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• Memcache on ubuntu server lucid and ruby 1.9.1

  - by Thiago

  I'm trying to set up a memcache server on the above setup. I'm getting the following error: /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support/dependencies.rb:443:in `load_missing_constant': uninitialized constant MemCache (NameError) from /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support/dependencies.rb:80:in `const_missing_with_dependencies' from /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support/dependencies.rb:92:in `const_missing' from /root/voicegateway/vendor/plugins/workling/lib/workling/clients/memcache_queue_client.rb:18:in `<class:MemcacheQueueClient>' from /root/voicegateway/vendor/plugins/workling/lib/workling/clients/memcache_queue_client.rb:14:in `<module:Clients>' from /root/voicegateway/vendor/plugins/workling/lib/workling/clients/memcache_queue_client.rb:13:in `<module:Workling>' from /root/voicegateway/vendor/plugins/workling/lib/workling/clients/memcache_queue_client.rb:12:in `<top (required)>' from /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support/dependencies.rb:156:in `require' from /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support/dependencies.rb:156:in `block in require' from /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support/dependencies.rb:521:in `new_constants_in' from /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support/dependencies.rb:156:in `require' from /root/voicegateway/vendor/plugins/workling/lib/workling/remote/runners/client_runner.rb:2:in `<top (required)>' from /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support/dependencies.rb:156:in `require' from /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support/dependencies.rb:156:in `block in require' from /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support/dependencies.rb:521:in `new_constants_in' from /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support/dependencies.rb:156:in `require' from /root/voicegateway/vendor/plugins/workling/lib/workling/remote/runners/starling_runner.rb:1:in `<top (required)>' from /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support/dependencies.rb:156:in `require' from /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support/dependencies.rb:156:in `block in require' from /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support/dependencies.rb:521:in `new_constants_in' from /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support/dependencies.rb:156:in `require' from /root/voicegateway/vendor/plugins/workling/lib/workling/remote.rb:3:in `<top (required)>' from /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support/dependencies.rb:380:in `load' from /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support/dependencies.rb:380:in `block in load_file' from /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support/dependencies.rb:521:in `new_constants_in' from /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support/dependencies.rb:379:in `load_file' from /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support/dependencies.rb:259:in `require_or_load' from /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support/dependencies.rb:425:in `load_missing_constant' from /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support/dependencies.rb:80:in `const_missing_with_dependencies' from /root/voicegateway/config/environments/development.rb:20:in `block in load_environment' from /var/lib/gems/1.9.1/gems/rails-2.3.8/lib/initializer.rb:386:in `eval' from /var/lib/gems/1.9.1/gems/rails-2.3.8/lib/initializer.rb:386:in `block in load_environment' from /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support/core_ext/kernel/reporting.rb:11:in `silence_warnings' from /var/lib/gems/1.9.1/gems/rails-2.3.8/lib/initializer.rb:379:in `load_environment' from /var/lib/gems/1.9.1/gems/rails-2.3.8/lib/initializer.rb:137:in `process' from /var/lib/gems/1.9.1/gems/rails-2.3.8/lib/initializer.rb:113:in `run' from /root/voicegateway/config/environment.rb:9:in `<top (required)>' from /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support/dependencies.rb:156:in `require' from /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support/dependencies.rb:156:in `block in require' from /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support/dependencies.rb:521:in `new_constants_in' from /var/lib/gems/1.9.1/gems/activesupport-2.3.8/lib/active_support/dependencies.rb:156:in `require' from /var/lib/gems/1.9.1/gems/rails-2.3.8/lib/commands/server.rb:84:in `<top (required)>' from ./server:3:in `require' from ./server:3:in `<main>' But memcache-client 1.8.3 is on the gem list. What's the problem?

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• More Stuff less Fluff

  - by brendonpage

  Originally posted on: http://geekswithblogs.net/brendonpage/archive/2013/11/08/more-stuff-less-fluff.aspxYAGNI – "You Aren't Going To Need It". This is an acronym commonly used in software development to remind developers to only write what they need. This acronym exists because software developers have gotten into the habit of writing everything they need to solve a problem and then everything they think they're going to possibly need in the future. Since we can't predict the future this results in a large portion of the code that we write never being used. That extra code causes unnecessary complexity, which makes it harder to understand and harder to modify when we inevitably have to write something that we didn't think of. I've known about YAGNI for some time now but I never really got it. The words made sense and the idea was clear but the concept never sank in. I was one of those devs who'd happily write a ton of code in the anticipation of future needs. In my mind this was an essential part of writing high quality code. I didn't realise that in doing so I was actually writing low quality code. If you are anything like me you are probably thinking "Lies and propaganda! High quality code needs to be future proof." I agree! But what makes code future proof? If we could see into the future the answer would be simple, code that allows for or meets all future requirements. Since we can't see the future the best we can do is write code that can easily adapt to future requirements, this means writing flexible code. Flexible code is: Fast to understand. Fast to add to. Fast to modify. To be flexible code has to be simple, this means only making it as complex as it needs to be to meet those 3 criteria. That is high quality code. YAGNI! The art is in deciding where to place the seams (abstractions) that will give you flexibility without making decisions about future functionality. Robert C Martin explains it very nicely, he says a good architecture allows you to defer decisions because if you can defer a decision then you have the flexibility to change it. I've recently had a YAGNI experience which brought this all into perspective. I was working on a new project which had multiple clients that connect to a server hosted in the cloud. I was tasked with adding a feature to the desktop client that would allow users to capture items that would then be saved to the cloud. My immediate thought was "Hey we have multiple clients so I should build a web service for these items, that way we can access them from other clients", so I went to work and this is what I created.  I stood back and gazed upon what I'd created with a warm fuzzy feeling. It was beautiful! Then the time came for the team to use the design I'd created for another feature with a new entity. Let's just say that they didn't get the same warm fuzzy feeling that I did when they looked at the design. After much discussion they eventually got it through to me that I'd bloated the design based on an assumption of future functionality. After much more discussion we cut the design down to the following. This design gives us future flexibility with no extra work, it is as complex as it needs to be. It has been a couple of months since this incident and we still haven't needed to access either of the entities from other clients. Using the simpler design allowed us to do more stuff with less stuff!

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• [EF + ORACLE] Updating and Deleting Entities

