{"id":1163,"date":"2018-02-18T08:17:22","date_gmt":"2018-02-18T08:17:22","guid":{"rendered":"https:\/\/fir3netwp.gmsrrpobkbd.com\/2018\/02\/18\/cisco-ios-how-to-configure-ospf\/"},"modified":"2021-07-31T09:14:00","modified_gmt":"2021-07-31T09:14:00","slug":"cisco-ios-how-to-configure-ospf","status":"publish","type":"post","link":"https:\/\/www.fir3net.com\/Networking\/Protocols\/cisco-ios-how-to-configure-ospf.html","title":{"rendered":"Cisco IOS &#8211; How to Configure OSPF"},"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-662d3aba90eed\" 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-662d3aba90eed\"  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\/cisco-ios-how-to-configure-ospf.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\/cisco-ios-how-to-configure-ospf.html\/#Basic_Configuration\" title=\"Basic Configuration\">Basic Configuration<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/www.fir3net.com\/Networking\/Protocols\/cisco-ios-how-to-configure-ospf.html\/#Passive_interface\" title=\"Passive interface\">Passive interface<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-4\" href=\"https:\/\/www.fir3net.com\/Networking\/Protocols\/cisco-ios-how-to-configure-ospf.html\/#HELLO_Intervals\" title=\"HELLO Intervals\">HELLO Intervals<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-5\" href=\"https:\/\/www.fir3net.com\/Networking\/Protocols\/cisco-ios-how-to-configure-ospf.html\/#DR_Election\" title=\"DR Election\">DR Election<\/a><\/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\/cisco-ios-how-to-configure-ospf.html\/#Cost\" title=\"Cost\">Cost<\/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\/cisco-ios-how-to-configure-ospf.html\/#Summary_routes\" title=\"Summary routes\">Summary routes<\/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\/cisco-ios-how-to-configure-ospf.html\/#Default_route\" title=\"Default route\">Default route<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-9\" href=\"https:\/\/www.fir3net.com\/Networking\/Protocols\/cisco-ios-how-to-configure-ospf.html\/#Loopbacks\" title=\"Loopbacks\">Loopbacks<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-10\" href=\"https:\/\/www.fir3net.com\/Networking\/Protocols\/cisco-ios-how-to-configure-ospf.html\/#Verification_Commands\" title=\"Verification Commands\">Verification Commands<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-11\" href=\"https:\/\/www.fir3net.com\/Networking\/Protocols\/cisco-ios-how-to-configure-ospf.html\/#Additional_Links\" title=\"Additional Links\">Additional Links<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-12\" href=\"https:\/\/www.fir3net.com\/Networking\/Protocols\/cisco-ios-how-to-configure-ospf.html\/#References\" title=\"References\">References<\/a><\/li><\/ul><\/nav><\/div>\n<h2 id=\"h.eyjaynd2cke0\"><span class=\"ez-toc-section\" id=\"Introduction\"><\/span>Introduction<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p id=\"h.d9nm6rjntj7e\">With this article, we will look at the basic commands used within Cisco IOS to configure OSPF.<\/p>\n<h2 id=\"h.nflvm9tem8vq\"><span class=\"ez-toc-section\" id=\"Basic_Configuration\"><\/span>Basic Configuration<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>To initially configure OSPF, at a minimum, you must configure three things &#8211; <strong>process ID<\/strong>, <strong>router ID<\/strong>, and the <strong>network<\/strong>.<\/p>\n<ul>\n<li><strong> Process ID<\/strong> &#8211; Defines the OSPF process ID that OSPF will run under. This is typically set to 1 on all devices.<\/li>\n<li><strong> Router ID<\/strong> &#8211; The router ID is a unique number that identifies the router. It is used as a tie breaker to a route if all other metrics are the same between 2 routers to a destination.<\/li>\n<li><strong> Network<\/strong> &#8211; Allows you to define a network based on a wildcard mask. Any interface with an IP within the specified network will have OSPF enabled and the IP will be advertised into OSPF.