http://rapidshare.com/files/327390865/Nursing_RS.part1.rar.html
http://rapidshare.com/files/327396283/Nursing_RS.part2.rar.html
http://rapidshare.com/files/327397308/Nursing_RS.part3.rar.html
Nursing books collection.
Tuesday, December 29, 2009
Tuesday, December 22, 2009
ACL + Wildcards
Wildcards don't have to be consecutive of binary 1s or 0s. Wildcard could be 0.255.0.0 or 0.0.66.0 etc. Routers examine each bit in IP address and compare it to wildcard. When router checks each wildcard bit, the logic is following: if bit equal to 0 than IP address' corresponding bit should match and if bit equal to 1 than IP address' bit doesn't have to match.
To get a wildcard from a subnet mask, we need to substract mask from 255.255.255.255.
255.255.255.255
− 255.255.252. 0
0. 0. 3. 255
The number range for standart ACLs is 1 to 99 and 1300 to 1999.
Standard ACLs should be placed near to the destination of the packets so that it does not unintentionally discard packets that should not be discarded.
The extended access-list command uses numbers between 100–199 and 2000–2699.
Extended ACLs should be placed as close as possible to the source of the packets.
To get a wildcard from a subnet mask, we need to substract mask from 255.255.255.255.
255.255.255.255
− 255.255.252. 0
0. 0. 3. 255
The number range for standart ACLs is 1 to 99 and 1300 to 1999.
Standard ACLs should be placed near to the destination of the packets so that it does not unintentionally discard packets that should not be discarded.
The extended access-list command uses numbers between 100–199 and 2000–2699.
Extended ACLs should be placed as close as possible to the source of the packets.
Routse summarization
For summarize the routes first I need to look at the least subnet.
Then I have to decide which block size to use based on whole range of subnets.
For example:
10.2.1.0/24
10.2.2.0/24
10.2.3.0/24
10.2.4.0/24
Can't use block size of 4 because then it's only 10.2.0.0 - 1.2.3.255 (10.2.4.0 won't be included).
I need to use block size - 8 - then final mask will be 255.255.255.248
10.2.0.0 255.255.255.248 - summary route
Example 2:
Then I have to decide which block size to use based on whole range of subnets.
For example:
10.2.1.0/24
10.2.2.0/24
10.2.3.0/24
10.2.4.0/24
Can't use block size of 4 because then it's only 10.2.0.0 - 1.2.3.255 (10.2.4.0 won't be included).
I need to use block size - 8 - then final mask will be 255.255.255.248
10.2.0.0 255.255.255.248 - summary route
Example 2:
- 172.1.4.128/25
- 172.1.7.0/24
- 172.1.6.0/24
- 172.1.5.0/24
- 172.1.4.0/25
Monday, December 7, 2009
Internal components + Boot sequence + Recovering Password
The Internal Components of a Cisco Router
Bootstrap Stored in the microcode of the ROM, the bootstrap is used to bring a router up during initialization. It will boot the router and then load the IOS.
POST (power-on self-test) Stored in the microcode of the ROM, the POST is used to check the basic functionality of the router hardware and determines which interfaces are present.
ROM monitor Stored in the microcode of the ROM, the ROM monitor is used for manufacturing, testing, and troubleshooting.
Mini-IOS Called the RXBOOT or bootloader by Cisco, the mini-IOS is a small IOS in ROM that can be used to bring up an interface and load a Cisco IOS into flash memory. The mini-IOS can also perform a few other maintenance operations.
RAM (random access memory) Used to hold packet buffers, ARP cache, routing tables, and also the software and data structures that allow the router to function.
Running-config is stored in RAM, and most routers expand the IOS from flash into RAM upon boot.
ROM (read-only memory) Used to start and maintain the router. Holds the POST and the bootstrap program, as well as the mini-IOS.
Flash memory Stores the Cisco IOS by default. Flash memory is not erased when the router is reloaded. It is EEPROM (electronically erasable programmable read-only memory) created by Intel.
