I didn't quite see the need to create the host table for the little lab network with a data server talking to a recording device, because I thought the switch in between would be enough. Anyway I decided to do some digging.
Linux
Obviously the host table is located in the “/etc/hosts” file, containg IP addresses and hostnames. Here's a sample below:
$ cat /etc/hosts
# Table of IP addresses and host names
127.0.0.1 localhost
192.168.1.2 myserver aliasname anotheralias
Windows
Windows 95/98/Me c:\windows\hosts
Windows NT/2000/XP Pro c:\winnt\system32\drivers\etc\hosts
Windows XP Home c:\windows\system32\drivers\etc\hosts
The host table is useful when you have a small number of servers in the group and you want to use some alias, and/ or there is no DNS or connection to the internet. The host table simple converts IP addresses to host names and the reverse.
It gets tricky when the host table is long and it gets messy.
Thursday, February 16, 2012
Cisco ICND1 Flashcard: Wireless LAN Implementation and Security
The Wireless Access notes for the CCNA Exam in short form.
The topic of Wireless LAN is covered in the ICND1 Exam
Wireless access is a half duplex CSMA/ CA (Carrier Sense Multiple Access - Collision Avoidance) half-duplex type of signal that uses RTS (ready to send) and CTS (clear to send) protocols. Yes I know it is wierd to place the acronym ahead of the definition at first use. For every packet sent, an RTS/CTS and acknowledgment must be received.
About the RF Wireless Signal
While setting up the Access Point, the following parameters are configured. Basic IP address (static or DHCP), subnet mask, default gateway; the wireless protocol being used could be 802.11a, b, g, n; channel adjustments namely channel 1, 6, 11 and a power adjustment. Security parameters include SSID which identifies the network, authentication scheme (WPA, WPA2 PSK) and the encryption method (TKIP, AES).
2.4 GHz used by the 802.11b and g, using DSSS. Max data rate of 11 Mbps (for 802.11g when using DSS) Other rates possible 1,2, 5.
5 GHz used by 802.11a, using OFDM data rate of 6, 9, 12, 18, 24, 36, 48 Mbps to 54 Mbps, 12 non-overlapping frequency channels. When 802.11g operates on OFDM the max data rate of 54 Mbps can be achieved.
The FCC has released three unlicensed bands for public use: 900MHz, 2.4GHz, and 5.7GHz. The 900MHz and 2.4GHz bands are referred to as the Industrial, Scientific, and Medical (ISM) bands, and the 5-GHz band is known as the Unlicensed National Information Infrastructure (UNII) band.
802.11a operating in the 5GHz radio band, makes it immune to interference from devices operating in the 2.4GHz band, like microwave ovens, cordless phones, and Bluetooth devices.
Quiz: Which two 802.11 standards have the highest data rate?
802.11a and 802.11g both up to 54 Mbps
Quiz: Which standards are most widely used today?
802.11b/g being the most widely used wireless network found today. 802.11b operates in the 2.4GHz unlicensed radio band, delivers a maximum data rate of 11Mbps
802.11g 400m 140m
802.11b 40m 140m
802.11a 35m 100m
802.11n 70m 250m
Modulation
802.11a and 802.11g uses OFDM
802.11b uses Direct Sequence Spread Spectrum (DSSS)
though 802.11g is DSSS/ OFDM
802.11n supports more channels using spatial division multiplex and more transmittes to reach a higher data rate of 600Mbps. It also uses OFDM (I need more info) and is backward compatible with 802.11a,b,g
802.11b
It is more accessible, has a higher CCK and data rate. There are 14 channels each 22MHz wide with a 5MHz separation. To completely avoid overlapping, the signalling requires a 5-channel separation; therefore only Channels 1, 6, and 11 are in use.
Wifi Equipment
The Wifi Alliance is a non government, no profit, industry trade organization that promotes interoperability between wifi product manufacturers, and promotes wireless growth. As for securing wireles networks, the evolution of encryption algorithms have come a long way.