  - by JTorrecilla

  Prologue In previous chapters we have seen how to insert data through EF, with and without sequences. In this one, we are going to see how to Update and delete Data from the DB. Updating data The update of the Entity Data (properties) is a very common and easy action. Before of change any of the properties of the Entity, we can check the EntityState property, and we can see that is EntityState.Unchanged.   For making an update it is needed to get the Entity which will be modified. In the following example, I use the GetEmployeeByNumber to get a valid Entity: 1: EMPLEADOS emp=GetEmployeeByNumber(2); 2: emp.Name="a"; 3: emp.Phone="2"; 4: emp.Mail="aa"; After modifying the desired properties of the Entity, we are going to check again Entitystate property, which now has the EntityState.Modified value. To persist the changes to the DB is necessary to invoke the SaveChanges function of our context. 1: context.SaveChanges(); After modifying the desired properties of the Entity, we are going to check again Entitystate property, which now has the EntityState.Modified value. To persist the changes to the DB is necessary to invoke the SaveChanges function of our context. If we check again the EntityState property we will see that the value will be EntityState.Unchanged.   Deleting Data Another easy action is to delete an Entity.   The first step to delete an Entity from the DB is to select the entity: 1: CLIENTS selectedClient = GetClientByNumber(15); 2: context.CLIENTES.DeleteObject(clienteSeleccionado); Before invoking the DeleteObject function, we will check EntityStet which value must be EntityState.Unchanged. After deleting the object, the state will be changed to EntitySate.Deleted. To commit the action we have to invoke the SaveChanges function. Aftar that, the EntityState property will be EntityState.Detached. Cascade Entity Framework lets cascade updates and deletes, although I never see cascade updates. What is a cascade delete? A cascade delete is an action that allows to delete all the related object to the object we desire to delete. This option could be established in the DB manager, or it could be in the EF model designer. For example: With a given relation (1-N) between clients and requests. The common situation must be to let delete those clients whose have no requests. If we select the relation between both entities, and press the second mouse button, we can see the properties panel of the relation. The props are: This grid shows the relations indicating the Master table(Clients) and the end point (Cabecera or Requests) The property “End 1 OnDelete” indicates the action to do when a Entity from the Master will be deleted. There are two options: - None: No action will be done, it is said, if a Entity has details entities it could not be deleted. - Cascade: It will delete all related entities to the master Entity. If we enable the cascade delete in a relation, and we invoke the DeleteObject function of the set, we could observe that all the related object indicates a Entitystate.Deleted state. Like an update, insert or common delete, until we commit the changes with SaveChanges function, the data would not be commited. Si habilitamos el borrado en cascada de una relación, e invocamos a la función DeleteObject del conjunto, podremos observar que todas las entidades de Detalle (de la relación indicada) presentan el valor EntityState.Deleted en la propiedad EntityState. Del mismo modo que en el borrado, inserción o actualización, hasta que no se invoque al método SaveChanges, los cambios no van a ser confirmados en la Base de Datos. Finally In this chapter we have seen how to update a Entity, how to delete an Entity and how to implement Cascade Deleting through EF. In next chapters we will see how to query the DB data.

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• Managing software projects - advice needed

  - by Callum

  I work for a large government department as part of an IT team that manages and develops websites as well as stand alone web applications. We’re running in to problems somewhere in the SDLC that don’t rear their ugly head until time and budget are starting to run out. We try to be “Agile” (software specifications are not as thorough as possible, clients have direct access to the developers any time they want) and we are also in a reasonably peculiar position in that we are not allowed to make profit from the services we provide. We only service the divisions within our government department, and can only charge for the time and effort we actually put in to a project. So if we deliver a project that we have over-quoted on, we will only invoice for the actual time spent. Our software specifications are not as thorough as they could be, but they always include at a minimum: Wireframe mockups for every form view A data dictionary of all field inputs Descriptions of any business rules that affect the system Descriptions of the outputs I’m new to software management, but I’ve overseen enough software projects now to know that as soon as users start observing demos of the system, they start making a huge amount of requests like “Can we add a few more fields to this report.. can we redesign the look of this interface.. can we send an email at this part of the workflow.. can we take this button off this view.. can we make this function redirect to a different screen.. can we change some text on this screen… can we create a special account where someone can log in and get access to X… this report takes too long to run can it be optimised.. can we remove this step in the workflow… there’s got to be a better image we can put here…” etc etc etc. Some changes are tiny and can be implemented reasonably quickly.. but there could be up to 50-100 or so of such requests during the course of the SDLC. Other change requests are what clients claim they “just assumed would be part of the system” even if not explicitly spelled out in the spec. We are having a lot of difficulty managing this process. With no experienced software project managers in our team, we need to come up with a better way to both internally identify whether work being requested is “out of spec”, and be able to communicate this to a client in such a manner that they can understand why what they are asking for is “extra” work. We need a way to track this work and be transparent with it. In the spirit of Agile development where we are not spec'ing software systems in to the ground and back again before development begins, and bearing in mind that clients have access to any developer any time they want it, I am looking for some tips and pointers from experienced software project managers on how to handle this sort of "scope creep" problem, in tracking it, being transparent with it, and communicating it to clients such that they understand it. Happy to clarify anything as needed. I really appreciate anyone who takes the time to offer some advice. Thanks.

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• SQL Server 2000 and SSL Encryption

  - by Angry_IT_Guru

  We are a datacenter that hsots a SQL Server 2000 environment which provides database services for a product we sell that is loaded as a rich-client applicatin at each of our many clients and their workstations. Currently today, the application uses straight ODBC connections from the client site to our datacenter. We need to begin encrypting the credentials -- since everything is clear-text today and the authentication is weakly encrypted -- and I'm trying to determine the best way to implement SSL on the server with minimizing the impact of the client. A few things, however: 1) We have our own Windows domain and all our servers are joined to our private domain. Our clietns no nothing of our domain. 2) Typically, our clients connect to our datacenter servers either by: a) Using TCP/IP address b) Using a DNS name that we publish via internet, zone transfers from our DNS servers to our customers, or the client can add static HOSTS entries. 3) From what I understand from enabling encryption is that I can go to the Network Utility and select the "encryption" option for the protocol that I wish to encrypt. Such as TCP/IP. 4) When the encryption option is selected, I have a choice of installing a third-party certificate or a self-signed. I have tested the self-signed, but do have potential issues. I'll explain in a bit. If I go with a third-party cert, such as Verisign, or Network solutions... what kind of certificate do I request? These aren't IIS certificates? When I go create a self-signed via Microsoft's certificate server, I have to select "Authentication certificate". What does this translate to in the third-party world? 5) If I create a self-signed certificate, I understand that the "issue to" name has to match the FQDN for the server that is running SQL. In my case, I have to use my private domain name. If I use this, what does this do for my clients when trying to connect to my SQL Server? Surely they cannot resolve my private DNS names on their network.... I've also verified that when the self-signed certificate is installed, it has to be in the local personal store for the user account that is running SQL Server. SQL Server will only start if the FQDN matches the "issue to" of the certificate and SQL is running under the account that has the certificate installed. If I use a self-signed certificate, does this mean I have to have every one of my clients install it to verify? 6) If I used a third-party certificate, which sounds like the best option, do all my clients have to have internet access when accessing my private servers of their private WAN connection to use to verify the certificate? What do I do about the FQDN? It sounds like they have to use my private domain name -- which is not published -- and can no longer use the one that I setup for them to use? 7) I plan on upgrading to SQL 2000 soon. Is setup of SSL any easier/better with SQL 2005 than SQL 2000? Any help or guiadance would be appreciated

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• amplified reflected attack on dns

  - by Mike Janson

  The term is new to me. So I have a few questions about it. I've heard it mostly happens with DNS servers? How do you protect against it? How do you know if your servers can be used as a victim? This is a configuration issue right? my named conf file include "/etc/rndc.key"; controls { inet 127.0.0.1 allow { localhost; } keys { "rndc-key"; }; }; options { /* make named use port 53 for the source of all queries, to allow * firewalls to block all ports except 53: */ // query-source port 53; /* We no longer enable this by default as the dns posion exploit has forced many providers to open up their firewalls a bit */ // Put files that named is allowed to write in the data/ directory: directory "/var/named"; // the default pid-file "/var/run/named/named.pid"; dump-file "data/cache_dump.db"; statistics-file "data/named_stats.txt"; /* memstatistics-file "data/named_mem_stats.txt"; */ allow-transfer {"none";}; }; logging { /* If you want to enable debugging, eg. using the 'rndc trace' command, * named will try to write the 'named.run' file in the $directory (/var/named"). * By default, SELinux policy does not allow named to modify the /var/named" directory, * so put the default debug log file in data/ : */ channel default_debug { file "data/named.run"; severity dynamic; }; }; view "localhost_resolver" { /* This view sets up named to be a localhost resolver ( caching only nameserver ). * If all you want is a caching-only nameserver, then you need only define this view: */ match-clients { 127.0.0.0/24; }; match-destinations { localhost; }; recursion yes; zone "." IN { type hint; file "/var/named/named.ca"; }; /* these are zones that contain definitions for all the localhost * names and addresses, as recommended in RFC1912 - these names should * ONLY be served to localhost clients: */ include "/var/named/named.rfc1912.zones"; }; view "internal" { /* This view will contain zones you want to serve only to "internal" clients that connect via your directly attached LAN interfaces - "localnets" . */ match-clients { localnets; }; match-destinations { localnets; }; recursion yes; zone "." IN { type hint; file "/var/named/named.ca"; }; // include "/var/named/named.rfc1912.zones"; // you should not serve your rfc1912 names to non-localhost clients. // These are your "authoritative" internal zones, and would probably // also be included in the "localhost_resolver" view above :

