Something you need to know first: Binary Odometer

10.1.1.254 + 1 = 10.1.1.255
10.1.1.255 + 1 = 10.1.2.0
10.1.2.0 + 1 = 10.1.2.1

in reverse:

10.1.2.0 – 1 = 10.1.1.255

Example 1

172.16.35.123/20 or 172.16.35.123 with the mask 255.255.240.0

Binary Method

Quick Method

Figure out the subnets:

1. network and host split in third octect
2. subtract: 256 – 240 = 16, it means that network are incrementing in values of 16: 0, 16, 32, 48…
3. 35 in the range of 32 and 48, so 172.16.35.123 is on subnet 172.16.32.0; next subnet is 172.16.48.0

First subnet = 172.16.32.0

Next subnet = 172.16.48.0

Broadcast address = next subnet – 1

First host = Subnet + 1

Last host = Broadcast – 1

Subnetting

• Class A subnetting (255.0.0.0) support 1677214 (2^24) host per network, that way too much
• Class B subnetting (255.255.0.0) support 16382 (2^16) host per network, that way too much
• Class C subnetting (255.255.255.0) support 254 (2^8) host, more likely we subnet down to at least 254 hosts or even further

If you subnetting a network only has 2 hosts, you can subnet with (255.255.255.254) or CIDR as /31

Network, host number

• Networks: 2^(network bits)
  • one allocate for the subnet
  • one allocate for the broadcast
• Hosts: 2^(host bits) – 2

Subnetting to be short

1. “stealing” or “taking away” bits from the host portion of an address, and
2. allocating those bits to network portion

Example 2

Origin network 10.128.192.0/18 need at least 30 subnets as many hosts as possible

1. draw the line with /18 to split network and host
2. 2^5 > 30, need 5 subnet bit, draw the line to split subnet and host
3. network/subnet portion is 8+8+7=23 bits, host portion is 32-23=9 bits

• First subnet: 10.128.192.0/23
• Second subnet: 10.128.194.0/23
• Last subnet: 10.128.254.0/23

tags: ccna

IP Addressing

• layer 3 logical address assigned by an administrator(MAC built in NIC)
• used to identify specific devices on a network
• every device on the internet has a unique IP Address

Street Analogy

• network address portion
  • identifies a specific network
  • routers route traffic via routing tables, is based on network address(Network ID), not ip address
• host address portion
  • identifies a specific endpoint on a network
  • we can use a protocal such as ARP to find the host

Ipv4

• connectionless protocal: no sessions formd when transmitted, no status info
• packets treated independently
  • may take different paths: load balancing, bandwidth, hopcount
• hierarchical addressing sturture
• best effort delivery
• format
  • 32 bit with 4 octets
  • like DHL or FedEx routing parcel based on an address

Classes

• Unicast Traffic
  • A
    • start with binary 0
    • range from 0(00000000).0.0.0 to 127(01111111).255.255.255
    • exceptions:
      • 127 is reserved for loopback: 127.0.0.1
      • 0 network is reserved for default network: 0.1.1.1
    • actual range from 1.0.0.0 to 126.255.255.255
    • portions
      • first 1 octets: Networks
      • last 3 octests: Hosts
  • B
    • start with binary 10
    • range from 128(10000000).0.0.0 to 191(10111111).255.255.255
    • portions
      • first 2 octets: Networks
      • last 2 octests: Hosts
  • C
    • start with binary 110
    • range from 192(11000000).0.0.0 to 223(11011111).255.255.255
    • portions
      • first 3 octets: Networks
      • last 1 octests: Hosts
• Multicast
  • D
    • start with binary 111
• reserved for other purposes
  • E
    • start with binary 1111

These classes replaced by Classless Inter-Domain Routing(CIDR) in 1993

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tags: ccna

OSI Model

• By International Organization of Standard

Benefits

• Standard and INTEROPERABILITY
• Split development/role: hide developer from lower layer
• Quicker development

Layers

You need to remember both the name and the layer number

• Layer7: Application
• Layer6: Presentation
• Layer5: Session
• Layer4: Transport
• Layer3: Network
• Layer2: DataLink
• Layer1: Physical

Trick: All People Sleeping Through Networking Don’t Pass

Network Engineer: Focus on 1, 2, 3, 4 Layers
Web Developer: Focus on 5, 6, 7 Layers

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