User:Itpastorn/dko/ccna1-3.1-8
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Ethernet Switching
Contents |
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.
[edit] Ethernet Switching
[edit] Layer 2 bridging
(How a bridge builds its table and selectively forwards frames.)
[edit] 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).
[edit] 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,
[edit] 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)
[edit] Switch modes
- Store-and-forward
- Cut-through
- Fast-forward switching
- Fragment-free switching
[edit] 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
[edit] Collision Domains and Broadcast Domains
[edit] Shared media environments
- 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.
[edit] 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
[edit] 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.
[edit] Layer 2 broadcasts
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.
[edit] Broadcast domains
Extended by layer 1 and layer 2 devices. Divided by layer 3 devices.
[edit] 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.
[edit] 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
[edit] Clarifications
[edit] 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
[edit] 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
[edit] Extra topics (in addition to CCNA)
- Adaptive switching (in CCNA 1 v 4.0)
[edit] 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