The IEEE writes out the technical standards or Engineering specs, publishes technical documentation or journals.
ITU-R is the international union that regulates RF usage bands including wireless.
Quiz: Who created WPA?
Answer: WPA was created by the Wifi Alliance based on the IEEE 802.11i standard
Common standards dealing with wireless client authentication, coding something from plaintext into ciphertext.
The AP encapsulates any 802.1x traffic that is bound for the authentication server and sends it to the server
Modes of Operation
Ad Hoc Mode
IBSS - Client directly connects to the server peer to peer, no access point.
Infrastructure Mode
BSS - clients connect to each other through a network resource. The BSSID is the MAC address of the RF interface card; B for basic.
ESS - Two or more BSS are connected by a common distibution system. E for extended. SSID is the wireless network advertised, user configured.
More than one BSS will form an ESS, that means when a group of BSS (or many AP's) in the WLAN have the same SSID, the client can be mobile and authenticate with the various AP's in the same BSS.
Wireless Zero Configuration
Three basic wireless access point parameters: SSID, authentication, RF channel with optional power. Microsoft has a feature that does all this automatically. Though most Wireless NIC vendors have their own software GUI as well.
Cisco’s Wireless Control System (WCS) actually requires zero configuration. This means the AP will automatically configure itself based on the controller’s information, check for channel overlap and interference and move to a non-overlapping channel; lower its transmitting level to limit interference called by Cisco as "auto RF controls."
I found a really good reference for the Wireless LAN topic. I'd hazard to say that I found nuggets of information that I had missed on the exam from my notes! Lookup the Cisco Tests blog.
The topic of Wireless LAN is covered in the ICND1 Exam
Connecting to a Wireless Network
This is how it happens at Starbucks, MacDonald's, the hotel offering free wireless internet, or your own home. Wireless Access Points send out beacons announcing the SSID, data rates and other information. The client's laptop wifi network card scans all channels while listening for beacons and responses from the AP. Then the client will associate to the AP with the strongest signal. Client repeats the scan if the signal becomes slow to associate to another AP while roaming. During the association phase, SSID, MAC address, and security settings are sent from the client to AP, and verified by the AP. The basic service area is the physical area of RF coverage provided by the AP.Wireless access is a half duplex CSMA/ CA (Carrier Sense Multiple Access - Collision Avoidance) half-duplex type of signal that uses RTS (ready to send) and CTS (clear to send) protocols. Yes I know it is wierd to place the acronym ahead of the definition at first use. For every packet sent, an RTS/CTS and acknowledgment must be received.
About the RF Wireless Signal
While setting up the Access Point, the following parameters are configured. Basic IP address (static or DHCP), subnet mask, default gateway; the wireless protocol being used could be 802.11a, b, g, n; channel adjustments namely channel 1, 6, 11 and a power adjustment. Security parameters include SSID which identifies the network, authentication scheme (WPA, WPA2 PSK) and the encryption method (TKIP, AES).
IBSS - Independent Basic Service Set Identifier, users connected in ad hoc mode without an AP
BSSID - Mac Address of the RF Interface Card
BSSID - Mac Address of the RF Interface Card
SSID - Net Admin configured network identified that is broadcast, sent in the clear
The frequencies of the unlicensed bands are:
900 MHz 2.4 GHz used by the 802.11b and g, using DSSS. Max data rate of 11 Mbps (for 802.11g when using DSS) Other rates possible 1,2, 5.
5 GHz used by 802.11a, using OFDM data rate of 6, 9, 12, 18, 24, 36, 48 Mbps to 54 Mbps, 12 non-overlapping frequency channels. When 802.11g operates on OFDM the max data rate of 54 Mbps can be achieved.
The FCC has released three unlicensed bands for public use: 900MHz, 2.4GHz, and 5.7GHz. The 900MHz and 2.4GHz bands are referred to as the Industrial, Scientific, and Medical (ISM) bands, and the 5-GHz band is known as the Unlicensed National Information Infrastructure (UNII) band.
