Nursing books links

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.

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.

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:

• 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

Do you see an octet that looks interesting to you? I do. It’s the third octet. 4, 5, 6, 7, and yes, it’s a block size of 4. So you can summarize 172.1.4.0 using a mask of 255.255.252.0, which means you will use a block size of 4 in the third octet. The IP addresses forwarded with this summary are 172.1.4.1 through 172.1.7.255.

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

1. Boot the router and interrupt the boot sequence by performing a break, which will take the router into ROM monitor mode.
2. Change the configuration register to turn on bit 6 (with the value 0x2142).
3. Reload the router.
4. Enter privileged mode.
5. Copy the startup-config file to running-config.
6. Change the password.
7. Reset the configuration register to the default value.
8. Save the router configuration.
9. Reload the router (optional).

Routing