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• ifconfig networking telnet

  - by jhon

  Hi guys, I'm newbie around networking, I have a question: what I want is to telnet a specific IP/server, let us say 192.168.128.1 then, I try $telnet 192.168.128.1 Trying... and that's all.. I never get connected one of my friends made some script that "fixes" it, AFTER running it I was able to connect to the server using $telnet 192.168.128.1 $ user: unfortunately I lost that script, so I'm here requesting your help. Reading my old notes, I remember that the script performed some modification to the entries listed by ifconfig -a, I also have the ifconfig's output (copy & paste) $ ifconfig -a adapter0: flags=5e080863,c0<UP,BROADCAST,NOTRAILERS,RUNNING,SIMPLEX,MULTICAST,GROUPRT,64BIT,CHECKSUM_OFFLOAD(ACTIVE),PSEG,LARGESEND,CHAIN> inet 192.168.128.150 netmask 0xffffff00 broadcast 192.168.128.255 tcp_sendspace 131072 tcp_recvspace 65536 rfc1323 0 adapter1: flags=5e080863,c0<UP,BROADCAST,NOTRAILERS,RUNNING,SIMPLEX,MULTICAST,GROUPRT,64BIT,CHECKSUM_OFFLOAD(ACTIVE),PSEG,LARGESEND,CHAIN> inet 192.168.251.150 netmask 0xffffff00 broadcast 192.168.251.255 tcp_sendspace 131072 tcp_recvspace 65536 rfc1323 0 adapter2: flags=5e080863,c0<UP,BROADCAST,NOTRAILERS,RUNNING,SIMPLEX,MULTICAST,GROUPRT,64BIT,CHECKSUM_OFFLOAD(ACTIVE),PSEG,LARGESEND,CHAIN> inet 192.168.250.150 netmask 0xffffff00 broadcast 192.168.250.255 tcp_sendspace 131072 tcp_recvspace 65536 rfc1323 0 lo0: flags=e08084b<UP,BROADCAST,LOOPBACK,RUNNING,SIMPLEX,MULTICAST,GROUPRT,64BIT> inet 127.0.0.1 netmask 0xff000000 broadcast 127.255.255.255 inet6 ::1/0 tcp_sendspace 131072 tcp_recvspace 131072 rfc1323 1 more than commands, I'm looking for some explanation why does "adding/changing" those entries enables me to connect to the server. I do not see the server ip (i.e 192.168.128.1) listed above. thanks

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• Internet service providers

  - by gautam kumar

  I am unclear about the differences between international, national, regional and local ISPs. Please explain the differences and their importance, with examples. I am new to this site, so please forgive me if my question is not up to your expectations.

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• Variable sized packet structs with vectors

  - by Rev316

  Lately I've been diving into network programming, and I'm having some difficulty constructing a packet with a variable "data" property. Several prior questions have helped tremendously, but I'm still lacking some implementation details. I'm trying to avoid using variable sized arrays, and just use a vector. But I can't get it to be transmitted correctly, and I believe it's somewhere during serialization. Now for some code. Packet Header class Packet { public: void* Serialize(); bool Deserialize(void *message); unsigned int sender_id; unsigned int sequence_number; std::vector<char> data; }; Packet ImpL typedef struct { unsigned int sender_id; unsigned int sequence_number; std::vector<char> data; } Packet; void* Packet::Serialize(int size) { Packet* p = (Packet *) malloc(8 + 30); p->sender_id = htonl(this->sender_id); p->sequence_number = htonl(this->sequence_number); p->data.assign(size,'&'); //just for testing purposes } bool Packet::Deserialize(void *message) { Packet *s = (Packet*)message; this->sender_id = ntohl(s->sender_id); this->sequence_number = ntohl(s->sequence_number); this->data = s->data; } During execution, I simply create a packet, assign it's members, and send/receive accordingly. The above methods are only responsible for serialization. Unfortunately, the data never gets transferred. Couple of things to point out here. I'm guessing the malloc is wrong, but I'm not sure how else to compute it (i.e. what other value it would be). Other than that, I'm unsure of the proper way to use a vector in this fashion, and would love for someone to show me how (code examples please!) :) Edit: I've awarded the question to the most comprehensive answer regarding the implementation with a vector data property. Appreciate all the responses!

