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• How to teach computer science ?

  - by proferikson

  I am just starting to teach computer science. It's just the basic level. I'm finding that I sometimes don't know how to approach topics in a way that lets students easily understand. I've found that the best thing is to use analogies. A terrible one, that worked well, was presenting recursion by using the process of eating a burger. (You eat one bite, then you eat the rest). Interesting real world examples do wonders here. I'd like to know the techniques you have used for teaching, or teachers you've had have used that proved particularly effective. I'd also like to know your best analogies and examples for topics in CS101, especially for those harder to grasp topics. I'm teaching the class in Java (as required).

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• Finding complexity of a program as a service [on hold]

  - by Seshu

  I would like to find the complexity of a specific code chunk written in Java. Is there a place/web site/service where I can find out the complexity of any arbitrary program. This program might include loops/recursion. Using theory we can compute complexity ourselves. But, just curious in finding if any service is out there to find such complexity. We have several code quality related tools does any of such tools will also find complexity of given code? Could any one point me or direct me to such a utility/site/service?

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• How to find Sub-trees in non-binary tree

  - by kenny

  I have a non-binary tree. I want to find all "sub-trees" that are connected to root. Sub-tree is a a link group of tree nodes. every group is colored in it's own color. What would be be the best approach? Run recursion down and up for every node? The data structure of every treenode is a list of children, list of parents. (the type of children and parents are treenodes) Clarification: Group defined if there is a kind of "closure" between nodes where root itself is not part of the closure. As you can see from the graph you can't travel from pink to other nodes (you CAN NOT use root). From brown node you can travel to it's child so this form another group. Finally you can travel from any cyan node to other cyan nodes so the form another group

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• Techniques for getting off the ground in any language

  - by AndyBursh

  When I start learning a new language, I have a couple of simple implementations that I like to complete to familiarise myself with the language. Currently, I write: Fibonacci and/or factorial to get the hang of writing and calling methods, and basic recursion Djikstras shortest path (with a node type) to get to grips with making classes (or whatever the language equivalent is) with methods and properties, and also using them in slightly more complex code. I was wondering: does anybody else have any techniques or tools they like to use when getting off the ground in a new language? I'm always looking for new things to add to my "start-up routine".

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• Why write clean, refactored code?

  - by Shamal Karunarathne

  Hi programming lovers, This is a question I've been asking myself for a long time. Thought of throwing out it to you. From my experience of working on several Java based projects, I've seen tons of codes which we call 'dirty'. The unconventional class/method/field naming, wrong way of handling of exceptions, unnecessarily heavy loops and recursion etc. But the code gives the intended results. Though I hate to see dirty code, it's time taking to clean them up and eventually comes the question of "is it worth? it's giving the desired results so what's the point of cleaning?" In team projects, should there be someone specifically to refactor and check for clean code? Or are there situations where the 'dirty' codes fail to give intended results or make the customers unhappy? Do feel free to comment and reply. And tell me if I'm missing something here. Thanks.

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• What if we run out of stack space in C# or Python?

  - by dotneteer

  Supposing we are running a recursive algorithm on a very large data set that requires, say, 1 million recursive calls. Normally, one would solve such a large problem by converting recursion to a loop and a stack, but what if we do not want to or cannot rewrite the algorithm? Python has the sys.setrecursionlimit(int) method to set the number of recursions. However, this is only part of the story; the program can still run our of stack space. C# does not have a equivalent method. Fortunately, both C# and Python have option to set the stack space when creating a thread. In C#, there is an overloaded constructor for the Thread class that accepts a parameter for the stack size: Thread t = new Thread(work, stackSize); In Python, we can set the stack size by calling: threading.stack_size(67108864) We can then run our work under a new thread with increased stack size.

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• What are the most common stumbling blocks when it comes to learning programming, in order of difficulty?

  - by blueberryfields

  I seem to remember that linked lists, recursion, pointers, and memory management are all good examples of stumbling blocks - places where the aspiring programmer typically ends up spending significant time trying to understand a concept before moving on and improving, and many end up giving up and not improving. I'm looking for a complete/comprehensive list of these types of stumbling blocks, in rough estimated order of difficulty to learn, with the goal of making sure that an educational program for programmers is structured to properly guide students through them Is this information available somewhere? Ideally, the difficulty to learn will be measured in some sort of objective manner (ie, % of students which consistently fail to learn the concept) What sources are most appropriate for obtaining this information?

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• How to find siblings of a tree?