<\/li>\n<\/ul>\n<p>Below shows you an example. The key thing to note here is the network command specifies that any interface with an IP of 10.0.0.3 will have OSPF enabled, and the IP advertised into OSPF and the LSDB.<\/p>\n<pre class=\"prettyprint\">R1# show run | sec ospf\r\nrouter ospf 1\r\n router-id 1.1.1.1\r\n network 10.0.0.3 0.0.0.0 area 0<\/pre>\n<h2 id=\"h.vbspgocifeef\"><span class=\"ez-toc-section\" id=\"Passive_interface\"><\/span>Passive interface<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>To explicitly disable an interface from OSPF, the following command can be used,<\/p>\n<pre class=\"prettyprint\">router ospf 1\r\n  ...\r\n  passive-interface gi0\/1<\/pre>\n<p>However, the recommended way (by Cisco) is to disable OSPF on all interfaces first and then to only enable OSPF on the required interfaces. Like so,<\/p>\n<pre class=\"prettyprint\">router ospf 1\r\n  ...\r\n  passive-interface default\r\n  no passive-interface gi0\/1<\/pre>\n<h2 id=\"h.2vh8lbspkguq\"><span class=\"ez-toc-section\" id=\"HELLO_Intervals\"><\/span>HELLO Intervals<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>The HELLO interval setting (default 10 seconds for broadcast network types) is changed on a per-interface basis.<\/p>\n<pre class=\"prettyprint\">interface gi0\/1\r\n  ...\r\n  ip ospf hello interval 1<\/pre>\n<p>To determine the current HELLO interval timer settings, the command <span class=\"codeinline\">show ip ospf interface<\/span> can be used.<\/p>\n<pre class=\"prettyprint\">R1# show ip ospf interface \r\nGigabitEthernet0\/1 is up, line protocol is up \r\n  Internet Address 10.0.128.6\/30, Area 0, Attached via Network Statement\r\n  Process ID 1, Router ID 1.1.1.1, Network Type BROADCAST, Cost: 1\r\n  Topology-MTID    Cost    Disabled    Shutdown      Topology Name\r\n        0           1         no          no            Base\r\n  Transmit Delay is 1 sec, State DR, Priority 2\r\n  Designated Router (ID) 1.1.1.1, Interface address 10.0.128.6\r\n  No backup designated router on this network\r\n  Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5<\/pre>\n<h2 id=\"h.eue7vg6tc0bg\"><span class=\"ez-toc-section\" id=\"DR_Election\"><\/span>DR Election<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>The priority determines which routers are selected as the designated router (DR) and backup designated router (BDR) of the area. <sup> <a id=\"ftnt_ref1\" href=\"#ftnt1\"> [1] <\/a> <\/sup> The router with the highest wins the election.<\/p>\n<p>The configuration to change the priority is configured on a per-interface basis. Like so:<\/p>\n<p><strong>Non-DR<\/strong><\/p>\n<pre class=\"prettyprint\">interface gi0\/1   ...   ip ospf priority 0<\/pre>\n<p><strong>DR<\/strong><\/p>\n<pre class=\"prettyprint\">interface gi0\/1   ...   ip ospf priority 1<\/pre>\n<h2 id=\"h.1y72gcml8sqm\"><span class=\"ez-toc-section\" id=\"Cost\"><\/span>Cost<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>OSPF uses a reference bandwidth of 100 Mbps (10^8) for cost calculation. The formula to calculate the cost is reference bandwidth divided by interface bandwidth ; <strong> Interface Cost= 10^8\/(interface bandwidth)<\/strong>. Calculated values are rounded up to the nearest single decimal value. This means that OSPF will calculate interfaces with speeds higher than 10 Mbps as a cost of 1 (Table 1). T he result of this is that OSPF routers in the network cannot make an accurate path calculation when comparing fast Ethernet interface versus a gigabit Ethernet interface as both interfaces has a cost of 1. <sup> <a id=\"ftnt_ref2\" href=\"#ftnt2\"> [2] <\/a><\/sup><\/p>\n<table class=\"table table-striped table-condensed\">\n<tbody>\n<tr>\n<th>Interface Type<\/th>\n<th>Cost<\/th>\n<\/tr>\n<tr>\n<td>100 Gbps<\/td>\n<td>1<\/td>\n<\/tr>\n<tr>\n<td>40 Gbps<\/td>\n<td>1<\/td>\n<\/tr>\n<tr>\n<td>10 Gbps<\/td>\n<td>1<\/td>\n<\/tr>\n<tr>\n<td>10 Gbps<\/td>\n<td>1<\/td>\n<\/tr>\n<tr>\n<td>1 Gbps<\/td>\n<td>1<\/td>\n<\/tr>\n<tr>\n<td>100 Mbps<\/td>\n<td>1<\/td>\n<\/tr>\n<tr>\n<td>10 Mbps<\/td>\n<td>10<\/td>\n<\/tr>\n<tr>\n<td>1.544 Mbps<\/td>\n<td>64<\/td>\n<\/tr>\n<tr>\n<td>768 Kbps<\/td>\n<td>133<\/td>\n<\/tr>\n<tr>\n<td>384 Kbps<\/td>\n<td>266<\/td>\n<\/tr>\n<tr>\n<td>128 Kbps<\/td>\n<td>781<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p style=\"text-align: center;\"><strong>Table 1<\/strong> &#8211; Default OSPF cost calculations.