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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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  • C# TCP Hole Punch (NAT Traversal) Library or something?

    - by user293531
    I want to do TCP Hole Punching (NAT Traversal) in C#. It can be done with a rendevouzs server if needed. I found http://sharpstunt.codeplex.com/ but can not get this to work. Ideally i need some method which i give a PortNumber (int) as parameter that after a call to this method is available ("Port Forwarded") at the NAT. It would be also ok if the methode just returns some port number which is then available at the NAT. Has anybody done this in C# ? Can you give me working examples for sharpstunt or something else? Thank you

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  • When binding a client TCP socket to a specific local port with Winsock, SO_REUSEADDR does not have a

    - by Checkers
    I'm binding a client TCP socket to a specific local port. To handle the situation where the socket remains in TIME_WAIT state for some time, I use setsockopt() with SO_REUSEADDR on a socket. It works on Linux, but does not work on Windows, I get WSAEADDRINUSE on connect() call when the previous connection is still in TIME_WAIT. MSDN is not exactly clear what should happen with client sockets: [...] For server applications that need to bind multiple sockets to the same port number, consider using setsockopt (SO_REUSEADDR). Client applications usually need not call bind at all—connect chooses an unused port automatically. [...] How do I avoid this?

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  • What happens with TCP packets between two Socket.BeginReceive calls?

    - by Rodrigo
    I have a doubt about socket programming. I am developing a TCP packet sniffer. I am using Socket.BeginAccept, Socket.BeginReceive to capture every packet, but when a packet is received I have to process something. It is a fast operation, but would take some milliseconds, and then call BeginReceive again. My question is, what would happen if some packets are sent while I am processing, and haven't called BeginReceive? Are packets lost, or are they buffered internally? Is there a limit?

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  • What alternative is there to writing a TCP/IP data relay?

    - by LoudNPossiblyRight
    I am about to write a tcp/ip data relay - application that passes a one way stream of data from one host/port to another host/port. Initially it will be generic, but later on i will customize it to the need of a specific business request. I am guessing that something generic already exists out there so my question is: Has anyone used a third party (preferably open source) data relay in a production environment, if so what is, and do you recommend it? Any platform is fine. Thanks.

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  • What structure of data use to communicate via tcp/ip in java?

    - by rmaster
    Let's assume I want to send many messages between 2 programs made in java that use TCP sockets. I think the most convienient way is to send objects like: PrintStream ps = new PrintStream(s.getOutputStream()); ObjectOutputStream oos = new ObjectOutputStream(ps); some_kind_of_object_here; oos.writeObject(some_kind_of_object_here); ps.print(oos); I want to send, strings, numbers, HashMaps, boolean values How can I do this using fx 1 object that can store all that properties? I though about ArrayList that is serializable and we can put there everything but is not elegant way. I want to send different types of data because user can choose from a variety of options that server can do for it. Any advices?

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  • Why is UDP + a software reliable ordering system faster than TCP?

    - by Ricket
    Some games today use a network system that transmits messages over UDP, and ensures that the messages are reliable and ordered. For example, RakNet is a popular game network engine. It uses only UDP for its connections, and has a whole system to ensure that packets can be reliable and ordered if you so choose. My basic question is, what's up with that? Isn't TCP the same thing as ordered, reliable UDP? What makes it so much slower that people have to basically reinvent the wheel?

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  • network will not work properly after having run TCP optimizer, but safe mode settings work perfectly. how to restore?

    - by michele
    I was experiencing some issues with my connection while playing online and I tried to optimize it by running TCP optimizer on my PC (Windows 7 64bit professional). I thought maybe the situation could improve. but it didn't. actually, I now get an extremely slow page loading time, probably due to a very low RWIN value of 1024. I understand that Windows 7 has a system to automatically adjust the RWIN value when needed. The setting from netsh is "normal" so I guess something else must be wrong. I tried every automatic tool out there to restore Windows' default values, but I had no success. I currently have what should be labeled as "default values" for everything TCP Optimizer initially changed, but the problem persists. The thing is, I just found out that running Windows in safe mode SOLVES the problem completely. The problem is that as soon as I reboot, I get the same issue all over again. So my question is: is there a way to use SAFE MODE network settings in NORMAL mode?