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• XML deserialization doubling up on entities

  - by Nathan Loding

  I have an XML file that I am attempting to deserialize into it's respective objects. It works great on most of these objects, except for one item that is being doubled up on. Here's the relevant portion of the XML: <Clients> <Client Name="My Company" SiteID="1" GUID="xxx-xxx-xxx-xxx"> <Reports> <Report Name="First Report" Path="/Custom/FirstReport"> <Generate>true</Generate> </Report> </Reports> </Client> </Clients> "Clients" is a List<Client> object. Each Client object has a List<Report> object within it. The issue is that when this XML is deserialized, the List<Report> object has a count of 2 -- the "First Report" Report object is in there twice. Why? Here's the C#: public class Client { [System.Xml.Serialization.XmlArray("Reports"), System.Xml.Serialization.XmlArrayItem(typeof(Report))] public List<Report> Reports; } public class Report { [System.Xml.Serialization.XmlAttribute("Name")] public string Name; public bool Generate; [System.Xml.Serialization.XmlAttribute("Path")] public string Path; } class Program { static void Main(string[] args) { List<Client> _clients = new List<Client>(); string xmlFile = "myxmlfile.xml"; System.Xml.Serialization.XmlSerializer xmlSerializer = new System.Xml.Serialization.XmlSerializer(typeof(List<Client>), new System.Xml.Serialization.XmlRootAttribute("Clients")); using (FileStream stream = new FileStream(xmlFile, FileMode.Open)) { _clients = xmlSerializer.Deserialize(stream) as List<Client>; } foreach(Client _client in _clients) { Console.WriteLine("Count: " + _client.Reports.Count); // This write "2" foreach(Report _report in _client.Reports) { Console.WriteLine("Name: " + _report.Name); // Writes "First Report" twice } } } }

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• BN_hex2bn magicaly segfaults in openSSL

  - by xunil154

  Greetings, this is my first post on stackoverflow, and i'm sorry if its a bit long. I'm trying to build a handshake protocol for my own project and am having issues with the server converting the clients RSA's public key to a Bignum. It works in my clent code, but the server segfaults when attempting to convert the hex value of the clients public RSA to a bignum. I have already checked that there is no garbidge before or after the RSA data, and have looked online, but i'm stuck. header segment: typedef struct KEYS { RSA *serv; char* serv_pub; int pub_size; RSA *clnt; } KEYS; KEYS keys; Initializing function: // Generates and validates the servers key /* code for generating server RSA left out, it's working */ //Set client exponent keys.clnt = 0; keys.clnt = RSA_new(); BN_dec2bn(&keys.clnt->e, RSA_E_S); // RSA_E_S contains the public exponent Problem code (in Network::server_handshake): // *Recieved an encrypted message from the network and decrypt into 'buffer' (1024 byte long)* cout << "Assigning clients RSA" << endl; // I have verified that 'buffer' contains the proper key if (BN_hex2bn(&keys.clnt->n, buffer) < 0) { Error("ERROR reading server RSA"); } cout << "clients RSA has been assigned" << endl; The program segfaults at BN_hex2bn(&keys.clnt->n, buffer) with the error (valgrind output) Invalid read of size 8 at 0x50DBF9F: BN_hex2bn (in /usr/lib/libcrypto.so.0.9.8) by 0x40F23E: Network::server_handshake() (Network.cpp:177) by 0x40EF42: Network::startNet() (Network.cpp:126) by 0x403C38: main (server.cpp:51) Address 0x20 is not stack'd, malloc'd or (recently) free'd Process terminating with default action of signal 11 (SIGSEGV) Access not within mapped region at address 0x20 at 0x50DBF9F: BN_hex2bn (in /usr/lib/libcrypto.so.0.9.8) And I don't know why it is, Im using the exact same code in the client program, and it works just fine. Any input is greatly appriciated!

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• Which key:value store to use with Python?

  - by Kurt

  So I'm looking at various key:value (where value is either strictly a single value or possibly an object) stores for use with Python, and have found a few promising ones. I have no specific requirement as of yet because I am in the evaluation phase. I'm looking for what's good, what's bad, what are the corner cases these things handle well or don't, etc. I'm sure some of you have already tried them out so I'd love to hear your findings/problems/etc. on the various key:value stores with Python. I'm looking primarily at: memcached - http://www.danga.com/memcached/ python clients: http://pypi.python.org/pypi/python-memcached/1.40 http://www.tummy.com/Community/software/python-memcached/ CouchDB - http://couchdb.apache.org/ python clients: http://code.google.com/p/couchdb-python/ Tokyo Tyrant - http://1978th.net/tokyotyrant/ python clients: http://code.google.com/p/pytyrant/ Lightcloud - http://opensource.plurk.com/LightCloud/ Based on Tokyo Tyrant, written in Python Redis - http://code.google.com/p/redis/ python clients: http://pypi.python.org/pypi/txredis/0.1.1 MemcacheDB - http://memcachedb.org/ So I started benchmarking (simply inserting keys and reading them) using a simple count to generate numeric keys and a value of "A short string of text": memcached: CentOS 5.3/python-2.4.3-24.el5_3.6, libevent 1.4.12-stable, memcached 1.4.2 with default settings, 1 gig memory, 14,000 inserts per second, 16,000 seconds to read. No real optimization, nice. memcachedb claims on the order of 17,000 to 23,000 inserts per second, 44,000 to 64,000 reads per second. I'm also wondering how the others stack up speed wise.

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• How can I log and retrieve error messages from a client-side desktop app?

  - by KeyboardMonkey

  Update: The service-based answers below are most likely the way to go, I am also curious to see if there are any out-the-box solutions anyone has tried in the field. Our system uses a client-server architecture, and with more clients using it I'm thinking of better ways to log client application errors, and get them sent to us. Currently we just show a simple error message, with a button that preps an email (with the default system email client) and the clients send this on to our support address. This contains extra info like the stack trace. We also tried saving errors to a network share in the company, but I'm not too keen on that archaic solution either. Now there are only two businesses that refer to clients as users, and I'm sure some of ours support both lifestyles, as they just ignore the email button, and sends a full screen-shot wrapped nicely in a word document. Some factors I'm thinking of include A solution to log errors, like the contrived one above, A robust solution; Logging to a SQL database won't work; if that fails too, then what? Is at least semi-automated, preferably to the point where the logs reach my side. It copes with load, our client base is growing and the current solution, and our inboxes, won't hold up. Minimise installing extra 3rd party components on clients, I want to keep the SPOF to a min. I'd love to hear about any experience or suggestions you have on how I can implement such a solution. System Details It's a Microsoft .Net 2 based system with a SQL backend. Some users work remotely over the net, so network shares aren't always available (unless they VPN, which is awesomely slow at any rate). We have users across different companies, their DB's are hosted on-site. We have remote access to 90% of them.