NVRAM (nonvolatile RAM) Used to hold the router and switch configuration. NVRAM is not erased when the router or switch is reloaded. Does not store an IOS. The configuration register is stored in NVRAM.
Configuration register Used to control how the router boots up. This value can be found as the last line of the show version command output and by default is set to 0x2102, which tells the router to load the IOS from flash memory as well as to load the configuration from NVRAM.
The default order of an IOS loading from a router is Flash, TFTP server, then ROM.
The Router Boot Sequence
1. The router performs a POST. The POST is stored in and run from ROM (read-only memory).
2. The bootstrap then looks for and loads the Cisco IOS software. The bootstrap is a program in ROM that is used to execute programs. The bootstrap program is responsible for finding where each IOS program is located and then loading the file. By default, the IOS software is loaded from flash memory in all Cisco routers.
3. The IOS software looks for a valid configuration file stored in NVRAM. This file is called startup-config and is only there if an administrator copies the running-config file into NVRAM. (As you already know, the new ISR routers have a small startupconfig file preloaded.)
4. If a startup-config file is in NVRAM, the router will copy this file and place it in RAM and call the file running-config. The router will use this file to run the router. The router should now be operational. If a startup-config file is not in NVRAM, the router will broadcast out any interface that detects carrier detect (CD) for a TFTP host looking for a configuration, and when that fails (typically it will fail—most people won’t even realize the router has attempted this process), it will start the setup mode configuration process.
Recovering Passwords
Bootstrap Stored in the microcode of the ROM, the bootstrap is used to bring a router up during initialization. It will boot the router and then load the IOS.
POST (power-on self-test) Stored in the microcode of the ROM, the POST is used to check the basic functionality of the router hardware and determines which interfaces are present.
ROM monitor Stored in the microcode of the ROM, the ROM monitor is used for manufacturing, testing, and troubleshooting.
Mini-IOS Called the RXBOOT or bootloader by Cisco, the mini-IOS is a small IOS in ROM that can be used to bring up an interface and load a Cisco IOS into flash memory. The mini-IOS can also perform a few other maintenance operations.
RAM (random access memory) Used to hold packet buffers, ARP cache, routing tables, and also the software and data structures that allow the router to function.
Running-config is stored in RAM, and most routers expand the IOS from flash into RAM upon boot.
ROM (read-only memory) Used to start and maintain the router. Holds the POST and the bootstrap program, as well as the mini-IOS.
Flash memory Stores the Cisco IOS by default. Flash memory is not erased when the router is reloaded. It is EEPROM (electronically erasable programmable read-only memory) created by Intel.
NVRAM (nonvolatile RAM) Used to hold the router and switch configuration. NVRAM is not erased when the router or switch is reloaded. Does not store an IOS. The configuration register is stored in NVRAM.
Configuration register Used to control how the router boots up. This value can be found as the last line of the show version command output and by default is set to 0x2102, which tells the router to load the IOS from flash memory as well as to load the configuration from NVRAM.
The default order of an IOS loading from a router is Flash, TFTP server, then ROM.
The Router Boot Sequence
1. The router performs a POST. The POST is stored in and run from ROM (read-only memory).
2. The bootstrap then looks for and loads the Cisco IOS software. The bootstrap is a program in ROM that is used to execute programs. The bootstrap program is responsible for finding where each IOS program is located and then loading the file. By default, the IOS software is loaded from flash memory in all Cisco routers.
3. The IOS software looks for a valid configuration file stored in NVRAM. This file is called startup-config and is only there if an administrator copies the running-config file into NVRAM. (As you already know, the new ISR routers have a small startupconfig file preloaded.)
4. If a startup-config file is in NVRAM, the router will copy this file and place it in RAM and call the file running-config. The router will use this file to run the router. The router should now be operational. If a startup-config file is not in NVRAM, the router will broadcast out any interface that detects carrier detect (CD) for a TFTP host looking for a configuration, and when that fails (typically it will fail—most people won’t even realize the router has attempted this process), it will start the setup mode configuration process.
