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IS-IS vs OSPF

  1. 1. IS-IS VERSUS OSPF WWW.NETPROTOCOLXPERT.IN
  2. 2. SIMILARITIES OF THESE TWO PROTOCOL ONE BY ONE – IS-IS Protocol and OSPF are both Link-State Interior Gateway Protocols. – IS-IS Protocol and OSPF are both uses Dijkstra SPF (Shortest Path First) algorithm. – These protocols have LSDBs and the LSDB similar structure – Both support VLSM (Variable Length Subnet Mask) – Both are very scalable protocols – Both has a fast convergence time after changes – Both are open standards – Both have hierarchical structures, there are two hierarchy level – Both protocols support LANs and point-to-point protocols in similar ways – Both protocol use periodic Hello messages for neighbour establishment
  3. 3. DIFFERENCES OF THESE TWO IMPORTANT PROTOCOLS – IS-IS Protocol works above Layer 2 next to IP, OSPF works on top of IP, – IS-IS Protocol routers belong to one area, OSPF routers belong multiple areas, links are in areas in OSPF – IS-IS Protocol uses DIS, OSPF uses DR and BDR, – OSPF has virtual-links, ISIS does not support this, – OSPF uses opaque LSA extensions, ISIS can be extended more by TLVs – OSPF has efficient packet types, ISIS has untidy structure because of TLVs, but more granular, – In OSPF small changes causes small packets, in ISIS even if small change, entire LSPs are sent.
  4. 4. OSPF IS-IS Top of IP Above L2, Next to IP Routers on Multiple Areas Routers on one Area DR and BDR DIS Virtual-link Support No Virtual-link Open LSA Extension TLVs Effective Packet Types More Granular (Different TVLs) Small Change, Small Packets Small Change, Entire LSP
  5. 5. OSPF IS-IS Host End System (ES) Router Intermediate System (IS) Link Circuit Packet Protocol data Unit (PDU) Designated Router (DR) Designated IS (DIS) Back-up DR (BDR) No Backup DIS Link-State Advertisement (LSA) Link-State PDU (LSP) Hello Packet IHH PDU Database Description (DD) CSNP Area Sub Domain (Area) Backbone Area Level 2 sub Domain Non Backbone Area Level 1 Area ABR L1/2 Router ASBR Any IS
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