Published on
August 28, 2010 23:09
OSI is the Open System Interconnection reference model for communications. The OSI model is mainly used as a point of reference for discussing other protocol specifications such as TCP/IP and Net Ware.
The OSI reference model consists of seven layers that each defines a set of typical networking functions. The upper layers (application, presentation, and session; or Layers 7, 6, and 5) define functions focused on the application. The lower four layers (transport, network, data link, and physical; or Layers 4, 3, 2, and 1) define functions focused on end-to-end delivery of the data. Layer 2 is where switching is based, while Layer 3 is where routing is based.
Here are example protocols for eachlayer:
- (7) Application – Telnet, HTTP, FTP, WWW browsers, NFS, SMTP gateways (Eudora, CC:mail, SNMP
- (6) Presentation – JPEG, ASCII, EBCDIC, TIFF, GIF, PICT, encryption, MPEG, MIDI
- (5) Session – RPC, SQL, NFS, NetBIOS , SSH, DECnet SCP
- (4) Transport – TCP, UDP, SPX
- (3) Network – IP, IPX, AppleTalk DDP
- (2) Data Link – IEEE 802.3/802.2, HDLC, Frame Relay, PPP, FDDI, ATM, IEEE 802.5/802.2
- (1) Physical – EIA/TIA-232, V.35, EIA/TIA-449, RJ-45, Ethernet, 802.3, 802.5, B8ZS
All following comparison operators have the standard mathematical interpretation and return a boolean value of True for true, False for false:
Comparison operations are supported by all objects!
This table summarizes the comparison operations:
| Operation |
Meaning |
| < |
strictly less than |
| <= |
less than or equal |
| > |
strictly greater than |
| >= |
greater than or equal |
| == |
equal |
| != |
not equal* |
| is |
object identity |
| is not |
negated object identity |
* != can also be written <>, but this is an obsolete usage kept for backwards compatibility only. New code should always use !=.
This is a very quick guide to setting up a Linux software RAID.
All these examples are same for RAID0 and RAID1
0. Disclaimer
Make sure you back up all your date, or you have empty hdds before you proceed.
1. Disk management
I’m using 2 same HDDs with 400Gigs.
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| Disk /dev/sdb: 400.0 GB, 400088457216 bytes
Disk /dev/sdc: 400.0 GB, 400088457216 bytes |
I created on both disks new partitions with parted (also you can use gparted):
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| /dev/sdb1 1 48641 390708801 83 Linux
/dev/sdc1 1 48641 390708801 83 Linux |
2. Raid creation
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| $ aptitude update
$ aptitude install mdadm |
For RAID-0
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| $ mdadm --create /dev/md0 --level=0 --raid-devices=2 /dev/sdb1 /dev/sdc1 |
For RAID-1
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| $ mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sdb1 /dev/sdc1 |
3. Get RAID information
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| $ fdisk -l
Disk /dev/md0: 800.1 GB, 800171491328 bytes |
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| $ cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md0 : active raid0 sdc1[1] sdb1[0]
781417472 blocks 64k chunks
unused devices: <none> |
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| $ mdadm --detail --scan
ARRAY /dev/md0 level=raid0 num-devices=2 metadata=00.90 UUID=fb3d1fd3:5dd2b871:01f9e43d:ac30fbff |
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| $ mdadm --detail /dev/md0
/dev/md0:
Version : 00.90
Creation Time : Fri Aug 27 21:27:51 2010
Raid Level : raid0
Array Size : 781417472 (745.22 GiB 800.17 GB)
Raid Devices : 2
Total Devices : 2
Preferred Minor : 0
Persistence : Superblock is persistent
Update Time : Fri Aug 27 22:46:13 2010
State : active
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0
Chunk Size : 64K
UUID : fb3d1fd3:5dd2b871:2ce552e4:6d63ea58
Events : 0.3
Number Major Minor RaidDevice State
0 8 17 0 active sync /dev/sdb1
1 8 33 1 active sync /dev/sdc1 |
4. Create file system
That all you have a running RAID array, to use it you need to create a filesystem for example ext3 one.
