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236 Cards in this Set

  • Front
  • Back
Same-layer interaction on different computers
The two computers use a protocol to communicate with the same layer on another computer. The protocol defined by each layer uses a header that is transmitted between the computers, to communicate what each computer wants to do.
Adjacent-Layer interaction on the same computer
On a single computer, one layer provides a service to a higher layer. The software or hardware that implements the higher layer requests that the next lower layer perform the needed function.
OSI Reference Model Layers
Application, Presentation, Session, Transport, Network, Data Link Physical
TCP/IP Reference Model Layers
Application, Transport, Internet, Network Access
NetWare Reference Model Layers
HTTP, SMTP, POP3, VoiP; IPX(SPX); Mac Protocols;
OSI Layering Benefits
Less Complex,Standard Interfaces, Easier to learn, Easier to develop, Multivendor interoperability, Modular Engineering
Decapsulation
On a computer that receives data over a network, the process in which the device interprets the lower-layer headers and when finished with each header, removes the header, revealing the next-higher-layer PDU.
Encapsulation
The placement of data from a higher-layer protocol behind the header (and in some cases, between a header and trailer) of the next-lower-layer protocol. For example, an IP packet could be encapsulated in an Ethernet header and trailer before being sent over an Ethernet.
Frame
A term refering to a data-link header and trailer, plus the data encapsulated between the header and trailer.
Networking Model
A generic term referring to any set of protocols and standards collected into a comprehensive grouping that, when followed by the devices in a network, allows all the devices to communicate. Examples include TCP/IP and OSI
Packet
A logical grouping of information that includes the network layer header and encapsulated data, but specifically does not include any headers and trailers below the network layer
Protocol data unit (PDU)
An OSI term to refer generically to a grouping of information by a particular layer of the OSIO mode. More specifically, an LxPDU would imply the data and headers as defined by Layer x.
Segment
In TCP, a term used to describe a TCP header and its encapsulated data (also called an L4PDU). Also in TCP, the process of accepting a large chunk of data from the application layer and breaking it into smaller pieces that fit into TCP segments. In Ethernet, a segment is either a single Ethernet cable to a single collision domain (no matter how many cables are used).
Application Layer (OSI)
Interfaces between network and application software. Also includes authentication services.
Presentation Layer (OSI)
Defines the format and organization of data. Includes encryption.
Session Layer (OSI)
Establishes and maintains end-to-end bidirectional flows between endpoints. Includes managing transaction flows.
Transport Layer (OSI)
Provides a variety of services between two host computers, including connection establishment and termination, flow control, error recovery, and segmentation of large data blocks into smaller parts for transmission.
Network Layer (OSI)
Logical addressing, routing, and path determination.
Data Link Layer (OSI)
Formats data into frames appropriate for transmission onto some physical medium. Defines rules for when the medium can be used. Defines means by which to recognize transmission errors.
Physical layer (OSI)
Defines the electrical, optical, cabling, connectors, and procedural details required for transmitting bits, represented as some form of energy passing over a physical medium.
Ethernet details
Speed: 10 Mbps
Alternate Name: 10BASE-T
Name of IEEE Standard: 802.3
Cable Type: Copper
Max Length:100m
Fast Ethernet details:
Speed: 100 Mbps
Alternate Name:100BASE-T
Name of IEEE Standard:802.3u
Cable Type: Copper
Max Length: 100m
Gigabit Ethernet details:
Speed: 1000 Mbp2
Alternate Name: 1000BASE-LX, 1000 BASE-SX
Name of IEEE Standard: 802.3z
Cable Type: Fiber
Max Length: 550m (SX), 5 km (LX)
Gigabit Ethernet details:
Speed: 1000 Mbps
Alternate Name: 1000BASE-T
Name of IEEE Standard: 802.ab
Cable Type:Copper
Max Length: 100m
CSMA/CD
- A device that wants to send a frame wait until the LAN is silent. In other words, no frames are currently being sent. Before attempting to send an electrical signal.
- If a collision still occurs, the devices that caused the collision wait a random amount of time and then try again.
EIA/TIA Standard Ethernet Cabling Pinouts - T568A
1 - Green/White
2 - Green
3 - Orange/White
4 - Blue
5 - Blue/White
6 - Orange
7 - Brown/White
8 - Brown
EIA/TIA Standard Ethernet Cabling Pinouts - T568B
1 - Orange/White
2 - Orange
3 - Green/White
4 - Blue
5 - Blue/White
6 - Green
7 - Brown/White
8 - Brown
Devices that transmit on 1,2 and Receive on 3,6
PC NICs, Routers, Wireless Access Point (Ethernet interface), Networked printers (printers that connected directly to the LAN)
Devices that transmit on 3,6 and Receive on 1,2
Hubs, Switches
Crossover Ethernet Cable
1 - 3
2 - 6
3 - 1
4 - 4
5 - 5
6 - 2
7 - 7
8 - 8
CSMA/CD algorithm
Step 1 - A device with a frame to send listens until the Ethernet is not busy.
