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• Is there a network "tee"-alike with one leg returning to /dev/null ?

  - by Steff Davies

  I've just built a new PostgreSQL server for my employers, which is happily replicating using WALs. I'm now left with the problem of verifying its performance. One nice way which came up in conversation is to break replication with the slave caught up and then direct all production traffic to both servers, discarding the responses from the new server and returning those from the current one to the clients. Once we're sure performance is OK, we re-sync the slave and can fail over with confidence. Bliss. This would require a TCP proxy capable of opening two outgoing connections for each incoming one, and discarding the data returned from one of them, which is a tricky thing to google for, it seems. Do the assembled brains know of such a thing, before I dive into libevent and write one?

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• Forwarding ports with ssh on Linux

  - by Patrick Klingemann

  I have a database server, let's call it: dbserver I have a web server with access to my dbserver, let's call it: webserver I have a development machine that I'd like to use to access a database on dbserver, let's call it: dev dbserver has a firewall rule set to allow TCP requests from webserver to dbserver:1433 I'd like to set up a tunnel from dev:1433 to dbserver:1433, so all requests to 1433 on dev are passed along to dbserver:1433 My sshd_config on webserver has the following rules set: AllowTcpForwarding yes GatewayPorts yes This is what I've tried: ssh -v -L localhost:1433:dbserver:1433 webserver In another terminal: telnet localhost 1433 Results in: Trying ::1... Connected to localhost. Escape character is '^]'. Connection closed by foreign host. Any idea what I'm doing wrong here? Thanks in advance!

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• Sharing internet connection from Windows XP using wi-fi router

  - by Darius

  Hi, I have an network configuration like: Ethernet cable from ISP connected to Windows XP machine, configured with static IP 192.168.0.3 Another ethernet connection from 2nd Windows XP machine's network adapter to a Wi-Fi router (D-Link Airport G+) XP set to "Share internet connection", the 2nd adapter configured as static to 192.169.0.1 D-Link Airport Wi-Fi router also configured as "static connection", it's IP set to 192.169.0.2, default gateway set to 192.169.0.1. Network mask everywhere is 24. Laptop computer connected with the router with static IP 192.169.0.3 The problems are: XP machine sees the router (it's able to ping it and access it via the web admin tool) The router somehow cannot PING the XP machine (using the tool provided by the web-based admin tool) The laptop computer cannot ping anything and cannot be pinged The router is only accessible when the ethernet cable is connected with a router's 1-4 LAN port, when I connect it via "WAN" port (which I believe is the proper one) it's not visible from the XP machine If you have similar experience with configuring a network like this I would really appreciate your help. I cannot use the Wi-Fi router with the ISP cable itself.

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• Does a bad Internet connection increase bandwidth usage?

  - by Synetech

  My (Rogers) cable connection has been pretty bad recently (channels 3 and 10 are particularly fuzzy—it’s analog, not digital cable). Not surprisingly, this has caused my cable modem to drop out and have to reestablish a connection a couple of times since it started. The poor connection of course means higher corruption (not necessarily dropped per se) which causes the TCP/IP stack to have to retransmit packets more often. Reduction of bandwidth throughput aside, I got to wondering if it increases the actual bandwidth usage. That is, if there is a high error rate on the line causing packets to have to be retransmitted: Does this increase a bandwidth monitoring program’s numbers? Does the ISP count the retransmitted packets toward the monthly cap? Based on what I remember from my university networking courses and common sense, I have a feeling that the answer to both questions is yes, but I cannot reliably measure the first, and have no authoritative answer for the second. I’m wondering if maybe the retransmitted packets are acknowledged as being duplicates and thus not counted somewhere along the line.

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• Should I limit end-user gigabit ports to avoid saturating uplink/trunk connections?

