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• Load balance to proxies

  - by LoveRight

  I have installed several proxy programs whose IP addresses are, for example, 127.0.0.1:8580(use http), 127.0.0.1:9050(use socks5). You may regrard them as Tor and its alternatives. You know, certain proxy programs are faster than others at times, while at other times, they would be slower. The Firefox add-in, AutoProxy and FoxyProxy Standard, can define a list of rules such as any urls matching the pattern *.google.com should be proxied to 127.0.0.1:8580 using socks5 protocol. But the rule is "static". I want *.google.com to be proxied to the fastest proxy, no matter which one. I think that is kind of load balancing. I thought I could set a rule that direct request of *.google.com to the address the load balancer listens, and the load balancer forwards the request to the fastest real proxy. I notice that tor uses socks5 protocol and some other applications use http. I feel confused that which protocol should the load balancer use. I also start to wonder about the feasibility of this solution. Any suggestions? My operating system is Windows 7 x64.

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• Need some constructive criticism on my SSE/Assembly attempt

  - by Brett

  Hello, I'm working on converting a bit of code to SSE, and while I have the correct output it turns out to be slower than standard c++ code. The bit of code that I need to do this for is: float ox = p2x - (px * c - py * s)*m; float oy = p2y - (px * s - py * c)*m; What I've got for SSE code is: void assemblycalc(vector4 &p, vector4 &sc, float &m, vector4 &xy) { vector4 r; __m128 scale = _mm_set1_ps(m); __asm { mov eax, p //Load into CPU reg mov ebx, sc movups xmm0, [eax] //move vectors to SSE regs movups xmm1, [ebx] mulps xmm0, xmm1 //Multiply the Elements movaps xmm2, xmm0 //make a copy of the array shufps xmm2, xmm0, 0x1B //shuffle the array subps xmm0, xmm2 //subtract the elements mulps xmm0, scale //multiply the vector by the scale mov ecx, xy //load the variable into cpu reg movups xmm3, [ecx] //move the vector to the SSE regs subps xmm3, xmm0 //subtract xmm3 - xmm0 movups [r], xmm3 //Save the retun vector, and use elements 0 and 3 } } Since its very difficult to read the code, I'll explain what I did: loaded vector4 , xmm0 _ p = [px , py , px , py ] mult. by vector4, xmm1 _ cs = [c , c , s , s ] _____________mult---------------------------- result,______ xmm0 = [px*c, py*c, px*s, py*s] reuse result, xmm0 = [px*c, py*c, px*s, py*s] shuffle result, xmm2 = [py*s, px*s, py*c, px*c] ___________subtract---------------------------- result, xmm0 = [px*c-py*s, py*c-px*s, px*s-py*c, py*s-px*c] reuse result, xmm0 = [px*c-py*s, py*c-px*s, px*s-py*c, py*s-px*c] load m vector4, scale = [m, m, m, m] ______________mult---------------------------- result, xmm0 = [(px*c-py*s)*m, (py*c-px*s)*m, (px*s-py*c)*m, (py*s-px*c)*m] load xy vector4, xmm3 = [p2x, p2x, p2y, p2y] reuse, xmm0 = [(px*c-py*s)*m, (py*c-px*s)*m, (px*s-py*c)*m, (py*s-px*c)*m] ___________subtract---------------------------- result, xmm3 = [p2x-(px*c-py*s)*m, p2x-(py*c-px*s)*m, p2y-(px*s-py*c)*m, p2y-(py*s-px*c)*m] then ox = xmm3[0] and oy = xmm3[3], so I essentially don't use xmm3[1] or xmm3[4] I apologize for the difficulty reading this, but I'm hoping someone might be able to provide some guidance for me, as the standard c++ code runs in 0.001444ms and the SSE code runs in 0.00198ms. Let me know if there is anything I can do to further explain/clean this up a bit. The reason I'm trying to use SSE is because I run this calculation millions of times, and it is a part of what is slowing down my current code. Thanks in advance for any help! Brett

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• jquery change load get url

  - by john morris

  Ok so I have a php page with data dynamically outputs depending on a $_GET variable ['file']. I have another page (index.php) which has a jQuery script that uses the load() function to load the php page. I have a list of links and when you click on one, it needs to change the $_GET variable to load, then refresh the load() jQuery variable. Heres a snippet: $("#remote-files").load("data.php?file=wat.txt"); $(".link1").mousedown(function() { $("#remote-files").load("data.php?file=link1.txt"); }); As you can see it loads the data into a div with the ID of remote-files. Is there a better way to do this, like update the page with the new get variable instead of redefining a new load function?

