Network Traffic & Interfaces
Encapsulation helps prepare Host Networks, starting with the local segment, and when necessary, beyond network boundaries.
At Layer-4, the Payload receives Network Protocol & Port information.
At Layer-3, IPv4 and IPv6 Addresses define the Sender & Receiver Internet address.
An IPv4 address is a logical, 32-bit address used in local and internetwork communication.
Inside the Layer-3 Packet, a Source & Destination IP Address exist to move traffic across Networks.
At Layer-2, MAC Addresses define a Network Device’s address for Link-Local communication.
The MAC is a unique 48-bit hexadecimal-based hardware address.
Inside the Layer-2 Frame, a Source & Destination MAC Address exist to help move traffic on the Local Network.
In order for networks to behavior, it’s important that Host Network Interfaces are configured with unique Layer-2 & Layer-3 Network Addresses.
Network interfaces identify the physical and logical ports on which a Host can receive or send Network traffic.
In addition to physical Network interface, like a Wired or Wireless Card, or group of Switch Ports, several types of logical interfaces exist, including:
Loopback, generally for testing & network administration
Bridge, like when joining a wired & wireless interface on the same local segment under a common network address
Virtual, which enables an interface to participate in a Virtual LAN,
Tunnel, for point-to-point links across WANs,
Network traffic can generally be described to move in either of two directions, relative to an interface: egress or ingress.
Egress describes traffic leaving an interface—think egress, or exit.
Ingress describes traffic approaching an interface—think ingress, or, in.
Colloquially, Network Traffic is also said to move “Downstream” or “Upstream” relative to a Network’s Topology, Devices, and/or Users.
In networking today, Hosts use both Layer-2 and Layer-3 Addresses to communicate via one of three methods.
Unicast traffic involves one-to-one communication, where either the intended recipient’s Layer-2 or Layer-3 Network Address is known.
For example, an ICMP Ping Reply is Unicast traffic.
Broadcast traffic is one-to-all communication, where all Hosts on the Layer-2 or Layer-3 Network are the intended recipients.
For example, a Host needing a DHCP Address would use the Layer-2 Broadcast address FF:FF:FF:FF:FF:FF in attempt to Discovery a DHCP Server on the Local Network.
All Hosts on the Local Network would receive the Broadcast message.
Multicast traffic is one-to-some communication, where not all, but some Network Devices are the intended recipients.
For example, Dynamic Routing protocols use Multicast addresses to communicate solely among Routers, but not with other Network Hosts.