{"id":241,"date":"2020-07-30T22:11:46","date_gmt":"2020-07-30T21:11:46","guid":{"rendered":"http:\/\/www.labtinker.net\/?p=241"},"modified":"2020-07-30T22:11:46","modified_gmt":"2020-07-30T21:11:46","slug":"fragmentation","status":"publish","type":"post","link":"https:\/\/labtinker.net\/?p=241","title":{"rendered":"Fragmentation"},"content":{"rendered":"\n<p class=\"wp-block-paragraph\">I think the joy of tinkering is that you don\u2019t have to do anything earth-shattering but just messing around can bring home elements you grasp theoretically or only get chance to see or work on occasionally in the wild.  This post is a little ropey as it was never intended for publication, but it\u2019s been a thin few weeks as I&#8217;m so-say studying for a cert. <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">I intended to investigate the effects of fragmentation on VPNs for reasons I can\u2019t quite remember. In the event I only got as far as looking at it on my two dummy \u2018ISP\u2019 routers before I found something better to do. However, even this was mildly interesting (well, you can be the judge of that)<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">My set up was simple, even by my standards: two routers in GNS3. One named RTR-LON for London and the other RTR-FRA for France \u2013 (the inconsistency in naming one router after a city and another after a country was my desire to accurately reflect the hodge-podge you find in most real-life networks and in no way a senior moment.)<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"445\" height=\"115\" src=\"http:\/\/18.135.13.153\/wp-content\/uploads\/2020\/07\/image-21.png\" alt=\"\" class=\"wp-image-242\" srcset=\"https:\/\/labtinker.net\/wp-content\/uploads\/2020\/07\/image-21.png 445w, https:\/\/labtinker.net\/wp-content\/uploads\/2020\/07\/image-21-300x78.png 300w\" sizes=\"auto, (max-width: 445px) 100vw, 445px\" \/><figcaption class=\"wp-element-caption\">Figure 1:  RTR-LON to RTR-FRA<\/figcaption><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">On the RTR-FRA we have a loopback ip address of 70.70.70.7 and so I did an extended ping from RTR-LON with a packet size of 2000 bytes.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">And thus we see a packet with a length of 1500 (the mtu of the interface) and a flag to tell us there are more fragments.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"454\" height=\"112\" src=\"http:\/\/18.135.13.153\/wp-content\/uploads\/2020\/07\/image-27.png\" alt=\"\" class=\"wp-image-249\" srcset=\"https:\/\/labtinker.net\/wp-content\/uploads\/2020\/07\/image-27.png 454w, https:\/\/labtinker.net\/wp-content\/uploads\/2020\/07\/image-27-300x74.png 300w\" sizes=\"auto, (max-width: 454px) 100vw, 454px\" \/><figcaption class=\"wp-element-caption\">Figure 2: There&#8217;s more to come.<\/figcaption><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">The next fragment contains the remainder of the packet <\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"499\" height=\"156\" src=\"http:\/\/18.135.13.153\/wp-content\/uploads\/2020\/07\/image-29.png\" alt=\"\" class=\"wp-image-251\" srcset=\"https:\/\/labtinker.net\/wp-content\/uploads\/2020\/07\/image-29.png 499w, https:\/\/labtinker.net\/wp-content\/uploads\/2020\/07\/image-29-300x94.png 300w\" sizes=\"auto, (max-width: 499px) 100vw, 499px\" \/><figcaption class=\"wp-element-caption\">Figure 3: The next fragment.<\/figcaption><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">So the overview in Wireshark looked like this&#8230; <\/p>\n\n\n\n<figure class=\"wp-block-image size-large is-resized\"><img loading=\"lazy\" decoding=\"async\" src=\"http:\/\/18.135.13.153\/wp-content\/uploads\/2020\/07\/image-30-1024x46.png\" alt=\"\" class=\"wp-image-252\" width=\"931\" height=\"41\" srcset=\"https:\/\/labtinker.net\/wp-content\/uploads\/2020\/07\/image-30-1024x46.png 1024w, https:\/\/labtinker.net\/wp-content\/uploads\/2020\/07\/image-30-300x13.png 300w, https:\/\/labtinker.net\/wp-content\/uploads\/2020\/07\/image-30-768x34.png 768w, https:\/\/labtinker.net\/wp-content\/uploads\/2020\/07\/image-30.png 1204w\" sizes=\"auto, (max-width: 931px) 100vw, 931px\" \/><figcaption class=\"wp-element-caption\">Figure 4: Blurry Wireshark capture<\/figcaption><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">OK, so let&#8217;s take it to the max. It turns out the biggest packet you can send with extended ping is 18024 on the virtual router I&#8217;m usiing.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"602\" height=\"213\" src=\"http:\/\/18.135.13.153\/wp-content\/uploads\/2020\/07\/image-31.png\" alt=\"\" class=\"wp-image-253\" srcset=\"https:\/\/labtinker.net\/wp-content\/uploads\/2020\/07\/image-31.png 602w, https:\/\/labtinker.net\/wp-content\/uploads\/2020\/07\/image-31-300x106.png 300w\" sizes=\"auto, (max-width: 602px) 100vw, 602px\" \/><figcaption class=\"wp-element-caption\">Figure 5: Turning it up to 11.<\/figcaption><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">And look how many fragments it takes to send one packet (though isn&#8217;t a fragment a packet in itself? But, it&#8217;s late and we all know what I mean.)<\/p>\n\n\n\n<figure class=\"wp-block-image size-large is-resized\"><img loading=\"lazy\" decoding=\"async\" src=\"http:\/\/18.135.13.153\/wp-content\/uploads\/2020\/07\/image-32-1024x204.png\" alt=\"\" class=\"wp-image-254\" width=\"1088\" height=\"217\" srcset=\"https:\/\/labtinker.net\/wp-content\/uploads\/2020\/07\/image-32-1024x204.png 1024w, https:\/\/labtinker.net\/wp-content\/uploads\/2020\/07\/image-32-300x60.png 300w, https:\/\/labtinker.net\/wp-content\/uploads\/2020\/07\/image-32-768x153.png 768w, https:\/\/labtinker.net\/wp-content\/uploads\/2020\/07\/image-32.png 1204w\" sizes=\"auto, (max-width: 1088px) 100vw, 1088px\" \/><figcaption class=\"wp-element-caption\">Figure 6: How many fragments?<\/figcaption><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">How many fragments. Go on, count them? To send one mega-ping&#8230;. I should get a life, shouldn&#8217;t I?<\/p>\n","protected":false},"excerpt":{"rendered":"<p>I think the joy of tinkering is that you don\u2019t have to do anything earth-shattering but just messing around can bring home elements you grasp theoretically or only get chance to see or work on occasionally in the wild. This post is a little ropey as it was never intended for publication, but it\u2019s been [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[9],"tags":[],"class_list":["post-241","post","type-post","status-publish","format-standard","hentry","category-networking"],"jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/labtinker.net\/index.php?rest_route=\/wp\/v2\/posts\/241","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/labtinker.net\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/labtinker.net\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/labtinker.net\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/labtinker.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=241"}],"version-history":[{"count":0,"href":"https:\/\/labtinker.net\/index.php?rest_route=\/wp\/v2\/posts\/241\/revisions"}],"wp:attachment":[{"href":"https:\/\/labtinker.net\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=241"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/labtinker.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=241"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/labtinker.net\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=241"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}