Step 2 - When the Ethernet is not busy, the sender(s) begin(s) sending the frame.
Step 3 - The sender(s) listen(s) to make sure that no collision occurred.
Step 4 - If a collision occurs, the devices that had been sending a frame each send a jamming signal to ensure that all stations recognize the collision.
Step 5 - After the jamming is complete, each sender randomizes a timer and waits that long before trying to resend the collided frame.
Step 6 - When each random timer expires, the process starts over with Step 1.
Structure of Unicast Ethernet Addresses
Organizationally Unique Identifier (OUI), Vender Assigned (NIC Cards, Interfaces)
Size, in bits - 24 Bits, 24 Bits
Size, in hex digits 6 Hex Digits, 6 Hex Digits
MAC
Media Access Control, 802.3 (Ethernet) defines the MAC sublayer of IEEE Ethernet.
Ethernet Address, NIC address, LAN address
Other name often used instead of MAC address. These terms describe the 6-byte address of the LAN interface card.
Burned-in address
The 6-byte address assigned by the vendor making the card.
Unicast address
An address that means "all devices that reside on this LAN right now."
Multicast address
On Ethernet, a multicast address implies some subset of all devices currently on the Ethernet LAN.
Full-Duplex
Generically, any communication in which two communication devices can concurrently send and receive data. In Ethernet LANs, the allowance for both devices to send and receive at the same time, allowed when both devices disable their CSMA/CD logic.
Half-Duplex
Generically, any communication in which only one device at a time can send data. In Ethernet LANs, the normal result of the CSMA/CD algoritm that enforces the rule that only one device should send at a time.
`Hub
A LAN device that provides a centralized connection point for LAN cabling, repeating any received electrical signal out all other ports, thereby creating a logical bus. Hubs do not interpret the electrical signals as a frame of bits, so hubs are considered to be Layer 1 devices.
Pinout
The documentation and implementation of which wires inside a cable connect to each pin position in any connector.
Protocol Type Field
A field in a LAN header that identifies the type of header that follows the LAN header. Includes the DIX Ethernet Type field, the IEEE 802.2 DSAP field, and the SNAP protocol Type field.
Shared Ethernet
An Ethernet that uses a hub, or even the original coaxial cabling, which results in the devices having to take turns sending data, sharing the available bandwidth.
Switch
A network device that filters, forwards, and floods Ethernet frames based on the destination address of each frame.
Switched Ethernet
An Ethernet that uses a switch, and particularly not a hub, so that the devices connected to one switch port do not have to contend to use the bandwidth available on another port. This term contrasts with shared Ethernet, in which the devices must share bandwidth, whereas switched Ethernet provides much more capacity, as the devices do not have to share the available bandwidth.
Twisted pair
Transmission medium consisting of two insulated wires, with the wires twisted around each other in a spiral. An electrical circuit flows over the wire pair, with the current in opposite directions on each wire, which significantly reduces the interference between the two wires.
Bit Rate of DS0
64 kps
Bit Rate of DS1 (T1)
1.544 Mbps (24 DS0s, plus 8 kpbs overhead)
Bit Rate of DS3 (T3)
44.736 Mbps (28 DS1s, plus management overhead)
Bit Rate of E1
2.048 Mbps (32 DS0s)
Bit Rate of E3
34.368 Mbps (16 E1s, plus management overhead)
Bit Rate of J1 (Y1)
2.048 Mbps (32 DS0s; Japanese standard)
HDLC Framing
Standard HDLC (No Type Field)
Flag - 1 Byte
Address - 1 Byte
Control - 1 Byte
Data - Variable
FCS - 4 Bytes

Proprietary Cisco HDLC (Adds Type Field)
Flag - 1 Byte
Address - 1 Byte
Control - 1 Byte
Type - 2 Byte
Data - Variable
FCS - 4 Bytes
Synchronous
The imposition of time ordering on a bit stream. Practically, a device tries to use the same speed as another device on the other end of a serial link. However, by examining transitions between voltage states on the link, the device can notice slight variation in the speed on each end and can adjust its speed accordingly.
