Notes

6.0
-Broadcasts consume bandwidth and slow network performance
-Large Ethernet networks consisting of many hosts are not efficient. It is better to divide larger networks into smaller, more manageable pieces
A hierarchical, layered design provides increased efficiency, optimization of function, and increased speed
hierarchical design is used to group devices into multiple networks that are organized in a layered approach.

Access Layer - This layer provides connections to hosts in a local Ethernet network.
Distribution Layer - This layer interconnects the smaller local networks.
Core Layer - This layer provides a high-speed connection between distribution layer devices. (Backbone/back up layer)

A hub simply accepts electronic signals from one port and regenerates (or repeats) the same message out all of the other ports. All hosts attached to the hub share the bandwidth, and will receive the message. Hosts ignore the messages that are not addressed to them

An Ethernet switch is a device that is used at the access layer. When a host sends a message to another host connected to the same switched network, the switch accepts and decodes the frames to read the physical (MAC) address portion of the message.

When a new host sends a message or responds to a flooded message, the switch immediately learns its MAC address and the port to which it is connected.


-Ethernet Broadcast in the Local Network-
Within the local network it is often necessary for one host to be able to send messages to all the other hosts at the same time. This can be done using a message known as a broadcast.

The broadcast MAC address is actually a 48-bit address made up of all ones. Because of their length, MAC addresses are usually represented in hexadecimal notation. The broadcast MAC address in hexadecimal notation is FFFF.FFFF.FFFF. Each F in the hexadecimal notation represents four ones in the binary address.
-Broadcast Domain-
A Local area network (LAN), a network with one or more Ethernet switches, is also reffered to as a broadcast domain.

-ARP-
ARP uses a three step process to discover and store the MAC address of a host on the local network when only the IPv4 address of the host is known:

1.The sending host creates and sends a frame addressed to a broadcast MAC address. Contained in the frame is a message with the IPv4 address of the intended destination host.
2.Each host on the network receives the broadcast frame and compares the IPv4 address inside the message with its configured IPv4 address. The host with the matching IPv4 address sends its MAC address back to the original sending host.
3.The sending host receives the message and stores the MAC address and IPv4 address information in a table called an ARP table.
7.0


-The default gateway address is the address of the router interface connected to the same local network as the source host. All hosts on the local network use the default gateway address to send messages to the router.
-Subnet Mask identifies what network you're on
-A default route is the interface through which the router forwards: A packet containing a destination IP network address that is not in the routing table of the router.
-The term local area network (LAN) refers to a local network, or a group of interconnected local networks that are under the same administrative control.

-Packet forwarding-
When a router encapsulates the frame to forward it out an Ethernet interface, it must include a destination Mac address.

Advantages of a single local segment:

Appropriate for simpler networks
Less complexity and lower network cost
Allows devices to be "seen" by other devices
Faster data transfer - more direct communication
Ease of device access

Disadvantages of a single local segment:

All hosts are in one broadcast domain which causes more traffic on the segment and may slow network performance
Harder to implement QoS (Quality of service)
Harder to implement security

Advantages of Host on a Remote Segment:

More appropriate for larger, more complex networks
Splits up broadcast domains and decreases traffic
Can improve performance on each segment
Makes the machines invisible to those on other local network segments
Can provide increased security
Can improve network organization

Disadvantages of Host on a Remote Segment:

Requires the use of routing (distribution layer)
Router can slow traffic between segments
More complexity and expense (requires a router)



If the router cannot determine where to forward a message, it will drop it.
A default route is the interface through which the router forwards a packet containing an unknown destination IP network address. This default route usually connects to another router that can forward the packet towards its final destination network.

Port - The interface used to forward packets to the network