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• Confusion Matrix of Bayesian Network

  - by iva123

  Hi, I'm trying to understand bayesian network. I have a data file which has 10 attributes, I want to acquire the confusion table of this data table ,I thought I need to calculate tp,fp, fn, tn of all fields. Is it true ? if it's then what i need to do for bayesian network. Really need some guidance, I'm lost.

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• What is the difference between causal models and directed graphical models?

  - by Neil G

  What is the difference between causal models and directed graphical models? or: What is the difference between causal relationships and directed probabilistic relationships? or, even better: What would you put in the interface of a DirectedProbabilisticModel class, and what in a CausalModel class? Would one inherit from the other? Collaborative solution: interface DirectedModel { map<Node, double> InferredProbabilities(map<Node, double> observed_probabilities, set<Node> nodes_of_interest) } interface CausalModel: DirectedModel { bool NodesDependent(set<Node> nodes, map<Node, double> context) map<Node, double> InferredProbabilities(map<Node, double> observed_probabilities, map<Node, double> externally_forced_probabilities, set<Node> nodes_of_interest) }

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• Using c#,c/c++ or java to improve BBN with GA

  - by madicemickael

  I have a little problem in my little project , I wish that someone here could help me! I am planning to use a bayesian network as a decision factor in my game AI and I want to improve the decision making every step of the way , anyone knows how to do that ? Any tutorials / existing implementations will be very good,I hope some of you could help me. I heard that a programmer in this community did a good implementation of this put together for poker game AI.I am planning to use it like him ,but in another poker(Texas) or maybe Rentz. Looking for C/c++ or c# or java code. Thanks , Mike

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• Efficient way to store a graph for calculation in Hadoop

  - by user337499

  I am currently trying to perform calculations like clustering coefficient on huge graphs with the help of Hadoop. Therefore I need an efficient way to store the graph in a way that I can easily access nodes, their neighbors and the neighbors' neighbors. The graph is quite sparse and stored in a huge tab separated file where the first field is the node from which an edge goes to the second node in field two. Thanks in advance!

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• Spreading dynamic with community structure

  - by YogurtFruit

  I have a data set which I hope to simulate the spreading dynamic with community structure. The steps I follow is import the data to a complex network with Networkx partition the network into some modules which are known as communities simulate the SIS model and draw plots with and without communities. Something confused me between step 2 and step 3. After partitioning, I get some communities which contains nodes number. The community numbers and nodes numbers are the only input to step 3, and how I simulate SIS with and without communities?

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• How to run a local and external website on same computer with 2 NIC's, 2 Routers and 3 seperate networks?

  - by CandN

  Hello and hopefully I can get some answers to my question, though I think I'm making it more complicated for myself than it has to be. My business is a used auto dealership, and I'm in the process of connecting it to the world - via ethernet from the business server [running Xubuntu] to the ISP's ethernet router/modem, so that I can host our own website (no more than 5-10 people probably visiting at any time - mainly paying their bill), as well as set up a web based internal-intranet site - via DD-WRT Router on the 2nd NIC on the business server - that'll be accessed over Wifi from employees personal devices. On the other end of this is trying to offer free wifi to customers that is completely seperate of the 2 mentioned above networks. Quick Rundown: 1. Web Site for Customers to access. I'm going to use no-ip.org for DNS for the moment being, so I'll have a site that customers can access from anywhere in the world at "mybiz.no-ip.org". This will be forwarded to NIC #1 on the server, possibly at an address like "108.69.." as its being provided an IP from the ISP's modem/router, that is from Time Warner, and they allow NO! configuration options. Web Site for employees to access. I'm trying not to use the server too much as a desktop, only for critical situations, so having a backend thats seperate from the front-facing website is critical. This will be the DD-WRT router hardwired into NIC #2 on the server. This WiFi will be password accessible. Public WiFi for customers. The DD-WRT can seperate networks if I'm correct, I just can't seem to understand how to seperate the 2 and still have internet access on both. I've done it before, but the "Public" wifi (with no password set to connect) kept dropping the connection like a problem was happening that I couldn't figure out. So if I could do a little drawing, this is how it would/should possibly look. ISP -- [Sends Public Facing IP of 108.69.*.1/8] -- ISP Modem Router ISP Modem Router (Ethernet Only) -- [Gives Private IP 108.69.*.2] -- Server NIC #1 Server NIC #1 -- [Gives Private IP 108.69.*.3] -- DD-WRT Router DD-WRT Router -- [DHCP Enabled Giving IP's 172.16.0.0/16] -- Employees Network | | --------- [DHCP Enabled Giving IP's 192.168.1.0/24] -- Public WIFI Hope it's not too confusing, but it anyone could give me some good direct tutorials on how to accomplish this, or if YOU know, then it'll be alot of help. Thanks to all in advance. Need anything else to be explained? Don't hesitate to ask! *Using The LAMP stack with Webmin/VirtualMin -Customer site is located in /var/www2/ -Private Employees site is located in /var/www/ Using no-ip.org's dynamic client updater