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• Apache load balancer limits with Tomcat over AJP

  - by PAS

  Hi All, I have Apache acting as a load balancer in front of 3 Tomcat servers. Occasionally, Apache returns 503 responses, which I would like to remove completely. All 4 servers are not under significant load in terms of CPU, memory, or disk, so I am a little unsure what is reaching it's limits or why. 503s are returned when all workers are in error state - whatever that means. Here are the details: Apache config: <IfModule mpm_prefork_module> StartServers 30 MinSpareServers 30 MaxSpareServers 60 MaxClients 200 MaxRequestsPerChild 1000 </IfModule> ... <Proxy *> AddDefaultCharset Off Order deny,allow Allow from all </Proxy> # Tomcat HA cluster <Proxy balancer://mycluster> BalancerMember ajp://10.176.201.9:8009 keepalive=On retry=1 timeout=1 ping=1 BalancerMember ajp://10.176.201.10:8009 keepalive=On retry=1 timeout=1 ping=1 BalancerMember ajp://10.176.219.168:8009 keepalive=On retry=1 timeout=1 ping=1 </Proxy> # Passes thru track. or api. ProxyPreserveHost On ProxyStatus On # Original tracker ProxyPass /m balancer://mycluster/m ProxyPassReverse /m balancer://mycluster/m Tomcat config: <Server port="8005" shutdown="SHUTDOWN"> <Listener className="org.apache.catalina.core.AprLifecycleListener" SSLEngine="on" /> <Listener className="org.apache.catalina.core.JasperListener" /> <Listener className="org.apache.catalina.mbeans.ServerLifecycleListener" /> <Listener className="org.apache.catalina.mbeans.GlobalResourcesLifecycleListener" /> <Service name="Catalina"> <Connector port="8080" protocol="HTTP/1.1" connectionTimeout="20000" redirectPort="8443" /> <Connector port="8009" protocol="AJP/1.3" redirectPort="8443" /> <Engine name="Catalina" defaultHost="localhost"> <Host name="localhost" appBase="webapps" unpackWARs="true" autoDeploy="true" xmlValidation="false" xmlNamespaceAware="false"> </Engine> </Service> </Server> Apache error log: [Mon Mar 22 18:39:47 2010] [error] (70007)The timeout specified has expired: proxy: AJP: attempt to connect to 10.176.201.10:8009 (10.176.201.10) failed [Mon Mar 22 18:39:47 2010] [error] ap_proxy_connect_backend disabling worker for (10.176.201.10) [Mon Mar 22 18:39:47 2010] [error] proxy: AJP: failed to make connection to backend: 10.176.201.10 [Mon Mar 22 18:39:47 2010] [error] (70007)The timeout specified has expired: proxy: AJP: attempt to connect to 10.176.201.9:8009 (10.176.201.9) failed [Mon Mar 22 18:39:47 2010] [error] ap_proxy_connect_backend disabling worker for (10.176.201.9) [Mon Mar 22 18:39:47 2010] [error] proxy: AJP: failed to make connection to backend: 10.176.201.9 [Mon Mar 22 18:39:47 2010] [error] (70007)The timeout specified has expired: proxy: AJP: attempt to connect to 10.176.219.168:8009 (10.176.219.168) failed [Mon Mar 22 18:39:47 2010] [error] ap_proxy_connect_backend disabling worker for (10.176.219.168) [Mon Mar 22 18:39:47 2010] [error] proxy: AJP: failed to make connection to backend: 10.176.219.168 [Mon Mar 22 18:39:47 2010] [error] proxy: BALANCER: (balancer://mycluster). All workers are in error state [Mon Mar 22 18:39:47 2010] [error] proxy: BALANCER: (balancer://mycluster). All workers are in error state [Mon Mar 22 18:39:47 2010] [error] proxy: BALANCER: (balancer://mycluster). All workers are in error state [Mon Mar 22 18:39:47 2010] [error] proxy: BALANCER: (balancer://mycluster). All workers are in error state [Mon Mar 22 18:39:47 2010] [error] proxy: BALANCER: (balancer://mycluster). All workers are in error state [Mon Mar 22 18:39:47 2010] [error] proxy: BALANCER: (balancer://mycluster). All workers are in error state Load balancer top info: top - 23:44:11 up 210 days, 4:32, 1 user, load average: 0.10, 0.11, 0.09 Tasks: 135 total, 2 running, 133 sleeping, 0 stopped, 0 zombie Cpu(s): 0.1%us, 0.2%sy, 0.0%ni, 99.2%id, 0.1%wa, 0.0%hi, 0.1%si, 0.3%st Mem: 524508k total, 517132k used, 7376k free, 9124k buffers Swap: 1048568k total, 352k used, 1048216k free, 334720k cached Tomcat top info: top - 23:47:12 up 210 days, 3:07, 1 user, load average: 0.02, 0.04, 0.00 Tasks: 63 total, 1 running, 62 sleeping, 0 stopped, 0 zombie Cpu(s): 0.2%us, 0.0%sy, 0.0%ni, 99.8%id, 0.1%wa, 0.0%hi, 0.0%si, 0.0%st Mem: 2097372k total, 2080888k used, 16484k free, 21464k buffers Swap: 4194296k total, 380k used, 4193916k free, 1520912k cached Catalina.out does not have any error messages in it. According to Apache's server status, it seems to be maxing out at 143 requests/sec. I believe the servers can handle substantially more load than they are, so any hints about low default limits or other reasons why this setup would be maxing out would be greatly appreciated.

