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  • Diagnosing Random Network Lag

    - by uesp
    I'm having trouble diagnosing some random lag on a 6 server LAMP cluster serving a MediaWiki site. While we're serving some 100 pages/sec the servers themselves are running fine with less than 0.5 load, no locked processes, no paging, no errors being logged, etc.... Lag is present on all servers and is random: one minute its fine the next it's there. DNS lookups on the servers are randomly slow. For example time nslookup google.com varies randomly from a few milliseconds to several seconds and sometimes times out entirely. While we use IP addresses internally on the cluster this may be a symptom of the root issue. We are not running our own DNS server. The Apache server-status pages randomly lag or time out. Benchmarking using ab between servers shows a few loads sometimes take 3000 ms (almost exactly). Benchmarking server-status on the local server itself usually shows no issue (it showed a lag only once among a few hundred tests). The servers are sitting behind a switch and a firewall which I don't have any access to so I don't know their setup or status. While we are under heavier than normal load a 2 Mbps incoming and 20 Mbps outgoing traffic shouldn't be stressing the switch or firewall should it? My feeling is that it is the switch/firewall or something above them in the ISP like their DNS but can't confirm it. I need some other tests or methods of diagnosing this lag to try and narrow down the ultimate cause.

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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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  • Android: Problems downloading images and converting to bitmaps

    - by Mike
    Hi all, I am working on an application that downloads images from a url. The problem is that only some images are being correctly downloaded and others are not. First off, here is the problem code: public Bitmap downloadImage(String url) { HttpClient client = new DefaultHttpClient(); HttpResponse response = null; try { response = client.execute(new HttpGet(url)); } catch (ClientProtocolException cpe) { Log.i(LOG_FILE, "client protocol exception"); return null; } catch (IOException ioe) { Log.i(LOG_FILE, "IOE downloading image"); return null; } catch (Exception e) { Log.i(LOG_FILE, "Other exception downloading image"); return null; } // Convert images from stream to bitmap object try { Bitmap image = BitmapFactory.decodeStream(response.getEntity().getContent()); if(image==null) Log.i(LOG_FILE, "image conversion failed"); return image; } catch (Exception e) { Log.i(LOG_FILE, "Other exception while converting image"); return null; } } So what I have is a method that takes the url as a string argument and then downloads the image, converts the HttpResponse stream to a bitmap by means of the BitmapFactory.decodeStream method, and returns it. The problem is that when I am on a slow network connection (almost always 3G rather than Wi-Fi) some images are converted to null--not all of them, only some of them. Using a Wi-Fi connection works perfectly; all the images are downloaded and converted properly. Does anyone know why this is happening? Or better, how can I fix this? How would I even go about testing to determine the problem? Any help is awesome; thank you!

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  • Set web browser (or other program) to use specific network

    - by Will
    my PC is connected to 3 different networks: 2 different LAN connections and a VPN connection. when i am connected to the vpn, i cannot browse to the LAN intranet as the DNS is all going through the vpn and it cannot see the domains on the LAN. Is there a way to set firefox/chrome/etc to use a specific connection, so that i don't have to disconnect from vpn to get to the other intranets?

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  • Maximise network transfer speed of various applications

    - by Alex
    When using nc, scp, wget to transfer files between 2 machines on a dedicated 2Mbps link, I get speeds between 0.5 and 1 Mbps. However, when I use iperf -c 10.0.1.4 -t 20 -P 12 (for example) I can maximise the speed of the link (getting stable 2Mbps). Is there a way to make single stream transfers (such as those done by scp) to utilise all/most of the link? Some kind of tcp settings, or iptables...?

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  • Network Bridging on Linux for OpenVPN

    - by Coyote
    I've been following all the OpenVPN Bridge tutorials I can, but I'm still missing something. Does anyone know of a super detailed tutorial\explanation of bridging? If anyone has bridging running, can I get a copy of your interfaces file to see how you've got it going. (Obviously change the ip address, just please change them consistently.)

