Network

System Administration - Network

Table of Contents

What is what?

  • IP ?

    • Each NIC card is defined by it’s IP. There are two defined IPs; Private and Public.

    • IP is consist of 4 octet [octet.octet.octet.octet]

    • Private IP: {10.0.0.0/8, 192.168.0.0/16, 172.16.0.0 : 172.32.0.0}.

  • Mask ? /8, /16, or /32

    • It’s the ip’s mask.

    • The mask define the range of ips.

  • How to calculate the IPs range?

    • Mask defines the fixed octet in the IP.

    • e.g., /8 means 8 bits = (255.0.0.0) Decimal = (11111111.00000000.00000000.00000000) Binary.

    • e.g., /16 means 16 bits = (255.255.0.0) Decimal = (11111111.11111111.00000000.00000000)

    • You can consider that the mask is bitwise add (logically operation) with the IP.

    • Subnet is a range of IP addresses: (Network Address + Mask) e.g., (192.168.1.0/24)

    • Accordingly, for example:

      • Each IP 10.x.x.x (/8) means that the Network address for this IP range all have a 1 fixed octet; all start with 10.x.x.x, starting from 10.0.0.0 till 10.255.255.255.

      • Each IP 192.168.x.x (/16) means that the Network address for this IP range all have a 2 fixed octet; all start with 192.168.x.x, starting from 192.168.0.0 till 192.168.255.255.

    IP: 192.168.1.130
Mask: 255.255.255.0   (/24)

IP:    11000000.10101000.00000001.10000010
Mask:  11111111.11111111.11111111.00000000
-----------------------------------------
AND:   11000000.10101000.00000001.00000000

Result: 192.168.1.0   ← network address

    Note:

    1. Octet means 8 bits. Each 8 bits can represent values from 0 to 255. We can’t name it digit; A digit is a single symbol from (0 to 9)

    2. The reason AND works (logical necessity, not convention); as mask bits {1 -> keep the IP bit, 0-> Zero it out}. This guarantees that All hosts in the same subnet produce the same network address, and Hosts in different subnets do not.

    3. Mask /32 means 4 Octet, so there is only one 1 IP assigned in the range.

Switch

graph TD
    SW[Switch]

    SW --> D1["NIC eth0"]
    SW --> D2["NIC eth1"]
    SW --> D3["NIC eth2"]

  • Each device connected to the a switch through port, can reach neighboring devices in the same switch; They share the same subnet.

Recall:

  1. layers: Physical Layer -> Data Link Layer -> Network Layer -> Transport Layer ….

  2. Data Link Layer deals with MAC addresses only, it is responsible for setting [Source: Device MAC address, Destination: Device MAC address].

  3. How in Data Link Layer we know the destination MAC address? using ARP “Address Resolution Protocol”; It check the target IP, the source checks its ARB cache for that target IP, if found, then it returns the associated MAC address, it not, then ARB request broadcast; it asks the switch to scan all related ports for that IP in order to learn target [IP:MAC address].

Router

graph TD
    R[Router]

    R --> SW1[Switch 1]
    R --> SW2[Switch 2]

    SW1 --> D1["NIC eth0"]
    SW1 --> D2["NIC eth1"]

    SW2 --> D3["NIC eth0"]
    SW2 --> D4["NIC eth1"]

  • In order to access a device that is not on the same switch, it has to reach out to the router, that connects to other switch.

VLAN

graph TD
    SW[Switch]

    subgraph VLAN_A
        A1[NIC eth0]
        A2[NIC eth1]
    end

    subgraph VLAN_B
        B1[NIC eth0]
    end

    SW --> A1
    SW --> A2
    SW --> B1

  • The idea here is to separate NIC/devices from each other, so they can’t reach each other directly.