Vint Cerf

TCP/IP is the other model and have 4 layers instead Application Transport Internet Network

Layer 3 Network

Routes data between physical networks by handling addressing via IP Handles packet fragmentation and error detection Router level Considered the most complex layer

Three types of IPv4 address:

  • unicast (acted on by a single recipient)
  • multicast (acted on only by members of a specific group)
  • broadcast (acted on by everyone in the network)

Actual payload of ping (as defined by RFC 792) was never fully identified so it is possible for someone to embed messages into the payload of an ICMP packet

Some IDS do look for this though

PDU (packet data unit)

IPv4 loopback address (denoting the software loopback of own machine) is 127.0.0.1 and MAC address of the broadcast message is FF:FF:FF:FF:FF:FF

Classless Inter-Domain Routing (CIDR)

CIDR addresses are allocated in virtual private cloud and in a subnet using CIDR notation A /16 block provides 65,536 IPv4 addresses. A /24 block provides 256 addresses.

CIDR is a method of representing IP addresses

IPv4 notation

  • /30 = 4 .225.252
  • /28 = 16 .255.240
  • /26 = 64 .255.192
  • /24 = 256 .255.0
  • /22 = 1024 .248.0
  • /20 = 4096 .240.0

IP

Subnets

https://www.ipchalk.com https://www.subnetting.net

Routable subnets

Non-routable subnets

Need more IP? Subnet.

network address host range broadcast
64.5.96.0 64.5.96.1-64.5.96.62 64.5.96.63
64.5.96.64 64.5.96.65-64.5.96.126 64.5.96.127
64.5.96.128 64.5.96.129-64.5.96.190 64.5.96.191
64.5.96.192 64.5.96.193-64.5.96.254 64.5.96.255

There are four subnets here. There are always an even number of subnets unless you didn’t divide it.

255.255.0.0 subnet mask 11111111.11111111.00000000.00000000

xxxxyyyy.xxxxyyyy.00000000.00000000 1. Depending on where the line is drawn, set to 0s. xxxxyyyy.xxxxyyyy.00000000.000|00000 2. Let’s say it is drawn where the vertical line is. xxxxyyyy.xxxxyyyy.00000000.000|00001 3. Then set to 1, that is the first usable address. xxxxyyyy.xxxxyyyy.00000000.000|11110 4. Then this is the last usable address. xxxxyyyy.xxxxyyyy.00000000.000|11111 5. This is the broadcast address.

IPSec

  • IPSec deals with host-to-host security.
  • IPSec provides network communication security for OS.
  • Typically used in VPN.
  • IPSec transaction are negotiated by IKE (internet key exchange).
  • IKE establishes a connection using something like a X.509 certificate which are issued by a CA.
  • Real world examples of a CA: Symantec, GoDaddy, Verizon, GlobalSign, Comodo
  • AH vs ESP
  • Transport Mode vs Tunnel Mode

Transport data across network Provides the addressing scheme to identify physical devices, bridges, switches, MAC addresses

“So, what is peering? In its most simple form, it is defined as the interconnection of two different networks so they can exchange traffic between them.” “Public peering is performed across a shared network called an Internet Exchange Point (IX or IXP).” “Private peering is performed by creating a direct physical connection (usually consisting of one or more 10GE fibers) between two networks.”

Layer 1 Physical

The physical medium for the network communication signals

Tx is transmit such as to Bluetooth speakers from a audio device. Rx is receive from a device (audio player of any sort) to Bluetooth headphones except AirPods.