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.
Ethernet Switching
[edit]Layer 2 bridging
[edit](How a bridge builds its table and selectively forwards frames.)
Layer 2 switching
[edit]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
[edit]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,
- 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
[edit]
- Store-and-forward
- Cut-through
- Fast-forward switching
- Fragment-free switching
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
Collision Domains and Broadcast Domains
[edit]Shared media environments
[edit]- 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
Collisions only occur in a shared media environment.
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
[edit]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
[edit]Protocols that use broadcasts:
- DHCP
- ARP
- Many service discovery protocols and services, like:
Broadcast MAC address: 0xFFFFFFFFFFFF
Excessive broadcasts drain bandwidth and CPU cycles from connected hosts.
Extended by layer 1 and layer 2 devices. Divided by layer 3 devices.
Introduction to data flow
[edit]- 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
[edit]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
Clarifications
[edit]Types of domains
[edit]- 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
[edit]- 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)
[edit]- Adaptive switching (in CCNA 1 v 4.0)
Additional resorces (besides Wikipedia)
[edit]- 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