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• Load-balancing between a Procurve switch and a server

  - by vlad

  Hello I've been searching around the web for this problem i've been having. It's similar in a way to this question: How exactly & specifically does layer 3 LACP destination address hashing work? My setup is as follows: I have a central switch, a Procurve 2510G-24, image version Y.11.16. It's the center of a star topology, there are four switches connected to it via a single gigabit link. Those switches service the users. On the central switch, I have a server with two gigabit interfaces that I want to bond together in order to achieve higher throughput, and two other servers that have single gigabit connections to the switch. The topology looks as follows: sw1 sw2 sw3 sw4 | | | | --------------------- | sw0 | --------------------- || | | srv1 srv2 srv3 The servers were running FreeBSD 8.1. On srv1 I set up a lagg interface using the lacp protocol, and on the switch I set up a trunk for the two ports using lacp as well. The switch showed that the server was a lacp partner, I could ping the server from another computer, and the server could ping other computers. If I unplugged one of the cables, the connection would keep working, so everything looked fine. Until I tested throughput. There was only one link used between srv1 and sw0. All testing was conducted with iperf, and load distribution was checked with systat -ifstat. I was looking to test the load balancing for both receive and send operations, as I want this server to be a file server. There were therefore two scenarios: iperf -s on srv1 and iperf -c on the other servers iperf -s on the other servers and iperf -c on srv1 connected to all the other servers. Every time only one link was used. If one cable was unplugged, the connections would keep going. However, once the cable was plugged back in, the load was not distributed. Each and every server is able to fill the gigabit link. In one-to-one test scenarios, iperf was reporting around 940Mbps. The CPU usage was around 20%, which means that the servers could withstand a doubling of the throughput. srv1 is a dell poweredge sc1425 with onboard intel 82541GI nics (em driver on freebsd). After troubleshooting a previous problem with vlan tagging on top of a lagg interface, it turned out that the em could not support this. So I figured that maybe something else is wrong with the em drivers and / or lagg stack, so I started up backtrack 4r2 on this same server. So srv1 now uses linux kernel 2.6.35.8. I set up a bonding interface bond0. The kernel module was loaded with option mode=4 in order to get lacp. The switch was happy with the link, I could ping to and from the server. I could even put vlans on top of the bonding interface. However, only half the problem was solved: if I used srv1 as a client to the other servers, iperf was reporting around 940Mbps for each connection, and bwm-ng showed, of course, a nice distribution of the load between the two nics; if I run the iperf server on srv1 and tried to connect with the other servers, there was no load balancing. I thought that maybe I was out of luck and the hashes for the two mac addresses of the clients were the same, so I brought in two new servers and tested with the four of them at the same time, and still nothing changed. I tried disabling and reenabling one of the links, and all that happened was the traffic switched from one link to the other and back to the first again. I also tried setting the trunk to "plain trunk mode" on the switch, and experimented with other bonding modes (roundrobin, xor, alb, tlb) but I never saw any traffic distribution. One interesting thing, though: one of the four switches is a Cisco 2950, image version 12.1(22)EA7. It has 48 10/100 ports and 2 gigabit uplinks. I have a server (call it srv4) with a 4 channel trunk connected to it (4x100), FreeBSD 8.0 release. The switch is connected to sw0 via gigabit. If I set up an iperf server on one of the servers connected to sw0 and a client on srv4, ALL 4 links are used, and iperf reports around 330Mbps. systat -ifstat shows all four interfaces are used. The cisco port-channel uses src-mac to balance the load. The HP should use both the source and destination according to the manual, so it should work as well. Could this mean there is some bug in the HP firmware? Am I doing something wrong?

