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By Administrator in All, Routing protocols

The OSPF and IS-IS routing protocols share a number of common features as both are link-state routing protocols based on the Dijkstra SPF (Shortest Path First) algorithm. Both protocols prevent routing loops, converge quickly, support a two-level hierarchy and variable length subnet masking.

Despite their many similarities, the two routing protocols do have several differences some of which are considered to be benefits of IS-IS over OSPF:

  • IS-IS is encapsulated directly at the data link layer, which makes it network layer protocol independent. OSPF is encapsulated into the IP network protocol. This difference makes IS-IS more flexible and adaptable to different topologies and technologies used.
  • OSPF uses various types of advertisement packets while all IS-IS advertisements follow the standard Type, Length, Value (TLV) format. The TLV form allows advertisements to be grouped together and leads to fewer packets exchanged in an IS-IS network as compared to an OSPF network.
  • Generally, IS-IS can support more routers in an area than OSPF.

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