  - by smallB

  On my interview for an internship, I was asked following question: On a whiteboard write the simplest algorithm with use of recursion which would take a root of a so called binary tree (so called because it is not strictly speaking binary tree) and make every child in this tree connected with its sibling. So if I have: 1 / \ 2 3 / \ \ 4 5 6 / \ 7 8 then the sibling to 2 would be 3, to four five, to five six and to seven eight. I didn't do this, although I was heading in the right direction. Later (next day) at home I did it, but with the use of a debugger. It took me better part of two hours and 50 lines of code. I personally think that this was very difficult question, almost impossible to do correctly on a whiteboard. How would you solve it on a whiteboard? How to apprehend this question without using a debugger?

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• How do I efficiently generate chunks to fill entire screen when my player moves?

  - by Trixmix

  In my game I generate chunks when the player moves. The chunks are all generated on the fly, but currently I just created a simple flat 8X8 floor. What happens is that when he moves to a new chunk the chunk in the direction of the player gets generated and its neighboring chunks. This is not efficient because the generator does not fill the entire screen. I did try to use recursion but its not as fast as I would like it to be. My question is what would be an efficient way of doing so? How does minecraft do so? When I say this I mean just the way it PICKS which chunks to generate and in what order. Not how they generate or how they are saved in regions, just the order/way it generates them. I just want to know what is a good way to load chunks around the player.

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• Am I getting Scheme wrong?

  - by nischayn22

  Inspired by the numerous posts about the importance of learning Lisp/Scheme I started to learn Scheme two days back, I am using the book "The little Schemer" and have completed half of it. But I still haven't learned anything new, the book teaches about recursion which I already understand and uses lambda (which I can think of a way to define a function in C). I still haven't got the concept of functional programming (please point to some example of functional compared to normal programming methods in C/C++ so I can get it). Am I learning in the wrong way? or is "The little Schemer" for a newbie in programming and I should look for some other books?

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• Number Game Algorithm

  - by 7Aces

  Problem Link - http://www.iarcs.org.in/inoi/2011/zco2011/zco2011-1b.php The task is to find the maximum score you can get in the game. Such problems, based on games, where you have to simulate, predict the result, or obtain the maximum possible score always seem to puzzle me. I can do it with recursion by considering two cases - first number picked or last number picked, each of which again branches into two states similarly, and so on... which finally can yield the max possible result. But it's a very time-inefficient approach, since time increases exponentially, due to the large test cases. What is the most pragmatic approach to the problem, and to such problems in general?

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• List item stuck in "Pending"

  - by Norgean

  Problem simplified: On approval, you have an event receiver that changes a field according to some weird and wonderful business logic. But the item remains in "Pending" state. Why?   First, you obviously need to turn off the event handling when you change things in the event receiver. If not, the event receiver will be called because the item changed. Infinite recursion is a bad thing. But you guessed that.   But that's not what was wrong. The culprit in my case was that items are set to require a new approval whenever the item is changed. This is good, but not what we want in this particular case. So force it back to approved after the other column has been changed.

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• django deleting models and overriding delete method

  - by Mike

  I have 2 models class Vhost(models.Model): dns = models.ForeignKey(DNS) user = models.ForeignKey(User) extra = models.TextField() class ApplicationInstalled(models.Model): user = models.ForeignKey(User) added = models.DateTimeField(auto_now_add=True) app = models.ForeignKey(Application) ver = models.ForeignKey(ApplicationVersion) vhost = models.ForeignKey(Vhost) path = models.CharField(max_length=100, default="/") def delete(self): # # remove the files # print "need to remove some files" super(ApplicationInstalled, self).delete() If I do the following >>> vhost = Vhost.objects.get(id=10) >>> vhost.id 10L >>> ApplicationInstalled.objects.filter(vhost=vhost) [<ApplicationInstalled: http://wiki.jy.com/>] >>> vhost.delete() >>> ApplicationInstalled.objects.filter(vhost=vhost) [] As you can see there is an applicationinstalled object linked to vhost but when I delete the vhost, the applicationinstalled object is gone but the print never gets called. Any easy way to do this without iterating through the objects in the vhost delete?

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• IP Address Lookup in VB.net (XP vs Windows 7)

  - by TheHockeyGeek

  Currently I use the following code to retrieve the IP address of the local workstation... strIPAddress = System.Net.Dns.GetHostEntry(strComputerName).AddressList(0).ToString() This is fine for the Windows XP workstations. However, in Vista and Windows 7, this returns the IPv6 address which is not used at all. Is there a method of setting this to work so it always returns the IPv4 address regardless of platform? I know I can increment the AddressList value to 1 and get the correct IP in Windows 7. The bad part is that this requires going through the motions of identifying the OS and choosing one or the other. The must be some way of specifying IPv4 only. Perhaps getting a result from DNS on the network rather than the workstation itself?

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• How do I verify a DKIM signature in PHP?