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  • If I can ping my DB server, is my SQL Server connection guaranteed to work?

    - by Matt
    If I can ping my DB server, is my SQL Server connection guaranteed to work? I am using a default connection string in my code. My program runs fine locally but overseas sites are having issues and I am wondering if SQL might be using a TCP or UDP port that is still blocked. Here is the connection string "Data Source=xxxx.xxxx.com; Initial Catalog = xxxxx; User ID=xxxxx;password=xxxxx"

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  • Can a stateless WCF service benefit from built-in database connection pooling?

    - by vladimir
    I understand that a typical .NET application that accesses a(n SQL Server) database doesn't have to do anything in particular in order to benefit from the connection pooling. Even if an application repeatedly opens and closes database connections, they do get pooled by the framework (assuming that things such as credentials do not change from call to call). My usage scenario seems to be a bit different. When my service gets instantiated, it opens a database connection once, does some work, closes the connection and returns the result. Then it gets torn down by the WCF, and the next incoming call creates a new instance of the service. In other words, my service gets instantiated per client call, as in [ServiceBehavior(InstanceContextMode = InstanceContextMode.PerCall)]. The service accesses an SQL Server 2008 database. I'm using .NET framework 3.5 SP1. Does the connection pooling still work in this scenario, or I need to roll my own connection pool in form of a singleton or by some other means (IInstanceContextProvider?). I would rather avoid reinventing the wheel, if possible.

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  • Java: Sharing a connection pool accross other J2SE Apps...?

    - by Zombies
    So I have a connection pool setup. Which is great and all since I have an application that really needs it. However what I would like to know is if it is possible to share this connection pool with other J2SE apps? Would this even be worth it, as opposed to creating a connection pool based on each apps needs? If it would be prudent, how can I accomplish this?

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  • VB6. DataEnvironment: How to Configure/Set Trusted Connection?

    - by Mblua
    Hi, I have a DataEnvironment component in my VB 6 application. I cant configure the DataEnvironment connection to use trusted connection without ask me how to connect. I could set prompt to never appear, but it doesnt connect becouse it doesnt use trusted. In this link you could see the screens of DataEnvironment Connection Options and the prompt. Google Presentation Link I need this program to be executed from a D.O.S console without prompt anything. Thanks a lot!

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  • Is there a generic way of dealing with varying connection strings in C#?

    - by James Wiseman
    I have an application that needs to connect to a SQL database, and execute a SQL Agent Job. The connection string I am trying to access is stored in the registry, which is easily enough pulled out. This appliction is to be run on multiple computers, and I cannot guarantee the format of this connection string being consistent across these computers. Two that I have pulled out for example are: Data Source=Server1;Initial Catalog=DB1;Integrated Security=SSPI; Data Source=Server2;Initial Catalog=DB1;Provider=SQLNCLI.1;Integrated Security=SSPI;Auto Translate=False; I can use an object of type System.Data.SqlClient.SqlConnection to connect to the database with the first connection string, howevever, I get the following error when I pass the second to it: keyword not supported: 'provider' Similarly, I can use the an object of type System.Data.OleDb.OleDbConnection to connect to the database with the second connection string, howevever, I get the following error when I pass the first to it: An OLEDB Provider was not specified in the ConnectionString' I can solve this by scanning the string for 'Provider' and doing the connect conditionally, however I can't help but feel that there is a better way of doing this, and handle the connection strings in a more generic fashion. Does anyone have any suggestions?

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  • access EF classes from a Class Library - exactly how do configure/test the connection string in the

    - by Greg
    Hi, I'm getting very confused about how to call my EF classes in a Class Library from the Client Project I have? Things worked fine when they were in the same project. Now I'm getting errors such as "Unable to load the specified metadata resource ". I've see various ideas / suggestions re how to fix the connection string (e.g. create an App.config in your client project & copy the connection string config from your class library, something about change the connection settings to copy to output, etc) QUESTION - Can someone provide a solid way on how to get EF class access from a separate project working? (i.e. how to get the correct connection information to the client somehow) thanks

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  • MySQL connection attempt works fine in 5.2.9 but not in 5.3.0 - Help?