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• Load balanced asp.net websites and required memory usage

  - by Matt

  Each of my servers has 8Gb RAM and the memory usage hovers around 7Gb. I have a load balancer available to me but at the moment I'm worried that putting my sites through it will cause the platform to fall over. The load balancer would be configured with a sticky round-robin where a new connection is round robin but subsequent connections for the same source ip will remain on the same server (until a limit is reached). Thats all standard stuff. How do I know what memory usage my sites will need across the platform when I put them through the load balancer? Rather than knowing that a site is using 150mb on a particular server I could face a situation where the 150mb is taken up on each of the servers. I know that with only 1 gb free I could have a serious problem on my hands. If I free up some memory then how can I work out what I need to have free to prevent this from happening? Thanks Matt

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• Load balancing Apache on a budget?

  - by Industrial

  Hi everyone, I am trying to get my head around the concept of load balancing to ensure availability and redundancy to keep users happy when things go wrong, rather than load balancing for the sake of offering blistering speed to millions of users. We're on a budget and trying to stick to the stuff where there's plenty of knowledge available, so running Apache on Ubuntu VPS's seems like the strategy until some famous search engine acquire us (Saturday irony included, please note). At least to me, it's a complete jungle of different solutions available. Apaches own mod_proxy & HAproxy are two that we found by a quick google search, but having zero experience of load balancing, I have no idea of what would be appropriate for our situation, or what we would look after while choosing a solution to solve our availability concerns. What is the best option for us? What should we do to get availability high whilst staying inside our budgets?

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• High server load - [jbd2/md1-8] using 99.99% IO

  - by Alex

  I've been having spike in load over the last week. This usually occurs once or twice a day. I've managed to identify from iotop that [jbd2/md1-8] is using 99.99 % IO. During the high load times there is no high traffic to the server. Server specs are: AMD Opteron 8 core 16 GB RAM 2x2.000 GB 7.200 RPM HDD Software Raid 1 Cloudlinux + Cpanel Mysql is properly tuned Apart from the spikes, the load usually is around 0.80 at most. I've searched around but can't find what [jbd2/md1-8] does exactly. Has anyone had this problem or does anyone know a possible solution? Thank you. UPDATE: TIME TID PRIO USER DISK READ DISK WRITE SWAPIN IO COMMAND 16:05:36 399 be/3 root 0.00 B/s 38.76 K/s 0.00 % 99.99 % [jbd2/md1-8]

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• Best Linux distro for load-balancers?

  - by Vimvq1987

  I wanted to try HAProxy/Linux Virtual Server like front-end load-balancers, but as far I know, they're Linux-based software. I don't have any experiences with Linux yet. so there're quite many questions to ask: What is the best Linux distro(s) for load-balancing? I plan to use VirtualPC to run some virtual machines. How much RAM is the best for each machine run that distro? I want to simulate a load-balancer with can handle about 100 hits/second, is it possible? Thank you very much!