  - by angrychimp

  I'll admit I'm not very adept at key verification. What I have is a script that downloads messages from a POP3 server, and I'm attempting to verify the DKIM signatures in PHP. I've already figured out the body hash (bh) validation check, but I can't figure out the header validation. http://www.dkim.org/specs/rfc4871-dkimbase.html#rfc.section.6.1.3 Below is an example of my message headers. I've been able to use the Mail::DKIM package to validate the signature in Perl, so I know it's good. I just can't seem to figure out the instructions in the RFC and translate them into PHP code. DomainKey-Signature: q=dns; a=rsa-sha1; c=nofws; s=angrychimp-1.bh; d=angrychimp.net; h=From:X-Outgoing; b=RVkenibHQ7GwO5Y3tun2CNn5wSnooBSXPHA1Kmxsw6miJDnVp4XKmA9cUELwftf9 nGiRCd3rLc6eswAcVyNhQ6mRSsF55OkGJgDNHiwte/pP5Z47Lo/fd6m7rfCnYxq3 DKIM-Signature: v=1; a=rsa-sha1; d=angrychimp.net; s=angrychimp-1.bh; c=relaxed/simple; q=dns/txt; [email protected]; t=1268436255; h=From:Subject:X-Outgoing:Date; bh=gqhC2GEWbg1t7T3IfGMUKzt1NCc=; b=ZmeavryIfp5jNDIwbpifsy1UcavMnMwRL6Fy6axocQFDOBd2KjnjXpCkHxs6yBZn Wu+UCFeAP+1xwN80JW+4yOdAiK5+6IS8fiVa7TxdkFDKa0AhmJ1DTHXIlPjGE4n5; To: [email protected] Message-ID: From: DKIM Tester Reply-To: [email protected] Subject: Automated DKIM Testing (angrychimp.net) X-Outgoing: dhaka Date: Fri, 12 Mar 2010 15:24:15 -0800 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline MIME-Version: 1.0 Return-Path: [email protected] X-OriginalArrivalTime: 12 Mar 2010 23:25:50.0326 (UTC) FILETIME=[5A0ED160:01CAC23B] I can extract the public key from my DNS just fine, and I believe I'm canonicalizing the headers correctly, but I just can't get the signature validated. I don't think I'm preparing my key or computing the signature validation correctly. Is this something that's possible (do I need pear extensions or something?) or is manually validating a DKIM signature in PHP just not feasible?

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• client ip address in ASP.NET (.asmx) webservices

  - by Zain Shaikh

  I am using ASP.Net (.asmx) web services with Silverlight. since there is no way to find client ip address in Silverlight, therefore I had to log this on service end. these are some methods I have tried: Request.ServerVariables(”REMOTE_HOST”) HttpContext.Current.Request.ServerVariables["REMOTE_ADDR"] HttpContext.Current.Request.ServerVariables["HTTP_X_FORWARDED_FOR"]; Request.UserHostAddress() Request.UserHostName() string strHostName = System.Net.Dns.GetHostName(); string clientIPAddress = System.Net.Dns.GetHostAddresses(strHostName).GetValue(0).ToString(); All the above methods work fine on my local system, but when I publish my service on production server. it starts giving errors. Error: Object reference not set to an instance of an object. StackTrace: at System.Web.Hosting.ISAPIWorkerRequestInProc.GetAdditionalServerVar(Int32 index) at System.Web.Hosting.ISAPIWorkerRequestInProc.GetServerVariable(String name) at System.Web.Hosting.ISAPIWorkerRequest.GetRemoteAddress() at System.Web.HttpRequest.get_UserHostAddress()

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• Outbound traffic being blocked for MIP/VIPped servers (Juniper SSG5)