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  • Adding Exchange Multi Tenant to an existing Exchange Network

    - by TiernanO
    I currently have an Exchange 2010 SP1 server in house, and due to some changes, it looks like i will need Multi Tenant support for a few extra domain names. Looking at the documentation i have found so far, it only mentions multi tenant support when upgrading from 2010 RTM - SP1, and not what you do if you have already got 2010 SP1 installed. So, from what i can gather, i have a few options: Install a new Exchange server with Multi Tenant support and migrate DBs over Back everything up and start again Something else... Any suggestions would be greatly appreciated... Thanks.

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  • Monitoring VPN users on my network

    - by Fen0x
    My company runs filters on contents available for browsing and I have to check if everyone is respecting the browsing policies. Recently I have spotted some users activate OpenVPN on their workstations and i have discovered that they connect on port 443 of an external server and then use a proxy to circumvent the company filters. Is there any method to monitor VPN connections on allowed ports or to avoid the connections?

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  • Two routers network routing settings

    - by xiamx
    I have two routers, Router A is connected to the internet, and Router B is connected to the LAN port of Router A. Router A: 192.168.1.1 Subnet 255.255.255.0 Router B: IP leased from router A: 192.168.1.2 gateway 192.168.0.1 subnet 255.255.255.0 I have a machine C plugged to router A with ip 192.168.1.3 also a machine D plugged to router B with ip 192.168.0.199 I want to access machine D from a machine C. What settings do I need to change to do that?

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  • Remote I/O costs with a Content Delivery Network

    - by x711Li
    As far as I know, the time complexity of scanning a directory and the amount of files in said directory are correlated due to I/O costs. Would the administrative costs of placing the files in a hashed directory tree for uploading/downloading files through a CDN API be worth it for the added efficiency? For instance, given a filename foo.mp3, the MD5 hash for this is 10ebb1120767e9de166e0f5905077cb1. Thus, storing foo.mp3 in ./10/eb/foo.mp3 would allow for less files per directory (assuming MD5 generates patterns with in Base36, this allows for 36^2 root directories with 36^2 subdirectories each and little chance of hash collision) Considering the directories themselves are not loaded, would the I/O costs of directory scanning still exist with direct uploading/downloading?

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  • Cannot access internal website after being connected to other network

    - by Dandroid
    I have a client who claim they cannot access their internal website when they have e.g. been out traveling. They have to reset their browser settings every time to be able to get access again. As they live on another continent and timezone it's hard for me to run live tests with them to see what changes in their browser settings. My first guess would be it's some sort of Proxy related issue, but I want to know if there could be other reasons for this? It's not the LAN itself, that we are sure of. It's browser specific only. Edit It's worth mentioning that it only happens when they turn off/restart their computers.

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  • programs hangs during socket interaction

    - by herrturtur
    I have two programs, sendfile.py and recvfile.py that are supposed to interact to send a file across the network. They communicate over TCP sockets. The communication is supposed to go something like this: sender =====filename=====> receiver sender <===== 'ok' ======= receiver or sender <===== 'no' ======= receiver if ok: sender ====== file ======> receiver I've got The sender and receiver code is here: Sender: import sys from jmm_sockets import * if len(sys.argv) != 4: print "Usage:", sys.argv[0], "<host> <port> <filename>" sys.exit(1) s = getClientSocket(sys.argv[1], int(sys.argv[2])) try: f = open(sys.argv[3]) except IOError, msg: print "couldn't open file" sys.exit(1) # send filename s.send(sys.argv[3]) # receive 'ok' buffer = None response = str() while 1: buffer = s.recv(1) if buffer == '': break else: response = response + buffer if response == 'ok': print 'receiver acknowledged receipt of filename' # send file s.send(f.read()) elif response == 'no': print "receiver doesn't want the file" # cleanup f.close() s.close() Receiver: from jmm_sockets import * s = getServerSocket(None, 16001) conn, addr = s.accept() buffer = None filename = str() # receive filename while 1: buffer = conn.recv(1) if buffer == '': break else: filename = filename + buffer print "sender wants to send", filename, "is that ok?" user_choice = raw_input("ok/no: ") if user_choice == 'ok': # send ok conn.send('ok') #receive file data = str() while 1: buffer = conn.recv(1) if buffer=='': break else: data = data + buffer print data else: conn.send('no') conn.close() I'm sure I'm missing something here in the sorts of a deadlock, but don't know what it is.

