\/revisions\/9988"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.rackspace.com\/en-gb\/wp-json\/wp\/v2\/media\/8250"}],"wp:attachment":[{"href":"https:\/\/www.rackspace.com\/en-gb\/wp-json\/wp\/v2\/media?parent=8248"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.rackspace.com\/en-gb\/wp-json\/wp\/v2\/categories?post=8248"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.rackspace.com\/en-gb\/wp-json\/wp\/v2\/tags?post=8248"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}