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• How can I join two simple home networks together using an ethernet cable?

  - by Ilia Jerebtsov

  I want to join two different home networks together like so: PC A1 PC A2 PC B1 PC B2 \ / \ / Gateway A <----- ethr. cable -----> Gateway B | | ADSL modem A ADSL modem B Both networks are of the basic residential type with identical configuration, with all PCs running Vista/7. The point is to temporarily join two apartments in a building for gaming and file sharing, and the holy grail would be: PCs on network A can access PCs on network B and vice-versa (file shares and gaming). Each network uses its own internet connection. Data between networks shouldn't take a trip through the internet (broadband upload speeds are severely capped) A network's internet access should continue working if the joining cable is disconnected with minimal configuration changes. How closely can this be achieved?

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• How can I join two simple home networks together using an ethernet cable?

  - by Ilia Jerebtsov

  I want to join two different home networks together like so: PC A1 PC A2 PC B1 PC B2 \ / \ / Gateway A <----- ethr. cable -----> Gateway B | | ADSL modem A ADSL modem B Both networks are of the basic residential type with identical configuration, with all PCs running Vista/7. The point is to temporarily join two apartments in a building for gaming and file sharing, and the holy grail would be: PCs on network A can access PCs on network B and vice-versa (file shares and gaming). Each network uses its own internet connection. Data between networks shouldn't take a trip through the internet (broadband upload speeds are severely capped) A network's internet access should continue working if the joining cable is disconnected with minimal configuration changes. How closely can this be achieved?

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• How do I fix VMware “Unidentified Networks” in Windows 7 Professional 64-bit SP1?

  - by Francis

  I have recently installed VMware Workstation 7 onto Windows 7 Professional 64-bit SP1 and both VMnet1 and VMnet8 appeared as "Unidentified Networks". I have tried editing HKLM\SYSTEM\CurrentControlSet\Control\Class{4D36E972-E325-11CE-BFC1-08002BE10318}, a tip provided by Mathews (Jul 23, 2009) but both virtual NICs still appeared as "Unidentified Networks". I will need both NICs to be listed as "Work" or "Private" and with Internet Access. What other solutions/workarounds? Thanks!

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• 6 Reasons Why You Can’t Move Your Cell Phone To Any Carrier You Want