  - by Mark S. Rasmussen

  As we've been having some problems with sporadic packet loss, I've been preparing a replacement router (also an SSG5) for our current Juniper SSG5. I've setup the new SSG5 identically to the old one. We have a /29 IP range with a single IP setup as a MIP map to a server and two others being used for VIP maps. Each VIP/MIP is accompanied by relevant policies. Long story short - we tried connected the new SSG5 and some things were not working as they should. No problem, I just reconnected the old one. However, some things are still broken, even when I reconnected the old one. I fear I may have inadvertently changed some settings while browsing through old settings in my attempt to reconfigure the new SSG5 unit. All inbound traffic seems to work as expected. However, the 192.168.2.202 server can't initiate any outbound connections. It works perfectly on the local network, but any pings or DNS lookups to external IP's fail. The MIP & VIP map to it works perfectly - I can access it through HTTP and RDP without issues. Any tips on what to debug, or where I've messed up my config? I've attached the full config here (with anonymized IPs): set clock timezone 1 set vrouter trust-vr sharable set vrouter "untrust-vr" exit set vrouter "trust-vr" unset auto-route-export exit set service "MyVOIP_UDP4569" protocol udp src-port 0-65535 dst-port 4569-4569 set service "MyVOIP_TCP22" protocol tcp src-port 0-65535 dst-port 22-22 set service "MyRDP" protocol tcp src-port 0-65535 dst-port 3389-3389 set service "MyRsync" protocol tcp src-port 0-65535 dst-port 873-873 set service "NZ_FTP" protocol tcp src-port 0-65535 dst-port 40000-41000 set service "NZ_FTP" + tcp src-port 0-65535 dst-port 21-21 set service "PPTP-VPN" protocol 47 src-port 2048-2048 dst-port 2048-2048 set service "PPTP-VPN" + tcp src-port 1024-65535 dst-port 1723-1723 set service "NZ_FMS_1935" protocol tcp src-port 0-65535 dst-port 1935-1935 set service "NZ_FMS_1935" + udp src-port 0-65535 dst-port 1935-1935 set service "NZ_FMS_8080" protocol tcp src-port 0-65535 dst-port 8080-8080 set service "CrashPlan Server" protocol tcp src-port 0-65535 dst-port 4280-4280 set service "CrashPlan Console" protocol tcp src-port 0-65535 dst-port 4282-4282 unset alg sip enable set auth-server "Local" id 0 set auth-server "Local" server-name "Local" set auth default auth server "Local" set auth radius accounting port 1646 set admin auth timeout 10 set admin auth server "Local" set admin format dos set vip multi-port set zone "Trust" vrouter "trust-vr" set zone "Untrust" vrouter "trust-vr" set zone "DMZ" vrouter "trust-vr" set zone "VLAN" vrouter "trust-vr" set zone "Untrust-Tun" vrouter "trust-vr" set zone "Trust" tcp-rst set zone "Untrust" block unset zone "Untrust" tcp-rst set zone "DMZ" tcp-rst set zone "VLAN" block unset zone "VLAN" tcp-rst set zone "Untrust" screen tear-drop set zone "Untrust" screen syn-flood set zone "Untrust" screen ping-death set zone "Untrust" screen ip-filter-src set zone "Untrust" screen land set zone "V1-Untrust" screen tear-drop set zone "V1-Untrust" screen syn-flood set zone "V1-Untrust" screen ping-death set zone "V1-Untrust" screen ip-filter-src set zone "V1-Untrust" screen land set interface ethernet0/0 phy full 100mb set interface ethernet0/3 phy full 100mb set interface ethernet0/4 phy full 100mb set interface ethernet0/5 phy full 100mb set interface ethernet0/6 phy full 100mb set interface "ethernet0/0" zone "Untrust" set interface "ethernet0/1" zone "Null" set interface "bgroup0" zone "Trust" set interface "bgroup1" zone "Trust" set interface "bgroup2" zone "Trust" set interface bgroup2 port ethernet0/2 set interface bgroup0 port ethernet0/3 set interface bgroup0 port ethernet0/4 set interface bgroup1 port ethernet0/5 set interface bgroup1 port ethernet0/6 unset interface vlan1 ip set interface ethernet0/0 ip 212.242.193.18/29 set interface ethernet0/0 route set interface bgroup0 ip 192.168.1.1/24 set interface bgroup0 nat set interface bgroup1 ip 192.168.2.1/24 set interface bgroup1 nat set interface bgroup2 ip 192.168.3.1/24 set interface bgroup2 nat set interface ethernet0/0 gateway 212.242.193.17 unset interface vlan1 bypass-others-ipsec unset interface vlan1 bypass-non-ip set interface ethernet0/0 ip manageable set interface bgroup0 ip manageable set interface bgroup1 ip manageable set interface bgroup2 ip manageable set interface bgroup0 manage mtrace unset interface bgroup1 manage ssh unset interface bgroup1 manage telnet unset interface bgroup1 manage snmp unset interface bgroup1 manage ssl unset interface bgroup1 manage web unset interface bgroup2 manage ssh unset interface bgroup2 manage telnet unset interface bgroup2 manage snmp unset interface bgroup2 manage