    - by Rich
    Hi, I'm having trouble making a secondary MySQL connection (to a separate, external DB) in my code. It works fine in PHP 5.2.9 but fails to connect in PHP 5.3.0. I'm aware of (at least some) of the changes needed to make successful MySQL connections in the newer version of PHP, and have succeeded before, so I'm not sure why it isn't working this time. I already have a db connection open to a local database. This function below is then used to make an additional connection to a separate, remote directory. The included config file simply contains the external database details (host, user, pass and name). I have checked and it is being included correctly. function connectDP() { global $dpConnection; include("secondary_db_config.php); $dpConnection = mysql_connect($dp_dbHost, $dp_dbUser, $dp_dbPass, true) or DIE("ERROR: Unable to connect to Deployment Platform"); mysql_select_db($dp_dbName, $dpConnection) or DIE("ERROR 006: Unable to select Deployment Platform Database"); } I then attempt to make this new connection simply by calling this function externally: connectDP(); But when loading the page (in 5.3.0), I get the message: ERROR: Unable to connect to Deployment Platform I'm using the optional new_link flag boolean as the fourth argument in the mysql_connect() function and it's still not working. I've been wracking my brain this morning trying to figure out why this connection doesn't work (while I've done something very similar elsewhere to a separate second database that does work). Any help would be appreciated. Thanks! Rich

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  • On SQL Developer and TNSNAMES.ORA

    - by thatjeffsmith
    Tnsnames.ora [DOCS] is a configuration file for SQL*Net that describes the network service names for the databases in your organization. Basically, it tells Oracle applications how to find your databases. This post is just a quick overview on how to get SQL Developer to ‘see’ this file and define a connection. There’s only a single prerequisite for having SQL Devleoper setup such that it can use TNSNAMES to connect: You have somewhere a tnsnames.ora file You don’t need a client, instant or otherwise, on your machine. You just need the file. Now, if you DO you have a client or HOME on your machine, SQL Developer will look for those and find the tnsnames file for you. IF we can’t find it at the usual places, you can simply tell us where it is via this preference: On the Database – Advanced page Once you’ve done this, assuming you have a file (or 10) in that directory, we’ll read it, parse it, and list the entries in the connection dialog. The File(s) That’s right, files. Just like SQL*Plus, we’ll read any file that starts with ‘tnsnames’ – that includes files you’ve renamed to .bak or .old. Kris talks about that more here. I have just the one, which is all I need anyway. There we go! Defining the Connection Just set the connection type to TNS. This is a lot easier to do than manually defining the connections – esp as they’re likely to frequently change in ‘the real world.’ No Client or Home Required That’s right. You don’t need an Oracle Client or $ORACLE_HOME to have SQL Developer see and read a TNS file. Just so you know I’m not cheating… SQL Dev doesn’t know which client to use and won’t use it even if it DID know… I’m able to define a new connection AND connect with these preferences ON|OFF.

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  • Millions of SYN_RECV connections, no DDoS

