Foundation of Computer Networking

How does DHCP works?

  1. DHCP Discover
  2. DHCP Offer
  3. DHCP Request
  4. DHCP Acknowledge

TCP/IP Model & OSI Model

ARP

Ethernet broadcast messages: ARP requests
Ethernet unicast messages: ARP replies

ARP Function

  1. Resolving IPV4 Addresses to MAC Addresses
    • For a frame to be placed on the LAN media, it must have a destination MAC Address
    • When a packet is sent to the data link layer to be encapsulated into a frame, the node refers to a table in its memory to find the data link layer address that is mapped to the destination IPV4 address
    • This table is called the ARP table or the ARP cache. The ARP table is stored in the RAM of the device
    • Each entry, or row, of the ARP table binds an IP address with a MAC address. The relationship between the two values called a Map.
    • It simply means that you can find the MAC address of an IP address in the table.
    • To begin a transmission, a transmitting node attempts to find the MAC address of the OP address of the destination node from ARP table.
    • If it is found, the transmitting node use it as the destination MAC address in the frame that encapsulates the IP packet.
    • The frame is then encoded onto the networking media
  2. Maintaining the ARP Table
    • The ARP table is maintained dynamically
    • There are two ways that a device can gather MAC addresses
    • One way is to monitor the traffic that occurs on the local network segment. As a node receives frames from the media, it can record the source IP and MAC address as a mapping in the ARP table.
    • Another wat a anode can get an address pair is to send an ARP request.
    • Entries in the ARP table are time stamped
    • If a device does not receive a frame from a particular device by the time, the time stamp expires, the entry for this device is removed from the ARP table.

ARP in Local Communication

ARP in Remote Communication

ARP Issuses

Calculation of Network Address and Broadcast Address

Calculation of addresses

MAC Address

Broadcast MAC Address

  • FF-FF-FF-FF-FF-FF

Multicast MAC Address

  • Multicast addresses allow a source device to send a packet to a group of devices.
  • The range of IPV4 multicast addresses is 224.0.0.0 – 239.255.255.255
  • The multicast MAC address is a special value that begins with 01-00-5E in hexadecimal.

IPV6 Shortest Form

  • Format: x:x:x:x:x:x:x:x (where x is a 16-bit field)
  • Leading zeros in a field are optional
  • Successive fields of zeros can be represented as :: only once per address

Examples:

  • 2031:0000:130F:0000:0000:09C0:876A:130B
    • Can be represented as 2031:0:130f::9c0:876a:130b
    • Cannot be represented as 2031::130f::9c0:876a:130b
  • FF01:0:0:0:0:0:0:1
    • FF01::1
  • 0:0:0:0:0:0:0:1
    • ::1
  • 0:0:0:0:0:0:0:0
    • ::

Collision Domain & Broadcast Domain

Collision Domain: Switch & Router Interface
Broadcast Domain: Router Interface

Ethernet Frame Fields and Size

Ethernet Switch

MAC Address Table

*Switches do not have MAC Addresses

How does switch handle unicast, multicast and broadcast MAC address?

Unicast

Broadcast

Multicast

VLSM

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