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• PEN daemon as load balancer, IIS web logs not showing true requester IPs

  - by Aszurom

  I have a Hercules vmware appliance, which is a micro-linux vm that runs the PEN daemon and acts as a server load-balancer. It takes any incoming request on the appliance's IP and routes it out to a number of alternate IPs. The logs of the daemon show the true IP of the browsers hitting the website. The logs of the websites themselves (iis 6 and 7) only show the requester IP as being that of the load balancer. The IT manager tells me that when we had a hardware appliance (serveriron XL) doing the load balancing, the web logs reflected the requester IPs accurately. Is there any way to get this resolved with the daemon, or will I be digging that out of the closet and plugging it back in?

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• Load balancing SMTP in a way that doesn't hide the source IP address

  - by makerofthings7

  I need to load balance SMTP to handle some applications that don't know how to use MX records. I set up a Netscaler using the TCP option on port 25 and now Exchange sees the source IP as that of the DMZ of the Netscaler for every connection, not the client. Obviously this prevents RBLs, Whitelists, and all other IP-based reputation to fail. It also make it impossible to whitelist a trusted IP for anonymous relay. Question How should I configure the NetScaler (or Windows Load Balancing) so that I can allow load balancing yet still maintain visibility of the source IP?

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• AWS SSL Load Balancer

  - by Jay Francis

  OK, I am looking for some pointers. Basically I have a white-label app/site that will allow users to setup their own domain to use for their customer front-end. We have 2 dedicated servers and a load balancer. The problem is SSL, we were thinking about using AWS ELB to handle the SSL loadbalancing, but cant seem to figure out if it will properly handle it, it seems to be setup to work with EC2 instances, but we are using externally hosted servers via a loadbalancer. A blog post by AWS looks similar to what we need but it only seems to work with EC2 instances. http://aws.typepad.com/aws/2011/08/elastic-load-balancer-ssl-support-options.html Anyone had experience setting ELS SSL load balancers up to work with external servers?

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• Load Balancer recommendations

  - by delerious010

  I provide hosting service for about 250 clients to date, and this is increasing on a monthly basis. For each client, I have 2 "services" configured for L4 balancing / persistence .. one on port 80, another for port 443 which redirects to another internal port as well as 4 servers per service. This equates to a total of 500 "services" and 2000 "servers". I'm currently running with a couple CoyotePoint load balancers, and have had a look at some Barracudas but so far I'm really not impressed by those. Could anyone recommend some good load balancers which would be able to support this sort of load ? And which offer a good API, or shell access to automate management.

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• High Load - Low IO - Low CPU usage

  - by devup

  I have a system whose load is rather high. As you can see from the top output below, CPU usage and I/O is negligible: top - 17:31:59 up 4 days, 2:34, 2 users, load average: 1.00, 0.99, 1.00 Tasks: 71 total, 1 running, 70 sleeping, 0 stopped, 0 zombie Cpu(s): 2.0%us, 2.0%sy, 0.0%ni, 95.9%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st Mem: 960720k total, 707288k used, 253432k free, 67328k buffers Swap: 2811896k total, 2644k used, 2809252k free, 528928k cached PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 15310 root 20 0 2512 1128 888 R 2.1 0.1 0:00.05 top I would appreciate any assistance with isolating the cause(s) of high load for when I/O and CPU are not factors.

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• Sticky sessions on load balancers with HTTP and HTTPS

  - by javano

  How does sticky sessions relate to HTTP and HTTPS; If I place a load balancer in front of some web app servers that run a front end that supports HTTPS, will the sessions remain "sticky" on a typical load balancer that lists "stick sessions" as one of it's supported features? I understand that question is partly open ended; To clarify, would I require a load balancer that supports sticky HTTPS session specifical or is "sticky sessions" a principal that functions agnostic of the HTTP payload, be it encrypted or not? Thank you.

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• Sticky Load Balancing with AWS

  - by John Wheal

  I have just setup a load balancer with AWS for a few instances as search engine crawlers were bringing down the site (it has millions of pages). Parts of the site allow you to login so I selected: Enable Application Generated Cookie Stickiness and everything works fine. I now wonder how this will effect my SEO and the crawlers. As I selected sticky load balancing does this mean that a crawler will be stuck on one server and therefore defeat the point in the load balancer? Any recommendations will be appreciated.