  - by Chris Hoffman

  You can buy a laptop or Wi-Fi tablet and use it on Wi-Fi anywhere in the world, so why are cell phones and devices with mobile data not portable between different cellular networks in the same country? Unlike with Wi-Fi, there are many different competing cellular network standards — both around the world and within countries. Cellular carriers also like locking you to their specific network and making it difficult to move. That’s what contracts are for. Phone Locking Many phones are sold locked to a specific network. When you buy a phone from a cellular carrier, they often lock that phone to their network so you can’t take it to a competitor’s network. That’s why you’ll often need to unlock a phone before you can move it to a different cellular provider or take it to a different country and use it on a local provider instead of roaming. Cellular carriers will generally unlock your phone for you as long as you’re no longer in a contract with them. However, unlocking a cell phone you’ve paid for without your carrier’s permission is currently a crime in the USA. GSM vs. CDMA Some cellular networks use the GSM (Global System for Mobile Communications) standard, while some use CDMA (Code-division multiple access). Worldwide, most cellular networks use GSM. In the USA, both GSM and CDMA are popular. Verizon, Sprint, and other carriers that use their networks use CDMA. AT&T, T-Mobile, and other carriers that use their networks are use GSM. These are two competing standards and are not interoperable. This means you can’t simply take a phone from Verizon to T-Mobile, or from AT&T to Sprint. These carriers have incompatible phones. CDMA Restrictions CDMA is more restricted than GSM. GSM phones have SIM cards. Simply open the phone, pop out the SIM card, and pop in a new SIM card to switch carriers. (In reality, it’s more complicated thanks to phone locking and other factors here.) CDMA phones don’t have removable modules like this. All CDMA phones ship locked to a specific network and you’d have to get both your old carrier and your new carrier to cooperate to switch phones between them. In reality, many people just consider CDMA phones eternally locked to a specific carrier. Frequencies Different cellular networks throughout the USA and the rest of the world use different frequencies. These radio frequencies have to be supported by your phone’s hardware or your phone simply can’t work on a network using those frequencies. Many GSM phones support three or four bands of frequencies — 900/1800/1900 MHz, 850/1800/1900 MHz, or 850/900/1800/1900 MHz. These are sometimes called “world phones” because they allow easier roaming. This allows the manufacturer to produce a phone that will support all GSM networks in the world and allows their customers to travel with those phones. If your phone doesn’t support the appropriate frequencies, it won’t work on certain networks. LTE Bands When it comes to newer, faster LTE networks, different frequencies are still a concern. LTE frequencies are generally known as “LTE bands.” To use a smartphone on a certain LTE network, that smartphone will have to support that LTE network’s frequency. Different models of phones are often created to work on different LTE networks around the world. However, phones are generally supporting more and more LTE networks and becoming more and more interoperable over time. SIM Card Sizes The SIM cards used in GSM phones come in different sizes. Newer phones use smaller SIM cards to save space and be more compact. This isn’t a big obstacle, as the different sizes of SIM cards — full-size SIM, mini-SIM, micro-SIM, and nano-SIM are actually compatible. The only difference between them is the size of the plastic card surrounding the SIM’s chip. The actual chip is the same size between all the SIM cards. This means you can take an old SIM card and cut the plastic off until it becomes a smaller-size SIM card that fits in a modern phone. Or, you can take a smaller-size SIM card and insert it into a tray so that it becomes a larger-size SIM card that fits in an older phone. Be aware that it’s very possible to damage your SIM card and make it not work properly by cutting it to the wrong dimensions. Your cellular carrier will often be able to cut your SIM card for you or give you a new one if you want to use an old SIM card in a new phone. Hopefully they won’t overcharge you for this service, too. Be sure to check what types of networks, frequencies, and LTE bands your phone supports before trying to move it between networks. You may have to buy a new phone when moving between certain cellular carriers. Image Credit: Morgan on Flickr, 22n on Flickr

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• Computer Networks UNISA - Chap 14 &ndash; Insuring Integrity &amp; Availability

