CCNA Study notes-TCP/IP,OSI and Ethernet

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Compare and Contrast OSI TCP/IP models


Encapsulation terminology for OSI and TCP/IP model:



Compare and contrast TCP and UDP protocols



Describe the impact of infrastructure components in an enterprise network

  • Firewall

    – Firewalls sit in the forwarding path of all packets so that firewall can protect the whole network
    – Firewall’s logic to discard/allow a packet:
    – Like ACLs, match the source and destination IP address
    – Like ACLs, identify applications by matching static well-known TCP/UDP ports
    – Know what additional TCP/UDP ports are used by a particular flow
    – Match the text in the URI of an HTTP request and match patterns to decide whether to allow or deny the download of the web page identified by that URI
    – Keep state information by storing information about each packet, and make decisions about filtering future packets based on the historic state information (a.k.a. stateful inspection/stateful firewall) (mitigates DoS attacks)
    – Security zones:
    – Security zones define which hosts can initiate new connections
    – DMZ:
    – Firewall security zone used to place servers that need to be available for use by users in the public Internet

  • Access points

    a. Autonomous wireless APs:
    – Communicates with wireless devices with 802.11 and radio waves
    – Converts header formats between 802.11 and 802.3
    – Performs control and management features e.g. authentication of new devices, definition of name of WLAN (SSID) etc.
    b. LWAPs:
    – Forwards data between wired and wireless LAN; allows roaming
    – Forwards data specifically through WLC with protocol e.g. CAPWAP

  • Wireless controllers

    – Provides centralised control/management functions and allows roaming


Compare and contrast collapsed core and three-tier architectures

Collapsed core:

– Instead of core tier, distribution switches can be cabled together with full/partial mesh
a. Access layer:
– Connects directly to end users and sends traffic to and from distribution switches
– Often has 2+ uplinks to distribution switches (redundancy)
– Uses star topology
b. Distribution layer:
– Provides a path through which the access switches can forward traffic to each other


– Uses less switch ports and cables
– Uses a hybrid design
– Core tier uses partial mesh and aggregates (clusters together) distribution switches


Compare and contrast network topologies:


– A design in which one central device connects to several others


a.Full mesh:
– For any set of network nodes, a design that connects a link between each pair of nodes; every node connects to each other
– Requires many links and many switch ports

b.Partial mesh:

– For any set of network nodes, a design that connects a link between some pairs of nodes, but not all; some nodes connect to each other


– Combination of different topologies in one network


Select the appropriate cabling type based on implementation requirements