User:Itpastorn/dko/ccna1-3.1-8

Ethernet Switching

Overview CCNA 1 - Module 8 (3.1)
 * Bridging and switching
 * The content-addressable memory (CAM) table
 * Latency
 * Switching modes
 * Spanning tree protocol (STP)
 * Collisions, broadcasts, collision domains, and broadcast domains
 * Which devices create, extend or divide collision domains and broadcast domains
 * Discuss data flow and problems with broadcasts
 * Network segmentation. The devices used to create segments.

Layer 2 bridging
(How a bridge builds its table and selectively forwards frames.)

Layer 2 switching
Bridges and switching divides collision domains but have no effect on a logical or broadcast domain. Data is dynamically stored in content-addressable memory (CAM).

Switch operation
Microsegments contain only the switch and the sending/receiving node. They enable full duplex. "Content-addressable memory (CAM) --- works backward compared to conventional memory." Enter data, get the address,

Latency

 * Media delays
 * Circuit delays
 * Software delays
 * Intra-switch delay (earliest possible point of switching is after the last bit in receiving MAC-address is detected)

Switch modes

 * Store-and-forward
 * Cut-through
 * Fast-forward switching
 * Fragment-free switching

Spanning-Tree Protocol
Bridge Protocol Data Units (BPDUs). BPDUs are exchanged regularly (every 2 seconds by default) and enable switches to keep track of network changes and to start and stop forwarding at ports as required.

STP switch port states:
 * Blocking
 * Listening
 * Learning
 * Forwarding
 * Disabled

Shared media environments
Collisions only occur in a shared media environment.
 * Shared media environment
 * Extended shared media environment (two or more segments connected through a hub or repeater)
 * Point-to-point network environment (e.g. dial up modem or DSL connection

Collision domains
layer 2 and layer 3 devices break up collision domains. Layer 1 devices extends collision domains. Maximum length of a CD: 5-4-3-2-1 rule

Segmentation
History: Ethernet evolved from the Aloha protocol. A segment with no hosts between two switches or a switch and a router still counts as one collision domain.

Layer 2 broadcasts
Protocols that use broadcasts: Broadcast MAC address: 0xFFFFFFFFFFFF
 * DHCP
 * ARP
 * Many service discovery protocols and services, like:
 * UPnP
 * Zeroconf, implemented by Bonjour and Avahi

Excessive broadcasts drain bandwidth and CPU cycles from connected hosts.

Broadcast domains
Extended by layer 1 and layer 2 devices. Divided by layer 3 devices.

Introduction to data flow

 * Layer 1 devices always forwards frames - regenerated and retimed.
 * Layer 2 devices forwards frames unless prevented
 * Layer 3 devices will not forward a frame unless it has to - if the IP address is outside of the broadcast domain and it has an identified location to send the packet to.

What is a network segment
Dictionary definitions: "A separate piece of something", "One of the parts into which an entity, or quantity is divided or marked off by or as if by natural boundaries"
 * Section of a network that is bounded by bridges, routers, or switches (Collission Domain)
 * Bus topology = between two repeaters
 * TCP or UDP segment

Types of domains

 * Collision domain
 * Broadcast domain
 * Windows Server domain (That you "log in to"). See also NIS, Kerberos and LDAP
 * Domain name on the Internet

Types of switches

 * By layer
 * Layer 2
 * Layer 3 (IP)
 * Layer 4
 * Layer 7
 * By mode
 * Store and Forward
 * Cut through
 * Fragment Free
 * Bandwith
 * Symmetric
 * Assymetric

Extra topics (in addition to CCNA)

 * Adaptive switching (in CCNA 1 v 4.0)

Additional resorces (besides Wikipedia)

 * CCNA 3 version 4 LAN Switching (demo) - Really, really good!
 * Switching at Learn Networking
 * The difference between a hub and a switch
 * How broadcasts work at Learn Networking
 * CCNA 1 Module 8 Exam Solutions

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