  - by MarkPearl

  After reading this section you should be able to Identify the characteristics of a network that keep data safe from loss or damage Protect an enterprise-wide network from viruses Explain network and system level fault tolerance techniques Discuss issues related to network backup and recovery strategies Describe the components of a useful disaster recovery plan and the options for disaster contingencies What are integrity and availability? Integrity – the soundness of a networks programs, data, services, devices, and connections Availability – How consistently and reliably a file or system can be accessed by authorized personnel A number of phenomena can compromise both integrity and availability including… security breaches natural disasters malicious intruders power flaws human error users etc Although you cannot predict every type of vulnerability, you can take measures to guard against the most damaging events. The following are some guidelines… Allow only network administrators to create or modify NOS and application system users. Monitor the network for unauthorized access or changes Record authorized system changes in a change management system’ Install redundant components Perform regular health checks on the network Check system performance, error logs, and the system log book regularly Keep backups Implement and enforce security and disaster recovery policies These are just some of the basics… Malware Malware refers to any program or piece of code designed to intrude upon or harm a system or its resources. Types of Malware… Boot sector viruses Macro viruses File infector viruses Worms Trojan Horse Network Viruses Bots Malware characteristics Some common characteristics of Malware include… Encryption Stealth Polymorphism Time dependence Malware Protection There are various tools available to protect you from malware called anti-malware software. These monitor your system for indications that a program is performing potential malware operations. A number of techniques are used to detect malware including… Signature Scanning Integrity Checking Monitoring unexpected file changes or virus like behaviours It is important to decide where anti-malware tools will be installed and find a balance between performance and protection. There are several general purpose malware policies that can be implemented to protect your network including… Every compute in an organization should be equipped with malware detection and cleaning software that regularly runs Users should not be allowed to alter or disable the anti-malware software Users should know what to do in case the anti-malware program detects a malware virus Users should be prohibited from installing any unauthorized software on their systems System wide alerts should be issued to network users notifying them if a serious malware virus has been detected. Fault Tolerance Besides guarding against malware, another key factor in maintaining the availability and integrity of data is fault tolerance. Fault tolerance is the ability for a system to continue performing despite an unexpected hardware or software malfunction. Fault tolerance can be realized in varying degrees, the optimal level of fault tolerance for a system depends on how critical its services and files are to productivity. Generally the more fault tolerant the system, the more expensive it is. The following describe some of the areas that need to be considered for fault tolerance. Environment (Temperature and humidity) Power Topology and Connectivity Servers Storage Power Typical power flaws include Surges – a brief increase in voltage due to lightening strikes, solar flares or some idiot at City Power Noise – Fluctuation in voltage levels caused by other devices on the network or electromagnetic interference Brownout – A sag in voltage for just a moment Blackout – A complete power loss The are various alternate power sources to consider including UPS’s and Generators. UPS’s are found in two categories… Standby UPS – provides continuous power when mains goes down (brief period of switching over) Online UPS – is online all the time and the device receives power from the UPS all the time (the UPS is charged continuously) Servers There are various techniques for fault tolerance with servers. Server mirroring is an option where one device or component duplicates the activities of another. It is generally an expensive process. Clustering is a fault tolerance technique that links multiple servers together to appear as a single server. They share processing and storage responsibilities and if one unit in the cluster goes down, another unit can be brought in to replace it. Storage There are various techniques available including the following… RAID Arrays NAS (Storage (Network Attached Storage) SANs (Storage Area Networks) Data Backup A backup is a copy of data or program files created for archiving or safekeeping. Many different options for backups exist with various media including… These vary in cost and speed. Optical Media Tape Backup External Disk Drives Network Backups Backup Strategy After selecting the appropriate tool for performing your servers backup, devise a backup strategy to guide you through performing reliable backups that provide maximum data protection. Questions that should be answered include… What data must be backed up At what time of day or night will the backups occur How will you verify the accuracy of the backups Where and for how long will backup media be stored Who will take responsibility for ensuring that backups occurred How long will you save backups Where will backup and recovery documentation be stored Different backup methods provide varying levels of certainty and corresponding labour cost. There are also different ways to determine which files should be backed up including… Full backup – all data on all servers is copied to storage media Incremental backup – Only data that has changed since the last full or incremental backup is copied to a storage medium Differential backup – Only data that has changed since the last backup is coped to a storage medium Disaster Recovery Disaster recovery is the process of restoring your critical functionality and data after an enterprise wide outage has occurred. A disaster recovery plan is for extreme scenarios (i.e. fire, line fault, etc). A cold site is a place were the computers, devices, and connectivity necessary to rebuild a network exist but they are not appropriately configured. A warm site is a place where the computers, devices, and connectivity necessary to rebuild a network exists with some appropriately configured devices. A hot site is a place where the computers, devices, and connectivity necessary to rebuild a network exists and all are appropriately configured.

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• How to insert in a blog sharing links to visitors Tweet, Facebook and so on social networks?

  - by Andry

  I am developing a web blog using ASP.NET, but I guess that the tech details like this, here, is not important. My aim is to insert in every post I create those nice buttons to the social networks account of my visitors so that they can quote or post the link to the blog entry in their space. How can I do this? I guess it also de3pend on the social network I want to use. Lets say, now, that I want to have links to Facebook, Tweet and Google circle accounts. Thankyou.

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• How can we tell what driven the Private bytes spiking.