802.11a operating in the 5GHz radio band, makes it immune to interference from devices operating in the 2.4GHz band, like microwave ovens, cordless phones, and Bluetooth devices.
Quiz: Which two 802.11 standards have the highest data rate?
802.11a and 802.11g both up to 54 Mbps
Quiz: Which standards are most widely used today?
802.11b/g being the most widely used wireless network found today. 802.11b operates in the 2.4GHz unlicensed radio band, delivers a maximum data rate of 11Mbps
Facts to consider: This is the sort of thought process in an exam question, the 802.11g standard delivers the same 54Mbps maximum data rate as 802.11a but runs in the 2.4GHz range—the same as 802.11b
Data rates for Indoor and Outdoor ranges.802.11g 400m 140m
802.11b 40m 140m
802.11a 35m 100m
802.11n 70m 250m
Modulation
802.11a and 802.11g uses OFDM
802.11b uses Direct Sequence Spread Spectrum (DSSS)
though 802.11g is DSSS/ OFDM
IEEE 802.11 was the first, original standardized WLAN at 1 and 2Mbps, running in the 2.4GHz
802.11n the New Wireless Standard802.11n supports more channels using spatial division multiplex and more transmittes to reach a higher data rate of 600Mbps. It also uses OFDM (I need more info) and is backward compatible with 802.11a,b,g
802.11b
It is more accessible, has a higher CCK and data rate. There are 14 channels each 22MHz wide with a 5MHz separation. To completely avoid overlapping, the signalling requires a 5-channel separation; therefore only Channels 1, 6, and 11 are in use.
Wifi Equipment
Access points, wireless controllers, wireless LAN client adapters, security and management servers, wireless management devices, wireless integrated switches and routers—even antennas and accessories
Key Players in WifiThe Wifi Alliance is a non government, no profit, industry trade organization that promotes interoperability between wifi product manufacturers, and promotes wireless growth. As for securing wireles networks, the evolution of encryption algorithms have come a long way.
The IEEE writes out the technical standards or Engineering specs, publishes technical documentation or journals.
ITU-R is the international union that regulates RF usage bands including wireless.
Quiz: Who created WPA?
Answer: WPA was created by the Wifi Alliance based on the IEEE 802.11i standard
Quiz: What is a rogue access point? An unsecured AP that has been placed on the WLAN.
WIFI EncryptionCommon standards dealing with wireless client authentication, coding something from plaintext into ciphertext.
- WEP is a bit outdated and too easy to break, very basic and static.
- Cisco adds CKIP and MIC to protect keys.
- Enhancements are TKIP MIC (Per Packet Keying Message Integrity Check)
- TKIP 802.1x EAP
- WPA uses TKIP/ MIC Encryption
- 802.11i/ WPA2 is the strongest level of WLAN security
- WPA2 includes a AES counter with CBC-MAC Protocol (AES-CCMP)
- Enhancement to TKIP is AES 128 bit, 192 bit, and 256 bit.
- LEAP uses TCP handshake like EAP-TLS and Radius
The AP encapsulates any 802.1x traffic that is bound for the authentication server and sends it to the server
Modes of Operation
Ad Hoc Mode
IBSS - Client directly connects to the server peer to peer, no access point.
Infrastructure Mode
BSS - clients connect to each other through a network resource. The BSSID is the MAC address of the RF interface card; B for basic.
ESS - Two or more BSS are connected by a common distibution system. E for extended. SSID is the wireless network advertised, user configured.
More than one BSS will form an ESS, that means when a group of BSS (or many AP's) in the WLAN have the same SSID, the client can be mobile and authenticate with the various AP's in the same BSS.