Clock source
The device to which the other devices on the link adjust their speed when using synchronous links.
CSU/DSU
Channel service unit/data service unit. Used on digital links as an interface to the telephone company in the United States. Routers typically use a short cable from a serial interface to a CSU/DSU, which is attached to the line from the telco with a similar configuration at the other router on the other end of the link.
Telco
Telephone Company.
Four-wire circuit
A line from the telco with four wires, composed of two twisted-pair wires. Each pair is used to send in one direction, so a four-wire ciruit allows full-duplex communications.
T1
A line from the telco that allows transmission of data at 1.544 Mbps.
E1
Similar to a T1, but used in Europe. It uses a rate of 2.048 Mbps and 32 64-kbps channels.
Access Link
In Frame Relay, the physical serial link that connects a Frame Relay DTE device, usually a router, to a Frame Relay switch. This access link uses the same physical layer standards as do point-to-point leased lines.
back-to-back link
A serial link between two routers, created without CSU/DSUs, by connecting a DTE cable to one router and a DCE cable to the other. Typically used in labs to build serial links without the expense of a actual leased line from the telco.
DTE (Layer 1)
Data Terminal Equipment. From a Layer 1 perspective, the DTE synchronizes its clock based on the clock sent by the DCE. From a packet-switching perspective, the DTE is the device outside the service provider's network, typically a router.
DCE (Layer 1)
Data communication equipment. From a physical layer perspective, the device providing the clocking on a WAN link, typically a CSU/DSU, is the DCE. From a packet-switching perspective, the service provider's switch, to which a router might connect, is considered the DCE.
Frame Relay
An International standard data-link protocol that defines the capabilities to create a frame-switched (packet-switched) service, allowing DTE devices (typically routers) to send data to many other devices using a single physical connection to the Frame Relay service.
HDLC
High-Level Data Link Control. A bit-oriented synchronous data link layer protocol developed by the International Organization Standardization (ISO).
Leased Line
A serial communication circuit between two points, provided by some service provider, typically a telephone company (telco). Because the telco does not sell a physical cable between the two endpoints, instead charging a monthly fee for the ability to send bit between the two sites, the service is considered to be a leased service.
Packet Switching
A generic reference to network services, typically WAN services, in which the service examines the contents of the transmitted data to make some type of forwarding decision. This term is mainly used to contrast with the WAN term circuit switching, in which the provider sets up a (Layer 1) circuit between two devices, and the provider makes no attempt to interpret the meaning of the bits.
PPP
Point-to-Point Protocol. A protocol that provides router-to-router and host-to-network connections over synchronous point-to-point and asynchronous point-to-point circuits.
Virtual Circuit
In packet-switched services like Frame Relay, VC refers to the ability of the two DTE devices (typically routers) to send and receive data directly to each other, which supplies the same function as a physical leased line (leased circuit), but doing so without a physical circuit. This term is meant as a contrast with a leased line or leased circuit.
Rules of IP addresses needing to be in the same grouping.
All IP addresses in the same group must not be separated by a router. IP addresses separated by a router must be in different groups.
Size of A Network
1 Byte of Network Bytes
3 Bytes of Host Bytes
2^24 -2 of Addresses per network
Size of B Network
2 Bytes of Network Bytes
2 Bytes of Host Bytes
2^16 -2 of Addresses per network
Seize of C Network
3 Bytes of Network Bytes
1 Byte of Host Bytes
2^24 - 2 of Addresses per network
Class A - Valid Network Range
1 to 126
1.0.0.0 to 126.0.0.0
126 Possible Networks
16,777,214 Possible Hosts
Class B - Valid Network Range
128 to 191
128.0.0.0 to 191.255.0.0
16,384 Possible Networks
65,534 Possible Hosts
Class C - Valid Network Range
192 to 223
192.0.0.0 - 223.255.255.0
2,097,152 Possible Networks
254 Possible Hosts
Simple Routing Logic
If the destination IP address is in the same subnet as I am, send the packet directly to that destination host.

If the destination IP address is not in the same subnet as I am, send the packet to my default gateway (a router's Ethernet interface on the subnet)
Router Forwarding Decisions and the IP Routing Table
Step 1 - Use the data - link FCS field to ensure that the frame had no errors; if errors occurred, discard the frame.
Step 2 - Assuming the frame was not discarded at step 1, discard the old data-link header and trailer, leaving the IP packet.
Step 3 - Compare the IP packet's destination IP address to the routing table, and find the route that matches the destination address. This route identifies the outgoing interface of the router, and possibly the next-hop router.