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  • VMware Workstation 7&8&9 does not generate /etc/vmware/network upon installation

    - by dash17291
    When I install VMware Workstation on Arch linux Virtual ethernet is not working. $ sudo tail /var/log/vnetlib Aug 28 22:20:33 VNLFileExists - Cannot check for file or directory: /etc/vmware/networking , error: No such file or directory Aug 28 22:20:33 VNLNetCfgLoad - Import file does not exist Aug 28 22:20:33 VNL_Load - Error loading the vnet configuration, file used: /etc/vmware/networking Aug 28 22:20:33 VNLNetCfgUnload - Requested cache is not loaded Database file is not present. Failed to initialize Aug 28 22:20:41 VNLFileExists - Cannot check for file or directory: /etc/vmware/networking , error: No such file or directory Aug 28 22:20:41 VNLNetCfgLoad - Import file does not exist Aug 28 22:20:41 VNL_Load - Error loading the vnet configuration, file used: /etc/vmware/networking Aug 28 22:20:41 VNLNetCfgUnload - Requested cache is not loaded Required modules compiled. Previously I have copied that file or directory (I don't remember) from a working installation, but now I need a real solution. It's strange for me, may be a hardware issue also because with Ubuntu the same thing happens on the same computer.

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  • Seeking recommendations on resolving sporadic network connectivity latency for Notes client

    - by Russell Maher
    I have Domino servers in geographically disperse data centers in the U.S. Sometimes when I open an NSF on one of those servers the connection times out then when I open the NSF again it connects immediately. This has been going on for years and during that time I have upgraded and changed my own internet connection and moved servers to different data centers. Of course I have direct connection documents using fixed IP addresses. When I do a Notes client Trace nothing is out of the ordinary. My business partner experiences the same thing from an entirely different city and different ISP but to the same servers. Never have any trouble connecting to the HTTP server, just over port 1352. Does anyone have any recommendations on a process to determine what is causing this problem?

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  • Network config / gear question