ssl unset interface bgroup2 manage web set interface ethernet0/0 vip 212.242.193.19 2048 "PPTP-VPN" 192.168.1.131 set interface ethernet0/0 vip 212.242.193.19 + 4280 "CrashPlan Server" 192.168.1.131 set interface ethernet0/0 vip 212.242.193.19 + 4282 "CrashPlan Console" 192.168.1.131 set interface ethernet0/0 vip 212.242.193.22 22 "MyVOIP_TCP22" 192.168.2.127 set interface ethernet0/0 vip 212.242.193.22 + 4569 "MyVOIP_UDP4569" 192.168.2.127 set interface ethernet0/0 vip 212.242.193.22 + 3389 "MyRDP" 192.168.2.202 set interface ethernet0/0 vip 212.242.193.22 + 873 "MyRsync" 192.168.2.201 set interface ethernet0/0 vip 212.242.193.22 + 80 "HTTP" 192.168.2.202 set interface ethernet0/0 vip 212.242.193.22 + 2048 "PPTP-VPN" 192.168.2.201 set interface ethernet0/0 vip 212.242.193.22 + 8080 "NZ_FMS_8080" 192.168.2.216 set interface ethernet0/0 vip 212.242.193.22 + 1935 "NZ_FMS_1935" 192.168.2.216 set interface bgroup0 dhcp server service set interface bgroup1 dhcp server service set interface bgroup2 dhcp server service set interface bgroup0 dhcp server auto set interface bgroup1 dhcp server auto set interface bgroup2 dhcp server auto set interface bgroup0 dhcp server option domainname iplan set interface bgroup0 dhcp server option dns1 192.168.1.131 set interface bgroup1 dhcp server option domainname nzlan set interface bgroup1 dhcp server option dns1 192.168.2.202 set interface bgroup2 dhcp server option dns1 8.8.8.8 set interface bgroup2 dhcp server option wins1 8.8.4.4 set interface bgroup0 dhcp server ip 192.168.1.2 to 192.168.1.116 set interface bgroup1 dhcp server ip 192.168.2.2 to 192.168.2.116 set interface bgroup2 dhcp server ip 192.168.3.2 to 192.168.3.126 unset interface bgroup0 dhcp server config next-server-ip unset interface bgroup1 dhcp server config next-server-ip unset interface bgroup2 dhcp server config next-server-ip set interface "ethernet0/0" mip 212.242.193.21 host 192.168.2.202 netmask 255.255.255.255 vr "trust-vr" set interface "serial0/0" modem settings "USR" init "AT&F" set interface "serial0/0" modem settings "USR" active set interface "serial0/0" modem speed 115200 set interface "serial0/0" modem retry 3 set interface "serial0/0" modem interval 10 set interface "serial0/0" modem idle-time 10 set pak-poll p1queue pak-threshold 96 set pak-poll p2queue pak-threshold 32 set flow tcp-mss unset flow tcp-syn-check set dns host dns1 0.0.0.0 set dns host dns2 0.0.0.0 set dns host dns3 0.0.0.0 set address "Trust" "192.168.1.0/24" 192.168.1.0 255.255.255.0 set address "Trust" "192.168.2.0/24" 192.168.2.0 255.255.255.0 set address "Trust" "192.168.3.0/24" 192.168.3.0 255.255.255.0 set ike respond-bad-spi 1 unset ike ikeid-enumeration unset ike dos-protection unset ipsec access-session enable set ipsec access-session maximum 5000 set ipsec access-session upper-threshold 0 set ipsec access-session lower-threshold 0 set ipsec access-session dead-p2-sa-timeout 0 unset ipsec access-session log-error unset ipsec access-session info-exch-connected unset ipsec access-session use-error-log set l2tp default ppp-auth chap set url protocol websense exit set policy id 1 from "Trust" to "Untrust" "Any" "Any" "ANY" permit traffic set policy id 1 exit set policy id 2 from "Untrust" to "Trust" "Any" "VIP(212.242.193.19)" "PPTP-VPN" permit traffic set policy id 2 exit set policy id 3 from "Untrust" to "Trust" "Any" "VIP(212.242.193.22)" "HTTP" permit traffic priority 0 set policy id 3 set service "MyRDP" set service "MyRsync" set service "MyVOIP_TCP22" set service "MyVOIP_UDP4569" exit set policy id 6 from "Trust" to "Trust" "192.168.1.0/24" "192.168.2.0/24" "ANY" deny set policy id 6 exit set policy id 7 from "Trust" to "Trust" "192.168.2.0/24" "192.168.1.0/24" "ANY" deny set policy id 7 exit set policy id 8 from "Trust" to "Trust" "192.168.3.0/24" "192.168.1.0/24" "ANY" deny set policy id 8 exit set policy id 9 from "Trust" to "Trust" "192.168.3.0/24" "192.168.2.0/24" "ANY" deny set policy id 9 exit set policy id 10 from "Untrust" to "Trust" "Any" "MIP(212.242.193.21)" "NZ_FTP" permit set policy id 10 exit set policy id 11 from "Untrust" to "Trust" "Any" "VIP(212.242.193.22)" "PPTP-VPN" permit set policy id 11 exit set policy id 12 from "Untrust" to "Trust" "Any" "VIP(212.242.193.22)" "NZ_FMS_1935" permit set policy id 12 set service "NZ_FMS_8080" exit set policy id 13 from "Untrust" to "Trust" "Any" "VIP(212.242.193.19)" "CrashPlan Console" permit set policy id 13 set service "CrashPlan Server" exit set nsmgmt bulkcli reboot-timeout 60 set ssh version v2 set config lock timeout 5 set snmp port listen 161 set snmp port trap 162 set vrouter "untrust-vr" exit set vrouter "trust-vr" unset add-default-route exit set vrouter "untrust-vr" exit set vrouter "trust-vr" exit