  - by ronin

  I have websites running on .Net Framework 2.0 environment. For recent every day my website becomes slow at certain time and I need to recycle my app pool. I checked the log file found that the private bytes will spike during that time slot. Through some research I already know that the managed code and unmanaged code consists of Privates and we can identify which one cause the spike based on "Bytes in all heaps" counter. But I can't find a way to dig deeper. Is there any way that I can find out what driven my private bytes spike? How can we see what the private bytes are being used for? Thanks, Ronin

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• trying to figure out how to bridge two virtual networks together and in turn bridge that to the internet for a virtual inline IDS/IPS system

  - by Tony robinson

  I'm trying to figure out how to bridge two vmware (server or workstation, workstation) or virtualbox networks together with a linux IDS/IPS system transparently inline between both the virtual networks. How do I accomplish this? I understand how to bridge to virtual networks together, but how to I make the linux virtual machine sit between them and force traffic to go across the transparent bridge? I would like to have something along the lines of: vmnet a various vms host-only network ---- inline linux box vmnet a boxes forced to go through here to get to the internet --- vmnet b network with internet access configured as either NAT or bridged -- internet I know that basically the linux box needs two virtual nics, one on vmnet a and vmnet b, but other than that, I don't know how to force all the traffic to go across the "transparent" bridging linux box on its way to the internet. Do vmnet a and b have to be the same ip network with the same default route? does vmnet a not have a default route and vmnet b have a default route? I've read in vmware forums that on the linux host you need to change permissions on the vmnet files for promiscuous mode? is this true? how do you configure this scenario on a windows box?

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• How to prevent Ubuntu from combining networks on 2 NIC server?

  - by SolarPower

  I've got a Ubuntu Server 10.10 with 2 network interfaces with a cable plugged into both going to switches on completely different networks with different routers. One network is the 10.1.10.X network with a separate gateway/router - the server has an IP of 10.1.10.50 with the gateway IP of 10.1.10.1. The other interface is 10.2.10.X, IP 10.2.10.50, gateway 10.2.10.1. All my Mac machines are on the 10.2.10.X network, and all servers on the 10.1.10.X. The ONLY connection between the two is this machine. From a Mac in my office, I CANNOT ping any computer on the 10.1.10.X network except the Ubuntu machine I'm talking about. However, under the Shared column in Finder, I can see every server on the other network listed. That makes me believe that somehow this Ubuntu machine is letting certain requests span both networks, which is a security problem. Hope this is enough info.

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• OpenVPN to connect remote networks, peer to peer instead of client/server possible?

  - by John Robertson

  I would like to connect two remote networks using OpenVPN. I am very new to this we are very small and don't have a sys/network admin. What are the possible setups to have both networks both live on a common LAN via OpenVPN? I would prefer to use the UDP peer model rather than client/server. Is there a way to set that up instead? I can't see how because no computer on existing network A has a routable address to any computer on existing network B and vice versa.

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• Can I use the Airport Express as a an uplink between two networks?

  - by Ant Swift

  I have two separate networks using different IP ranges, 192.168.0.* for the wired only, isolated network and 192.160.1.* for the wireless only network which is connected to the internet. The wired network has a network printer setup and working and I want to be able to share it out to members of the wireless network (see diagram below). In short I need some kind of uplink between the two networks. Currently running a cable is out since there is no suitable route. I have a spare Airport Express and I am wondering if I could attach it to the wired network and have it join the wireless and act as the uplink between the two. Anyone know if the device is capable of this?

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• Career in Artificial Intelligence [closed]

  - by Rohit S

  AI has many branches and seems like it has a bigger scope. I have seen a tutorial of Neural Networks and I'm a little confused whether Neural Networks is another branch of AI or it is a technique which is being used in branches of AI. I am mainly interested in creating software like Neural Networks that can be trained for doing a task. I like to make things automated with programming languages. So can I start with Neural Networks? And also a very important matter: what will be the scope of a job in future and in which companies?

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• How to restrict access to other Wifi networks in range?

  - by meetpd

  Is there a way to access connecting to other wifi networks in range? I have an office and there are few wifi networks in range. Some of them are not password protected and invariably I get connected to that wifi first. I have talked to the person who owns that wifi. But he is somehow not listening about adding password to his network. So, is there a way I can block that Wifi network completely so that I do not connect to it? I have Win 7 and Mac at my office.

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• What can be done to improve time synchronization on networks with sporadic internet access?