  - by Joel Coel

  We have a campus with 16 buildings and older 850nm 1Gbps fiber links between the buildings, that all come to a core switch for our servers that also uses 1Gbps ports. We're finally starting to replace our aging 10/100 end-user switches, and much of what we're looking at are 1 Gbps units. My question is, since the trunk/uplink lines are still 1Gbps, if I were to install 1 Gbps switches for end users, should I limit the ports to 100Mbps until I can also upgrade the trunks to avoid allowing a bad-behaving host to saturate a trunk line (since we're a college, we have plenty of mis-behaving hosts) and thereby create a DoS situation for a building, or will TCP congestion control typically take care of that for me? What if we have a lot of UDP traffic (games, video chats, even a small amount of bittorrent)?

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• Best network tuning variables for a Linux proxy

  - by smarthall

  What are the best settings to tune so that Linux can handle a very large amount of TCP connections such as would be seen by a proxy server or a webserver? I'm using Centos6 and squid and am seeing a large amount of TIME_WAIT connections backing up until finally the machine stops responding. The machine isn't loaded at the time, and is having trouble making ingoing and outgoing connections. I've had several suggestions of tuning /proc/sys/net/ipv4/tcp_tw_reuse and /proc/sys/net/ipv4/tcp_tw_reuse but they mention bad interactions with load balancers and NAT both of which are used in my situation.

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• Automatically connect to 3G dialup connection

  - by Philipp

  I have a notebook with an internal 3G modem (a HUAWEI Mobile Connect) which appears to the system as a dialup modem. When I want to connect to the Internet, I need to open the charms bar, click settings, network, the modem and "connect" to open the dialup dialog on the desktop. When the connection is interrupted for some reason, I need to repeat these steps. Is there a way to configure Windows 8 to automatically (and preferably silently in the background) connect with this modem at system startup and automatically restore the connection should it get interrupted? As an operating system which is developed for mobile devices, I would expect it to be able to somehow be able to manage a always-on 3g connection.

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• Tool/Program/Script/Formula for deciphering Active Directory Connection Strings for 3rd party user i

  - by I.T. Support

  We're using WSFTP, which has an Active Directory Integration module. To populate the user accounts you need to provide a connection string akin to: OU=Users,DC=domain,DC=com CN=Domain Users,OU=Users,DC=domain,DC=com Questions: Is there a Tool/Program/Script/Formula that allows me to decipher how these strings might look based on what I can see in Active Directory Users & Computers? Is there a proper/accepted name for these types of connection strings? I don't even know what to Google to get more information about how to format one properly How would I troubleshoot the connection string if I think it looks correctly formatted, but it isn't working? Thanks!

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• Problem with internet connection

  - by vijay.shad

  Hi all, I am working on windows vista. I have got two internet connections, one is wifi connection with high speed. And other is mobile network connection. There is a very strange problem I am getting. When I connect to wi-fi connection I an not able to serf internet(actually not all the sites). I am able to search on Google but when i click on any link in the search list it does not open. But I am able to serf all the pages in google.com domain and also all the pages in stackoverflow domain. But i am not able to go to page http://repo1.maven.org/maven2 But When I am connected by my mobile network. I am able to serf any site. Can you please tell me what might me the problem with my settings.

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• How to make sure you server NIC performance is at best on Windows?

  - by Bobb

  I realised that I followed some obscure paper on setting NICs on Windows for too long. It might be outdated with new hardware released in past couple of years and with W2008R2. I read a bit about offloading and RSS settings on Windows and I realiased that it is very much circumstantial. Noone can really say - enable that and disable this. etc. So what I really want is for my next server try and setup testing environment and measure how my particular application will behave with different settings. The target is going to be latency of TCP primarily. Please note I am talking about latency inside the box. Are there precision tools for Windows to measure latency (down to microseconds)? P.S. I know this is not easy question. Windows time drift is awful problem for any precision test but still I am sure I am not the fist person to need that... Please share your experience

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• Postfix connection lost after AUTH

  - by user84104

  Looking at the logs on my mailservers, I have noticed messages like the following: Nov 29 12:09:38 mta postfix/smtpd[8362]: connect from unknown[183.13.165.14] Nov 29 12:09:39 mta postfix/smtpd[8362]: lost connection after AUTH from unknown[183.13.165.14] Nov 29 12:09:39 mta postfix/smtpd[8362]: disconnect from unknown[183.13.165.14] Nov 29 12:09:39 mta postfix/smtpd[8409]: connect from unknown[183.13.165.14] Nov 29 12:09:40 mta postfix/smtpd[8409]: lost connection after AUTH from unknown[183.13.165.14] Nov 29 12:09:40 mta postfix/smtpd[8409]: disconnect from unknown[183.13.165.14] There are no SASL failures in these cases. There are SASL failures are logged at other times, but never with lost connection after AUTH. What is happening here, and should I do any about it? These are not MXs, and already have smtpd_client_connection_rate_limit set. Possibly related: The systems require either SMTPS or STARTTLS before AUTH is announced.