<\/p>\n<p>There are two methods for changing the calculated costs &#8211; <strong>auto-cost<\/strong> and<strong> interface cost<\/strong>.<\/p>\n<p>The <span class=\"codeinline\">auto-cost reference-bandwidth<\/span>\u00a0command allows you to change the reference bandwidth that OSPF uses to calculate its metrics:<\/p>\n<pre class=\"prettyprint\">router ospf 1   ...     auto-cost reference-bandwidth 1000000<\/pre>\n<p><span class=\"uk-badge uk-badge-warning\">REMEMBER<\/span> You must ensure the reference bandwidth is consistent across all routers.<\/p>\n<p><span class=\"codeinline\">ip ospf cost<\/span> can also be used to change the OSPF cost. However, this works on a per-interface basis and will override the calculated cost.<\/p>\n<pre class=\"prettyprint\">int gi0\/1\r\n  ...\r\n  ip ospf cost 1234<\/pre>\n<p>To verify the interface cost, the following command is used:<\/p>\n<pre class=\"prettyprint\">show ip ospf interface | inc Cost\r\n  Process ID 1, Router ID 1.1.1.1, Network Type BROADCAST, Cost: 1\r\n  Topology-MTID    Cost    Disabled    Shutdown      Topology Name\r\n  Process ID 1, Router ID 1.1.1.1, Network Type BROADCAST, Cost: 1\r\n  Topology-MTID    Cost    Disabled    Shutdown      Topology Name<\/pre>\n<h2 id=\"h.ulu1ejcnpami\"><span class=\"ez-toc-section\" id=\"Summary_routes\"><\/span>Summary routes<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>OSPF, unlike EIGRP, doesn\u2019t support automatic summarization. Also, unlike EIGRP, where you can summarize routes on every router in an EIGRP network, OSFP can summarize routes only on ABRs and ASBRs. <sup> <a id=\"ftnt_ref3\" href=\"#ftnt3\"> [3] <\/a> <\/sup> Route summarization both decreases the amount of OSPF traffic and also reduce the computation cycles required for SPF calculations.<\/p>\n<p>OSPF provides two types of route summarization &#8211; <strong>Inter-Area Summarization<\/strong> and <strong>External Summarization<\/strong>.<\/p>\n<p><strong> Inter-Area Summarization <\/strong> is performed on the Area Border Router (ABR) only. Routes are summarized from one OSPF area to another.<\/p>\n<pre class=\"prettyprint\">router ospf 1\r\n  ...\r\n  summary-address 10.0.0.0 255.255.0.0<\/pre>\n<p><strong> External Summarization <\/strong> can only be done on the ASBR (Autonomous System Boundary Router). Routes are summarized to an external destinations.<\/p>\n<pre class=\"prettyprint\">router ospf 1\r\n  ...\r\n  area 0 range 10.1.1.0 255.255.255.0<\/pre>\n<h2 id=\"h.9clcw4glbk2h\"><span class=\"ez-toc-section\" id=\"Default_route\"><\/span>Default route<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>OSPF, by default doe not generate a default route into the OSPF domain. In order for OSPF to generate a default route, the <span class=\"codeinline\"> default-information originate <\/span> command is used.<\/p>\n<pre class=\"prettyprint\">router ospf 1\r\n  ...\r\n  default-information originate<\/pre>\n<h2 id=\"h.obrmqsetnh8w\"><span class=\"ez-toc-section\" id=\"Loopbacks\"><\/span>Loopbacks<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>A good practice to help with OSPF administration and troubleshooting is to also configure the loopback on the device, inline with its configured router id, so that it is pingable.\u00a0Like so:<\/p>\n<pre class=\"prettyprint\">interface Loopback1\r\n  ...\r\n  ip address 1.1.1.1 255.255.255.255<\/pre>\n<p>router ospf 1<br \/>\n&#8230;<br \/>\nnetwork 1.1.1.1 0.0.0.0 area 0<\/p>\n<h2 id=\"h.meahypquh41h\"><span class=\"ez-toc-section\" id=\"Verification_Commands\"><\/span>Verification Commands<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>Below are some of the key commands you can use to verify and troubleshoot your OSPF configuration.