1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Need help understanding the OSI model

Discussion in 'General Cisco Certifications' started by zr79, Feb 10, 2009.

  1. zr79

    zr79 Byte Poster

    I am trying to get a clearer understanding of the OSI model.

    Say you have a home LAN connected to your 3-in-1 modem/router/switch.

    So a pc on this LAN requests say www.somesite.com. So the PC sends a packet header to the

    switch containing its MAC address, LAN IP and the websites address, the switch stores the

    MAC address and hence remember this MAC address in its MAC table in it's memory.

    The switch then forwards this packet/header to the router then uses NAT to route between LAN and internet ips and takes this header and sends it to

    to the modem to be modulated and the modem then send this header to the websites server via the internet and somewhere in this process the internet ip is added to the header.

    The website packets start coming back into the modem(which demodulates the signal) and

    passes the packet and header back to the router in packets of about 64kb at a time or something, the router translates the internet ip back to the LAN subnets and passes the packet to the switch, the switch reads the MAC address in the header and passes the packet to the corresponding PC.

    How much of this is correct?
    Certifications: A+
  2. hbroomhall

    hbroomhall Petabyte Poster Gold Member

    It is mostly correct. But where does OSI come in this? :p

    (The 'real' Internet address is substituted by NAT for your local one.)

    There is, of course, a lot more complexity involved. In particular you don't mention the DNS lookup that translates the website name into an Internet IP address.

    Certifications: ECDL A+ Network+ i-Net+
    WIP: Server+
  3. UKDarkstar
    Honorary Member

    UKDarkstar Terabyte Poster

    See if this helps you understand better
    Certifications: BA (Hons), MBCS, CITP, MInstLM, ITIL v3 Fdn, PTLLS, CELTA
    WIP: CMALT (about to submit), DTLLS (on hold until 2012)

Share This Page