{"id":1158,"date":"2018-02-10T21:13:49","date_gmt":"2018-02-10T21:13:49","guid":{"rendered":"https:\/\/fir3netwp.gmsrrpobkbd.com\/2018\/02\/10\/what-is-igmp\/"},"modified":"2021-07-27T15:49:30","modified_gmt":"2021-07-27T15:49:30","slug":"what-is-igmp","status":"publish","type":"post","link":"https:\/\/www.fir3net.com\/Networking\/Protocols\/what-is-igmp.html","title":{"rendered":"What is IGMP?"},"content":{"rendered":"<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_65 counter-hierarchy ez-toc-counter ez-toc-grey ez-toc-container-direction\">\n<p class=\"ez-toc-title\">Table of Contents<\/p>\n<label for=\"ez-toc-cssicon-toggle-item-662e1b8f0364a\" class=\"ez-toc-cssicon-toggle-label\"><span class=\"\"><span class=\"eztoc-hide\" style=\"display:none;\">Toggle<\/span><span class=\"ez-toc-icon-toggle-span\"><svg style=\"fill: #999;color:#999\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" class=\"list-377408\" width=\"20px\" height=\"20px\" viewBox=\"0 0 24 24\" fill=\"none\"><path d=\"M6 6H4v2h2V6zm14 0H8v2h12V6zM4 11h2v2H4v-2zm16 0H8v2h12v-2zM4 16h2v2H4v-2zm16 0H8v2h12v-2z\" fill=\"currentColor\"><\/path><\/svg><svg style=\"fill: #999;color:#999\" class=\"arrow-unsorted-368013\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"10px\" height=\"10px\" viewBox=\"0 0 24 24\" version=\"1.2\" baseProfile=\"tiny\"><path d=\"M18.2 9.3l-6.2-6.3-6.2 6.3c-.2.2-.3.4-.3.7s.1.5.3.7c.2.2.4.3.7.3h11c.3 0 .5-.1.7-.3.2-.2.3-.5.3-.7s-.1-.5-.3-.7zM5.8 14.7l6.2 6.3 6.2-6.3c.2-.2.3-.5.3-.7s-.1-.5-.3-.7c-.2-.2-.4-.3-.7-.3h-11c-.3 0-.5.1-.7.3-.2.2-.3.5-.3.7s.1.5.3.7z\"\/><\/svg><\/span><\/span><\/label><input type=\"checkbox\"  id=\"ez-toc-cssicon-toggle-item-662e1b8f0364a\"  aria-label=\"Toggle\" \/><nav><ul class='ez-toc-list ez-toc-list-level-1 ' ><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/www.fir3net.com\/Networking\/Protocols\/what-is-igmp.html\/#Introduction\" title=\"Introduction\">Introduction<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/www.fir3net.com\/Networking\/Protocols\/what-is-igmp.html\/#Versions\" title=\"Versions\">Versions<\/a><ul class='ez-toc-list-level-3' ><li class='ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/www.fir3net.com\/Networking\/Protocols\/what-is-igmp.html\/#IGMPv1\" title=\"IGMPv1\">IGMPv1<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-4\" href=\"https:\/\/www.fir3net.com\/Networking\/Protocols\/what-is-igmp.html\/#IGMPv2\" title=\"IGMPv2\">IGMPv2<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-5\" href=\"https:\/\/www.fir3net.com\/Networking\/Protocols\/what-is-igmp.html\/#IGMPv3\" title=\"IGMPv3\">IGMPv3<\/a><\/li><\/ul><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-6\" href=\"https:\/\/www.fir3net.com\/Networking\/Protocols\/what-is-igmp.html\/#IGMP_Snooping\" title=\"IGMP Snooping\">IGMP Snooping<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-7\" href=\"https:\/\/www.fir3net.com\/Networking\/Protocols\/what-is-igmp.html\/#IGMP_Querier\" title=\"IGMP Querier\">IGMP Querier<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-8\" href=\"https:\/\/www.fir3net.com\/Networking\/Protocols\/what-is-igmp.html\/#References\" title=\"References\">References<\/a><\/li><\/ul><\/nav><\/div>\n<h2 id=\"h.20pa2iim6bk5\" class=\"c14\"><span class=\"ez-toc-section\" id=\"Introduction\"><\/span><span class=\"c10 c9\">Introduction<\/span><span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p class=\"c2\"><span class=\"c9\"><strong>IGMP (Internet Group Management Protocol)<\/strong> is a Layer 3 protocol (IP protocol number 2) and is a key component (Figure 1) to IP multicast. The role of IGMP<\/span><span class=\"c9\">\u00a0i<\/span><span class=\"c9\">s to notify a local multicast <\/span><span class=\"c3\">router<\/span><span class=\"c9\">\u00a0when a <\/span><span class=\"c3\">host<\/span><span class=\"c0\">\u00a0wants to receive multicast traffic for a specific group.