    - by ThomK
    We have such server structure: reverse proxy (nginx) - worker (uwsgi) - postgresql / memcached. All servers are in local network behind router, with NATed external ip:ports (http/s 80/443 to proxy, and ssh 22 to all servers). Problem is, that sometimes proxy server netstat reports MILLIONS of SYN_RECV connections. From same IP / same ports. Like that: nginx ~ # netstat -n | grep 83.238.153.195 tcp 0 0 192.168.1.1:80 83.238.153.195:3107 SYN_RECV tcp 0 0 192.168.1.1:80 83.238.153.195:3107 SYN_RECV tcp 0 0 192.168.1.1:80 83.238.153.195:3107 SYN_RECV tcp 0 0 192.168.1.1:80 83.238.153.195:3107 SYN_RECV tcp 0 0 192.168.1.1:80 83.238.153.195:3107 SYN_RECV tcp 0 0 192.168.1.1:80 83.238.153.195:3107 SYN_RECV tcp 0 0 192.168.1.1:80 83.238.153.195:3107 SYN_RECV tcp 0 0 192.168.1.1:80 83.238.153.195:3107 SYN_RECV tcp 0 0 192.168.1.1:80 83.238.153.195:3107 SYN_RECV tcp 0 0 192.168.1.1:80 83.238.153.195:3107 SYN_RECV [...] And this is not DDoS, because all IPs affected belongs to our website users. On side note, users says that it's not affecting them. Website is online and working, but... that particular one (from example above) told me that website is down and Firefox can't connect. I've done tcpdump. 19:42:14.826011 IP 83.238.153.195.zephyr-srv > 192.168.1.1.http: Flags [S], seq 1845850583, win 65535, options [mss 1412,nop,wscale 0,nop,nop,sackOK], length 0 19:42:14.826042 IP 192.168.1.1.http > 83.238.153.195.zephyr-srv: Flags [S.], seq 2835837547, ack 1845850584, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:42:17.887331 IP 83.238.153.195.zephyr-srv > 192.168.1.1.http: Flags [S], seq 1845850583, win 65535, options [mss 1412,nop,wscale 0,nop,nop,sackOK], length 0 19:42:17.887343 IP 192.168.1.1.http > 83.238.153.195.zephyr-srv: Flags [S.], seq 2835837547, ack 1845850584, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:42:19.065497 IP 192.168.1.1.http > 83.238.153.195.zephyr-srv: Flags [S.], seq 2835837547, ack 1845850584, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:42:23.918064 IP 83.238.153.195.zephyr-srv > 192.168.1.1.http: Flags [S], seq 1845850583, win 65535, options [mss 1412,nop,wscale 0,nop,nop,sackOK], length 0 19:42:23.918076 IP 192.168.1.1.http > 83.238.153.195.zephyr-srv: Flags [S.], seq 2835837547, ack 1845850584, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:42:25.265499 IP 192.168.1.1.http > 83.238.153.195.zephyr-srv: Flags [S.], seq 2835837547, ack 1845850584, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:42:37.265501 IP 192.168.1.1.http > 83.238.153.195.zephyr-srv: Flags [S.], seq 2835837547, ack 1845850584, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:42:37.758051 IP 83.238.153.195.2107 > 192.168.1.1.http: Flags [S], seq 564208067, win 65535, options [mss 1412,nop,wscale 0,nop,nop,sackOK], length 0 19:42:37.758069 IP 192.168.1.1.http > 83.238.153.195.2107: Flags [S.], seq 3188568660, ack 564208068, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:42:40.714360 IP 83.238.153.195.2107 > 192.168.1.1.http: Flags [S], seq 564208067, win 65535, options [mss 1412,nop,wscale 0,nop,nop,sackOK], length 0 19:42:40.714374 IP 192.168.1.1.http > 83.238.153.195.2107: Flags [S.], seq 3188568660, ack 564208068, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:42:41.665503 IP 192.168.1.1.http > 83.238.153.195.2107: Flags [S.], seq 3188568660, ack 564208068, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:42:46.751073 IP 83.238.153.195.2107 > 192.168.1.1.http: Flags [S], seq 564208067, win 65535, options [mss 1412,nop,wscale 0,nop,nop,sackOK], length 0 19:42:46.751087 IP 192.168.1.1.http > 83.238.153.195.2107: Flags [S.], seq 3188568660, ack 564208068, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:42:47.665498 IP 192.168.1.1.http > 83.238.153.195.2107: Flags [S.], seq 3188568660, ack 564208068, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:42:59.865499 IP 192.168.1.1.http > 83.238.153.195.2107: Flags [S.], seq 3188568660, ack 564208068, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:01.265500 IP 192.168.1.1.http > 83.238.153.195.zephyr-srv: Flags [S.], seq 2835837547, ack 1845850584, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:13.320382 IP 83.238.153.195.2114 > 192.168.1.1.http: Flags [S], seq 2136055006, win 65535, options [mss 1412,nop,wscale 0,nop,nop,sackOK], length 0 19:43:13.320399 IP 192.168.1.1.http > 83.238.153.195.2114: Flags [S.], seq 3754336171, ack 2136055007, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:16.320556 IP 83.238.153.195.2114 > 192.168.1.1.http: Flags [S], seq 2136055006, win 65535, options [mss 1412,nop,wscale 0,nop,nop,sackOK], length 0 19:43:16.320569 IP 192.168.1.1.http > 83.238.153.195.2114: Flags [S.], seq 3754336171, ack 2136055007, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:17.665498 IP 192.168.1.1.http > 83.238.153.195.2114: Flags [S.], seq 3754336171, ack 2136055007, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:22.250069 IP 83.238.153.195.2114 > 192.168.1.1.http: Flags [S], seq 2136055006, win 65535, options [mss 1412,nop,wscale 0,nop,nop,sackOK], length 0 19:43:22.250080 IP 192.168.1.1.http > 83.238.153.195.2114: Flags [S.], seq 3754336171, ack 2136055007, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:23.665500 IP 192.168.1.1.http > 83.238.153.195.2114: Flags [S.], seq 3754336171, ack 2136055007, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:23.865501 IP 192.168.1.1.http > 83.238.153.195.2107: Flags [S.], seq 3188568660, ack 564208068, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:35.665498 IP 192.168.1.1.http > 83.238.153.195.2114: Flags [S.], seq 3754336171, ack 2136055007, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:37.903038 IP 83.238.153.195.2213 > 192.168.1.1.http: Flags [S], seq 2918118729, win 65535, options [mss 1412,nop,wscale 0,nop,nop,sackOK], length 0 19:43:37.903054 IP 192.168.1.1.http > 83.238.153.195.2213: Flags [S.], seq 4145523337, ack 2918118730, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:40.772899 IP 83.238.153.195.2213 > 192.168.1.1.http: Flags [S], seq 2918118729, win 65535, options [mss 1412,nop,wscale 0,nop,nop,sackOK], length 0 19:43:40.772912 IP 192.168.1.1.http > 83.238.153.195.2213: Flags [S.], seq 4145523337, ack 2918118730, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:41.865500 IP 192.168.1.1.http > 83.238.153.195.2213: Flags [S.], seq 4145523337, ack 2918118730, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:46.793057 IP 83.238.153.195.2213 > 192.168.1.1.http: Flags [S], seq 2918118729, win 65535, options [mss 1412,nop,wscale 0,nop,nop,sackOK], length 0 19:43:46.793069 IP 192.168.1.1.http > 83.238.153.195.2213: Flags [S.], seq 4145523337, ack 2918118730, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:47.865500 IP 192.168.1.1.http > 83.238.153.195.2213: Flags [S.], seq 4145523337, ack 2918118730, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:49.465503 IP 192.168.1.1.http > 83.238.153.195.zephyr-srv: Flags [S.], seq 2835837547, ack 1845850584, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 Anyone have some thoughts on that?