Recovering Passwords
- Boot the router and interrupt the boot sequence by performing a break, which will take the router into ROM monitor mode.
- Change the configuration register to turn on bit 6 (with the value 0x2142).
- Reload the router.
- Enter privileged mode.
- Copy the startup-config file to running-config.
- Change the password.
- Reset the configuration register to the default value.
- Save the router configuration.
- Reload the router (optional).
Wednesday, December 2, 2009
Tuesday, December 1, 2009
IP addressing
IPv4
00000000 = 0
01111111 = 127
10000000 = 128
10111111 = 191
11011111 = 223
11101111 = 239
Reserved IP Address Space
Address Class Reserved Address Space
Class A 10.0.0.0 through 10.255.255.255
Class B 172.16.0.0 through 172.31.255.255
Class C 192.168.0.0 through 192.168.255.255
- Network Address Range: Class A
00000000 = 0
01111111 = 127
- Network Address Range: Class B
10000000 = 128
10111111 = 191
- Network Address Range: Class C
11011111 = 223
- Network Address Range: Class D
11101111 = 239
Reserved IP Address Space
Address Class Reserved Address Space
Class A 10.0.0.0 through 10.255.255.255
Class B 172.16.0.0 through 172.31.255.255
Class C 192.168.0.0 through 192.168.255.255
IP Header
Possible Protocols Found in the Protocol Field of an IP Header
Protocol Protocol Number
Protocol Protocol Number
- ICMP 1
- IP in IP (tunneling) 4
- IGRP 9
- EIGRP 88
- OSPF 89
- IPv6 41
- GRE 47
- Layer 2 tunnel (L2TP) 115
RFC
- RFC 768 is UDP
- RFC 3232 defines well-known ports
- RFC 791 discuss IP
- RFC 1256 is an annex to ICMP
OSI layers remarks
Serial interrface = V.35 physical int
Transport layer:
TCP creates a virtual circuit!
UDP doesn’t create a virtual circuit!
And both check FCS field for CRC errors.
The types of flow control are buffering, windowing, and congestion avoidance.
Windows are used to control the amount of outstanding, unacknowledged data segments.
Data-link layer standards:
10BaseT 10Mbps using category 3 UTP wiring up to 100 meters. Unlike with the 10Base2 and 10Base5 networks, each device must connect into a hub or switch, and you can have only one host per segment or wire. Uses an RJ45 connector (8-pin modular connector) with a physical star topology and a logical bus.
100BaseTX (IEEE 802.3u) EIA/TIA category 5, 6, or 7 UTP two-pair wiring. One user per segment; up to 100 meters long. It uses an RJ45 connector with a physical star topology and a logical bus.
100BaseFX (IEEE 802.3u) Uses fiber cabling 62.5/125-micron multimode fiber. Point-to-point topology; up to 412 meters long. It uses an ST or SC connector, which are mediainterface connectors.
1000BaseCX (IEEE 802.3z) Copper twisted-pair called twinax (a balanced coaxial pair) that can only run up to 25 meters.
1000BaseT (IEEE 802.3ab) Category 5, four-pair UTP wiring up to 100 meters long.
1000BaseSX (IEEE 802.3z) MMF using 62.5- and 50-micron core; uses an 850 nano-meter laser and can go up to 220 meters with 62.5-micron, 550 meters with 50-micron.
1000BaseLX (IEEE 802.3z) Single-mode fiber that uses a 9-micron core and 1300 nanometer laser and can go from 3 kilometers up to 10 kilometers.
Transport layer:
TCP creates a virtual circuit!
UDP doesn’t create a virtual circuit!
And both check FCS field for CRC errors.
The types of flow control are buffering, windowing, and congestion avoidance.
Windows are used to control the amount of outstanding, unacknowledged data segments.