Step 4 - Encapsulate the IP packet inside a new data-link header and trailer, appropriate for the outgoing interface, and forward the frame.
ARP
Address Resolution Protocol. An Internet protocol used to map an IP address to a MAC address.
Default gateway/ default router
On an IP host, the IP address of some router to which the host sends packets when the packet's destination address is on a subnet other than the local subnet.
DHCP
Dynamic Host Configuration Protocol. A protocol used by hosts to dynamically discover and lease an IP address, and learn the correct subnet mask, default gateway, and DNS server IP addresses.
DNS
Domain Name System. An application layer protocol used throughout the Internet for translating hostnames into their associated IP addresses.
host part
A term used to describe a part of an IPv4 address taht is used to uniquely identify a host inside a subnet. The host part is identified by the bits of value 0 in the subnet mask.
IP address
Internet Protocol. The network layer protocol in the TCP/IP stack, providing routing and logical addressing standards and services.
logical address
A generic reference to addresses as defined by Layer 3 protocols, which do not have to be concerned with the physical details of the underlying physical media. Used mainly to contrast these addresses with data-link addresses, which are generically considered to be physical addresses because they differ based on the type of physical medium.
network broadcast address
In IPv4, a special address in each classful network that can be used to broadcast a packet to all hosts in that same classful network. Numerically, the address has the same value as the network number in the network part of the address, and all 255s in the host octets - for example, 10.255.255.255 is the network broadcast address for classful network.
network number/network address
A number that used dotted decimal notation like IP addresses, but the number itself represents all hosts in a single Class A, B, or C network
network part
The portionof an IPv4 address that is either 1,2, or 3 octects/bytes long, based on whether the address is in a Class A, B, or C network.
routing table
A list of routes in a router, with each route listing the destination subnet and mask, the router interface out which to forward packets destined to that subnet, and, as needed, the next-hop router's IP address.
subnet broadcast address
A special address in each subnet specifically the largest numeric address in the subnet, designed so that packets sent to this address should be delivered to all hosts in that subnet.
subnet number/subnet address
In IPv4, a dotted decimal number that represents all addresses in a single subnet. Numerically, the smallest value in the range of numbers in a subnet, reserved so that it cannot be used as a unicast IP address by a host.
subnet part
In a subnetted IPv4 address, interpreted with classful addressing rules, one of three parts of the structure of an IP address, with the subnet part uniquely identifying different subnets of a classful IP network.
TCP/IP Transport Layer Feature - Multiplexing using ports
Function that allows receiving hosts to choose the correct application for which the data is destined, based on the port number
TCP/IP Transport Layer Feature - Error recovery
Process of numbering and acknowledging data with Sequence and Acknowledgement header fields.
TCP/IP Transport Layer Feature - Flow control using windowing
Process that uses window sizes to protect buffer space and routing devices.
TCP/IP Transport Layer Feature - Connection establishment and termination
Process used to initialize port numbers and Sequence and Acknowledgment fields.
TCP/IP Transport Layer Feature - Ordered data transfer and data segmentation
Continuous stream of bytes from an upper-layer process that is "segment" for transmission and delivered to upper-layer processes at the receiving device, with the bytes in the same order.
FTP Port Number
20 (data) & 21 (control)
SSH Port Number
22
Telnet Port Number
23
SMTP Port Number
25 TCP
DNS Port Number
UDP, TCP 53
DHCP Port Number
UDP 67,68
TFTP Port Number
UDP 69
HTTP (WWW) Port Number
TCP 80
POP3 Port Number
TCP 110
SNMP Port Number
UDP 161
SSL Port Number
TCP 443
RTP-based Voice (VoiP) and Video
UDP, 16, 384 - 32, 767
Connection-oriented protocol
A protocol that requires an exchange an exchange of message before data transfer begins or that has a required preestablished correlation between two endpoints.
Connectionless protocol
A protocol that does not require an exchange of messages and that does not require a preestablished correlation between two endpoints.
Low Delay
VoiP requires a very low delay between the sending phone and the receiving phone - typically less than 200 milliseconds (.2 seconds). This is a much lower delay than what is required by typical data applications.
Low Jitter
Jitter is the variation in delay. VoiP requires very low jitter as well, whereas data applications can tolerate much higher jitter. For example, the jitter for consecutive VoIP packets should not exceed (.03 seconds), or the quality degrades.
Loss
if a VoIP packet is lost in transit because of errors of because a router doesn't have room to store the packet while waiting to send it, the VoIP packet is not delivered across the network. Because of the delay and jitter issues, there is no need to try to recover the lost packet. It would be useless by the time it was recovered. Lost packets can sound like a break in the sound of the VoIP call.
