IP

Internet Protocol

Addressing hosts
Encapsulating data
Global routing capability
- Determined by the use of a subnet mask
Connectionless, best-effort
- TCP vs UDP

Understanding IP

Address
- Ex: 10.1.1.5
Subnet mask
- What if we want to send a transmission to a host of 10.1.2.5, is that on my local network or is that on a different network?
- It depend on the subnet mask.
- The subnet mask lets us know where a network begins and ends, and it lets us determine which of the IP address, which portions of it, which bits, out host bits versus network bits.
- Ex: 255.255.255.0
  - Sometimes abbreviated as a /24 (24 contiguous ones in binary)
  - The first octet, the second octet and the third octet in their entirety are used for network bits, and the last octet is used for host bits.
Network address
- Ex: 10.1.1.0
  - It's something that we would see in a routing table, the first host is typically .1, the last host in a range like this is gonna be 254.
Broadcast address
- Layer 2 broadcast address is gonna be all Fs, because in layer 2 MAC addresses are the main language.
- Layer 3 broadcast depends on if it is directed broadcast, or a general broadcast.
  - General broadcast is gonna be 255.255.255.255, this is called "shouting" to a layer 3 destination
  - There is also an specific network broadcast address, in this example it would be 10.1.1.255. Targeting this address is also called a directed broadcast.
    - This is a host, that is reserved and it's not gonna be assigned to an endpoint, this represents all hosts, this is how we talk to all hosts within the 10.1.1.0 network.

Routing Table

When we do ipconfig on a Windows DOS prompt we get:

Ethernet adapter Ethernet 2:

   Connection-specific DNS Suffix  . :
   Link-local IPv6 Address . . . . . : fe80::8424:d364:766:b75e%19
   IPv4 Address. . . . . . . . . . . : 10.119.41.246
   Subnet Mask . . . . . . . . . . . : 255.255.254.0
   Default Gateway . . . . . . . . . : 10.119.40.1

...

This command list all network interfaces both physical and virtual.

The route print command on Windows DOS will print your routing table.

netstat -r is an altarnate command for this same function (works on MacOS and Linux).

C:\Users\mxmarin18>route print
===========================================================================
Interface List
 19...38 14 28 a2 83 f4 ......Realtek USB GbE Family Controller #2
 11...48 51 c5 21 fc 5f ......Intel(R) Wi-Fi 6 AX201 160MHz
  4...48 51 c5 21 fc 60 ......Microsoft Wi-Fi Direct Virtual Adapter
  5...4a 51 c5 21 fc 5f ......Microsoft Wi-Fi Direct Virtual Adapter #2
  9...48 51 c5 21 fc 63 ......Bluetooth Device (Personal Area Network)
  1...........................Software Loopback Interface 1
===========================================================================

IPv4 Route Table
===========================================================================
Active Routes:
Network Destination        Netmask          Gateway       Interface  Metric
          0.0.0.0          0.0.0.0      10.119.40.1    10.119.41.246     25
      10.119.40.0    255.255.254.0         On-link     10.119.41.246    281
    10.119.41.246  255.255.255.255         On-link     10.119.41.246    281
    10.119.41.255  255.255.255.255         On-link     10.119.41.246    281
        127.0.0.0        255.0.0.0         On-link         127.0.0.1    331
        127.0.0.1  255.255.255.255         On-link         127.0.0.1    331
  127.255.255.255  255.255.255.255         On-link         127.0.0.1    331
        224.0.0.0        240.0.0.0         On-link         127.0.0.1    331
        224.0.0.0        240.0.0.0         On-link     10.119.41.246    281
  255.255.255.255  255.255.255.255         On-link         127.0.0.1    331
  255.255.255.255  255.255.255.255         On-link     10.119.41.246    281
===========================================================================
Persistent Routes:
  None

IPv6 Route Table
===========================================================================
Active Routes:
 If Metric Network Destination      Gateway
  1    331 ::1/128                  On-link
 19    281 fe80::/64                On-link
 19    281 fe80::8424:d364:766:b75e/128
                                    On-link
  1    331 ff00::/8                 On-link
 19    281 ff00::/8                 On-link
===========================================================================
Persistent Routes:
  None

Interface List

The interface list has got interface identifiers for each of our network interfaces
- Here is where you can identify your NIC, WiFi card/adapter, Virtual Ethernet Adapters, and the Software Loopback Interface, which is just a logical interface that each system has and has the identifier 1.
- Format:
  - ID...MAC-Address......Name-of-device.

Route Table

The least specific route in the universe is 0.0.0.0, also called the gateway of last resort or the default route.
- This is a /0
- Zero bits have to match in order to use this exit.
For example if we look at 10.119.41.246 255.255.255.255 (Destination/Netmask)
- Do I know how to get to 10.119.41.246? YES that's me!, that /32 means that host is here.
A directed Broadcast would look something like this: 10.119.41.255. 255.255.255.255
For example on 224.0.0.0 24.0.0.0. (Destination/Netmask) Everything from 224 to 240 is gonna be multicast
For Broadcast we would look at something like 255.255.255.255 255.255.255.255