Data-link layer standards:
Media Access Control (MAC) 802.3 Defines how packets are placed on the media. Contention media access is “first come/first served” access where everyone shares the same bandwidth— hence the name. Physical addressing is defined here, as well as logical topologies. What’s a logical topology? It’s the signal path through a physical topology. Line discipline, error notification (not correction), ordered delivery of frames, and optional flow control can also be used at this sublayer.
Logical Link Control (LLC) 802.2 Responsible for identifying Network layer protocols and then encapsulating them. An LLC header tells the Data Link layer what to do with a packet once a frame is received. It works like this: A host will receive a frame and look in the LLC header to find out where the packet is destined—say, the IP protocol at the Network layer. The LLC can also provide flow control and sequencing of control bits.
Logical Link Control (LLC) 802.2 Responsible for identifying Network layer protocols and then encapsulating them. An LLC header tells the Data Link layer what to do with a packet once a frame is received. It works like this: A host will receive a frame and look in the LLC header to find out where the packet is destined—say, the IP protocol at the Network layer. The LLC can also provide flow control and sequencing of control bits.
The switches and bridges I talked about near the beginning of the chapter both work at the Data Link layer and filter the network using hardware (MAC) addresses.
MAC address is a 48-bit long.
Encapsulating a frame within a different type of frame is called tunneling.
Hubs at the Physical Layer.
The Physical layer specifies the electrical, mechanical, procedural, and functional requirements for activating, maintaining, and deactivating a physical link between end systems. This layer is also where you identify the interface between the data terminal equipment (DTE) and the data communication equipment (DCE). The DCE is usually located at the service provider, while the DTE is the attached device. The services available to the DTE are most often accessed via a modem or channel service unit/data service unit (CSU/DSU).
The IEEE extended the 802.3 Committee to two new committees known as 802.3u (Fast Ethernet) and 802.3ab (Gigabit Ethernet on category 5) and then finally 802.3ae (10Gbps over fiber and coax).
Attenuation is the loss of signal strength as it travels the length of a cable and is measured in decibels(dB).
Crosstalk is the unwanted signal interference from adjacent pairs in the cable.
10Base2 10Mbps, baseband technology, up to 185 meters in length. Known as thinnet and can support up to 30 workstations on a single segment. Uses a physical and logical bus with AUI connectors. Base means baseband technology (which is a signaling method for communication on the network), and the 2 means almost 200 meters. 10Base2 Ethernet cards use BNC (British Naval Connector, Bayonet Neill Concelman, or Bayonet Nut Connector) and T-connectors to connect to a network.
10Base5 10Mbps, baseband technology, up to 500 meters in length. Known as thicknet. Uses a physical and logical bus with AUI connectors. Up to 2,500 meters with repeaters and 1,024 users for all segments.10BaseT 10Mbps using category 3 UTP wiring up to 100 meters. Unlike with the 10Base2 and 10Base5 networks, each device must connect into a hub or switch, and you can have only one host per segment or wire. Uses an RJ45 connector (8-pin modular connector) with a physical star topology and a logical bus.
100BaseTX (IEEE 802.3u) EIA/TIA category 5, 6, or 7 UTP two-pair wiring. One user per segment; up to 100 meters long. It uses an RJ45 connector with a physical star topology and a logical bus.
100BaseFX (IEEE 802.3u) Uses fiber cabling 62.5/125-micron multimode fiber. Point-to-point topology; up to 412 meters long. It uses an ST or SC connector, which are mediainterface connectors.
1000BaseCX (IEEE 802.3z) Copper twisted-pair called twinax (a balanced coaxial pair) that can only run up to 25 meters.
1000BaseT (IEEE 802.3ab) Category 5, four-pair UTP wiring up to 100 meters long.
1000BaseSX (IEEE 802.3z) MMF using 62.5- and 50-micron core; uses an 850 nano-meter laser and can go up to 220 meters with 62.5-micron, 550 meters with 50-micron.
1000BaseLX (IEEE 802.3z) Single-mode fiber that uses a 9-micron core and 1300 nanometer laser and can go from 3 kilometers up to 10 kilometers.
