Quest4 Cisco CCNA Mini-Cram

Created by Jay Banks

Note: This document is still evolving and will be added to as time permits.

 IP address classes
  Class Range Default
Subnet Mask
    A 1-126
    B 128-191
    C 192-223
    D 224 - 239
 OSI Reference Model - Layers
Layer   Name
1 Physical
2 Data Link
3 Network
4 Transport
5 Session
6 Presentation
7 Application
 Switching types
Cut-through: Reads, processes, and forwards packets as soon as the destination address is looked up and the outgoing port is determined.
Store and forward: Frames are completely processed before being forwarded out the appropriate port.


Protocols by OSI layer
  OSI Layer
       Protocols, services, etc.
Physical: 802.3, 802.5, X.25, FDDI
Data Link: MAC, LLC, Frame Relay, LAPB, PPP
Transport: ARP, RARP, TCP, SPX, NBP, UDP
Session: SCP, SQL, NFS, ZIP, RPC
Presentation: JPEG, GIF, ASCII, EBCDIC, encryption, HTML
Application: Telnet, FTP, SMTP
 Well-known ports
Port Number       Assignment
20/21 FTP TCP
23 Telnet TCP
110 POP3 TCP
161/162 SNMP TCP
443 HTTP over
secure socket layer


 Steps of data encapsulation
1 Application input is converted to data
2 Data is converted to segments
3 Segments are converted to packets
4 Packets are converted into frames
5 Frames are converted into bits
 Special and Private IP Addresses
Class A
Class B
Class C or 0.0.0.x (Loop Back)
Network & Host or Host addresses of all 1s: or



LAN Basics

Hubs direct incoming data packets to all devices connected to the hub. Hubs can be thought of as a physical extension of the network cabling media. There are two types of hubs, passive and active. Important points to remember about hubs: all devices on the hub share bandwidth; all devices on the hub are in the same collision domain; and all devices on the hub are in the same broadcast domain.  

Bridges are layer 2 devices (Data Link layer) which are usually used to segment a LAN into two segments. Bridges examine frames, keeping local traffic local, and forwarding any non-local traffic. Each port on a bridge is a separate collision domain. Important points to remember about bridges: each segment connected to a bridge is in a separate collision domain; all segments on a bridge are in the same broadcast domain; and bridges forward all broadcast messages.

Switches are layer 2 devices (Data Link layer), which operate very similar to bridges, but allow for more network segments. In fact, switches are often referred to as multi-port bridges. Each port on a switch provides dedicated bandwidth. Important points to remember about switches: each segment connected to a switch is in a separate collision domain, and all segments on a switch are in the same broadcast domain.

Routers are layer 3 devices (Network layer), which are used to connect dissimilar LANs and to connect LANS to WANs (Wide Area Networks). Routers determine a data packets destination based on the IP destination addresses found in packet headers, and then routes the packet to its destination using the best available route. Like bridges and switches, routers create separate collision domains on each segment connected to the router, but unlike bridges or switches, routers do not forward broadcast traffic by default. Important points to remember about routers: each segment connected to a router is in a separate collision domain, and each segment on a router is also in a separate broadcast domain.

LAN segmentation creates more, smaller, collision domains by creating more segments with fewer hosts on each segment. Segmentation of a LAN can be accomplished with a bridge, switch or a router. LAN segmentation does not occur with a hub.

 VLAN Basics

VLAN (Virtual LAN) is a method of logically segmenting a network by grouping network nodes into different subnetworks. This is accomplished by assigning a switch port to its own subgroup of networked nodes. Note that these subgroups are not limited by physical location. For example, the accounting department could have rooms on the first, third, and fourth floors of a building, and also share these same floors with the billing department. Rather than attempting to physically create networks for each department or force the departments to always be confined to certain geographical locations within the building, a VLAN could be created for each of the departments.

VLAN benefits include increased security and broadcast management. In a VLAN, broadcasts, as well as any other type of data transmission, are VLAN specific, meaning that members of VLAN1 will not receive broadcasts or be able to view any other data intended for members of VLAN2.

VLANs require a router to communicate between different VLANs. Members of VLAN1 can only communicate with members of VLAN1. For VLAN1 to communicate with VLAN2, a router is required.

VLANs can be created on a switch by, port address (most common), MAC address, User ID, and IP address.

VLANs can span multiple switches, but doing so requires that a VLAN trunking protocol be enabled on each switch port used in a VLAN. VLAN trunking protocols, such as ISL (Inter-Switch Linking) or IEEE 802.1Q are disabled by default on all ports. 




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