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• Unit Testing a Java Chat Application

  - by Epitaph

  I have developed a basic Chat application in Java. It consists of a server and multiple client. The server continually monitors for incoming messages and broadcasts them to all the clients. The client is made up of a Swing GUI with a text area (for messages sent by the server and other clients), a text field (to send Text messages) and a button (SEND). The client also continually monitors for incoming messages from other clients (via the Server). This is achieved with Threads and Event Listeners and the application works as expected. But, how do I go about unit testing my chat application? As the methods involve establishing a connection with the server and sending/receiving messages from the server, I am not sure if these methods should be unit tested. As per my understanding, Unit Testing shouldn't be done for tasks like connecting to a database or network. The few test cases that I could come up with are: 1) The max limit of the text field 2) Client can connect to the Server 3) Server can connect to the Client 4) Client can send message 5) Client can receive message 6) Server can send message 7) Server can receive message 8) Server can accept connections from multiple clients But, since most of the above methods involve some kind of network communication, I cannot perform unit testing. How should I go about unit testing my chat application?

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• BN_hex2bn magically segfaults in openSSL

  - by xunil154

  Greetings, this is my first post on stackoverflow, and i'm sorry if its a bit long. I'm trying to build a handshake protocol for my own project and am having issues with the server converting the clients RSA's public key to a Bignum. It works in my clent code, but the server segfaults when attempting to convert the hex value of the clients public RSA to a bignum. I have already checked that there is no garbidge before or after the RSA data, and have looked online, but i'm stuck. header segment: typedef struct KEYS { RSA *serv; char* serv_pub; int pub_size; RSA *clnt; } KEYS; KEYS keys; Initializing function: // Generates and validates the servers key /* code for generating server RSA left out, it's working */ //Set client exponent keys.clnt = 0; keys.clnt = RSA_new(); BN_dec2bn(&keys.clnt->e, RSA_E_S); // RSA_E_S contains the public exponent Problem code (in Network::server_handshake): // *Recieved an encrypted message from the network and decrypt into 'buffer' (1024 byte long)* cout << "Assigning clients RSA" << endl; // I have verified that 'buffer' contains the proper key if (BN_hex2bn(&keys.clnt->n, buffer) < 0) { Error("ERROR reading server RSA"); } cout << "clients RSA has been assigned" << endl; The program segfaults at BN_hex2bn(&keys.clnt->n, buffer) with the error (valgrind output) Invalid read of size 8 at 0x50DBF9F: BN_hex2bn (in /usr/lib/libcrypto.so.0.9.8) by 0x40F23E: Network::server_handshake() (Network.cpp:177) by 0x40EF42: Network::startNet() (Network.cpp:126) by 0x403C38: main (server.cpp:51) Address 0x20 is not stack'd, malloc'd or (recently) free'd Process terminating with default action of signal 11 (SIGSEGV) Access not within mapped region at address 0x20 at 0x50DBF9F: BN_hex2bn (in /usr/lib/libcrypto.so.0.9.8) And I don't know why it is, Im using the exact same code in the client program, and it works just fine. Any input is greatly appriciated!

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• JQuery UI drag and drop doesn't notice DOM changes happening during the dragging ?

  - by user315677

  Hi everybody, I have a html table in which each line (<tr>) represents a group of client computers. Each line can be expanded to show the clients belonging to the group. The <tr> containing the clients are always generated but hidden and showed when clicking the plus button at the beginning of each line. The clients themselves (they are <div>) can be dragged and dropped in another group as long as this group is already expanded. So far it works fine. What I am trying to achieve now is that the client can be dragged to a collapsed group and after a second or so hovering the group it will be expanded and the client can be dropped amongst the other clients of the group. I programmed the hover using the in and outevents of the droppable and it expands the group all right, but (and now it starts to be hard to explain with words ;) the behavior of the droppable (the client) is still as if the table line that appeared were not there : the in out and drop events of the droppable are fired on the old position of the elements, and the in out and drop events of the newly appeared <tr> are never fired. It looks as if JQuery memorizes the position, size etc. of the elements when the drag starts, and these values are not updated if there is a change in the DOM before the drop happens... Can someone confirm this behavior is normal, or can it be caused by another problem in my own code ? Any workaround ? (the question is quite bloated already so I don't include any code but I'll gladly upload it if required)

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• Do I need to implement an XMPP server?

  - by WTFITS

  (newbie alert) I need to program a multiparty communication service for a course project, and I am considering XMPP for it. The service needs following messaging semantics: 1) server will provide a method of registering and unregistering an address such as [email protected]/SomeResource. (for now I will do it manually). 2) server will provide a method of forwarding incoming messages from, say, [email protected]/SomeResource to [email protected]/someOtherResource, assuming that the latter is registered, and a method for removing this forwarding. (for now I will do it manually). 3) anonymous clients can send messages to, say, [email protected]/someresource (one way traffic only). If there is any forwarding setup, the message will be forwarded. Finally if the address is [email protected]/someresource is registered, the message will be stored for later delivery (or immediate if a retrieving client is online - see below). If no forwarding and unregistered, message will be silently dropped. 4) clients can connect and retrieve messages from a registered address. Exact method of authenticating clients (e.g., passwords?) is yet to be determined. Eventually, I want to add support for clients to connect from a web browser so they can register/unregister and set/remove forwarding themselves. Thus, the server will have to do some non-standard switching. Will I need to implement an XMPP server for this? I guess some (or all?) of this can also be done using a XMPP client bot

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• Are bad data issues that common?

  - by Water Cooler v2

  I've worked for clients that had a large number of distinct, small to mid-sized projects, each interacting with each other via properly defined interfaces to share data, but not reading and writing to the same database. Each had their own separate database, their own cache, their own file servers/system that they had dedicated access to, and so they never caused any problems. One of these clients is a mobile content vendor, so they're lucky in a way that they do not have to face the same problems that everyday business applications do. They can create all those separate compartments where their components happily live in isolation of the others. However, for many business applications, this is not possible. I've worked with a few clients, one of whose applications I am doing the production support for, where there are "bad data issues" on an hourly basis. Yeah, it's that crazy. Some data records from one of the instances (lower than production, of course) would have been run a couple of weeks ago, and caused some other user's data to get corrupted. And then, a data script will have to be written to fix this issue. And I've seen this happening so much with this client that I have to ask. I've seen this happening at a moderate rate with other clients, but this one just seems to be out of order. If you're working with business applications that share a large amount of data by reading and writing to/from the same database, are "bad data issues" that common in your environment?

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• Sequential access to asynchronous sockets

  - by Lars A. Brekken

  I have a server that has several clients C1...Cn to each of which there is a TCP connection established. There are less than 10,000 clients. The message protocol is request/response based, where the server sends a request to a client and then the client sends a response. The server has several threads, T1...Tm, and each of these may send requests to any of the clients. I want to make sure that only one of these threads can send a request to a specific client at any one time, while the other threads wanting to send a request to the same client will have to wait. I do not want to block threads from sending requests to different clients at the same time. E.g. If T1 is sending a request to C3, another thread T2 should not be able to send anything to C3 until T1 has received its response. I was thinking of using a simple lock statement on the socket: lock (c3Socket) { // Send request to C3 // Get response from C3 } I am using asynchronous sockets, so I may have to use Monitor instead: Monitor.Enter(c3Socket); // Before calling .BeginReceive() And Monitor.Exit(c3Socket); // In .EndReceive I am worried about stuff going wrong and not letting go of the monitor and therefore blocking all access to a client. I'm thinking that my heartbeat thread could use Monitor.TryEnter() with a timeout and throw out sockets that it cannot get the monitor for. Would it make sense for me to make the Begin and End calls synchronous in order to be able to use the lock() statement? I know that I would be sacrificing concurrency for simplicity in this case, but it may be worth it. Am I overlooking anything here? Any input appreciated.