Exam essentials
Remember the possible causes of LAN traffic congestion. Too many hosts in a broadcast domain, broadcast storms, multicasting, and low bandwidth are all possible causes of LAN traffic congestion.
Understand the difference between a collision domain and a broadcast domain. Collision domain is an Ethernet term used to describe a network collection of devices in which one particular device sends a packet on a network segment, forcing every other device on that same segment to pay attention to it. On a broadcast domain, a set of all devices on a network segment hear all broadcasts sent on that segment.
Understand the difference between a hub, a bridge, a switch, and a router. Hubs create one collision domain and one broadcast domain. Bridges break up collision domains but create one large broadcast domain. They use hardware addresses to filter the network. Switches are really just multiple port bridges with more intelligence. They break up collision domains but create one large broadcast domain by default. Switches use hardware addresses to filter the network. Routers break up broadcast domains (and collision domains) and use logical addressing to filter the network.
Remember the difference between connection-oriented and connectionless network services.
Connection-oriented services use acknowledgments and flow control to create a reliable session. More overhead is used than in a connectionless network service. Connectionless services are used to send data with no acknowledgments or flow control. This is considered unreliable.
Remember the OSI layers. You must remember the seven layers of the OSI model and what function each layer provides. The Application, Presentation, and Session layers are upper layers and are responsible for communicating from a user interface to an application. The Transport layer provides segmentation, sequencing, and virtual circuits. The Network layer provides logical network addressing and routing through an internetwork. The Data Link layer provides framing and placing of data on the network medium. The Physical layer is responsible for taking 1s and 0s and encoding them into a digital signal for transmission on the network segment.
Remember the types of Ethernet cabling and when you would use them. The three types of cables that can be created from an Ethernet cable are straight-through (to connect a PC’s or a router’s Ethernet interface to a hub or switch), crossover (to connect hub to hub, hub to switch, switch to switch, or PC to PC), and rolled (for a console connection from a PC to a router or switch).
Understand how to connect a console cable from a PC to a router and start HyperTerminal.
Take a rolled cable and connect it from the COM port of the host to the console port of a router. Start HyperTerminal and set the BPS to 9600 and flow control to None.
Remember the three layers in the Cisco three-layer model. The three layers in the Cisco hierarchical model are the core, distribution, and access layers.
Remember the various configuration register commands and settings. The 0x2102 setting is the default on all Cisco routers and tells the router to look in NVRAM for the boot sequence. 0x2101 tells the router to boot from ROM, and 0x2142 tells the router to not load the startupconfig in NVRAM to provide password recovery.
Remember how to back up an IOS image. By using the privileged-mode command copy flash tftp, you can back up a file from flash memory to a TFTP (network) server.
Remember how to restore or upgrade an IOS image. By using the privileged-mode command copy tftp flash, you can restore or upgrade a file from a TFTP (network) server to flash memory.
Remember what you must complete before you back up an IOS image to a network server.
Make sure that you can access the network server, ensure that the network server has adequate space for the code image, and verify the file naming and path requirement.
Remember how to save the configuration of a router. There are a couple of ways to do this, but the most common, as well as most tested, method is copy running-config startup-config.
Remember how to erase the configuration of a router. Type the privileged-mode command erase startup-config and reload the router.
Understand when to use CDP. Cisco Discovery Protocol can be used to help you document as well as troubleshoot your network.
Remember what the output from the show cdp neighbors command shows. The show cdp neighbors command provides the following information: device ID, local interface, holdtime, capability, platform, and port ID (remote interface).
Understand how to telnet into a router and keep your connection but return to your originating console. If you telnet to a router or switch, you can end the connection by typing exit at any time. However, if you want to keep your connection to a remote device but still come back to your original router console, you can press the Ctrl+Shift+6 key combination, release it, and then press X.
Remember the command to verify your Telnet sessions. The command show sessions will provide you with information about all the sessions your router has with other routers.