Denial of Service (DoS)
An attack whose purpose whose purpose is to break things.
Reconnaissance attack
The kind of attack may be disruptive as a side effect, but its goal is gathering information to perform an access attack.
Access attacks
An attempt to steal data, typically data for some financial advantage, for a competitive advantage with another company, or even for international espionage.
Common Security Issues in an Enterprise
- Access from the wireless LAN
- Infected mobile laptops
- Disgruntled employees
anti-x
The term used by Cisco to refer to a variety of security tools that help prevent various attacks including antivirus, anti-phishing, and anti-spam.
connection establishment
The process by which a connection-oriented protocol creates a connection. With TCP, a connection is established by a three-way transmission of TCP segments
firewall
A device that forwards packets between the less secure and more secure parts of the network, applying rules that determine which packets are allowed to pass, and which are not.
Forward acknowledgement
A process used by protocols that do error recovery in which the number that acknowledges data lists the next data that should be sent, not the last data that was successfully received.
Intrusion Detection System
A security function that examines more complex traffic patterns against a list of both known attack signatures and general characteristics of how attacks may be carried out, rating each perceived threat and reporting the threats.
Intrusion Prevention Systen
A security function that examines more complex traffic patterns against a list of both known attack signatures and general characteristics of how attacks may be carried out, rating each perceived threat and reacting to prevent the more significant threats.
Positive Acknowledgement and Retransmission (PAR)
A generic reference to how the error recovery feature works in many protocols, including TCP, in which the receivef must send an acknowledgment that either implies that the data was (positively) received, or send an acknowledgement that implies that some data was lost, so the sender can then resend the lost data.
sliding windows
For protocols such as TCP that allow the receiving device to dictate the amount of data the sender can send before receiving an acknowledgment-- a concept called a window--a reference to the fact that the mechanism to gran future windows is typically jsut a number that grows upwards slowly after each acknowledgment, sliding upward.
Virtual private network (VPN)
The process of securing communication between two devices whose packets pass over some public and unsecure network, typically the Internet. VPNs encrypt packets so that the communication is private and authenicate the identity of the endpoints.
web server
Software running on some computer, that stores web pages and sends those web pages to web clients (web browsers) that request the web pages.
Switching Logic
Deciding when to forward a frame or when to filter (not forward) a frame, based on the destination MAC address.

Learning MAC addresses by examining the source MAC address of each frame received by the bridge.

Create a (Layer 2) loop-free environment with other bridges by using Spanning Tree Protocol (STP)
Switching Method - Store and forward
The switch fully receive all bits in the frame (store) before forwarding the fram (forward). This allows the switch to check the FCS before forwarding the frame.
Cut-through
The switch forwards the frame as soon as it can. This reduces latency but does not allow the switch to discard frames that fail the FCS check.
Fragment-free
The switch forwards the frame after receiving the first 64 bytes of the frame, thereby avoiding forwarding frames that were errored due to a collision.
LAN Switching Summary
Switch ports connected to a single device microsegment the LAN, providing dedicated bandwidth to that single device.
Switches allow multiple simultaneous conversation between devices on differeent ports.
Switch ports connected to a single device support full duplex, in effect doubling the amount of bandwidth available to the device.
Switches support rate adaption, which means that devices that use different Ethernet speeds can communicate through the switch (hubs cannot).
Collision Domain
a set of network interface cards (NIC) for which a frame sent by one NIC could result in a collision with a fram sent by any other NIC in the same collision domain.
Broadcast Domain
A set of NICs for which a broadcast frame sent by one NIC is received by all other NICs in the same broadcast domain.
Flooding
The result of the LAN switch forwarding process for broadcasts and unknown unicast frames. Switches forward these frames out all interfaces, except the interface in which the frame arrived. Switched also forward multicasts by default, although this behaviour can be changed.
Spanning Tree Protocol (STP)
A bridge protocol that uses the Spanning Tree algorithm, allowing a switch to dynamically work around loops in a network topology by creating a spanning tree. Switches exchange bridge protocol data unit (BPDU) messages with other bridges to detect loops and then remove the loops by shutting down selected bridge interfaces.
virtual LAN
A group of devices, connected to one or more switches, with the devices grouped into a single broadcast domain through switch configuration. VLANs allow switch administrators to separate the devices connected to the switches into separate VLANs without requiring separate physical switches, gaining design advantages of separating the traffic without the expense of buying additional hardware.