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• Appending an existing XML file with c#

  - by Farstucker

  I have an existing XML file that I would like to append without changing the format. Existing File looks like this: <Clients> <User username="farstucker"> <UserID>1</UserID> <DOB /> <FirstName>Steve</FirstName> <LastName>Lawrence</LastName> <Location>NYC</Location> </User> </Clients> How can I add another user using this format? My existing code is: string fileLocation = "clients.xml"; XmlTextWriter writer; if (!File.Exists(fileLocation)) { writer = new XmlTextWriter(fileLocation, null); writer.WriteStartDocument(); // Write the Root Element writer.WriteStartElement("Clients"); // End Element and Close writer.WriteEndElement(); writer.Close(); } // Append new data here Ive thought about using XmlDocument Fragment to append the data but Im not certain if I can maintain the existing format ( and empty tags ) without messing up the file. Any advice you could give is much appreciated. EDIT Ive changed the code to read the original XML but the file keeps getting overwritten.

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• Beginner Question on traversing a EF4 model

  - by user564577

  I have a basic EF4 model with two entities. I'm using Self Tracking Entities Client has ClientAddresses relationship on clientkey = clientkey. (1 to many) How do i get a list/collection of client entities (STE) and their addresses (STE) but only ones where they live in a particular state or some such filter on the address??? This seems to filter and bring back clients but doesnt bring back addresses. var j = from client in context.Clients where client.ClientAddresses.All(c => c.ZIP == "80923") select client; I cant get this to create the Addresses because ClientAddresses is IEnumerable and it needs a TrackableCollection var query = from t1 in context.Clients join t2 in context.ClientAddresses on t1.ClientKey equals t2.ClientKey where t2.ZIP == "80923" select new Client { FirstName = t1.FirstName, LastName = t1.LastName, IsEnabled = t1.IsEnabled, ClientKey = t1.ClientKey, ChangeUser = t1.ChangeUser, ChangeDate = t1.ChangeDate, ClientAddresses = from a in t1.ClientAddresses select new ClientAddress { AddressKey = a.AddressKey, AddressLine1 = a.AddressLine1, AddressLine2 = a.AddressLine2, AddressTypeCode = a.AddressTypeCode, City = a.City, ClientKey = a.ClientKey, State = a.State, ZIP = a.ZIP } }; Any pointers would be appreciated. Thanks Edit: This seems to work.... var j = from client in context.Clients.Include("ClientAddresses") where client.ClientAddresses.Any(c => c.ZIP == "80923") select client;

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• Redirect requests only if the file is not found?

  - by ZenBlender

  I'm hoping there is a way to do this with mod_rewrite and Apache, but maybe there is another way to consider too. On my site, I have directories set up for re-skinned versions of the site for clients. If the web root is /home/blah/www, a client directory would be /home/blah/www/clients/abc. When you access the client directory via a web browser, I want it to use any requested files in the client directory if they exist. Otherwise, I want it to use the file in the web root. For example, let's say the client does not need their own index.html. Therefore, some code would determine that there is no index.html in /home/blah/www/clients/abc and will instead use the one in /home/blah/www. Keep in mind that I don't want to redirect the client to the web root at any time, I just want to use the web root's file with that name if the client directory has not specified its own copy. The web browser should still point to /clients/abc whether the file exists there or in the root. Likewise, if there is a request for news.html in the client directory and it DOES exist there, then just serve that file instead of the web root's news.html. The user's experience should be seamless. I need this to work for requests on any filename. If I need to, for example, add a new line to .htaccess for every file I might want to redirect, it rather defeats the purpose as there is too much maintenance needed, and a good chance for errors given the large number of files. In your examples, please indicate whether your code goes in the .htaccess file in the client directory, or the web root. Web root is preferred. Thanks for any suggestions! :)

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• How add logic to Views? Ruby on Rails

  - by Gotjosh

  Right now I'm building a project management app in rails, here is some background info: Right now i have 2 models, one is User and the other one is Client. Clients and Users have a one-to-one relationship (client - has_one and user - belongs_to which means that the foreign key it's in the users table) So what I'm trying to do it's once you add a client you can actually add credentials (add an user) to that client, in order to do so all the clients are being displayed with a link next to that client's name meaning that you can actually create credentials for that client. What i can't figure it out how to do is, that if you actually have credentials in the database (meaning that there's a record in the users table with your client id) then don't display that link. Here's what i thought that would work <% for client in @client%> <h5> <h4><%= client.id %></h4> <a href="/clients/<%= client.id %>"><%= client.name %></a> <% for user in @user %> <% if user.client_id = client.id %> <a href="/clients/<%= client.id %>/user/new">Credentials</a> <%end%> <% end %> </h5> <% end %> And here's the controller: def index @client = Client.find_all_by_admin(0) @user = User.find(:all) end but instead it just puts the link the amount of times per records in the user table. Any help?

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• How to explain to client that you can't give them some of the source

  - by Bo

  We have a number of AS/Flex components that we've built over time and improved upon. They've been turned into components so they can be reused in different projects and save us time. So you can think of them as part of an in-house framework of sorts. We're now realizing that it doesn't make sense to release the source code for these components to the various clients as part of the project, because technically this code isn't really owned by the clients. So my question When a client comes to you, how do you explain to them that you can't give them the full source code for those components. The client doesn't understand the difference, he just expects you to give them all the code for the site that he paid you to do. He doesn't understand that this code has taken you a lot longer to write than what he's paying for his site. But since he doesn't understand, he would get turned off and thinks you're ripping him off or something. How do you handle this situation? What do you tell clients upfront? Do you advertise it on your site from the very beginning? How do you handle their objections so they still hire you? As a side question, how often do you give AS and Flex source code to your clients? In the case when the code doesn't have any in-house components that you reuse in several projects, and in the case when it does have in-house components.

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• Sending Messages to SignalR Hubs from the Outside