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• Ip address of the client machine

  - by Zerotoinfinite

  Hi, Please let me know how to get the client IP address, I have tried all of the below things , but I am getting the same output 127.0.0.1 string strClientIP; strClientIP = Request.UserHostAddress.ToString(); string strHostName = System.Net.Dns.GetHostName(); string clientIPAddress = System.Net.Dns.GetHostAddresses(strHostName).GetValue(0).ToString(); string ipaddress = string.Empty ; ipaddress = Request.ServerVariables["HTTP_X_FORWARDED_FOR"]; if (ipaddress == "" || ipaddress == null) ipaddress = Request.ServerVariables["REMOTE_ADDR"]; Please tel me how can I get the correct IP !

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• Packing a long binary integer in Ruby

  - by user1056142

  I'm trying to send a very long binary integer over UDP (on the order of 200 bits). When I try to use Array's pack method, it complains the string I'm trying to convert is too large. Am I going about this the wrong way? ruby-1.8.7-p352 :003 > [0b1101001010101101111010100101010011010101010110010101010101010010010101001010101010101011101010101010101111010101010101010101].pack('i') RangeError: bignum too big to convert into `unsigned long' from (irb):3:in `pack' from (irb):3 This number is supposed to represent a DNS query packet (this is for a homework assignment; we're not allowed to use any DNS libraries).

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• What to filter when providing very limited open WiFi to a small conference or meeting?