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  • Is there a way to determine which service does an outgoing connection?

    - by fluxtendu
    I'm redoing my firewall configuration with more restrictive policies and I would like to determine the provenance (and/or destination) of some outgoing connections. I have an issue because they come from svchost.exe and go to web content/application delivery providers - or similar: 5 IP in range: 82.96.58.0 - 82.96.58.255 --> Akamai Technologies akamaitechnologies.com 3 IP in range: 93.150.110.0 - 93.158.111.255 --> Akamai Technologies akamaitechnologies.com 2 IP in range: 87.248.194.0 - 87.248.223.255 --> LLNW Europe 2 llnw.net 205.234.175.175 --> CacheNetworks, Inc. cachefly.net 188.121.36.239 --> Go Daddy Netherlands B.V. secureserver.net So is it possible to know which service does a particular connection? Or what's your recommendation about the rules applied to these ones? (Comodo Firewall & Windows 7)

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  • Postgresql connection refused

    - by Jonathan
    I'm trying to remotely connect to my postgresql database. I have two virtual machines set up both running ubuntu 14.04. I am trying to connect to the second vm using the first vm using psql -h 10.0.1.23 -U postgres -d postgres But I receive the error: Could not connect to server: Connection refused Is the server running on host "10.0.1.23" and accepting TCP/IP connections on port 5432? I have changed the pg_hba.conf and added host all all 10.0.1.64/24 md5 host all all * md5 host all all 0.0.0.0/0 md5 And changed the postgresql.conf listen_address=" * " In an attempt to allow all incoming connections. I have also tried to change the firewall settings, but I am unsure of whether or not the ports are properly listening for the connection. Edit: Output of netstat -an | grep -E '^tcp[^6].*LISTEN' tcp 0 0 127.0.1.1:53 0.0.0.0:* LISTEN tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN tcp 0 0 127.0.0.1:631 0.0.0.0:* LISTEN tcp 0 0 0.0.0.0:23 0.0.0.0:* LISTEN tcp 0 0 127.0.0.1:5432 0.0.0.0:* LISTEN

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  • Why is a non-blocking TCP connect() occasionally so slow on Linux?