    - by mcgee1234
    I have been tasked with setting up a fairly straightforward rack in a data center (we do not even need a whole rack, but this is the smallest allotment available). In a nutshell, 4 to 6 servers need to be able to reach 2 (maybe 3) vendors. The servers needs to be reachable over the internet. A little more detail - the networks the servers need to reach are inside of the data center, and are "trusted". Connections to these networks will be achieved through intra data center cross connects. It is kind of like a manufacturing line where we receive data from one vendor (burst-able up to 200 Mbits), churn through it on the servers, and then send out data to another vendor (bursts up to 20 Mbits). This series of events is very latency sensitive, so much so that it is common practice not to use NAT or a firewall on these segments (or so I hear). To reach the servers over the internet, I plan to use a site to site VPN. (This part is only relevant as far as hardware selection goes). I have 2 configurations in mind: Cisco 2911 (2921) (with the additional wan ports module) and a layer 2 switch - in this scenario, I would use the router also for VPN. Cisco 3560 layer 3 switch to interconnect the networks inside of the data center and an ASA 5510 (which is total overkill, but the 5505 is not rack mountable) as a firewall for the Wan side (internet) and VPN. I envision the setup to be as follows: Internet - ASA - 3560 Vendors - 3560 - Servers The general idea is that the ASA acts as a firewall and VPN device and the 3560 does all the heavy lifting. The first is a fairly traditional setup but my concern is performance. The second is somewhat unorthodox in that the vendors are directly connected to the layer 3 switch without passing through a firewall. Based on my understanding however, a layer 3 switch will perform substantially better as it will do hardware (ASIC) vs. software switching. (Note that number 2 is a little over the budget, but not unworkable (double negative, ugh)) Since this is my first time dealing with a data center, I am not sure what the IP space is going to look like. I suspect I will retain a block(s) of public IPs, vlan them to individual interfaces for the vendor connections and the servers (which will not reachable from the wan side of course) and setup routing on the switch. So here are my questionss: Is there a substantial performance difference between 1 and 2, i.e. hardware based switching on a layer 3 vs a software base on the 2911? I have trolled the internet and found a lot of Cisco literature, but nothing that I could really use to get a good handle. The vendors we connect to are secure and trusted (famous last words) and as I understand it, it is common practice not to NAT or firewall these connections (because of the aforementioned latency sensitivity). But what what kind of latency are we really talking about if I push the data through a router (or even ASA for that matter)? For our purposes, 5 ms will not kill us, 20 or 30 can be very costly. Others measure in microseconds, but they are out of our league. Is there any issues with using public IPs on a layer 3 switch? I am certainly not married to either of these configs, and I am totally open to any ideas. My knowledge (and I use the term loosely) is largely from books so I welcome any advice / insight. Thanks in advance.

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  • Creating a network adapter - how hard is it?

    - by Vilx-
    I'm interested in building a little (commercial) device on top of Arduino. I want it to be able to interface with network. Network as in standard Ethernet, Cat5, RJ-45, etc. I know that there is an Ethernet Shield, but it costs even more than the Arduino itself, and it's pretty big. Naturally, I want my device to be as small and as cheap as possible. So I'm thinking about recreating an Ethernet module myself. The problem is - I haven't got any experience with Ethernet, nor do I have a good idea where to start looking. Thus I can't even say if my ideas are feasible. Ultimately I would like the device to have three ports - one for incoming signal, two for outgoing, so the device is essentially a little switch where it is plugged in itself as well. The switching capabilities need not be very fast - the volume of data will be low. 10Mbit is more than enough, can be even slower. If that is not possible, a single port for controlling the device itself will also do. Another possibility I'm considering is power line communications - sending information through power lines. That's another area I've no experience with. What hardware should I be looking at, and where can I find information about the necessary software? So - can anyone tell me if these ideas are feasible, and if yes - where should I start looking?

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  • Design for fastest page download

    - by mexxican
    I have a file with millions of URLs/IPs and have to write a program to download the pages really fast. The connection rate should be at least 6000/s and file download speed at least 2000 with avg. 15kb file size. The network bandwidth is 1 Gbps. My approach so far has been: Creating 600 socket threads with each having 60 sockets and using WSAEventSelect to wait for data to read. As soon as a file download is complete, add that memory address(of the downloaded file) to a pipeline( a simple vector ) and fire another request. When the total download is more than 50Mb among all socket threads, write all the files downloaded to the disk and free the memory. So far, this approach has been not very successful with the rate at which I could hit not shooting beyond 2900 connections/s and downloaded data rate even less. Can somebody suggest an alternative approach which could give me better stats. Also I am working windows server 2008 machine with 8 Gig of memory. Also, do we need to hack the kernel so as we could use more threads and memory. Currently I can create a max. of 1500 threads and memory usage not going beyond 2 gigs [ which technically should be much more as this is a 64-bit machine ]. And IOCP is out of question as I have no experience in that so far and have to fix this application today. Thanks Guys!