<\/span><\/p>\n<p class=\"c2\" style=\"text-align: center;\"><picture><source srcset=\"https:\/\/www.fir3net.com\/wp-content\/uploads\/2018\/02\/images_articles_igmp_igmp-highlevel1.avif 871w,https:\/\/www.fir3net.com\/wp-content\/uploads\/2018\/02\/images_articles_igmp_igmp-highlevel1-300x95.avif 300w,https:\/\/www.fir3net.com\/wp-content\/uploads\/2018\/02\/images_articles_igmp_igmp-highlevel1-768x244.avif 768w\" sizes=\"(max-width: 871px) 100vw, 871px\" type=\"image\/avif\"><source srcset=\"https:\/\/www.fir3net.com\/wp-content\/uploads\/2018\/02\/images_articles_igmp_igmp-highlevel1.webp 871w,https:\/\/www.fir3net.com\/wp-content\/uploads\/2018\/02\/images_articles_igmp_igmp-highlevel1-300x95.webp 300w,https:\/\/www.fir3net.com\/wp-content\/uploads\/2018\/02\/images_articles_igmp_igmp-highlevel1-768x244.webp 768w\" sizes=\"(max-width: 871px) 100vw, 871px\" type=\"image\/webp\"><img src=\"https:\/\/www.fir3net.com\/wp-content\/uploads\/2018\/02\/images_articles_igmp_igmp-highlevel1.png\" height=\"277\" width=\"871\" srcset=\"https:\/\/www.fir3net.com\/wp-content\/uploads\/2018\/02\/images_articles_igmp_igmp-highlevel1.png 871w, https:\/\/www.fir3net.com\/wp-content\/uploads\/2018\/02\/images_articles_igmp_igmp-highlevel1-300x95.png 300w, https:\/\/www.fir3net.com\/wp-content\/uploads\/2018\/02\/images_articles_igmp_igmp-highlevel1-768x244.png 768w\" sizes=\"(max-width: 871px) 100vw, 871px\" class=\" size-full wp-image-1156 sp-no-webp\" alt=\"igmp-highlevel1\" loading=\"lazy\" decoding=\"async\"  > <\/picture><\/p>\n<p class=\"c7\" style=\"text-align: center;\"><strong><span class=\"c3\">Figure 1<\/span><\/strong><span class=\"c0\">\u00a0&#8211; Summary of Multicast Components.<\/span><\/p>\n<p class=\"c2\"><span class=\"c0\">There are 3 versions of IGMP &#8211; IGMPv1, IGMPv2, and IGMPv3.<\/span><\/p>\n<h2 class=\"c2\"><span class=\"ez-toc-section\" id=\"Versions\"><\/span>Versions<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<h3 id=\"h.62au6qu8gn4o\" class=\"c11\"><span class=\"ez-toc-section\" id=\"IGMPv1\"><\/span><span class=\"c5\">IGMPv1<\/span><span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p class=\"c2\"><span class=\"c0\">With IGMPv1, it introduced the following IGMP membership messages:<\/span><\/p>\n<ul class=\"c4 lst-kix_9j72orey7eoh-0 start\">\n<li class=\"c1\"><strong><span class=\"c3\">Membership Query<\/span><\/strong><span class=\"c0\">\u00a0&#8211; Sent by the multicast router on 224.0.01 (with a TTL of 1) to find multicast clients.<\/span><\/li>\n<li class=\"c1\"><strong><span class=\"c3\">Membership Report<\/span><\/strong><span class=\"c0\">\u00a0 &#8211; At the point the client receives the multicast query, the client sends a membership report back to the router. This contains the group or groups that the client wants to receive.<\/span><\/li>\n<\/ul>\n<p class=\"c2 c12\" style=\"text-align: center;\"><picture><source srcset=\"https:\/\/www.fir3net.com\/wp-content\/uploads\/2018\/02\/images_articles_igmp_igmpreport2.avif 846w,https:\/\/www.fir3net.com\/wp-content\/uploads\/2018\/02\/images_articles_igmp_igmpreport2-300x76.avif 300w,https:\/\/www.fir3net.com\/wp-content\/uploads\/2018\/02\/images_articles_igmp_igmpreport2-768x195.avif 768w\" sizes=\"(max-width: 646px) 100vw, 646px\" type=\"image\/avif\"><source srcset=\"https:\/\/www.fir3net.com\/wp-content\/uploads\/2018\/02\/images_articles_igmp_igmpreport2.webp 846w,https:\/\/www.fir3net.com\/wp-content\/uploads\/2018\/02\/images_articles_igmp_igmpreport2-300x76.webp 300w,https:\/\/www.fir3net.com\/wp-content\/uploads\/2018\/02\/images_articles_igmp_igmpreport2-768x195.webp 768w\" sizes=\"(max-width: 646px) 100vw, 646px\" type=\"image\/webp\"><img