5 thoughts on “Which OSI layer does IS-IS operate?

  1. I believe L2.

    “The intermediate systems communicate between each other by using Layer 2 of the OSI model directly. This means there is no technical need for IP or any other higher layer protocol. The interfacing with the data link layer (Layer 2) primarily involves operations for detecting, forming, and maintaining routing adjacencies with neighboring routers over various types of interconnecting network media or links. This also makes IS-IS relatively more secure than other routing protocols that run over IP.”

    Designing for Cisco Network Service Architectures (ARCH) Foundation Learning Guide, Fourth Edition

  2. Answer is B, IS-IS is L2 protocol. It does not use IP to carry routing information messages.

    We can see this clear from the fact it support IPv6 without the need for modification unlike OSPF which was rewritten in OSPF v3 to support IPv6

    1. Do you knoe the answer for this?
      Refer to the exhibit. An engineer is designing a new firewall for an organization and must provision Network Address Traslation. This new firewall must support basic Internet access for the organization as well as provide inbound connectivity to the mail server. The infrastructure has only one public IP address available for use on the new firewall. Which two forms forms of NAT must be configured? (2)
      a. NAT overloading for the inbound traffic on port 25
      b. Static NAT for the inbound traffic on port 25
      c. Dynamic NAT for the outbound traffic <<<<
      d. Dynamic NAT to the inbound traffic on port 25
      e. NAT overloading for the outbound traffic <<<

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