    - by pts
    I was trying to measure the speed of a TCP server I'm writing, and I've noticed that there might be a fundamental problem of measuring the speed of the connect() calls: if I connect in a non-blocking way, connect() operations become very slow after a few seconds. Here is the example code in Python: #! /usr/bin/python2.4 import errno import os import select import socket import sys def NonBlockingConnect(sock, addr): while True: try: return sock.connect(addr) except socket.error, e: if e.args[0] not in (errno.EINPROGRESS, errno.EALREADY): raise os.write(2, '^') if not select.select((), (sock,), (), 0.5)[1]: os.write(2, 'P') def InfiniteClient(addr): while True: sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM, 0) sock.setblocking(0) sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) # sock.connect(addr) NonBlockingConnect(sock, addr) sock.close() os.write(2, '.') def InfiniteServer(server_socket): while True: sock, addr = server_socket.accept() sock.close() server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM, 0) server_socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) server_socket.bind(('127.0.0.1', 45454)) server_socket.listen(128) if os.fork(): # Parent. InfiniteServer(server_socket) else: addr = server_socket.getsockname() server_socket.close() InfiniteClient(addr) With NonBlockingConnect, most connect() operations are fast, but in every few seconds there happens to be one connect() operation which takes at least 2 seconds (as indicated by 5 consecutive P letters on the output). By using sock.connect instead of NonBlockingConnect all connect operations seem to be fast. How is it possible to get rid of these slow connect()s? I'm running Ubuntu Karmic desktop with the standard PAE kernel: Linux narancs 2.6.31-20-generic-pae #57-Ubuntu SMP Mon Feb 8 10:23:59 UTC 2010 i686 GNU/Linux

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  • How to get Acknowlegement in TCP communication in Java

    - by Sunil Kumar Sahoo
    I have written a socket program in Java. Both server and client can sent/receive data to each other. But I found that if client sends data to server using TCP then internally TCP sends acknowledgement to the client once the data is received by the server. I want to detect or handle that acknowledgement. How can I read or write data in TCP so that I can handle TCP acknowledgement. Thanks Sunil Kumar Sahoo

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  • BlackBerry OS 7.1 secured TLS connection is closed after very short time

    - by MrVincenzo
    To make a long story short: Same client-server configuration, same network topology, same device (Bold 9900) - works perfectly well on OS 7.0 but doesn't work as expected on OS 7.1 and the secured tls connection is being closed by the server after a very short time. My application opens a secured tls connection to a server. The connection is kept alive by a application layer keep-alive mechanism and remains open until the client closes it. Attached is a simplified version of the actual code that opens connection and reads from the socket. The code works perfectly on OS 5.0-7.0 but doesn't work as expected on OS 7.1. When running on OS 7.1, the blocking read() returns with -1 (end of the stream has been reached) after very short time (10-45 seconds). For OS 5.0-7.0 the call to read() remains blocking until next data arrives and the connection is never closed by the server. Connection connection = Connector.open(connectionString); connInputStream = connection.openInputStream(); while (true) { try { retVal = connInputStream.read(); if (-1 == retVal) { break; // end of stream has been reached } } catch (Exception e ) { // do error handling } // data read from stream is handled here } UPDATE 1: Apparently, the problem appears only when I use secured tls connection (either using mobile network or WiFi) on OS 7.1. Everything works as expected when opening a non secured connection on OS 7.1. For tls on mobile networks I use the following connection string: connectionString = "tls://someipaddress:443;deviceside=false;ConnectionType=mds-public;EndToEndDesired"; For tls on Wifi I use the following connection string: connectionString = "tls://someipaddress:443;deviceside=true;interface=wifi;EndToEndRequired" UPDATE 2: The connection is never idle. I am constantly receiving and sending data on it. The issue appears both when using mobile connection and WiFi. The issue appears both on real OS 7.1 devices and simulators. I am starting to suspect that it is somehow related either to the connection string I am using or to the tls handshake. UPDATE 3: According to Wireshark's captures that I made with the OS 7.1 simulator, the secured tls connection is being closed by the server (client receives FIN). For the moment I don't have the server's private key therefore I unable to debug the tls handshake.

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