src=\"https:\/\/www.fir3net.com\/wp-content\/uploads\/2018\/02\/images_articles_igmp_igmpreport2.png\" height=\"164\" width=\"646\" srcset=\"https:\/\/www.fir3net.com\/wp-content\/uploads\/2018\/02\/images_articles_igmp_igmpreport2.png 846w, https:\/\/www.fir3net.com\/wp-content\/uploads\/2018\/02\/images_articles_igmp_igmpreport2-300x76.png 300w, https:\/\/www.fir3net.com\/wp-content\/uploads\/2018\/02\/images_articles_igmp_igmpreport2-768x195.png 768w\" sizes=\"(max-width: 646px) 100vw, 646px\" class=\" size-full wp-image-1157 sp-no-webp\" alt=\"igmpreport2\" loading=\"lazy\" decoding=\"async\"  > <\/picture><\/p>\n<p class=\"c7\" style=\"text-align: center;\"><strong><span class=\"c3\">Figure 2<\/span><\/strong><span class=\"c0\">\u00a0&#8211; IGMP Messages (IGMPv1)<\/span><\/p>\n<p class=\"c2\"><span class=\"c0\">However, IGMPv1 had two problems:<\/span><\/p>\n<ul class=\"c4 lst-kix_g5ho7veodixq-0 start\">\n<li class=\"c1\"><strong><span class=\"c3\">No Leave Group message<\/span><\/strong><span class=\"c0\">\u00a0&#8211; When a client no longer wanted to receive traffic for a multicast group, it would have to wait for the membership report to timeout, and another membership query was sent so it could report this to the router.<\/span><\/li>\n<li class=\"c1\"><strong><span class=\"c3\">Queries<\/span><\/strong><span class=\"c0\">\u00a0&#8211; When multiple membership routers are present on a single segment, multiple membership queries would be sent. This was highly inefficient.\u00a0<\/span><\/li>\n<\/ul>\n<h3 id=\"h.s8fcdzgpmi6x\" class=\"c11\"><span class=\"ez-toc-section\" id=\"IGMPv2\"><\/span><span class=\"c5\">IGMPv2<\/span><span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p class=\"c2\"><span class=\"c0\">IGMPv2 looked to address the issues with IGMPv1, and added the following features:<\/span><\/p>\n<ul class=\"c4 lst-kix_4xzlqj6q8dgp-0 start\">\n<li class=\"c1\"><strong><span class=\"c3\">Leave Group Message<\/span><\/strong><span class=\"c9\">\u00a0&#8211; The Leave Group message was added. This allows a client to inform the router that it no longer wants to be a member\/receive traffic from particular a multicast group.<\/span><\/li>\n<li class=\"c1\"><strong><span class=\"c3\">Group-specific Query Message<\/span><\/strong><span class=\"c0\">\u00a0&#8211; In addition to being able to send membership queries to 224.0.0.1, IGMPv2 also adds the ability to query an individual group. The group-specific query message is sent by the querying router after it has received a leave message, this is to ensure there are no further clients within the group wanting to receive the multicast stream. <\/span><\/li>\n<li class=\"c1\"><strong><span class=\"c3\">Designated Querier<\/span><\/strong><span class=\"c0\">\u00a0&#8211; Rather than every router upon a given segment sending IGMP queries, a Designated Querier (DQ) is elected. Only the DQ is permitted to send IGMP queries. The DQ election process is based on the router (within the segment) with the lowest IP being elected as the DQ.<\/span><\/li>\n<\/ul>\n<h3 id=\"h.5yzxmmbcykbw\" class=\"c11\"><span class=\"ez-toc-section\" id=\"IGMPv3\"><\/span><span class=\"c9 c17\">IGMPv3<\/span><span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p class=\"c2\"><span class=\"c0\">IGMPv3 adds support for <strong>Source Specific Multicast (SSM)<\/strong>. This provides the ability to specify, and join based on the source for the multicast group, instead of only being able to join based on any source\/multicast group, as per IGMPv1 and IGMPv2.