{"id":743,"date":"2011-04-19T11:04:26","date_gmt":"2011-04-19T10:04:26","guid":{"rendered":"http:\/\/mccltd.net\/blog\/?p=743"},"modified":"2015-02-21T09:29:58","modified_gmt":"2015-02-21T09:29:58","slug":"rfc-2597-assured-forwarding-per-hop-behavior-group","status":"publish","type":"post","link":"http:\/\/darenmatthews.com\/blog\/?p=743","title":{"rendered":"RFC 2597 Assured Forwarding Per-Hop Behaviour Group"},"content":{"rendered":"<p>RFC 2597 defines four Assured Forwarding groups, denoted by the letters &#8220;AF&#8221; followed by two digits:<!--more--><\/p>\n<ul>\n<li>The first digit denotes the AF class number and can range from 1 through 4 (these values correspond to the three most-significant bits of the codepoint or the IPP value that the codepoint falls under). Incidentally, the AF class number does not in itself represent hierarchy (that is, AF class 4 does not necessarily get any preferential treatment over AF class 1).<\/li>\n<li>The second digit refers to the level of drop precedence within each AF class and can range from 1 (lowest drop precedence) through 3 (highest drop precedence).<\/li>\n<\/ul>\n<p><a rel=\"attachment wp-att-744\" href=\"http:\/\/darenmatthews.com\/blog\/?attachment_id=744\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-744\" title=\"RFC2597\" src=\"http:\/\/darenmatthews.com\/blog\/wp-content\/uploads\/2010\/04\/RFC2597.jpg\" alt=\"RFC2597\" width=\"364\" height=\"151\" srcset=\"http:\/\/darenmatthews.com\/blog\/wp-content\/uploads\/2010\/04\/RFC2597.jpg 364w, http:\/\/darenmatthews.com\/blog\/wp-content\/uploads\/2010\/04\/RFC2597-300x124.jpg 300w\" sizes=\"(max-width: 364px) 100vw, 364px\" \/><\/a>The three levels of drop precedence are analogous to the three states of a traffic light:<\/p>\n<ul>\n<li>Drop precedence 1, also known as the &#8220;conforming&#8221; state, is comparable to a green traffic light.<\/li>\n<li>Drop precedence 2, also known as the &#8220;exceeding&#8221; state, is comparable to a yellow traffic light (where a moderate allowance in excess of the conforming rate is allowed to prevent erratic traffic patterns).<\/li>\n<li>Drop precedence 3, also known as the &#8220;violating&#8221; state, is comparable to a red traffic light.<\/li>\n<\/ul>\n<p><strong>Policing:<\/strong><\/p>\n<p>Packets within an AF class are always initially marked to drop precedence of 1 and can only be remarked to drop precedence 2 or 3 by a policer, which meters traffic rates and determines if the traffic is exceeding or violating a given traffic contract.<\/p>\n<p>Then, for example, during periods of congestion on an RFC 2597-compliant node, packets remarked AF33 (representing the highest drop precedence for AF class 3) would be dropped more often than packets remarked AF32; in turn, packets remarked AF32 would be dropped more often than packets marked AF31.<\/p>\n<div id=\"attachment_745\" style=\"width: 498px\" class=\"wp-caption aligncenter\"><a rel=\"attachment wp-att-745\" href=\"http:\/\/darenmatthews.com\/blog\/?attachment_id=745\"><img aria-describedby=\"caption-attachment-745\" loading=\"lazy\" class=\"size-full wp-image-745\" title=\"RFC 3246 An Expedited Forwarding Per-Hop Behavior\" src=\"http:\/\/darenmatthews.com\/blog\/wp-content\/uploads\/2010\/04\/RFC-3246-An-Expedited-Forwarding-Per-Hop-Behavior.jpg\" alt=\"RFC 3246 An Expedited Forwarding Per-Hop Behaviour\" width=\"488\" height=\"183\" srcset=\"http:\/\/darenmatthews.com\/blog\/wp-content\/uploads\/2010\/04\/RFC-3246-An-Expedited-Forwarding-Per-Hop-Behavior.jpg 488w, http:\/\/darenmatthews.com\/blog\/wp-content\/uploads\/2010\/04\/RFC-3246-An-Expedited-Forwarding-Per-Hop-Behavior-300x112.jpg 300w\" sizes=\"(max-width: 488px) 100vw, 488px\" \/><\/a><p id=\"caption-attachment-745\" class=\"wp-caption-text\">RFC 3246 An Expedited Forwarding Per-Hop Behaviour<\/p><\/div>\n","protected":false},"excerpt":{"rendered":"<p>RFC 2597 defines four Assured Forwarding groups, denoted by the letters &#8220;AF&#8221; followed by two digits:<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[27,76],"tags":[21],"_links":{"self":[{"href":"http:\/\/darenmatthews.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/743"}],"collection":[{"href":"http:\/\/darenmatthews.com\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/darenmatthews.com\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/darenmatthews.com\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/darenmatthews.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=743"}],"version-history":[{"count":6,"href":"http:\/\/darenmatthews.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/743\/revisions"}],"predecessor-version":[{"id":763,"href":"http:\/\/darenmatthews.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/743\/revisions\/763"}],"wp:attachment":[{"href":"http:\/\/darenmatthews.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=743"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/darenmatthews.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=743"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/darenmatthews.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=743"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}