Default console port settings
9600 bits/second
No hardware flow control
8-bit ASCII
No parity bits
1 stop bit
Global Configuration Mode
Enable
configure terminal
Cisco Switch Memory Type - RAM
Working Memory and running configuration
Cisco Switch Memory Type - Flash
Cisco IOS Software
Cisco Switch Memory Type - ROM
Bootstrap Program
Cisco Switch Memory Type - NVRAM
Startup Configuration
Startup-config
Stores the initial configuration used any time te switch reloads Cisco IOS.
Running-config
Stores the currently used configuration commands. This file changes dynamically when someone enters commands in configuration mode.
line console 0
Global command that changes the context to console configuration mode.
line vty 1st-vty 2nd-vty
Global command that changes the context to vty configuration mode for the range of vty lines listed in the command.
login
Line (console and vty) configuration mode. Tells IOS to prompt for a password (no username).
password pass-value
Line (console and vty) configuration mode. Lists the password required if the login command (with no other parameters) is configured.
interface type port-number
Global command that changes the context to interface mode - for example, interface Fastethernet 0/1
(no) shutdown
Interface subcommand that disables or enables the interface, respectively.
hostname name
Global command that sets this switch's hostname, which is also used as the first part of the switch's command prompt.
enable secret pass-value
Global command that sets automatically encrypted enable secret password. The password is used for any user to reach enable mode.
enable password pass-value
Global command that sets the clear-text enable password, which is used only when the enable secret password is not configured.
exit
Moves back to the next higher mode in configuration mode.
end
Exits configuration mode and goes back to enable mode from any of the configuration submodes.
Ctrl-Z
This is nut a command, but rather a two-key combination (the Ctrl key and the letter z) that together do the same thing as the end command.
Configuring Usernames and Secure Sheel (SSH)
# Line vty 0 15
# transport input telnet ssh
# username user-value password pass-value
# ip domain-name domain-value
# crypto key generate rsa
show history
Lists the commands currently held in the history buffer.
history size x
From console or vty line configuration mode, sets the default number of commands saved in the history buffer for the user(s) of the console or vty lines, respectively.
terminal history size x
From EXEC mode, this command allows a single user to set, just for this one connection, the size of his or her history buffer.
Command to configure IP on a switch
# configure terminal
# interface vlan 1
# ip address /network address/ /subnet/
# no shutdown
# exit
# ip default-gateway /network address/
show mac address-table dynamic
Lists the dynamically learned entries in the switch's address (forwarding) table.
show dhcp lease
Lists any information the switch acquires as a DHCP client. This includes IP address, subnet, and default gateway information.
show crypto key mypubkey rsa
Lists the public and shared key created for use with SSH using the crypto key generate rsa global configuration command.
show interfaces vlan 1
Lists the interface status, the switch's IP address and mask, and much more.
show port-security interface type number
Lists an interface's port security configuration settings and security operational status.
CDP discovers several useful details from the neighboring Cisco devices:
Device Identifier, Address list, Local interface, Port Identifier, Capabilities list, Platform
show cdp neighbors [type number]
Lists one summary line of information about each neighbor or just the neighbor found on a specific interface if an interface was listed.
show cdp neighbors detail
Lists one large set (approximately 15 lines) of information, one set for every neighbor.
show cdp entry name
Lists the same information as the show cdp neighbors detail command, but only for the named neighbor (case-sensitive).
Excessive noise
Symptoms - many input errors, few collisions
Causes - Wrong cable category (Cat 5, 5e, 6): damaged cabled; EMI
Collisions
Symptoms - More than roughly .1% of all frames are collisions
Causes - Duplex mismatch (seen on the half-duplex side); jabber; Dos attack
late Collisions
Symptoms - Increasing late collisions
Causes - Collisions domain or single cable too long; duplex mismatch
CDP neighbor
A device on the other end of some communications cable that is advertising CDP updates
up and up
Jargon referring to the two interface states on a Cisco IOS router or switch (line status and protocol status), with the first "up" referring to the line status, and the second "up" referring to the protocol status. An interface in this state should be able to pass data-link frames.
error disabled
An interface state on LAN switches that is the result of one of many security violations
ITU-R
Worldwide standardization of communications that use radiated energy, particularly managing the assignment of frequencies
IEEE
Standardization of wireless LANs (802.11)
Wi-Fi Alliance
An industry consortium that encourages interoperability of products that implement WLAN standards through their Wi-Fi certified program.
Federal Communications Commission (FCC)
The U.S. government agency with that regulates the usage of various communications frequencies in the U.S.