  - by Tim Farley

  Executive Summary The basic question is: if you have a very limited bandwidth WiFi to provide Internet for a small meeting of only a day or two, how do you set the filters on the router to avoid one or two users monopolizing all the available bandwidth? For folks who don't have the time to read the details below, I am NOT looking for any of these answers: Secure the router and only let a few trusted people use it Tell everyone to turn off unused services & generally police themselves Monitor the traffic with a sniffer and add filters as needed I am aware of all of that. None are appropriate for reasons that will become clear. ALSO NOTE: There is already a question concerning providing adequate WiFi at large (500 attendees) conferences here. This question concerns SMALL meetings of less than 200 people, typically with less than half that using the WiFi. Something that can be handled with a single home or small office router. Background I've used a 3G/4G router device to provide WiFi to small meetings in the past with some success. By small I mean single-room conferences or meetings on the order of a barcamp or Skepticamp or user group meeting. These meetings sometimes have technical attendees there, but not exclusively. Usually less than half to a third of the attendees will actually use the WiFi. Maximum meeting size I'm talking about is 100 to 200 people. I typically use a Cradlepoint MBR-1000 but many other devices exist, especially all-in-one units supplied by 3G and/or 4G vendors like Verizon, Sprint and Clear. These devices take a 3G or 4G internet connection and fan it out to multiple users using WiFi. One key aspect of providing net access this way is the limited bandwidth available over 3G/4G. Even with something like the Cradlepoint which can load-balance multiple radios, you are only going to achieve a few megabits of download speed and maybe a megabit or so of upload speed. That's a best case scenario. Often it is considerably slower. The goal in most of these meeting situations is to allow folks access to services like email, web, social media, chat services and so on. This is so they can live-blog or live-tweet the proceedings, or simply chat online or otherwise stay in touch (with both attendees and non-attendees) while the meeting proceeds. I would like to limit the services provided by the router to just those services that meet those needs. Problems In particular I have noticed a couple of scenarios where particular users end up abusing most of the bandwidth on the router, to the detriment of everyone. These boil into two areas: Intentional use. Folks looking at YouTube videos, downloading podcasts to their iPod, and otherwise using the bandwidth for things that really aren't appropriate in a meeting room where you should be paying attention to the speaker and/or interacting.At one meeting that we were live-streaming (over a separate, dedicated connection) via UStream, I noticed several folks in the room that had the UStream page up so they could interact with the meeting chat - apparently oblivious that they were wasting bandwidth streaming back video of something that was taking place right in front of them. Unintentional use. There are a variety of software utilities that will make extensive use of bandwidth in the background, that folks often have installed on their laptops and smartphones, perhaps without realizing.Examples: Peer to peer downloading programs such as Bittorrent that run in the background Automatic software update services. These are legion, as every major software vendor has their own, so one can easily have Microsoft, Apple, Mozilla, Adobe, Google and others all trying to download updates in the background. Security software that downloads new signatures such as anti-virus, anti-malware, etc. Backup software and other software that "syncs" in the background to cloud services. For some numbers on how much network bandwidth gets sucked up by these non-web, non-email type services, check out this recent Wired article. Apparently web, email and chat all together are less than one quarter of the Internet traffic now. If the numbers in that article are correct, by filtering out all the other stuff I should be able to increase the usefulness of the WiFi four-fold. Now, in some situations I've been able to control access using security on the router to limit it to a very small group of people (typically the organizers of the meeting). But that's not always appropriate. At an upcoming meeting I would like to run the WiFi without security and let anyone use it, because it happens at the meeting location the 4G coverage in my town is particularly excellent. In a recent test I got 10 Megabits down at the meeting site. The "tell people to police themselves" solution mentioned at top is not appropriate because of (a) a largely non-technical audience and (b) the unintentional nature of much of the usage as described above. The "run a sniffer and filter as needed" solution is not useful because these meetings typically only last a couple of days, often only one day, and have a very small volunteer staff. I don't have a person to dedicate to network monitoring, and by the time we got the rules tweaked completely the meeting will be over. What I've Got First thing, I figured I would use OpenDNS's domain filtering rules to filter out whole classes of sites. A number of video and peer-to-peer sites can be wiped out using this. (Yes, I am aware that filtering via DNS technically leaves the services accessible - remember, these are largely non-technical users attending a 2 day meeting. It's enough). I figured I would start with these selections in OpenDNS's UI: I figure I will probably also block DNS (port 53) to anything other than the router itself, so that folks can't bypass my DNS configuration. A savvy user could get around this, because I'm not going to put a lot of elaborate filters on the firewall, but I don't care too much. Because these meetings don't last very long, its probably not going to be worth the trouble. This should cover the bulk of the non-web traffic, i.e. peer-to-peer and video if that Wired article is correct. Please advise if you think there are severe limitations to the OpenDNS approach. What I Need Note that OpenDNS focuses on things that are "objectionable" in some context or another. Video, music, radio and peer-to-peer all get covered. I still need to cover a number of perfectly reasonable things that we just want to block because they aren't needed in a meeting. Most of these are utilities that upload or download legit things in the background. Specifically, I'd like to know port numbers or DNS names to filter in order to effectively disable the following services: Microsoft automatic updates Apple automatic updates Adobe automatic updates Google automatic updates Other major software update services Major virus/malware/security signature updates Major background backup services Other services that run in the background and can eat lots of bandwidth I also would like any other suggestions you might have that would be applicable. Sorry to be so verbose, but I find it helps to be very, very clear on questions of this nature, and I already have half a solution with the OpenDNS thing.

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• Async Socket Listener on separate thread - VB.net

  - by TheHockeyGeek

  I am trying to use the code from Microsoft for an Async Socket connection. It appears the listener runs in the main thread locking the GUI. I am new at both socket connections and multi-threading all at the same time. Having a hard time getting my mind wrapped around this all at once. The code used is at http://msdn.microsoft.com/en-us/library/fx6588te.aspx Using this example, how can I move the listener to its own thread? Public Shared Sub Main() ' Data buffer for incoming data. Dim bytes() As Byte = New [Byte](1023) {} ' Establish the local endpoint for the socket. Dim ipHostInfo As IPHostEntry = Dns.GetHostEntry(Dns.GetHostName()) Dim ipAddress As IPAddress = ipHostInfo.AddressList(1) Dim localEndPoint As New IPEndPoint(ipAddress, 11000) ' Create a TCP/IP socket. Dim listener As New Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp) ' Bind the socket to the local endpoint and listen for incoming connections. listener.Bind(localEndPoint) listener.Listen(100)

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• How to run a DHCP service on Windows 7 Home