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• Taskbar Disappears Over Remote Desktop Connection When Outside Local Network

  - by CMikeB1

  I've got a machine on my home network running Windows Server 2012 (Based on Win8) and rather than attach a monitor I remote desktop in and it works fine on my local network. The problem is, when I try to access it from outside my local network the taskbar disappears completely. When I minimize an application rather than minimize to the taskbar it simply closes the window as small as it can as if the taskbar never existed (see photos at ). I've messed with the connection properties (show/hide desktop background, etc.) with no luck. I've used the following methods to remote in and they all are fine when on the local network and taskbar-less from outside: Remote Desktop Connection on Mac Remote Desktop Connection on Windows Jump Desktop on iOS using RDP To access the computer from outside my local network I'm using a Linksys router and mapping to the server IP, port 3389. See Photos: http://i.stack.imgur.com/FyUeQ.png http://i.stack.imgur.com/9MnVr.png

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• Automatically send a string when opening a raw connection in putty

  - by MBraedley

  I have a program running on a server that accepts TCP/IP connections on a specified port. When a connection is made, this program waits for the user (i.e. me) to send a string which identifies the type of user. Once the user identifies themselves, the program will start sending data that is relevant to that user type. I want to automate the first step and have putty automatically send the user identification string once the connection is made. I've been through the settings, and can't seem to find anything like "send following commands on connection". Any help would be appreciated.

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• SQL connection is too slow

  - by user66905

  We have a business web application in ASP.NET + SQL Server 2008. In the beginning, SQL Server and IIS were on the same machine. Now we bought another machine. Current configuration is IIS machine plus SQL Server machine, and they are connected by a 1gb LAN connection. With this configuration our web application is slower than before. Max bandwidth is 1-2% of network, about 15mbps. When we use another threads to the same SQL Server from the same IIS machine, network use is higher. So this is no problem with SQL Server. Ho we can make higher bandwidth for this SQL connection? Specs: .Net 3.5 SQL Server 2008 Standard file transfer can use 100% of LAN SQL connection by TCP/IP protocol SQL logins Pool tested with enable and

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• What happens if a server never receives the RST packet?

  - by Rob

  Someone recently decided to show me a POC of a new Denial of Service method using SYN/TCP he's figured out. I thought it was complete nonsense, but after explaining to him about SYN-SYN/ACK-RST, he left me speechless. He told me "what if the server you're using to trick into sending the SYN/ACK packets can't receive the RST packet?" I have no idea. He claims that the server will continue trying to send SYN/ACK packets, and that the packetrate will continue to build up. Is there any truth to this? Can anyone elaborate? Apparently, the way it works is this: He spoofs the IP of the SYN packet to the target's IP. He then sends the SYN packet to a handful of random servers They all reply with their SYN/ACK packet to the target IP, of course The target responds with RST, as we know BUT somehow he keeps the target from sending the RST or keeps the random servers from processing it With this, apparently the servers will continue trying to send the SYN/ACK packets, thus producing a somewhat of a "snowball" effect.

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• Which interface defines the physical address of a Dialup connection

  - by Debabratta

  I use dial up connection to connect to the Internet. When I type ipconfig/all in the command prompt it shows me a physical address along with description for the dial up connection. The description field shows WAN(PPP/SLIP)Interface. I want to know upon which this physical address depends? It depends on my computer or ISP. On changing my ISP, physical address for this dialup connection will change or remain same? Please give some idea.

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• How to tune Windows 2008r2 and IIS to maximize single file download speeds?