Direct Sequences Spread Spectrum (DSSS)
(802.11)
Orthogonal Frequency Division Multiplexing (OFDM)
(802.11b, 802.11g)
Frequency Hopping Spread Spectrum (FHSS)
(802.11a, 802.11g)
Physical Installation of a router
Connect any LAN cables to the LAN ports.

If using an external CSU/DSU, connect the router's serial interface to the CSU/DSU, and the CSU/DSU to the line from the telco.

If using an internal CSU/DSU, connect the router's serial interface to the line from the telco.

Connect the router's console port to a PC (using a rollover cable), as needed, to configure the router.

Connect a power cable from a power outlet to the power port on the router.

Turn on the router.
Differences between Switch CLI and Router CLI
The configuration of IP addresses differs in some ways.

The questions asked in setup mode differ.

Routers have an auxiliary (Aux) port, intended to be connected to an external modem and phone line, to allow remote users to dial into the router, and access the CLI, by making a phone call.
Line status
Location - First status code.
General Meaning - Refers to the Layer 1 status - for example, is the cable installed, is it the right/wrong cable, is the device on the other end powered on?
Protocol status
Location - Second status code
General Meaning - Refers generally to the Layer 2 status. It is always down if the line status is down. If the line status is up, a protocol status of down usually is caused by mismatched data link layer configuration.
Administratively down, down
The interface has a shutdown command configured on it.
down, down
The interface has a no shutdown command configured, but the physical layer has a problem. For example, no cable has been attached to the interface, or with Ethernet, the switch interface on the other end of the cable is shut down, or the switch is powered off.
up, down
Almost always refers to data link layer problems, most often configuration problems. For example, serial links have this combination when one router was configured to use PPP, and the other defaults to use HDLC.
up, up
All is well, interface is functioning.
Router powers on steps
1. The router performs a power-on self-test (POST) to discover the hardware components and verify that all components work properly.
2. The router copies a bootstrap program from ROM into RAM, and runs the bootstrap program.
3. The bootstrap program decides which IOS image (or other OS) to load into RAM, and loads that OS. After loading the IOS image, the bootstrap program hands over control of the router hardware to the newly loaded OS.
4. If the bootstrap program loaded IOS, IOS finds the configuration file (typically the startup-config file in NVRAM) and loads it into RAM as the running-config.
ROM Monitor
Common Name - ROMMON
Stored In - ROM
Used in ... Old and new routers
Boot ROM
Common Name - RxBoot, boot helper
Stored In - ROM
Used in... Only in older routers
boot field in the configuration register
1. If boot field = 0, use the ROMMON OS.
2. If boot field =1, load the first IOS file found in Flash memory.
3. If boot field = 2-F:
a. Try each boot system command in the startup-config file, in order, until one works.
b. If none of the system commands work, load the first IOS file found in Flash memory.
show version information
The IOS version, the uptime (the length of the that has passed since the last reload), The reason for the last reload of IOS, the time of the last loading of IOS, the source from which the router loaded the current IOS, the amount of RAM memory, the number and types of interfaces, the amount of NVRAM memory, The amount of Flash memory, the configuration register's current and future setting (if different)
Interior Gateway Protocol
A routing protocol that was designed and intended for use inside a single autonomous system.
Exterior Gateway Protocol
A routing protocol that was designed and intended for use between different autonomous system.
Distance Vectors
RIP-1, RIP-2, IGRP
Link-state
OSPF, Integrated IS-IS
Balanced hybrid (also called advanced distance vector)
EIGRP
Classless vs Classful routing protocols
Classless - Supports VLSM, Sends subnet mask in routing updates, Supports manual route summarization.
Classful supports none of these.
RIP-2 Configuration
router rip
version 2
network /net-number
(Optional) passive-interface /type /number
show ip protocols
Lists information about the RIP configuration, plus the IP addresses of neighboring RIP routers from which the local router has learned routes.
DSL key features
DSL allows analog voice signals and digital data signals to be sent over the same local loop wiring at the same time.
The local loop must be connected to something besides a traditional voice switch at the local CO, in this case a device called a DSL access multiplexer (DSLAM).
DSL allows for a concurrent voice call to be up at the same time as the data connection.
Unlike modems, DSL's data component is always on; in otehr words, you do not have to signal or dial a phone number to set up a data circuit.
Compare circuits and packet switching
Circuits - Service implemented as OSI Layer 1. Point-to-Point
Packet Switching - Service implemented as OSI Layer 2. Multipoint (more than two)
Inside host
Refers to a host in the enterprise network.