<\/span><\/p>\n<h2 id=\"h.t4mtkodyszzj\" class=\"c14\"><span class=\"ez-toc-section\" id=\"IGMP_Snooping\"><\/span><span class=\"c9 c10\">IGMP Snooping<\/span><span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p class=\"c2\"><span class=\"c0\">As previously mentioned, IGMP operates at Layer 3. Because of this, switches have no understanding of IGMP messages. In addition, it is not possible for the switch to add the multicast MAC address to the forwarding table, this is because the multicast MAC address is never used as a source address. This results in the multicast traffic being flooded to all hosts within the broadcast domain.<\/span><\/p>\n<p class=\"c2\"><span class=\"c0\">IGMP Snooping is a feature, enabled upon layer 2 switches, that inspects the IGMP transmissions between the host and the router. Through this inspection, a mapping is built containing which hosts in a particular VLAN need to receive the multicast transmission.\u00a0<\/span><span class=\"c0\">The switch then uses this information to\u00a0forward multicast traffic for a given multicast group to ONLY the receivers within the given VLAN.<\/span><\/p>\n<h2 id=\"h.jyx3y75yegdk\" class=\"c14\"><span class=\"ez-toc-section\" id=\"IGMP_Querier\"><\/span><span class=\"c10 c9\">IGMP Querier<\/span><span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p class=\"c2\"><span class=\"c0\">When a multicast host wants to join a multicast group, it generates a multicast report, containing the groups that it wants to receive traffic for. However, when there is no multicast router upon the segment to originate an IGMP membership query from, the host has no-one to send its membership report to. <\/span><\/p>\n<p class=\"c2\"><span class=\"c9\">The role of the IGMP snooping querier (also known as an IGMP forwarder) is to send out periodic IGMP <\/span><span class=\"c9\">queries that trigger IGMP report messages from hosts that want to receive IP multicast traffic. IGMP snooping then listens to these IGMP reports to establish appropriate forwarding.<\/span><sup class=\"c9\"><a id=\"ftnt_ref1\" href=\"#ftnt1\">[1]<\/a><\/sup><\/p>\n<h2><span class=\"ez-toc-section\" id=\"References\"><\/span>References<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p class=\"c8\"><a id=\"ftnt1\" href=\"#ftnt_ref1\">[1]<\/a><span class=\"c20\">\u00a0&#8220;Cisco Nexus 5000 Series NX-OS Software Configuration Guide &#8230;.&#8221; <\/span><span class=\"c18\"><a class=\"c19\" href=\"https:\/\/www.google.com\/url?q=https:\/\/www.cisco.com\/c\/en\/us\/td\/docs\/switches\/datacenter\/nexus5000\/sw\/configuration\/guide\/cli_rel_4_0_1a\/CLIConfigurationGuide\/IGMPSnooping.html&amp;sa=D&amp;ust=1518300268035000&amp;usg=AFQjCNHeJKKL7M1_hVnbdUcNYOi8G_pufg\">https:\/\/www.cisco.com\/c\/en\/us\/td\/docs\/switches\/datacenter\/nexus5000\/sw\/configuration\/guide\/cli_rel_4_0_1a\/CLIConfigurationGuide\/IGMPSnooping.html<\/a><\/span><span class=\"c13\">. Accessed 10 Feb. 2018.<\/span><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Introduction IGMP (Internet Group Management Protocol) is a Layer 3 protocol (IP protocol number 2) and is a key component (Figure 1) to IP multicast. The role of IGMP\u00a0is to notify a local multicast router\u00a0when a host\u00a0wants to receive multicast traffic for a specific group. Figure 1\u00a0&#8211; Summary of Multicast Components. There are 3 versions &#8230; <a title=\"What is IGMP?\" class=\"read-more\" href=\"https:\/\/www.fir3net.com\/Networking\/Protocols\/what-is-igmp.html\" aria-label=\"Read more about What is IGMP?\">Read more<\/a><\/p>\n","protected":false},"author":2,"featured_media":1155,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[13],"tags":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v22.5 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>What is IGMP? - Fir3net<\/title>\n<meta name=\"description\" content=\"Introduction IGMP (Internet Group Management Protocol) is a Layer 3 protocol (IP protocol number 2) and is a key component (Figure 1) to IP multicast. 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