<\/p>\n<table class=\"table table-striped table-condensed\">\n<tbody>\n<tr>\n<th>Command<\/th>\n<th>Description<\/th>\n<\/tr>\n<tr>\n<td>show ip protocols<\/td>\n<td>Show detailed information about the OSPF process.<\/td>\n<\/tr>\n<tr>\n<td>show ip ospf neighbors<\/td>\n<td>Show details about OSPF neighbors.<\/td>\n<\/tr>\n<tr>\n<td>show ip ospf interface<\/td>\n<td>Show detailed OSPF information about OSPF interfaces.<\/td>\n<\/tr>\n<tr>\n<td>debug ip ospf adj<\/td>\n<td>Debug the OSPF adjacency process.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p style=\"text-align: center;\"><strong>Table 2<\/strong> &#8211; Verification commands.<\/p>\n<h2><span class=\"ez-toc-section\" id=\"Additional_Links\"><\/span>Additional Links<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p><a href=\"https:\/\/www.google.com\/url?q=https:\/\/sites.google.com\/site\/amitsciscozone\/home\/important-tips\/ospf\/ospf-packet-types&amp;sa=D&amp;ust=1518944984545000&amp;usg=AFQjCNHMpgC32AJfnWfWpt1pMutAwRTNzQ\"> https:\/\/sites.google.com\/site\/amitsciscozone\/home\/important-tips\/ospf\/ospf-packet-types <\/a><\/p>\n<h2><span class=\"ez-toc-section\" id=\"References\"><\/span>References<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p><a id=\"ftnt1\" href=\"#ftnt_ref1\"> [1] <\/a> &#8220;interfaces &lt;interface&gt; &lt;interface-name&gt; ip ospf priority &#8230; &#8211; Brocade.&#8221; <a href=\"https:\/\/www.google.com\/url?q=http:\/\/www.brocade.com\/content\/html\/en\/vrouter5600\/35r6\/vrouter-35r6-ospf\/GUID-0D44C556-C65B-436D-BE28-0ABC4F588E66.html&amp;sa=D&amp;ust=1518944984546000&amp;usg=AFQjCNEbW1l1nExKufjKnoU1ekuosQ-OnQ\"> http:\/\/www.brocade.com\/content\/html\/en\/vrouter5600\/35r6\/vrouter-35r6-ospf\/GUID-0D44C556-C65B-436D-BE28-0ABC4F588E66.html <\/a> . Accessed 17 Feb. 2018.<br \/>\n<a id=\"ftnt2\" href=\"#ftnt_ref2\"> [2] <\/a> &#8220;How to configure OSPF cost &#8211; Cisco Support Community.&#8221; 22 Jun. 2009, <a href=\"https:\/\/www.google.com\/url?q=https:\/\/supportforums.cisco.com\/t5\/network-infrastructure-documents\/how-to-configure-ospf-cost\/ta-p\/3133153&amp;sa=D&amp;ust=1518944984546000&amp;usg=AFQjCNH5UcydDW1lrrasN3MLvCU3PmxK9Q\"> https:\/\/supportforums.cisco.com\/t5\/network-infrastructure-documents\/how-to-configure-ospf-cost\/ta-p\/3133153 <\/a> . Accessed 18 Feb. 2018.<br \/>\n<a id=\"ftnt3\" href=\"#ftnt_ref3\"> [3] <\/a> &#8220;OSPF summarization &#8211; Study CCNA.&#8221; <a href=\"https:\/\/www.google.com\/url?q=http:\/\/study-ccna.com\/ospf-summarization\/&amp;sa=D&amp;ust=1518944984547000&amp;usg=AFQjCNFmZ1A_-ynixwUHFzd0P8q9ftq1GA\"> http:\/\/study-ccna.com\/ospf-summarization\/ <\/a> . Accessed 18 Feb. 2018.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Introduction With this article, we will look at the basic commands used within Cisco IOS to configure OSPF. Basic Configuration To initially configure OSPF, at a minimum, you must configure three things &#8211; process ID, router ID, and the network. Process ID &#8211; Defines the OSPF process ID that OSPF will run under. This is &#8230; <a title=\"Cisco IOS &#8211; How to Configure OSPF\" class=\"read-more\" href=\"https:\/\/www.fir3net.com\/Networking\/Protocols\/cisco-ios-how-to-configure-ospf.html\" aria-label=\"Read more about Cisco IOS &#8211; How to Configure OSPF\">Read more<\/a><\/p>\n","protected":false},"author":2,"featured_media":1162,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[12],"tags":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v22.5 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>Cisco IOS - How to Configure OSPF - Fir3net<\/title>\n<meta name=\"description\" content=\"Introduction With this article, we will look at the basic commands used within Cisco IOS to configure OSPF. 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