Inside local
Refers to an IP address in an IP header, with that address representing a local host as the packet passes over the local enterprise network (not the Internet). In this case, 192.168.1.101 and .102 are inside local IP addresses.
Inside global
Refers to an IP address in an IP address in an IP header, with that address representing a local host as the packet passes over the global Internet (not the enterprise). In this case 64.100.1.1 is the one inside global IP address,
Inside interface
The router interface connected to the same LAN as the inside hosts.
Outside interface
The router interface connected to the Internet.
ADSL
Asymmetric digital subscriber line. One of many DSL technologies, ADSL is designed to deliver more bandwidth downstream (from the central office to the customer site) than upstream.
ATM
Asynchronous Transfer Mode. The international standard for cell relay in which multiple service types (such as voice, video, and data) are conveyed in fixed-length (53-byte) cells. Fixed-length cells allows cell processing to occur in hardware, thereby reducing transit delays.
Configure HDLC
1. Configure the interface IP address using the ip address interface subcommand.
2. The following tasks are required only when the specifically listed conditions are true:
a) If an encapsulation protocol interface subcommand that lists a protocol besides HDLC already exists on the interface, use the "encapsulation hdlc" interface subcommandto enable HDLC.
b) If the interface line status is administratively down, enable the interface using the no shutdown interface subcommand.
c) If the serial link is a back-to-back serial link in a lab (or a simulator), configure the clocking rate using the clock rate speed" interface subcommand, but only on the one router with the DCE cable (per the show controllers serial number command)
3. The following steps are always optional, and have no impact on whether the link works and passes IP traffic:
a) configure the link's speed using the bandwidth speed-in-kbps interface subcommand.
b) For documentation purposes, configure a description of the purpose of the interface using the description text interface subcommand.
encapsulation { hdlc | ppp | frame-relay }
Serial interface subcommand that defines the data-link protocol to use on the link.
clock rate [speed]
Serial interface subcommand that, when used on an interface with a DCE cable, sets the clock speed in bps.
bandwidth [speed-kbps]
Interface subcommand that sets the router's opinion of the link speed, in kbps, but has no effect on the actual speed.
description [text]
Interface subcommand that can set a text description of the interface.
Configure HDLC
1. Configure the interface IP address using the ip address interface subcommand.
2. The following tasks are required only when the specifically listed conditions are true:
a) If an encapsulation protocol interface subcommand that lists a protocol besides HDLC already exists on the interface, use the "encapsulation hdlc" interface subcommandto enable HDLC.
b) If the interface line status is administratively down, enable the interface using the no shutdown interface subcommand.
c) If the serial link is a back-to-back serial link in a lab (or a simulator), configure the clocking rate using the clock rate speed" interface subcommand, but only on the one router with the DCE cable (per the show controllers serial number command)
3. The following steps are always optional, and have no impact on whether the link works and passes IP traffic:
a) configure the link's speed using the bandwidth speed-in-kbps interface subcommand.
b) For documentation purposes, configure a description of the purpose of the interface using the description text interface subcommand.
show ip nat translation
Lists the NAT/PAT translation table entries.
encapsulation { hdlc | ppp | frame-relay }
Serial interface subcommand that defines the data-link protocol to use on the link.
show dhcp server
Lists information learned from a DHCP server, by a router acting as a DHCP client.
clock rate [speed]
Serial interface subcommand that, when used on an interface with a DCE cable, sets the clock speed in bps.
clear ip nat translation *
Lists several important settings on serial links, including encapsulation, bandwidth, keepalives, the two status codes, description, and IP address/mask
bandwidth [speed-kbps]
Interface subcommand that sets the router's opinion of the link speed, in kbps, but has no effect on the actual speed.
show controllers serial [number]
Lists whether a cable is connected to the interface, and if so, whether it is a DTE or DCE cable
description [text]
Interface subcommand that can set a text description of the interface.
show interfaces [type number] description
Lists a single line per interface (or if the interface is included, just one line of output total) that lists the interface status and description
show ip nat translation
Lists the NAT/PAT translation table entries.
show dhcp server
Lists information learned from a DHCP server, by a router acting as a DHCP client.
clear ip nat translation *
Lists several important settings on serial links, including encapsulation, bandwidth, keepalives, the two status codes, description, and IP address/mask
show controllers serial [number]
Lists whether a cable is connected to the interface, and if so, whether it is a DTE or DCE cable
show interfaces [type number] description
Lists a single line per interface (or if the interface is included, just one line of output total) that lists the interface status and description