  - by uSlackr

  We recently put up an IIS site (on WinSvr 2008r2) that is used almost exclusively for downloading files over the internet. The data exists as a large collection of .zip files ranging from 1MB - 35GB in size. We want to allow a lot of downloads during a day (more than 500GB) but have implemented an outbound ASA throttle at 60mbps in order to preserve bandwidth for other uses. The total link speed is 100mbps. Here's the interesting part: While we can serve up multiple downloads to hit the 60mbps cap, we cannot get any single download to exceed 2.5M bytes/sec (20 Mbits/s). Is there any TCP or IIS tuning we can do to push up individual download speeds? Or something else to look at?

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• Can a network interface be configured to have a default gateway for UDP packets?

  - by Vaibhav

  It is quite possible that my question may not make a lot of sense. I apologize, but I am not a networking guy, and that's my excuse. To elaborate, WikiPedia defines "Default Gateway" as a node on a "TCP/IP" network. And the way it works is that if a network interface is sending a packet to an IP address not present on its subnet, it sends it out to the default gateway (which then knows what to do with that packet). Is this true if a UDP packet (datagram) is involved? I mean, if my network interface is sending a UDP packet to an IP address that is not present on its subnet, would it automatically send it to the Default Gateway as well?

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• Out of nowhere, ssh_exchange_identification: Connection closed by remote host

  - by disusered

  I am running Ubuntu 10.10 on a remote box. I ssh to it everyday without issues but today out of the blue, I get the following error: ssh_exchange_identification: Connection closed by remote host If I connect with -vv, I get the following: OpenSSH_5.6p1, OpenSSL 0.9.8r 8 Feb 2011 debug1: Reading configuration data /Users/bla/.ssh/config debug1: Applying options for ubuntu-server debug1: Reading configuration data /etc/ssh_config debug1: Applying options for * debug2: ssh_connect: needpriv 0 debug1: Connecting to ubuntu-server.com [123.123.123.123] port 22. debug1: Connection established. debug2: key_type_from_name: unknown key type '-----BEGIN' debug2: key_type_from_name: unknown key type '-----END' debug1: identity file /Users/bla/.ssh/id_rsa type -1 debug1: identity file /Users/bla/.ssh/id_rsa-cert type -1 ssh_exchange_identification: Connection closed by remote host If I remove the key, I get the exact same output (sans "debug2: key_type_...). I've managed to log in physically and checked my hosts.allow and hosts.deny but they have no entries. I tried removing and reinstalling OpenSSH, checked authorized_keys and ~/.ssh permissions and tried connecting from other computers only to get the same error. I'm at my wits end, any help would be greatly appreciated.

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• Monitoring/logging a malfunctioning internet connection

  - by Pekka

  I have a mysterious internet connection problem: Every 15-20 minutes, the connection will become very slow, and take 2-3 minutes for anything to load. I've had a technician from the ISP over here to test the hardware, and everything is in pristine condition. They have no other explanation than a configuration error on my machine, a possibility I can exclude 90% because I'm experiencing the same problems with another machine. I will have to monitor the situation now, and I would like to run a program that logs when internet connections become slow. I thought about putting something together using at and wget. Does anybody know of some other tool for this that does this out of the box - maybe something with an adjustable request frequency, logging connection speeds etc.?

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• Too Many ESTABLISHED connection from a single IP address in Apache

  - by ananthan

  netstat -ntp |grep 80 shows too many ESTABLISHED connection from single IP address. Around 300 of them and it is not an attack and user is using a 2G connection to access Apache. This is the case with other 2G connections also. As a result of this Apache is running out of children. Earlier it was showing too many close_wait and after enabling tcp_tw_reuse and tcp_tw-recycle there is not much close_wait but the number of ESTABLISHED connections increased. We are using Ubuntu 11.04 having 48 GB ram keepalive On keepalive timeout 10 max clients 800 max-request-perchild 4000 timeout 300 I have set syn_ack to 1 and syn_retries to 2. On wifi there is no such issue. Connections are closing properly, but with 2G connections Apache is running out of children and too many ESTABLISHED connection. also i have tried setting timeout from default 300 to 30,but since our project is image hosting for mobile phones,clients couldn't upload images properly as they are getting frequent time out.Also there were a lot of 408 messages so changed it to the default 300