WPA
Enterprise mode
used for Business, Education, Government and a term for products tested to be interoperable for authentication in PSK + IEEE 802.1x EAP
Personal mode
for SOHO, home, personal and interoperable in PSK mode of operation only
Issues with Roaming
- Consider the range of combined calls form an extended service area
- Allow 10-15% overlap to allow users to roam without losing RF connection
- Configure three access points with the same SSID so user can roam wirelesly without dropping connectivity
- Allow the range of 15-20% overlap for wireless voice
- Shift the data rate while moving: 11 Mbps, 5.5 Mbps, 2 Mbps
- The higher data rate requires stronger signals at the receiver; a lower data rate, the range is longer
- The clients want the highest data rate
- If there are transmission errors, reduce the data rate
Wireless Zero Configuration
Three basic wireless access point parameters: SSID, authentication, RF channel with optional power. Microsoft has a feature that does all this automatically. Though most Wireless NIC vendors have their own software GUI as well.
Cisco’s Wireless Control System (WCS) actually requires zero configuration. This means the AP will automatically configure itself based on the controller’s information, check for channel overlap and interference and move to a non-overlapping channel; lower its transmitting level to limit interference called by Cisco as "auto RF controls."
I found a really good reference for the Wireless LAN topic. I'd hazard to say that I found nuggets of information that I had missed on the exam from my notes! Lookup the Cisco Tests blog.
Wednesday, February 15, 2012
The Linsanity of Super Lintendo
 |
| Valentine Cupcakes by Nora, Bliss & Co. in Calgary |
While most people were eating Valentine cupcakes, my very lucky sister in law was at the big Raptors and Knicks game at the Air Canada Center! I haven't seen Jeremy Lin play basketball, I don't know what he looks like, but he is all over my friends' facebook posts.
"So tonight, all the good little Asian boys and girls will put down their violins, close the piano covers, postpone Calculus club and put away their Chinese/Korean school homework. Bubble tea shops will be empty from east to west, and even Battle.net will be silent and barren. They will quiver with excitement over their bowls of rice as they turn on the TV. And for what? A basketball game. Yes, this is Linsanity." quote from buddy Thomas, about the you-know-who.
 |
| Linsanity Game on Valentines Day |
There's already a Wikipedia article written about him, throngs of asian girls and boys are drawn to him because he is the guy who made it big on the NBA from out of nowhere (well Harvard actually), he's smart, friendly, fairly tall for an asian guy, and is a Christian. I use the term asian because he's actually an American born Taiwanese, meaning his ancestors are from Taiwan and not China (very much different).
Day in the Life: Jeremy Lin. (Sneakers all in a row? Now that's hot).
http://www.youtube.com/watch?v=CLzrLXQIbwM
Anyways I really should go back to studying for the CCNA, practising piano, violin, playing Nintendo or whatever good asian kids are supposed to do.
Test Tips for CCNA, Simulators and a bullet-proof Guarantee!
1. Manage your time
The number one hint I have to give everyone: the CCNA Exam is a test of power and speed, you have to know your material solid and answer the questions quickly. The prof said that the number one reason for failure on the exam is not lack of preparation (I could argue with that) but rather, running out of time! You have remember to ask yourself, "Is this your final answer?" because once you click "yes" or "submit", there is no back button, you cannot go back!
2. Core Knowledge
Videos for ICND1 and ICND2 free on the Cisco Learning Network.
Here is a breakdown of the core areas the exam was testing, taken from my real score sheet in November 2011. I am not breaking any oaths or sharing any secrets about the exam.
A good collection of resources at www.cisco.com/go/ccna-study
3. Hands On Experience
Apparently the original purpose of CCNA was to certify someone already with the job experience as a Network Administrator, who has spent years on the job doing this. In fact Cisco never offered Bootcamp courses and it was the training delivery vendors that developed their own courses to cover relevant subjects, in preparation for the CCNA Exam. Now it seems like everyone is taking the boot camp courses: the newbies, managers, purchasers. The courses often come with extra lab time on the router simulation lab, but it is better to have your own equipment. Unfortunately not many people have access to a test lab or one with enough routers to generate any trouble to troubleshoot!
Packet Tracer is another program folks use for router simulation. My buddy recommends http://www.gns3.net/ and it's free, if you have your own IOS images then you're set.