  - by Ricardo Peres

  Introduction You are by now probably familiarized with SignalR, Microsoft’s API for real-time web functionality. This is, in my opinion, one of the greatest products Microsoft has released in recent time. Usually, people login to a site and enter some page which is connected to a SignalR hub. Then they can send and receive messages – not just text messages, mind you – to other users in the same hub. Also, the server can also take the initiative to send messages to all or a specified subset of users on its own, this is known as server push. The normal flow is pretty straightforward, Microsoft has done a great job with the API, it’s clean and quite simple to use. And for the latter – the server taking the initiative – it’s also quite simple, just involves a little more work. The Problem The API for sending messages can be achieved from inside a hub – an instance of the Hub class – which is something that we don’t have if we are the server and we want to send a message to some user or group of users: the Hub instance is only instantiated in response to a client message. The Solution It is possible to acquire a hub’s context from outside of an actual Hub instance, by calling GlobalHost.ConnectionManager.GetHubContext<T>(). This API allows us to: Broadcast messages to all connected clients (possibly excluding some); Send messages to a specific client; Send messages to a group of clients. So, we have groups and clients, each is identified by a string. Client strings are called connection ids and group names are free-form, given by us. The problem with client strings is, we do not know how these map to actual users. One way to achieve this mapping is by overriding the Hub’s OnConnected and OnDisconnected methods and managing the association there. Here’s an example: 1: public class MyHub : Hub 2: { 3: private static readonly IDictionary<String, ISet<String>> users = new ConcurrentDictionary<String, ISet<String>>(); 4:  5: public static IEnumerable<String> GetUserConnections(String username) 6: { 7: ISet<String> connections; 8:  9: users.TryGetValue(username, out connections); 10:  11: return (connections ?? Enumerable.Empty<String>()); 12: } 13:  14: private static void AddUser(String username, String connectionId) 15: { 16: ISet<String> connections; 17:  18: if (users.TryGetValue(username, out connections) == false) 19: { 20: connections = users[username] = new HashSet<String>(); 21: } 22:  23: connections.Add(connectionId); 24: } 25:  26: private static void RemoveUser(String username, String connectionId) 27: { 28: users[username].Remove(connectionId); 29: } 30:  31: public override Task OnConnected() 32: { 33: AddUser(this.Context.Request.User.Identity.Name, this.Context.ConnectionId); 34: return (base.OnConnected()); 35: } 36:  37: public override Task OnDisconnected() 38: { 39: RemoveUser(this.Context.Request.User.Identity.Name, this.Context.ConnectionId); 40: return (base.OnDisconnected()); 41: } 42: } As you can see, I am using a static field to store the mapping between a user and its possibly many connections – for example, multiple open browser tabs or even multiple browsers accessing the same page with the same login credentials. The user identity, as is normal in .NET, is obtained from the IPrincipal which in SignalR hubs case is stored in Context.Request.User. Of course, this property will only have a meaningful value if we enforce authentication. Another way to go is by creating a group for each user that connects: 1: public class MyHub : Hub 2: { 3: public override Task OnConnected() 4: { 5: this.Groups.Add(this.Context.ConnectionId, this.Context.Request.User.Identity.Name); 6: return (base.OnConnected()); 7: } 8:  9: public override Task OnDisconnected() 10: { 11: this.Groups.Remove(this.Context.ConnectionId, this.Context.Request.User.Identity.Name); 12: return (base.OnDisconnected()); 13: } 14: } In this case, we will have a one-to-one equivalence between users and groups. All connections belonging to the same user will fall in the same group. So, if we want to send messages to a user from outside an instance of the Hub class, we can do something like this, for the first option – user mappings stored in a static field: 1: public void SendUserMessage(String username, String message) 2: { 3: var context = GlobalHost.ConnectionManager.GetHubContext<MyHub>(); 4: 5: foreach (String connectionId in HelloHub.GetUserConnections(username)) 6: { 7: context.Clients.Client(connectionId).sendUserMessage(message); 8: } 9: } And for using groups, its even simpler: 1: public void SendUserMessage(String username, String message) 2: { 3: var context = GlobalHost.ConnectionManager.GetHubContext<MyHub>(); 4:  5: context.Clients.Group(username).sendUserMessage(message); 6: } Using groups has the advantage that the IHubContext interface returned from GetHubContext has direct support for groups, no need to send messages to individual connections. Of course, you can wrap both mapping options in a common API, perhaps exposed through IoC. One example of its interface might be: 1: public interface IUserToConnectionMappingService 2: { 3: //associate and dissociate connections to users 4:  5: void AddUserConnection(String username, String connectionId); 6:  7: void RemoveUserConnection(String username, String connectionId); 8: } SignalR has built-in dependency resolution, by means of the static GlobalHost.DependencyResolver property: 1: //for using groups (in the Global class) 2: GlobalHost.DependencyResolver.Register(typeof(IUserToConnectionMappingService), () => new GroupsMappingService()); 3:  4: //for using a static field (in the Global class) 5: GlobalHost.DependencyResolver.Register(typeof(IUserToConnectionMappingService), () => new StaticMappingService()); 6:  7: //retrieving the current service (in the Hub class) 8: var mapping = GlobalHost.DependencyResolver.Resolve<IUserToConnectionMappingService>(); Now all you have to do is implement GroupsMappingService and StaticMappingService with the code I shown here and change SendUserMessage method to rely in the dependency resolver for the actual implementation. Stay tuned for more SignalR posts!

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• C#/.NET Little Wonders: The Timeout static class