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• connection prob

  - by user56944

  Hey guys I use Clear internet ie wireless to get my connection. I play a game online Eve Online which has had on and off CTD(crash to desktop) due to the connection timing out. Usually I have trouble only late at night after work but today I had no connection at 4 pm. They ran a trace route and Im using Ping plotter to do a trace in real time. I have 100% packet loss at hop 2 and Im getting varible loss at hop 6 at ae-72-70.ebr2.Dallas1.Level3.net Also had windows send a dump to Microsoft mentioning the eve file has a problem requiring it to close. Any thoughts ? TIA!

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• What purpose does “using” serve when used the following way

  - by user287745

  What purpose does “using” serve when used the following way:- ONE EXAMPLE IS THIS, (AN ANSWERER- @richj - USED THIS CODE TO SOLVE A PROBLEM THANKS) private Method(SqlConnection connection) { using (SqlTransaction transaction = connection.BeginTransaction()) { try { // Use the connection here .... transaction.Commit(); } catch { transaction.Rollback(); throw; } } } OTHER EXAMPLE I FOUND WHILE READING ON MICROSOFT SUPPORT SITE public static void ShowSqlException(string connectionString) { string queryString = "EXECUTE NonExistantStoredProcedure"; StringBuilder errorMessages = new StringBuilder(); using (SqlConnection connection = new SqlConnection(connectionString)) { SqlCommand command = new SqlCommand(queryString, connection); try { command.Connection.Open(); command.ExecuteNonQuery(); } catch (SqlException ex) { for (int i = 0; i < ex.Errors.Count; i++) { errorMessages.Append("Index #" + i + "\n" + "Message: " + ex.Errors[i].Message + "\n" + "LineNumber: " + ex.Errors[i].LineNumber + "\n" + "Source: " + ex.Errors[i].Source + "\n" + "Procedure: " + ex.Errors[i].Procedure + "\n"); } Console.WriteLine(errorMessages.ToString()); } } } I AM doing at top of page as using system.data.sqlclient etc so why this using thing in middle of code, What if I omit it (I know the code will work) but what functionality will I be losing

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• Stream a continously growing file over tcp/ip

  - by Grinner

  Hello, I have a project I'm working on, where a piece of Hardware is producing output that is continuously being written into a textfile. What I need to do is to stream that file as it's being written over a simple tcp/ip connection. I'm currently trying to that through simple netcat, but netcat only sends the part of the file that is written at the time of execution. It doesn't continue to send the rest. Right now I have a server listening to netcat on port 9000 (simply for test-purposes): netcat -l 9000 And the send command is: netcat localhost 9000 < c:\OUTPUTFILE So in my understanding netcat should actually be streaming the file, but it simply stops once everything that existed at the beginning of the execution has been sent. It doesn't kill the connection, but simply stops sending new data. How do I get it to stream the data continuously? Thanks for any help!

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• NHibernate is not connecting to sql server.

  - by user177883

  When i set up a regular connection, it works, however when i try to use nhibernate, hibernate.cfg.xml, i m getting the following error. Message="A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified)" Source=".Net SqlClient Data Provider" What would be the reason for this and how can i resolve it ? I doubt that it s a network or sql server configuration error. <?xml version="1.0" ?> <hibernate-configuration xmlns="urn:nhibernate-configuration-2.2" > <session-factory> <property name="connection.provider">NHibernate.Connection.DriverConnectionProvider</property> <property name="dialect">NHibernate.Dialect.MsSql2005Dialect</property> <property name="connection.driver_class">NHibernate.Driver.SqlClientDriver</property> <property name="connection.connection_string">Server=(ServerName\DEV_ENV);Initial Catalog=dbName;User Id=SA;Password=PASS</property> <property name="proxyfactory.factory_class">NHibernate.ByteCode.LinFu.ProxyFactoryFactory, NHibernate.ByteCode.LinFu</property> </session-factory> </hibernate-configuration>

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