4. Read the Fine Print
Rather I should say, read between the lines. For multiple choice questions, there will always be an obvious oddball answer, and perhaps one or two that are very close but there is something that makes one answer more correct or superior.Unless of course the question was, choose two then you should make sure you choose two.
If you're really pressed for time, well you still have to give an answer for every question. Make a guess, pick C or ACDC whatever random pattern you have to resort to in a bind.
5. Get it Right the First time...
However, heaven forbid if you should fall short of 825/ 1000, read the fine print on the vendor's exam guarantee. I took my bootcamp course with the Global Knowledge and I'd have to say their certification guarantee is bullet proof. Upon course completion you get one CCNA exam voucher and 10 hours of lab time with KAPLAN. If you have fail the exam, fax in the fail results and ask for a voucher for the retake exam (within one year of the course date). If you fail the second round, perhaps you should reconsider your career choice. JK! Global Knowledge offers a free retake of the course (provide your own course materials from the first run). Then I suppose the brave could do the exam a third time. Just remember you will have to recertifiy again in three years anyway.
The number one hint I have to give everyone: the CCNA Exam is a test of power and speed, you have to know your material solid and answer the questions quickly. The prof said that the number one reason for failure on the exam is not lack of preparation (I could argue with that) but rather, running out of time! You have remember to ask yourself, "Is this your final answer?" because once you click "yes" or "submit", there is no back button, you cannot go back!
2. Core Knowledge
Videos for ICND1 and ICND2 free on the Cisco Learning Network.
Here is a breakdown of the core areas the exam was testing, taken from my real score sheet in November 2011. I am not breaking any oaths or sharing any secrets about the exam.
- Describe how a network works
- Configure, verify, troubleshoot a switch with VLANs and interswitch communications
- Implement an IP addressing scheme and IP services to meet network requirements in a medium-size Enterprise branch office network
- Configure, verify, and troubleshoot basic router operation and routing on Cisco devices
- Explain and select the appropriate administrative tasks required for WLAN
- Identify security threats to a network and describe general methods to mitigate those threats
- Implement, verify and troubleshoot NAT and ACLs in a medium-size Enterprise branch office network
- Implement and verify WAN links
A good collection of resources at www.cisco.com/go/ccna-study
3. Hands On Experience
Apparently the original purpose of CCNA was to certify someone already with the job experience as a Network Administrator, who has spent years on the job doing this. In fact Cisco never offered Bootcamp courses and it was the training delivery vendors that developed their own courses to cover relevant subjects, in preparation for the CCNA Exam. Now it seems like everyone is taking the boot camp courses: the newbies, managers, purchasers. The courses often come with extra lab time on the router simulation lab, but it is better to have your own equipment. Unfortunately not many people have access to a test lab or one with enough routers to generate any trouble to troubleshoot!
Packet Tracer is another program folks use for router simulation. My buddy recommends http://www.gns3.net/ and it's free, if you have your own IOS images then you're set.
4. Read the Fine Print
Rather I should say, read between the lines. For multiple choice questions, there will always be an obvious oddball answer, and perhaps one or two that are very close but there is something that makes one answer more correct or superior.Unless of course the question was, choose two then you should make sure you choose two.
If you're really pressed for time, well you still have to give an answer for every question. Make a guess, pick C or ACDC whatever random pattern you have to resort to in a bind.
5. Get it Right the First time...
However, heaven forbid if you should fall short of 825/ 1000, read the fine print on the vendor's exam guarantee. I took my bootcamp course with the Global Knowledge and I'd have to say their certification guarantee is bullet proof. Upon course completion you get one CCNA exam voucher and 10 hours of lab time with KAPLAN. If you have fail the exam, fax in the fail results and ask for a voucher for the retake exam (within one year of the course date). If you fail the second round, perhaps you should reconsider your career choice. JK! Global Knowledge offers a free retake of the course (provide your own course materials from the first run). Then I suppose the brave could do the exam a third time. Just remember you will have to recertifiy again in three years anyway.
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