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• Use HAProxy or Nginx to Load Balance between VPS

  - by xperator

  I want to load balance + failover backup multiple vps webservers hosted on different providers. I heard that for HAProxy you need multiple server under the same subnet, plus a shared (virtual) ip address between load balancers. But it's not possible in my case cause every VPS is on different node/network. Is there a way to use HAProxy in this kind of setup ? ( Please explain how briefly, I don't want to hear your "YES" answer ) What about NginX? Is it possible to achieve same result with Nginx ? (when servers are located on different nets) I know about Round Rubin DNS, but it doesn't provide a real failover solution, neither a load balance between servers.

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• Clustering with Vsphere and Apache load balacing

  - by Anonymous2011

  I was looking at Vsphere to automatically load balance my apache web servers, and mysql servers but will this actually do the job? I know it says it does auto load balancing but not actually sure it quite means what I want to achieve. Is there an easier way to set up a php-apache and mysql cluster within virtual machines? Or are there any guides to clustering? (I have tried googling without much luck) Any help towards understanding/setting up clustering and load balancing within virtual machines appreciated.

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• Load-balanced Linux server across internet?

  - by LinuxGnut

  I'm investigating setting up a load balanced server solution consisting of three CentOS 5.4 boxes. Two of these boxes will reside in one facility, while a third will reside in a different facility. I'm currently working to set up heartbeat, ldirectord, ipvsadm to load-balance the machines, but I'm not sure its going to work with I'm not overly familiar with the details behind how all of these work, but is the load balancing going to work correctly when these servers are not all on the same LAN? I'm not sure if heartbeat is using SNMP to send signals or not, which would only work over a LAN. Has anyone tried this or found a different solution?

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• Nginx load distribution and multi-domain SSL

  - by Steve Clark

  I'm researching into the best methods of two new parts of our infrastructure, hopefully finding a single solution for both. 1) We're currently running a single application server, and we're going to be adding an additional application server and load balance between the two. 2) We handle a few thousand domains across the application server(s), and we're looking to support SSL. The best method i've come across so far is using nginx for it's Load Distribution to serve the requests to the application servers, and for it's SSL support. If a request is using SSL, nginx accepts the request on, terminates SSL and pipes to apache (app servers). Now, that's all good, but i'm yet to figure out how we can let nginx handle multiple domains using SSL. We're potentially looking at using UCC SSL Certs, so we can support 150 domains on a single certificate, with each cert on a single IP. I'm all new to this (My experience is just with physical load balancers and a single domains on SSL), so any advice would be very much appreciated.

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• A really unique case of Load Balancing

  - by Shamshun

  I have an internet connection which has limited up/down bandwidth per IP address. What I want to do is to get multiple IP addresses on a "single" LAN interface, and use a load balancer to distribute traffic through them. I was successful at getting 100 ip addresses on a single interface. my problem is that Linux and Windows use the first ip address of an interface by default, so my bandwidth is not increased. I would appreciate if someone tells me what Load Balancing software has the ability to distribute load between multiple IPs on a single interface. I have tried to do so on both Win7 and Backtrack-LinuxR2

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• C# Assembly.GetTypes() - ReflectionTypeLoadException

  - by Veskechky

  We implement a plugin framework for our application and load plugin assemblies using Assembly.Loadfrom. We then use GetTypes() and further examine the types with each plugin file for supported Interfaces. A path for the plugins is provided by the user and we cycle through each of the files in the folder to see if it (the plugin) supports our plugin interface. If it does, we create an instance, if not we move onto the next file. We build two versions of software from the one code base (appA_1 and appA_2). Loading the plugins works well when the plugins are loaded by the application that was built at the same time as the plugin file. However if we build appA_2 and point to the plugin folder of appA_1, we get an exception when GetTypes() is called. A basic version of our code is; var pluginAssembly = Assembly.LoadFrom(FileName); foreach (var pluginType in pluginAssembly.GetTypes()) { We get a "ReflectionTypeLoadException" exception. This is concerning because we want our application to be able to load the types of any plugin, built by anyone. Is there something we are missing?

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• Am I Writing Assembly Or NASM?