  - by James Michael Hare

  Once again, in this series of posts I look at the parts of the .NET Framework that may seem trivial, but can help improve your code by making it easier to write and maintain. The index of all my past little wonders posts can be found here. When I started the “Little Wonders” series, I really wanted to pay homage to parts of the .NET Framework that are often small but can help in big ways.  The item I have to discuss today really is a very small item in the .NET BCL, but once again I feel it can help make the intention of code much clearer and thus is worthy of note. The Problem - Magic numbers aren’t very readable or maintainable In my first Little Wonders Post (Five Little Wonders That Make Code Better) I mention the TimeSpan factory methods which, I feel, really help the readability of constructed TimeSpan instances. Just to quickly recap that discussion, ask yourself what the TimeSpan specified in each case below is 1: // Five minutes? Five Seconds? 2: var fiveWhat1 = new TimeSpan(0, 0, 5); 3: var fiveWhat2 = new TimeSpan(0, 0, 5, 0); 4: var fiveWhat3 = new TimeSpan(0, 0, 5, 0, 0); You’d think they’d all be the same unit of time, right?  After all, most overloads tend to tack additional arguments on the end.  But this is not the case with TimeSpan, where the constructor forms are:     TimeSpan(int hours, int minutes, int seconds);     TimeSpan(int days, int hours, int minutes, int seconds);     TimeSpan(int days, int hours, int minutes, int seconds, int milliseconds); Notice how in the 4 and 5 parameter version we suddenly have the parameter days slipping in front of hours?  This can make reading constructors like those above much harder.  Fortunately, there are TimeSpan factory methods to help make your intention crystal clear: 1: // Ah! Much clearer! 2: var fiveSeconds = TimeSpan.FromSeconds(5); These are great because they remove all ambiguity from the reader!  So in short, magic numbers in constructors and methods can be ambiguous, and anything we can do to clean up the intention of the developer will make the code much easier to read and maintain. Timeout – Readable identifiers for infinite timeout values In a similar way to TimeSpan, let’s consider specifying timeouts for some of .NET’s (or our own) many methods that allow you to specify timeout periods. For example, in the TPL Task class, there is a family of Wait() methods that can take TimeSpan or int for timeouts.  Typically, if you want to specify an infinite timeout, you’d just call the version that doesn’t take a timeout parameter at all: 1: myTask.Wait(); // infinite wait But there are versions that take the int or TimeSpan for timeout as well: 1: // Wait for 100 ms 2: myTask.Wait(100); 3:  4: // Wait for 5 seconds 5: myTask.Wait(TimeSpan.FromSeconds(5); Now, if we want to specify an infinite timeout to wait on the Task, we could pass –1 (or a TimeSpan set to –1 ms), which what the .NET BCL methods with timeouts use to represent an infinite timeout: 1: // Also infinite timeouts, but harder to read/maintain 2: myTask.Wait(-1); 3: myTask.Wait(TimeSpan.FromMilliseconds(-1)); However, these are not as readable or maintainable.  If you were writing this code, you might make the mistake of thinking 0 or int.MaxValue was an infinite timeout, and you’d be incorrect.  Also, reading the code above it isn’t as clear that –1 is infinite unless you happen to know that is the specified behavior. To make the code like this easier to read and maintain, there is a static class called Timeout in the System.Threading namespace which contains definition for infinite timeouts specified as both int and TimeSpan forms: Timeout.Infinite An integer constant with a value of –1 Timeout.InfiniteTimeSpan A static readonly TimeSpan which represents –1 ms (only available in .NET 4.5+) This makes our calls to Task.Wait() (or any other calls with timeouts) much more clear: 1: // intention to wait indefinitely is quite clear now 2: myTask.Wait(Timeout.Infinite); 3: myTask.Wait(Timeout.InfiniteTimeSpan); But wait, you may say, why would we care at all?  Why not use the version of Wait() that takes no arguments?  Good question!  When you’re directly calling the method with an infinite timeout that’s what you’d most likely do, but what if you are just passing along a timeout specified by a caller from higher up?  Or perhaps storing a timeout value from a configuration file, and want to default it to infinite? For example, perhaps you are designing a communications module and want to be able to shutdown gracefully, but if you can’t gracefully finish in a specified amount of time you want to force the connection closed.  You could create a Shutdown() method in your class, and take a TimeSpan or an int for the amount of time to wait for a clean shutdown – perhaps waiting for client to acknowledge – before terminating the connection.  So, assume we had a pub/sub system with a class to broadcast messages: 1: // Some class to broadcast messages to connected clients 2: public class Broadcaster 3: { 4: // ... 5:  6: // Shutdown connection to clients, wait for ack back from clients 7: // until all acks received or timeout, whichever happens first 8: public void Shutdown(int timeout) 9: { 10: // Kick off a task here to send shutdown request to clients and wait 11: // for the task to finish below for the specified time... 12:  13: if (!shutdownTask.Wait(timeout)) 14: { 15: // If Wait() returns false, we timed out and task 16: // did not join in time. 17: } 18: } 19: } We could even add an overload to allow us to use TimeSpan instead of int, to give our callers the flexibility to specify timeouts either way: 1: // overload to allow them to specify Timeout in TimeSpan, would 2: // just call the int version passing in the TotalMilliseconds... 3: public void Shutdown(TimeSpan timeout) 4: { 5: Shutdown(timeout.TotalMilliseconds); 6: } Notice in case of this class, we don’t assume the caller wants infinite timeouts, we choose to rely on them to tell us how long to wait.  So now, if they choose an infinite timeout, they could use the –1, which is more cryptic, or use Timeout class to make the intention clear: 1: // shutdown the broadcaster, waiting until all clients ack back 2: // without timing out. 3: myBroadcaster.Shutdown(Timeout.Infinite); We could even add a default argument using the int parameter version so that specifying no arguments to Shutdown() assumes an infinite timeout: 1: // Modified original Shutdown() method to add a default of 2: // Timeout.Infinite, works because Timeout.Infinite is a compile 3: // time constant. 4: public void Shutdown(int timeout = Timeout.Infinite) 5: { 6: // same code as before 7: } Note that you can’t default the ShutDown(TimeSpan) overload with Timeout.InfiniteTimeSpan since it is not a compile-time constant.  The only acceptable default for a TimeSpan parameter would be default(TimeSpan) which is zero milliseconds, which specified no wait, not infinite wait. Summary While Timeout.Infinite and Timeout.InfiniteTimeSpan are not earth-shattering classes in terms of functionality, they do give you very handy and readable constant values that you can use in your programs to help increase readability and maintainability when specifying infinite timeouts for various timeouts in the BCL and your own applications. Technorati Tags: C#,CSharp,.NET,Little Wonders,Timeout,Task

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• Installing a DHCP Service On Win2k8 ( Windows Server 2008 )

  - by Akshay Deep Lamba

  Introduction Dynamic Host Configuration Protocol (DHCP) is a core infrastructure service on any network that provides IP addressing and DNS server information to PC clients and any other device. DHCP is used so that you do not have to statically assign IP addresses to every device on your network and manage the issues that static IP addressing can create. More and more, DHCP is being expanded to fit into new network services like the Windows Health Service and Network Access Protection (NAP). However, before you can use it for more advanced services, you need to first install it and configure the basics. Let’s learn how to do that. Installing Windows Server 2008 DHCP Server Installing Windows Server 2008 DCHP Server is easy. DHCP Server is now a “role” of Windows Server 2008 – not a windows component as it was in the past. To do this, you will need a Windows Server 2008 system already installed and configured with a static IP address. You will need to know your network’s IP address range, the range of IP addresses you will want to hand out to your PC clients, your DNS server IP addresses, and your default gateway. Additionally, you will want to have a plan for all subnets involved, what scopes you will want to define, and what exclusions you will want to create. To start the DHCP installation process, you can click Add Roles from the Initial Configuration Tasks window or from Server Manager à Roles à Add Roles. Figure 1: Adding a new Role in Windows Server 2008 When the Add Roles Wizard comes up, you can click Next on that screen. Next, select that you want to add the DHCP Server Role, and click Next. Figure 2: Selecting the DHCP Server Role If you do not have a static IP address assigned on your server, you will get a warning that you should not install DHCP with a dynamic IP address. At this point, you will begin being prompted for IP network information, scope information, and DNS information. If you only want to install DHCP server with no configured scopes or settings, you can just click Next through these questions and proceed with the installation. On the other hand, you can optionally configure your DHCP Server during this part of the installation. In my case, I chose to take this opportunity to configure some basic IP settings and configure my first DHCP Scope. I was shown my network connection binding and asked to verify it, like this: Figure 3: Network connection binding What the wizard is asking is, “what interface do you want to provide DHCP services on?” I took the default and clicked Next. Next, I entered my Parent Domain, Primary DNS Server, and Alternate DNS Server (as you see below) and clicked Next. Figure 4: Entering domain and DNS information I opted NOT to use WINS on my network and I clicked Next. Then, I was promoted to configure a DHCP scope for the new DHCP Server. I have opted to configure an IP address range of 192.168.1.50-100 to cover the 25+ PC Clients on my local network. To do this, I clicked Add to add a new scope. As you see below, I named the Scope WBC-Local, configured the starting and ending IP addresses of 192.168.1.50-192.168.1.100, subnet mask of 255.255.255.0, default gateway of 192.168.1.1, type of subnet (wired), and activated the scope. Figure 5: Adding a new DHCP Scope Back in the Add Scope screen, I clicked Next to add the new scope (once the DHCP Server is installed). I chose to Disable DHCPv6 stateless mode for this server and clicked Next. Then, I confirmed my DHCP Installation Selections (on the screen below) and clicked Install. Figure 6: Confirm Installation Selections After only a few seconds, the DHCP Server was installed and I saw the window, below: Figure 7: Windows Server 2008 DHCP Server Installation succeeded I clicked Close to close the installer window, then moved on to how to manage my new DHCP Server. How to Manage your new Windows Server 2008 DHCP Server Like the installation, managing Windows Server 2008 DHCP Server is also easy. Back in my Windows Server 2008 Server Manager, under Roles, I clicked on the new DHCP Server entry. Figure 8: DHCP Server management in Server Manager While I cannot manage the DHCP Server scopes and clients from here, what I can do is to manage what events, services, and resources are related to the DHCP Server installation. Thus, this is a good place to go to check the status of the DHCP Server and what events have happened around it. However, to really configure the DHCP Server and see what clients have obtained IP addresses, I need to go to the DHCP Server MMC. To do this, I went to Start à Administrative Tools à DHCP Server, like this: Figure 9: Starting the DHCP Server MMC When expanded out, the MMC offers a lot of features. Here is what it looks like: Figure 10: The Windows Server 2008 DHCP Server MMC The DHCP Server MMC offers IPv4 & IPv6 DHCP Server info including all scopes, pools, leases, reservations, scope options, and server options. If I go into the address pool and the scope options, I can see that the configuration we made when we installed the DHCP Server did, indeed, work. The scope IP address range is there, and so are the DNS Server & default gateway. Figure 11: DHCP Server Address Pool Figure 12: DHCP Server Scope Options So how do we know that this really works if we do not test it? The answer is that we do not. Now, let’s test to make sure it works. How do we test our Windows Server 2008 DHCP Server? To test this, I have a Windows Vista PC Client on the same network segment as the Windows Server 2008 DHCP server. To be safe, I have no other devices on this network segment. I did an IPCONFIG /RELEASE then an IPCONFIG /RENEW and verified that I received an IP address from the new DHCP server, as you can see below: Figure 13: Vista client received IP address from new DHCP Server Also, I went to my Windows 2008 Server and verified that the new Vista client was listed as a client on the DHCP server. This did indeed check out, as you can see below: Figure 14: Win 2008 DHCP Server has the Vista client listed under Address Leases With that, I knew that I had a working configuration and we are done!