Delete RAID array:
To make sure it doesn’t come back, you need to delete the RAID super blocks…
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| mdadm --misc --zero-superblock /dev/sdb1
mdadm --misc --zero-superblock /dev/sdc1 |
You can mount your raid partition automatically on server start:
And add this line to it:
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| /dev/md0 /mnt ext3 defaults 0 0 |
md0 will automatically mounted to /mnt/
Start a partially built array:
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| $ mdadm --run /dev/md0
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md0 : active raid1 sdb1[0] sdc1[1]
390708736 blocks [2/2] [UU]
[>....................] resync = 0.0% (277568/390708736) finish=70.3min speed=92522K/sec |
Some basic postgre commands:
\d [NAME] describe table, index, sequence, or view
\d{t|i|s|v|S} [PATTERN] (add "+" for more detail)
list tables/indexes/sequences/views/system tables
\da [PATTERN] list aggregate functions
\db [PATTERN] list tablespaces (add "+" for more detail)
\dc [PATTERN] list conversions
\dC list casts
\dd [PATTERN] show comment for object
\dD [PATTERN] list domains
\df [PATTERN] list functions (add "+" for more detail)
\dg [PATTERN] list groups
\dn [PATTERN] list schemas (add "+" for more detail)
\do [NAME] list operators
\dl list large objects, same as \lo_list
\dp [PATTERN] list table, view, and sequence access privileges
\dT [PATTERN] list data types (add "+" for more detail)
\du [PATTERN] list users
\l list all databases (add "+" for more detail)
Published on
August 24, 2010 23:00 Tags: ATM, CCNA4, Certification, CHAP, Cisco, CISCO Enterprise, Frame Relay, ISDN, PPP, X25.
- WANs generally connect devices that are separated by a broader geographical area than can be served by a LAN.
- WANs use the services of carriers, such as telephone companies, cable companies, satellite systems, and network providers.
- WANs use serial connections of various types to provide access to bandwidth over large geographic areas.
The Hierarchical Network Model
Access layer-Grants user access to network devices. In a network campus, the access layer generally incorporates switched LAN devices with ports that provide connectivity to workstations and servers. In the WAN environment, it may provide teleworkers or remote sites access to the corporate network across WAN technology.
Distribution layer-Aggregates the wiring closets, using switches to segment workgroups and isolate network problems in a campus environment. Similarly, the distribution layer aggregates WAN connections at the edge of the campus and provides policy-based connectivity.
Core layer (also referred to as the backbone) – A high-speed backbone that is designed to switch packets as fast as possible. Because the core is critical for connectivity, it must provide a high level of availability and adapt to changes very quickly. It also provides scalability and fast convergence.
Enterprise Campus Architecture:
An enterprise campus network is a building or group of buildings connected into one network that consists of many LANs.
It is generally limited to a fixed geographic area, but it can span several neighboring buildings.
The architecture is modular and scalable and can easily expand to include additional buildings or floors as required.
Enterprise Branch Architecture:
This module allows businesses to extend the applications and services found at the enterprise campus to thousands of remote locations and users or to a small group of branches.
Enterprise Data Center Architecture:
Data centers are responsible for managing and maintaining the many data systems that are vital to modern business operations.
This module centrally houses the data and resources to enable users to effectively create, collaborate, and interact.
Enterprise Teleworker Architecture:
This module leverages the network resources of the enterprise from home using broadband services such as cable modem or DSL to connect to the corporate network.
Typically implemented using remote access VPNs.
Enterprise Edge Architecture:
This module often functions as a liaison between the campus module and the other modules in the Enterprise Architecture.
PAP - 2 Way handshake
PAP usernames and passwords are sent as clear text strings, which can be intercepted and reused.
CHAP is a more secure procedure for connecting to a system than PAP
CHAP – 3 Way handshake
CHAP authentication sends a challenge message to the remote device. The remote device encrypts the challenge value with a shared secret and returns the encrypted value and its name to the local router in a Response message.
Continue reading ‘CISCO CCNA-4 – Accessing the WAN Chapter one’