  - by anregen

  I'm looking for advice setting up time servers for a very non-typical network. I support many closed networks that have occasional access to the internet. A network would get access most days for a few hours, but would frequently go 1-3 weeks blacked-out. The computers/servers on this network are mostly *nix-based, but not all the same flavor. The entire network is mobile, so when it connects, it will have very different hops/latency to internet time servers. The servers on the closed network are powered-off frequently (at least daily). Right now, my gut tells me to use NTP (because I hate re-learning all the stuff that someone else already got working pretty well). But I have several issues, and am looking for someone with experience in this type of strange situation. I currently have no solution in place, I'm simply letting the internal clocks drift. This results in errors of ~600s in a majority of networks. I have seen mismatch worse than 10,000s. Is there something "better" than NTP in this situation? I know NTP likes to have very frequent, consistent access to servers that give nearly identical answers. I won't have that. How many internal NTP servers should I configure, so that during periods of internet blackout, I have internal time that is consistent within the closed network? There is no human access. No matter how large the mismatch, the server(s) must attempt to correct itself. Discrete steps are very bad. No matter how large the mismatch, the correction must be "slewed", not "stepped". I understand that this could take many hours to correct.

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• Why does my computer not always automatically request a new DHCP lease when switching networks?

  - by KingJ

  I've noticed an interesting problem recently where my laptop will not automatically refresh my DHCP lease when changing between wireless networks. Instead, it will attempt to use the existing lease for the new network. Of course, since each network has different settings any connections will fail when using the old lease. While Windows will eventually request a new DHCP lease, it's often much faster for me to release the old lease and request a new, correct, lease. It puzzles me as to why this is not automatically done when associating to the network? One possible cause is that the laptop is put to sleep while connected to one network, then woken when in range of the other network. Nevertheless, I would expect that the lease would be renewed when the laptop associates to the other network rather than attempting to use the old lease. It should be noted that the two networks are completely different, both in terms of size, number of APs, network settings, SSIDs etc. One network is my home network and the other one is the campus-wide network at my University.

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• Java Script – Content delivery networks (CDN) can bit you in the butt.

  - by Ryan Ternier

  As much as I love the new CDN’s that Google, Microsoft and a few others have publically released, there are some strong gotchas that could come up and bite you in the ass if you’re not careful. But before we jump into that, for those that are not 100% sure what a CDN is (besides Canadian).   Content Delivery Network. A way of distributing your static content across various servers in different physical locations.  Because this static content is stored on many servers around the world, whenever a user needs to access this content, they are given the closest server to their location for this data. Already you can probably see the immediate bonuses to a system like this: Lower bandwidth Even small script files downloaded thousands of times will start to take a noticeable hit on your bandwidth meter. Less connections/hits to your web server which gives better latency If you manage many servers, you don’t need to manually update each server with scripts. A user will download a script for each website they visit. If a user is redirected to many domains/sub-domains within your web site, they might download many copies of the same file. When a system sees multiple requests from the same  domain, they will ignore the download   Those are just a handful of the many bonuses a CDN will give you. And for the average website, a CDN is great choice. Check out the following CDN links for their solutions: Google AJAX Library: http://code.google.com/apis/ajaxlibs/ Microsoft Ajax library: http://www.asp.net/ajaxlibrary/cdn.ashx The Gotcha There is always a catch. Here are some issues I found with using CDN’s that hopefully can help you make your decision. HTTP / HTTPS If you are running a website behind SSL, make sure that when you reference your CDN data that you use https:// vs. http://. If you forget this users will get a very nice message telling them that their secure connection is trying to access unsecure data. For a developer this is fairly simple, but general users will get a bit anxious when seeing this. Trusted Sites Internet Explorer has this really nifty feature that allows users to specify what sites they trust, and by some defaults IE7 only allows trusted sites to be viewed.  No problem, they set your website as trusted. But what about your CDN? If a user sets your websites to trusted, but not the CDN, they will not download those static files. This has the potential to totally break your web site. Pedantic Network Admins This alone is sometimes the killer of projects. However, always be careful when you are going to use a CDN for a professional project. If a network / security admin sees that you’re referencing an outside source, or that a call from a website might hit an outside domain.. panties will be bunched, emails will be spewed out and well, no one wants that.

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