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• Computer Networks UNISA - Chap 10 &ndash; In Depth TCP/IP Networking

  - by MarkPearl

  After reading this section you should be able to Understand methods of network design unique to TCP/IP networks, including subnetting, CIDR, and address translation Explain the differences between public and private TCP/IP networks Describe protocols used between mail clients and mail servers, including SMTP, POP3, and IMAP4 Employ multiple TCP/IP utilities for network discovery and troubleshooting Designing TCP/IP-Based Networks The following sections explain how network and host information in an IPv4 address can be manipulated to subdivide networks into smaller segments. Subnetting Subnetting separates a network into multiple logically defined segments, or subnets. Networks are commonly subnetted according to geographic locations, departmental boundaries, or technology types. A network administrator might separate traffic to accomplish the following… Enhance security Improve performance Simplify troubleshooting The challenges of Classful Addressing in IPv4 (No subnetting) The simplest type of IPv4 is known as classful addressing (which was the Class A, Class B & Class C network addresses). Classful addressing has the following limitations. Restriction in the number of usable IPv4 addresses (class C would be limited to 254 addresses) Difficult to separate traffic from various parts of a network Because of the above reasons, subnetting was introduced. IPv4 Subnet Masks Subnetting depends on the use of subnet masks to identify how a network is subdivided. A subnet mask indicates where network information is located in an IPv4 address. The 1 in a subnet mask indicates that corresponding bits in the IPv4 address contain network information (likewise 0 indicates the opposite) Each network class is associated with a default subnet mask… Class A = 255.0.0.0 Class B = 255.255.0.0 Class C = 255.255.255.0 An example of calculating  the network ID for a particular device with a subnet mask is shown below.. IP Address = 199.34.89.127 Subnet Mask = 255.255.255.0 Resultant Network ID = 199.34.89.0 IPv4 Subnetting Techniques Subnetting breaks the rules of classful IPv4 addressing. Read page 490 for a detailed explanation Calculating IPv4 Subnets Read page 491 – 494 for an explanation Important… Subnetting only applies to the devices internal to your network. Everything external looks at the class of the IP address instead of the subnet network ID. This way, traffic directed to your network externally still knows where to go, and once it has entered your internal network it can then be prioritized and segmented. CIDR (classless Interdomain Routing) CIDR is also known as classless routing or supernetting. In CIDR conventional network class distinctions do not exist, a subnet boundary can move to the left, therefore generating more usable IP addresses on your network. A subnet created by moving the subnet boundary to the left is known as a supernet. With CIDR also came new shorthand for denoting the position of subnet boundaries known as CIDR notation or slash notation. CIDR notation takes the form of the network ID followed by a forward slash (/) followed by the number of bits that are used for the extended network prefix. To take advantage of classless routing, your networks routers must be able to interpret IP addresses that don;t adhere to conventional network class parameters. Routers that rely on older routing protocols (i.e. RIP) are not capable of interpreting classless IP addresses. Internet Gateways Gateways are a combination of software and hardware that enable two different network segments to exchange data. A gateway facilitates communication between different networks or subnets. Because on device cannot send data directly to a device on another subnet, a gateway must intercede and hand off the information. Every device on a TCP/IP based network has a default gateway (a gateway that first interprets its outbound requests to other subnets, and then interprets its inbound requests from other subnets). The internet contains a vast number of routers and gateways. If each gateway had to track addressing information for every other gateway on the Internet, it would be overtaxed. Instead, each handles only a relatively small amount of addressing information, which it uses to forward data to another gateway that knows more about the data’s destination. The gateways that make up the internet backbone are called core gateways. Address Translation An organizations default gateway can also be used to “hide” the organizations internal IP addresses and keep them from being recognized on a public network. A public network is one that any user may access with little or no restrictions. On private networks, hiding IP addresses allows network managers more flexibility in assigning addresses. Clients behind a gateway may use any IP addressing scheme, regardless of whether it is recognized as legitimate by the Internet authorities but as soon as those devices need to go on the internet, they must have legitimate IP addresses to exchange data. When a clients transmission reaches the default gateway, the gateway opens the IP datagram and replaces the client’s private IP address with an Internet recognized IP address. This process is known as NAT (Network Address Translation). TCP/IP Mail Services All Internet mail services rely on the same principles of mail delivery, storage, and pickup, though they may use different types of software to accomplish these functions. Email servers and clients communicate through special TCP/IP application layer protocols. These protocols, all of which operate on a variety of operating systems are discussed below… SMTP (Simple Mail transfer Protocol) The protocol responsible for moving messages from one mail server to another over TCP/IP based networks. SMTP belongs to the application layer of the ODI model and relies on TCP as its transport protocol. Operates from port 25 on the SMTP server Simple sub-protocol, incapable of doing anything more than transporting mail or holding it in a queue MIME (Multipurpose Internet Mail Extensions) The standard message format specified by SMTP allows for lines that contain no more than 1000 ascii characters meaning if you relied solely on SMTP you would have very short messages and nothing like pictures included in an email. MIME us a standard for encoding and interpreting binary files, images, video, and non-ascii character sets within an email message. MIME identifies each element of a mail message according to content type. MIME does not replace SMTP but works in conjunction with it. Most modern email clients and servers support MIME POP (Post Office Protocol) POP is an application layer protocol used to retrieve messages from a mail server POP3 relies on TCP and operates over port 110 With POP3 mail is delivered and stored on a mail server until it is downloaded by a user Disadvantage of POP3 is that it typically does not allow users to save their messages on the server because of this IMAP is sometimes used IMAP (Internet Message Access Protocol) IMAP is a retrieval protocol that was developed as a more sophisticated alternative to POP3 The single biggest advantage IMAP4 has over POP3 is that users can store messages on the mail server, rather than having to continually download them Users can retrieve all or only a portion of any mail message Users can review their messages and delete them while the messages remain on the server Users can create sophisticated methods of organizing messages on the server Users can share a mailbox in a central location Disadvantages of IMAP are typically related to the fact that it requires more storage space on the server. Additional TCP/IP Utilities Nearly all TCP/IP utilities can be accessed from the command prompt on any type of server or client running TCP/IP. The syntaxt may differ depending on the OS of the client. Below is a list of additional TCP/IP utilities – research their use on your own! Ipconfig (Windows) & Ifconfig (Linux) Netstat Nbtstat Hostname, Host & Nslookup Dig (Linux) Whois (Linux) Traceroute (Tracert) Mtr (my traceroute) Route

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