{"id":1185,"date":"2020-11-20T18:19:00","date_gmt":"2020-11-20T18:19:00","guid":{"rendered":"http:\/\/bytereign.com\/?p=1185"},"modified":"2025-04-22T10:22:40","modified_gmt":"2025-04-22T09:22:40","slug":"ospf-open-shortest-path-first-quick-reference-notes","status":"publish","type":"post","link":"https:\/\/bytereign.com\/?p=1185","title":{"rendered":"OSPF (Open Shortest Path First): Quick Reference Notes"},"content":{"rendered":"\t\t
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Quick OSPF notes, made for network professionals seeking insights into key attributes, the link-state routing protocol, and network convergence.<\/span><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t

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Open Shortest Path First (OSPF)<\/span><\/p>

\u00a0<\/p>

Basic Information<\/span><\/p>

  1. Version: v2<\/span><\/li>
  2. Standard: RFC 2328<\/span><\/li>
  3. Algorithm: Dijkstra<\/span><\/li>
  4. Type: IGP – Link – State<\/span><\/li>
  5. Metric: Cost (Bandwidth)<\/span><\/li>
  6. Administrative Distance: 110<\/span><\/li>
  7. Transport: 89<\/span><\/li>
  8. Authentication: Plaintext, MD5<\/span><\/li><\/ol>

    \u00a0<\/span><\/p>

    Packet Types<\/span><\/p>

    1. Hello Packets<\/span><\/li>
    2. Database Description<\/span><\/li>
    3. Link State Request<\/span><\/li>
    4. Link State Update<\/span><\/li>
    5. Link State Acknowledge<\/span><\/li><\/ol>
      \u00a0<\/div>

      OSPF Table Types<\/span><\/p>

      1. Neighbor table<\/span><\/li>
      2. Topology table<\/span><\/li>
      3. Routing table<\/span><\/li><\/ol>
        \u00a0<\/span><\/div>

        OSPF \u2013 Neighbor Adjacency States<\/span><\/p>

        1. Down \u2013 No Hellos have been learned from the neighboring router.<\/span><\/li>
        2. Init \u2013 Hello packet has been learned from the neighbor, but two-way communication has not yet been initialized.<\/span><\/li>
        3. 2-Way \u2013 Bidirectional communication has been built, Designated and Backup Designated Routers are selected at this stage.<\/span><\/li>
        4. Ex-Start \u2013 The routers are planning to share the link-state information. Master\/slave relations are established between routers.<\/span><\/li>
        5. Exchange \u2013 The routers are switching Database Descriptors (DBDs), the router will query a neighbor\u2019s DBD to decide if it has data to share.<\/span><\/li>
        6. Loading \u2013 The routers are finally switching Link State Advertisements, including data about all links connected to each router. Routers will share their topology tables.<\/span><\/li>
        7. Full \u2013 The routers are completely synchronized.<\/span><\/li><\/ol>
          \u00a0<\/span><\/div>

          Path Selection<\/span><\/p>

          1. Select the longest match, the most specific route.<\/span><\/li>
          2. Select the path with the lowest administrative distance.<\/span><\/li>
          3. Select most preferred route origination within OSPF.<\/span><\/li>
          4. Select the lowest cumulative cost.<\/span><\/li><\/ol>
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            OSPF Session Establishment between peers<\/span><\/p>

            1. Neighbor discovery<\/span><\/li>
            2. Link-state information exchange<\/span><\/li>
            3. Best-path calculation<\/span><\/li><\/ol>

              \u00a0<\/span><\/p>

              OSPF Network Types<\/span><\/p>

              1. Broadcast Multi-Access – OSPF will elect DRs and BDRs<\/span><\/li>
              2. Point-to-Point – OSPF will not elect DRs and BDRs<\/span><\/li>
              3. Point-to-Multipoint – OSPF will not elect DRs and BDRs<\/span><\/li>
              4. Non-broadcast Multi-access Network – OSPF will elect DRs and BDRs<\/span><\/li><\/ol>

                \u00a0<\/span><\/p>

                Link-state advertisements (LSAs)<\/span><\/p>

                1. Router LSA (Type 1)<\/span><\/li>
                2. Network LSA (Type 2)<\/span><\/li>
                3. Network Summary LSA (Type 3)<\/span><\/li>
                4. ASBR Summary LSA (Type 4)<\/span><\/li>
                5. External LSA (Type 5)<\/span><\/li>
                6. Multicast OSPF LSA (MOSPF – Type 6)<\/span><\/li>
                7. NSSA External LSA (Type 7)<\/span><\/li><\/ol>

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                  OSPF defines two types of external routes<\/span><\/p>

                  1. Type 2 (E2) \u2013 Includes only the external cost to the destination Network.<\/span><\/li>
                  2. Type 1 (E1) \u2013 Includes both the external cost, and the internal cost.<\/span><\/li><\/ol>

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                    OSPF Commands of Cisco, Juniper & Alcatel<\/span><\/p>

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                    Cisco OSPF Commands<\/span><\/p>

                    1. show ip ospf database<\/span><\/li>
                    2. show ip ospf interface<\/span><\/li>
                    3. show ip ospf neighbor<\/span><\/li>
                    4. show route ospf<\/span><\/li>
                    5. show ospf statistics<\/span><\/li><\/ol>

                      \u00a0<\/span><\/p>

                      Juniper OSPF Commands<\/span><\/p>

                      1. show ospf database<\/span><\/li>
                      2. show ospf interface<\/span><\/li>
                      3. show ospf neighbor<\/span><\/li>
                      4. show route protocol ospf<\/span><\/li>
                      5. show ospf statistics<\/span><\/li><\/ol>

                        \u00a0<\/span><\/p>

                        Alcatel OSPF Commands<\/span><\/p>

                        1. show router ospf database<\/span><\/li>
                        2. show router ospf interface<\/span><\/li>
                        3. show router ospf neighbor<\/span><\/li>
                        4. show router ospf routes<\/span><\/li>
                        5. show router ospf statistics<\/span><\/li><\/ol>

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                          Other important OSPF topics<\/span><\/p>

                          1. OSPF Passive-Interfaces<\/span><\/li>
                          2. OSPF Authentication<\/span><\/li>
                          3. OSPF Virtual Links<\/span><\/li>
                          4. OSPF SPF Timers<\/span><\/li>
                          5. Inter-Area OSPF Summarization<\/span><\/li>
                          6. External OSPF Summarization<\/span><\/li><\/ol>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t","protected":false},"excerpt":{"rendered":"

                            Quick OSPF notes, made for network professionals seeking insights into key attributes, the link-state routing protocol, and network convergence. Open Shortest Path<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_eb_attr":"","footnotes":""},"categories":[1,49],"tags":[],"class_list":["post-1185","post","type-post","status-publish","format-standard","hentry","category-blog","category-network-engineering"],"_links":{"self":[{"href":"https:\/\/bytereign.com\/index.php?rest_route=\/wp\/v2\/posts\/1185","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/bytereign.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/bytereign.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/bytereign.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/bytereign.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1185"}],"version-history":[{"count":43,"href":"https:\/\/bytereign.com\/index.php?rest_route=\/wp\/v2\/posts\/1185\/revisions"}],"predecessor-version":[{"id":1810,"href":"https:\/\/bytereign.com\/index.php?rest_route=\/wp\/v2\/posts\/1185\/revisions\/1810"}],"wp:attachment":[{"href":"https:\/\/bytereign.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1185"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/bytereign.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1185"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/bytereign.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1185"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}