  - by Joshua Lim

  I'm trying to setup a DHCP server on Windows 7 Home, tried using a couple of freeware which I found on the Internet but none seemed to work. What I did: On the Windows 7 machine which I install the DHCP Server with the range 192.168.1.12-192.168.1.256. I set the Gigabit Ethernet adapter to a static IP address of 192.168.1.11 and subnet mask of 255.255.255.0. When I did an IP config, it showed. Ethernet adapter Local Area Connection: Connection-specific DNS Suffix . : Description . . . . . . . . . . . : Broadcom NetLink (TM) Gigabit Ethernet Physical Address. . . . . . . . . : 8C-73-6E-75-A7-56 DHCP Enabled. . . . . . . . . . . : No Autoconfiguration Enabled . . . . : Yes Link-local IPv6 Address . . . . . : fe80::196d:b6bb:8f93:2555%12(Preferred) IPv4 Address. . . . . . . . . . . : 192.168.1.11(Preferred) Subnet Mask . . . . . . . . . . . : 255.255.255.0 Default Gateway . . . . . . . . . : DNS Servers . . . . . . . . . . . : fec0:0:0:ffff::1%1 fec0:0:0:ffff::2%1 fec0:0:0:ffff::3%1 NetBIOS over Tcpip. . . . . . . . : Enabled I connected another Window 7 machine to the "DHCP server" using a cross cable and set network adapter on that machine to automatically detect IP address. The client fails to acquire the correct IP address from the DHCP server and showed the autoconfigured IPv4 address instead. Here's the information returned by config /all on the client machine. Ethernet adapter Local Area Connection: Connection-specific DNS Suffix . : Description . . . . . . . . . . . : Atheros AR8152/8158 PCI-E Fast Ethernet Controller (NDIS 6.20) Physical Address. . . . . . . . . : 54-04-A6-40-96-4B DHCP Enabled. . . . . . . . . . . : Yes Autoconfiguration Enabled . . . . : Yes Link-local IPv6 Address . . . . . : fe80::4885:4082:5572:5a85%12(Preferred) Autoconfiguration IPv4 Address. . : 169.254.90.133(Preferred) Subnet Mask . . . . . . . . . . . : 255.255.0.0 Default Gateway . . . . . . . . . : DHCPv6 IAID . . . . . . . . . . . : 341050534 DHCPv6 Client DUID. . . . . . . . : 00-01-00-01-17-54-78-12-00-08-CA-46-4C-5A DNS Servers . . . . . . . . . . . : fec0:0:0:ffff::1%1 fec0:0:0:ffff::2%1 fec0:0:0:ffff::3%1 NetBIOS over Tcpip. . . . . . . . : Enabled DHCP client are running on both machines. I've tried many times but failed. Googling also returned no useful information for my scenario. Have I missed out any step? Thanks.

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• How to get or own your own IP address?

  - by Cory

  The website we running let people register their own URL and redirect to our website to their user account. Lets it is something similar to Blogspot.com where users can have their own URL. The problem is that in order to do this we need to have static IP address for the DNS redirection to work. We can easily get static IP addresses from most hosting companies, but if we change our hosting company it means we will have to force all our users to change their DNS setting to our new IP address. This if very problematic. Is there a way of owning our own IP address that we can take it with us to wherever hosting company we decide to go with? Or there there other easier solutions out there?

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• Unable to connect to Linux (Virtual OS-vmware) through Putty on Windows

  - by RBA

  Hi, I want to access my Linux box (Virtual OS) through Putty on Windows using Run command: putty -ssh -P 22 192.168.171.130,,, but it is returning an error message, not able to connect. But few days back I was able to connect it today. But not now. Why?? Windows IP Configuration Host Name . . . . . . . . . . . . : rba7791fd466 Primary Dns Suffix . . . . . . . : Node Type . . . . . . . . . . . . : Unknown IP Routing Enabled. . . . . . . . : No WINS Proxy Enabled. . . . . . . . : No Ethernet adapter VMware Network Adapter VMnet1: Connection-specific DNS Suffix . : Description . . . . . . . . . . . : VMware Virtual Ethernet Adapter for VMnet1 Physical Address. . . . . . . . . : 00-50-56-C0-00-01 Dhcp Enabled. . . . . . . . . . . : No IP Address. . . . . . . . . . . . : 192.168.234.1 Subnet Mask . . . . . . . . . . . : 255.255.255.0 Default Gateway . . . . . . . . . : Ethernet adapter Wireless Network Connection: Connection-specific DNS Suffix . : Description . . . . . . . . . . . : Dell Wireless 1395 WLAN Mini-Card Physical Address. . . . . . . . . : 00-24-2B-60-A0-88 Dhcp Enabled. . . . . . . . . . . : Yes Autoconfiguration Enabled . . . . : Yes IP Address. . . . . . . . . . . . : 10.0.0.2 Subnet Mask . . . . . . . . . . . : 255.255.255.0 Default Gateway . . . . . . . . . : 10.0.0.1 DHCP Server . . . . . . . . . . . : 10.0.0.1 DNS Servers . . . . . . . . . . . : 10.0.0.1 Lease Obtained. . . . . . . . . . : Friday, August 28, 2009 4:11:09 AM Lease Expires . . . . . . . . . . : Saturday, August 29, 2009 4:11:09 AM Ubuntu Configuration eth0 inet addr:192.168.171.130

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• Centos or Debian as a server OS ?

  - by Andrei Savu

  What would you choose for a server used for web hosting, dns and email and why?

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