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  • mapping server 2008 network drive to vista home premium x64

    - by rboorgapally
    We have a windows server 2008 box at my work place. I want to map a drive from the server to my laptop. I use windows vista home premium x64. I am connected to my workplace through VPN. i can map the drive when I use the administrator account on the server. But the log on is unsuccessful if I use my personal account on the server to map the drive. My personal account on the server is part of Administrators group. Can any one help me with this?

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  • Mirror network packets from WiFi to Ethernet in an ASUS Router RT N53

    - by fazineroso
    I have an ASUS RT N53 router, running the default firmware (Linux 2.6.22 with busybox and uclibc). I need to capture data packets from some Wi-Fi devices I have connected to that router (iPad and some smartphones), but the router is not forwarding any package coming from Wi-Fi devices to the Ethernet Ports. Any idea how can I proceed? Available tools in the router are iptables (no tee option, though), ebtables, brctl... Currently the ethernet and Wifi devices are forming a bridge: # brctl show bridge name bridge id STP enabled interfaces br0 8000.50465dc06be2 no vlan0 eth1 No ebtables rules: # ebtables -L Bridge table: filter Bridge chain: INPUT, entries: 0, policy: ACCEPT Bridge chain: FORWARD, entries: 0, policy: ACCEPT Bridge chain: OUTPUT, entries: 0, policy: ACCEPT

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  • Network tries to reindentify itself now and then

    - by Don Young
    When the computer starts up it connects itself to the router (ZTE 4G router) automatically, but after I have surfed the web for a while, it tries to identify itself, meaning you get that little blue circle next to the little screen at the corner. When browsing it does not cause any problems, but if I'm streaming a video the video will then stop, I'll have to refresh the page to make the video start again. And if I'm playing a game, LoL for example, the game will freeze for about 2 seconds then continue again (due to lost connection to the internet). I have no virus on my computer, although I had before. I have reset my router, restarted my computer, updated my ethernet driver, checked so that the IPv4 is set on automatic and tried different router channels. I have had this router for a few months and the problem just started recently. Here is the ipconfig screen:

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  • Connecting to network device behind NAT from local LAN using the external port and IP

    - by lumbric
    I noticed at several different LANs connected to the Internet through a NAT the following phenomena. There is a server in the LAN and there is a port forwarding to reach this server also from outside the LAN through the NAT. E.g. consider a LAN with the address 192.168.0.* and a SSH server at 192.168.0.2 with port 22 and a forwarding from port 2222 at the NAT 192.168.0.1 to 192.168.0.2:22. If the NAT's external IP is 44.33.22.11, one can connect to the SSH server through 44.33.22.11:2222. Surprisingly this works only from outside the LAN. If one tries to connect to 44.33.22.11:2222 from behind the NAT, there is no answer. Of course one could simply use 192.168.0.2:22, but often it is simpler to use the external IP. The typical use case for me is the configuration on a laptop computer. Usually the user uses any arbitrary Internet connection to connect to his home or office server, but sometimes he will use also the LAN to connect to it and it would be annoying to have to different configurations or bookmarks. Why does it fail to connect from inside the LAN? Is there any good work around?

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  • Client Server communication in Java - which approach to use?

    - by markovuksanovic
    I have a typical client server communication - Client sends data to the server, server processes that, and returns data to the client. The problem is that the process operation can take quite some time - order of magnitude - minutes. There are a few approaches that could be used to solve this. Establish a connection, and keep it alive, until the operation is finished and the client receives the response. Establish connection, send data, close the connection. Now the processing takes place and once it is finished the server could establish a connection to the client to send the data. Establish a connection, send data, close the connection. Processing takes place. client asks server, every n minutes/seconds if the operation is finished. If the processing is finished the client fetches the data. I was wondering which approach would be the best way to use. Is there maybe some "de facto" standard for solving this problem? How "expensive" is opening a socket in Java? Solution 1. seems pretty nasty to me, but 2. and 3. could do. The problem with solution 2. is that the server needs to know on which port the client is listening, while solution 3. adds some network overhead.

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