Remember how to build a static host table on a router. By using the global configuration command ip host host_name ip_address, you can build a static host table on your router. You can apply multiple IP addresses against the same host entry.
Remember how to verify your host table on a router. You can verify the host table with the show hosts command.
Remember the steps to subnet in your head. Understand how IP addressing and subnetting work. First, determine your block size by using the 256-subnet mask math. Then count your
subnets and determine the broadcast address of each subnet—it is always the number right before the next subnet. Your valid hosts are the numbers between the subnet address and the broadcast address.
Understand the various block sizes. This is an important part of understanding IP addressing and subnetting. The valid block sizes are always 4, 8, 16, 32, 64, 128, etc. You can determine your block size by using the 256-subnet mask math.
Remember the four diagnostic steps. The four simple steps that Cisco recommends for troubleshooting are ping the loopback address, ping the NIC, ping the default gateway, and ping the remote device.
You must be able to find and fix an IP addressing problem. Once you go through the four troubleshooting steps that Cisco recommends, you must be able to determine the IP addressing problem by drawing out the network and finding the valid and invalid hosts addressed in your network.
Understand the troubleshooting tools that you can use from your host and a Cisco router
ping 127.0.0.1 tests your local IP stack. tracert is a Windows DOS command to track the path a packet takes through an internetwork to a destination. Cisco routers use the command traceroute, or just trace for short. Don’t confuse the Windows and Cisco commands. Although they produce the same output, they don’t work from the same prompts. ipconfig /all will display your PC network configuration from a DOS prompt, and arp -a (again from a DOS prompt) will display IP-to-MAC-address mapping on a Windows PC.
Understand the difference between a collision domain and a broadcast domain. Collision domain is an Ethernet term used to describe a network collection of devices in which one particular device sends a packet on a network segment, forcing every other device on that same segment to pay attention to it. On a broadcast domain, a set of all devices on a network segment hear all broadcasts sent on that segment.
Understand the difference between a hub, a bridge, a switch, and a router. Hubs create one collision domain and one broadcast domain. Bridges break up collision domains but create one large broadcast domain. They use hardware addresses to filter the network. Switches are really just multiple port bridges with more intelligence. They break up collision domains but create one large broadcast domain by default. Switches use hardware addresses to filter the network. Routers break up broadcast domains (and collision domains) and use logical addressing to filter the network.
Remember the difference between connection-oriented and connectionless network services.
Connection-oriented services use acknowledgments and flow control to create a reliable session. More overhead is used than in a connectionless network service. Connectionless services are used to send data with no acknowledgments or flow control. This is considered unreliable.
Remember the OSI layers. You must remember the seven layers of the OSI model and what function each layer provides. The Application, Presentation, and Session layers are upper layers and are responsible for communicating from a user interface to an application. The Transport layer provides segmentation, sequencing, and virtual circuits. The Network layer provides logical network addressing and routing through an internetwork. The Data Link layer provides framing and placing of data on the network medium. The Physical layer is responsible for taking 1s and 0s and encoding them into a digital signal for transmission on the network segment.
Remember the types of Ethernet cabling and when you would use them. The three types of cables that can be created from an Ethernet cable are straight-through (to connect a PC’s or a router’s Ethernet interface to a hub or switch), crossover (to connect hub to hub, hub to switch, switch to switch, or PC to PC), and rolled (for a console connection from a PC to a router or switch).
Understand how to connect a console cable from a PC to a router and start HyperTerminal.
Take a rolled cable and connect it from the COM port of the host to the console port of a router. Start HyperTerminal and set the BPS to 9600 and flow control to None.
Remember the three layers in the Cisco three-layer model. The three layers in the Cisco hierarchical model are the core, distribution, and access layers.
Remember the various configuration register commands and settings. The 0x2102 setting is the default on all Cisco routers and tells the router to look in NVRAM for the boot sequence. 0x2101 tells the router to boot from ROM, and 0x2142 tells the router to not load the startupconfig in NVRAM to provide password recovery.