  - by cam

  I'm fed up with this. I've been trying to just get a grip on assembly for awhile, but I feel like I'm coding towards my compiler rather than a language. I've been using this tutorial, and so far it's giving me hell. I'm using NASM, which may be the problem, but I figured it was the most popular one. I'm simply trying to learn the most general form of assembly, so I decided to learn x86. I keep running into stupid errors, like not being able to increment a variable. Here's the latest one: not being able to use div. mov bx, 0; mov cx, 0; jmp start; start: inc cx; mov ax, cx; div 3; <-- invalid combination of opcode and operand cmp ah,0; jz totalvalue; mov ax, cx; div 5; <-- invalid combination of opcode and operand cmp ah, 0; jz totalvalue; cmp cx, 1000; jz end; totalvalue: add bx,cx; jmp start; jmp end; end: mov ah,4ch; mov al,00; int 21h; Should I change compilers? It seems like division should be standard. Do I need to read two tutorials (one on NASM, and one on x86?). Any specific help on this problem?

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• Compile Assembly Output generated by VC++?

  - by SDD

  I have a simple hello world C program and compile it with /FA. As a consequence, the compiler also generates the corresponding assembly listing. Now I want to use masm/link to assemble an executable from the generated .asm listing. The following command line yields 3 linker errors: \masm32\bin\ml /I"C:\Program Files (x86)\Microsoft Visual Studio 9.0\VC\include" /c /coff asm_test.asm \masm32\bin\link /SUBSYSTEM:CONSOLE /LIBPATH:"C:\Program Files (x86)\Microsoft Visual Studio 9.0\VC\lib" asm_test.obj indicating that the C-runtime functions were not linked to the object files produced earlier: asm_test.obj : error LNK2001: unresolved external symbol @__security_check_cookie@4 asm_test.obj : error LNK2001: unresolved external symbol _printf LINK : error LNK2001: unresolved external symbol _wmainCRTStartup asm_test.exe : fatal error LNK1120: 3 unresolved externals Here is the generated assembly listing ; Listing generated by Microsoft (R) Optimizing Compiler Version 15.00.30729.01 TITLE c:\asm_test\asm_test\asm_test.cpp .686P .XMM include listing.inc .model flat INCLUDELIB OLDNAMES PUBLIC ??_C@_0O@OBPALAEI@hello?5world?$CB?6?$AA@ ; `string' EXTRN @__security_check_cookie@4:PROC EXTRN _printf:PROC ; COMDAT ??_C@_0O@OBPALAEI@hello?5world?$CB?6?$AA@ CONST SEGMENT ??_C@_0O@OBPALAEI@hello?5world?$CB?6?$AA@ DB 'hello world!', 0aH, 00H ; `string' CONST ENDS PUBLIC _wmain ; Function compile flags: /Ogtpy ; COMDAT _wmain _TEXT SEGMENT _argc$ = 8 ; size = 4 _argv$ = 12 ; size = 4 _wmain PROC ; COMDAT ; File c:\users\octon\desktop\asm_test\asm_test\asm_test.cpp ; Line 21 push OFFSET ??_C@_0O@OBPALAEI@hello?5world?$CB?6?$AA@ call _printf add esp, 4 ; Line 22 xor eax, eax ; Line 23 ret 0 _wmain ENDP _TEXT ENDS END I am using the latest masm32 version (6.14.8444).

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• Alignment in assembly

  - by jena

  Hi, I'm spending some time on assembly programming (Gas, in particular) and recently I learned about the align directive. I think I've understood the very basics, but I would like to gain a deeper understanding of its nature and when to use alignment. For instance, I wondered about the assembly code of a simple C++ switch statement. I know that under certain circumstances switch statements are based on jump tables, as in the following few lines of code: .section .rodata .align 4 .align 4 .L8: .long .L2 .long .L3 .long .L4 .long .L5 ... .align 4 aligns the following data on the next 4-byte boundary which ensures that fetching these memory locations is efficient, right? I think this is done because there might be things happening before the switch statement which caused misalignment. But why are there actually two calls to .align? Are there any rules of thumb when to call .align or should it simply be done whenever a new block of data is stored in memory and something prior to this could have caused misalignment? In case of arrays, it seems that alignment is done on 32-byte boundaries as soon as the array occupies at least 32 byte. Is it more efficient to do it this way or is there another reason for the 32-byte boundary? I'd appreciate any explanation or hint on literature.

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