{"id":688,"date":"2014-03-26T06:08:27","date_gmt":"2014-03-26T06:08:27","guid":{"rendered":"http:\/\/demo.mythemeshop.com\/magxp\/?p=9"},"modified":"2017-04-22T17:50:43","modified_gmt":"2017-04-22T17:50:43","slug":"configure-rhel-6-centos-6-with-two-nics","status":"publish","type":"post","link":"https:\/\/likeroot.com\/blog\/configure-rhel-6-centos-6-with-two-nics\/","title":{"rendered":"How To Configure RHEL 6 \/ CentOS 6 With two NICs in the same subnet"},"content":{"rendered":"<p>Since CentOS\/RHEL6 onwards (newer kernels higher than 2.6.32 ) asymmetric routing doesn\u2019t work anymore out of the box. There was a change in rp_filter settings causing this issue.<\/p>\n<p> The &#8220;rp_filter&#8221; stands for reverse path filtering. The reverse path filter will check if the source of a packet that was received on a certain interface is reachable trough the same interface it was received. The purpose is to prevent spoofed packets, with a changed source address, not being processed\/routed further. In a router it could also prevent routing packets that have a private IP as source to the Internet as they obviously will never find their way back.<\/p>\n<p>Since RHEL 6 and its derivative CentOS 6, rp_filter, which can be controlled by kernel parameters, is set on a default value of 1. This means that the rp_filter is operational in strict mode and does exactly what it is designed for.<\/p>\n<p>Possible value are:<\/p>\n<div class=\"message_box announce\"><p> 0: No source validation<br \/>\n    1: Strict mode (failed packets are discarded), described in RFC3704<br \/>\n    2: Loose mode, only discards the packet when it isn\u2019t routable over any of the interfaces on the host.<\/p><\/div>\n<p>In short, there are two options:<\/p>\n<p>1) edit the file &#8220;<strong>\/etc\/sysctl.conf<\/strong>&#8221;<\/p>\n<p>change the value from 1 to 2 in the following line:<\/p>\n<pre>net.ipv4.conf.default.rp_filter = 1<\/pre>\n<p>Add this line:<\/p>\n<pre>net.ipv4.conf.all.rp_filter = 2<\/pre>\n<p>After edit, it should look like this:<\/p>\n<pre>net.ipv4.conf.default.rp_filter = 2\r\nnet.ipv4.conf.all.rp_filter = 2<\/pre>\n<p>reload the configuration by typing<\/p>\n<pre>sysctl -p <\/pre>\n<p>Now you should be able to ping both IPs<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Since CentOS\/RHEL6 onwards (newer kernels higher than 2.6.32 ) asymmetric routing doesn\u2019t work anymore out of the box. There was a change in rp_filter settings causing this issue. The &#8220;rp_filter&#8221; stands for reverse path filtering. The reverse path filter will check if the source of a packet that was received on a certain interface is reachable trough the same interface it was received. The purpose is to prevent spoofed packets, with a changed source address, not being processed\/routed further. In a router it could also prevent routing packets that have a private IP as source to the Internet as they <\/p>\n","protected":false},"author":1,"featured_media":980,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[8,13,14],"class_list":["post-688","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-tutorials","tag-advertising","tag-marketing","tag-software","has_thumb"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v28.2 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>How To Configure RHEL 6 \/ CentOS 6 With two NICs in the same subnet - Likeroot Server Technologies<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/likeroot.com\/blog\/configure-rhel-6-centos-6-with-two-nics\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"How To Configure RHEL 6 \/ CentOS 6 With two NICs in the same subnet - Likeroot Server Technologies\" \/>\n<meta property=\"og:description\" content=\"Since CentOS\/RHEL6 onwards (newer kernels higher than 2.6.32 ) asymmetric routing doesn\u2019t work anymore out of the box. There was a change in rp_filter settings causing this issue. The &#8220;rp_filter&#8221; stands for reverse path filtering. The reverse path filter will check if the source of a packet that was received on a certain interface is reachable trough the same interface it was received. The purpose is to prevent spoofed packets, with a changed source address, not being processed\/routed further. 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