Remember how to back up an IOS image. By using the privileged-mode command copy flash tftp, you can back up a file from flash memory to a TFTP (network) server.
Remember how to restore or upgrade an IOS image. By using the privileged-mode command copy tftp flash, you can restore or upgrade a file from a TFTP (network) server to flash memory.
Remember what you must complete before you back up an IOS image to a network server.
Make sure that you can access the network server, ensure that the network server has adequate space for the code image, and verify the file naming and path requirement.
Remember how to save the configuration of a router. There are a couple of ways to do this, but the most common, as well as most tested, method is copy running-config startup-config.
Remember how to erase the configuration of a router. Type the privileged-mode command erase startup-config and reload the router.
Understand when to use CDP. Cisco Discovery Protocol can be used to help you document as well as troubleshoot your network.
Remember what the output from the show cdp neighbors command shows. The show cdp neighbors command provides the following information: device ID, local interface, holdtime, capability, platform, and port ID (remote interface).
Understand how to telnet into a router and keep your connection but return to your originating console. If you telnet to a router or switch, you can end the connection by typing exit at any time. However, if you want to keep your connection to a remote device but still come back to your original router console, you can press the Ctrl+Shift+6 key combination, release it, and then press X.
Remember the command to verify your Telnet sessions. The command show sessions will provide you with information about all the sessions your router has with other routers.
Remember how to build a static host table on a router. By using the global configuration command ip host host_name ip_address, you can build a static host table on your router. You can apply multiple IP addresses against the same host entry.
Remember how to verify your host table on a router. You can verify the host table with the show hosts command.
Remember the steps to subnet in your head. Understand how IP addressing and subnetting work. First, determine your block size by using the 256-subnet mask math. Then count your
subnets and determine the broadcast address of each subnet—it is always the number right before the next subnet. Your valid hosts are the numbers between the subnet address and the broadcast address.
Understand the various block sizes. This is an important part of understanding IP addressing and subnetting. The valid block sizes are always 4, 8, 16, 32, 64, 128, etc. You can determine your block size by using the 256-subnet mask math.
Remember the four diagnostic steps. The four simple steps that Cisco recommends for troubleshooting are ping the loopback address, ping the NIC, ping the default gateway, and ping the remote device.
You must be able to find and fix an IP addressing problem. Once you go through the four troubleshooting steps that Cisco recommends, you must be able to determine the IP addressing problem by drawing out the network and finding the valid and invalid hosts addressed in your network.
Understand the troubleshooting tools that you can use from your host and a Cisco router
ping 127.0.0.1 tests your local IP stack. tracert is a Windows DOS command to track the path a packet takes through an internetwork to a destination. Cisco routers use the command traceroute, or just trace for short. Don’t confuse the Windows and Cisco commands. Although they produce the same output, they don’t work from the same prompts. ipconfig /all will display your PC network configuration from a DOS prompt, and arp -a (again from a DOS prompt) will display IP-to-MAC-address mapping on a Windows PC.
Cisco hierarchical model
The following are the three layers and their typical functions:
The core layer is literally the core of the network. At the top of the hierarchy, the core layer is responsible for transporting large amounts of traffic both reliably and quickly. The only purpose of the network’s core layer is to switch traffic as fast as possible. The traffic transported acrossthe core is common to a majority of users. However, remember that user data is processed at the distribution layer, which forwards the requests to the core if needed. If there is a failure in the core, every single user can be affected. Therefore, fault tolerance at this layer is an issue. The core is likely to see large volumes of traffic, so speed and latency are driving concerns here. Given the function of the core, we can now consider some design specifics. Let’s start with some things we don’t want to do:
The distribution layer is sometimes referred to as the workgroup layer and is the communication point between the access layer and the core. The primary functions of the distribution layer are to provide routing, filtering, and WAN access and to determine how packets can access the core, if needed. The distribution layer must determine the fastest way that network service requests are handled—for example, how a file request is forwarded to a server. After the distribution layer determines the best path, it forwards the request to the core layer if necessary. The core layer then quickly transports the request to the correct service.
The distribution layer is the place to implement policies for the network. Here you can exercise considerable flexibility in defining network operation. There are several actions that generally should be done at the distribution layer:
belong to one of the other layers.
The Access Layer
The access layer controls user and workgroup access to internetwork resources. The access layer is sometimes referred to as the desktop layer. The network resources most users need will be available locally. The distribution layer handles any traffic for remote services. The following are some of the functions to be included at the access layer:
- The core layer: backbone
- The distribution layer: routing
- The access layer: switching
The core layer is literally the core of the network. At the top of the hierarchy, the core layer is responsible for transporting large amounts of traffic both reliably and quickly. The only purpose of the network’s core layer is to switch traffic as fast as possible. The traffic transported acrossthe core is common to a majority of users. However, remember that user data is processed at the distribution layer, which forwards the requests to the core if needed. If there is a failure in the core, every single user can be affected. Therefore, fault tolerance at this layer is an issue. The core is likely to see large volumes of traffic, so speed and latency are driving concerns here. Given the function of the core, we can now consider some design specifics. Let’s start with some things we don’t want to do:
- Don’t do anything to slow down traffic. This includes using access lists, routing between virtual local area networks (VLANs), and implementing packet filtering.
- Don’t support workgroup access here.
- Avoid expanding the core (i.e., adding routers) when the internetwork grows. If performance becomes an issue in the core, give preference to upgrades over expansion.
- Design the core for high reliability. Consider data-link technologies that facilitate both speed and redundancy, such as FDDI, Fast Ethernet (with redundant links), or even ATM.
- Design with speed in mind. The core should have very little latency.
- Select routing protocols with lower convergence times. Fast and redundant data-link connectivity is no help if your routing tables are shot!
The distribution layer is sometimes referred to as the workgroup layer and is the communication point between the access layer and the core. The primary functions of the distribution layer are to provide routing, filtering, and WAN access and to determine how packets can access the core, if needed. The distribution layer must determine the fastest way that network service requests are handled—for example, how a file request is forwarded to a server. After the distribution layer determines the best path, it forwards the request to the core layer if necessary. The core layer then quickly transports the request to the correct service.
The distribution layer is the place to implement policies for the network. Here you can exercise considerable flexibility in defining network operation. There are several actions that generally should be done at the distribution layer:
- Routing
- Implementing tools (such as access lists), packet filtering, and queuing
- Implementing security and network policies, including address translation and firewalls
- Redistributing between routing protocols, including static routing
- Routing between VLANs and other workgroup support functions
- Defining broadcast and multicast domains
belong to one of the other layers.
The Access Layer
The access layer controls user and workgroup access to internetwork resources. The access layer is sometimes referred to as the desktop layer. The network resources most users need will be available locally. The distribution layer handles any traffic for remote services. The following are some of the functions to be included at the access layer:
- Continued (from distribution layer) use of access control and policies
- Creation of separate collision domains (segmentation)
- Workgroup connectivity into the distribution layer
Binary Math
Binary to Decimal Memorization Chart
Binary Decimal
10000000 128
11000000 192
11100000 224
11110000 240
11111000 248
11111100 252
11111110 254
11111111 255
11100000 224
11110000 240
11111000 248
11111100 252
11111110 254
11111111 255
Various show commands
- show cdp
- show cdp neighbors
The show cdp neighbors command provides the following information: device ID, local interface, holdtime, capability, platform, and port ID (remote interface).
- sh cdp neighbors detail
- sh cdp entry *
- show cdp entry * protocols
Protocol information for ap :
IP address: 10.1.1.2
Protocol information for R2 :
IP address: 10.4.4.2 - show cdp entry * version
Version information for ap :
Cisco IOS Software, C1240 Software (C1240-K9W7-M), Version
12.3(8)JEA, RELEASE SOFTWARE (fc2)
[lines omitted] - show protocols
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