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• Need help identifing what resources (eg. In MIT OpenCourseWare) can help me prepare for a test [closed]

  - by jiewmeng

  I am entering uni soon. I can sit for a placement test to see if I elegible for exemptions. The details are http://www.comp.nus.edu.sg/undergraduates/TestScope11_12.html Or CS2100 Computer Organisation (please click title) The objective of this module is to familiarise students with the fundamentals of computing devices. Through this module students will understand the basics of data representation, and how the various parts of a computer work, separately and with each other. This allows students to understand the issues in computing devices, and how these issues affect the implementation of solutions. Topics covered include data representation systems, combinational and sequential circuit design techniques, assembly language, processor execution cycles, pipelining, memory hierarchy and input/output systems. Recommended Textbooks Digital Design: Principles and Practices [DDPP] by John F. Wakerly, Prentice-Hall. ISBN 0-13-324500-4. Computer Organizations and Design (The hardware/software interface) by David A. Patterson and John L. Hennessy. CS2105 Introduction to Computer Networks (please click title) This course aims to provide a broad introduction to computer networks and some appreciations of network application programming. It covers a range of topics including basic data communication and computer network concepts, protocols, networked computing concepts and principles, network applications development and network security. The emphasis of teaching is on the working principles and application of computer networks. As an integral part of the course, tutorials and practical assignments enforcing learning will also be given. These assignments provide an early exposure in network application programming and they should be able to complete by using personal computers and school's network facilities. Topics included: An overview of computer networks and the Internet Basic data communications Application layer Transport layer Network layer and routing Link layer and local area networks Recommended Textbook James F. Kurose & Keith W. Ross, Computer networking: A top-down approach featuring internet, Addison Wesley, 2001 I am wondering what resources eg. MIT OpenCourseWare or other universities resources are available to help he perpare for these particular modubles. I am thinking does the Networking one look like CCNA? The computer oragization. Its like electronics, assembly etc? I learnt some electronics in Poly but looking at the sample papers, uni looks very different... I have about 1 month to prepare if I want any chance of exempting from these modules :) any help?

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• Wifi problems after upgrading to 13.10

  - by Simon

  I just upgraded to Ubuntu 13.10, but since the upgrade I don't have internet access via wifi anymore. I can: See networks Connect to a network Ping myself (localhost, 192.168.0.103) I can't: Ping others (including other devices on the same wireless network, including the gateway/router) Resolve hosts Access any other external resource, whether on my own network or on the internet Using Wireshark, I noticed my computer is continuously sending ARP-requests like "Who has 192.168.0.1 [which is the gateway]? Tell 192.168.0.103". It doesn't get any replies though. When I ping another IP-address for which it knows the mac-address (from cache), it turns out a packet loss of 90% occurs, and even if a packet manages to arrive it takes around 3000ms. The output of route -n is: Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 0.0.0.0 192.168.0.1 0.0.0.0 UG 0 0 0 eth1 192.168.0.0 0.0.0.0 255.255.255.0 U 9 0 0 eth1 192.168.122.0 0.0.0.0 255.255.255.0 U 0 0 0 virbr0 Before upgrading, wifi worked fine. Using other devices, wifi still works fine.Resetting the router didn't help. Ethernet still works after upgrading. Any suggestions? Update: I'm using the wl driver. Here's the relevant output of some commands: lspci | grep Wireless 03:00.0 Network controller: Broadcom Corporation BCM4313 802.11bgn Wireless Network Adapter (rev 01) cat /etc/modprobe.d/blacklist.conf [...] blacklist mac80211 blacklist brcm80211 blacklist cfg80211 blacklist lib80211_crypt_tkip blacklist lib80211 blacklist b43 cat /etc/rc.local sudo modprobe -r lib80211 sudo insmod /lib/modules/3.2.0-30-generic-pae/kernel/net/wireless/lib80211.ko sudo insmod /lib/modules/3.2.0-30-generic-pae/kernel/net/wireless/lib80211_crypt_wep.ko sudo insmod /lib/modules/3.2.0-30-generic-pae/kernel/net/wireless/lib80211_crypt_tkip.ko sudo insmod /lib/modules/3.2.0-30-generic-pae/kernel/net/wireless/lib80211_crypt_ccmp.ko sudo modprobe wl exit 0 The last lines are probably how I got wireless working after the previous upgrade (wireless has been a problem after each upgrade). Update 2: added information about the exact hardware below. The hardware is an integrated device, so I ran lspci -nn | grep -i network. The output is: 03:00.0 Network controller [0280]: Broadcom Corporation BCM4313 802.11bgn Wireless Network Adapter [14e4:4727] (rev 01)

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• PHP - Internal APIs/Libraries - What makes sense?

  - by Mark Locker

  I've been having a discussion lately with some colleagues about the best way to approach a new project, and thought it'd be interesting to get some external thoughts thrown into the mix. Basically, we're redeveloping a fairly large site (written in PHP) and have differing opinions on how the platform should be setup. Requirements: The platform will need to support multiple internal websites, as well as external (non-PHP) projects which at the moment consist of a mobile app and a toolbar. We have no plans/need in the foreseeable future to open up an API externally (for use in products other than our own). My opinion: We should have a library of well documented native model classes which can be shared between projects. These models will represent everything in our database and can take advantage of object orientated features such as inheritance, traits, magic methods, etc. etc. As well as employing ORM. We can then add an API layer on top of these models which can basically accept requests and route them to the appropriate methods, translating the response so that it can be used platform independently. This routing for each method can be setup as and when it's required. Their opinion: We should have a single HTTP API which is used by all projects (internal PHP ones or otherwise). My thoughts: To me, there are a number of issues with using the sole HTTP API approach: It will be very expensive performance wise. One page request will result in several additional http requests (which although local, are still ones that Apache will need to handle). You'll lose all of the best features PHP has for OO development. From simple inheritance, to employing the likes of ORM which can save you writing a lot of code. For internal projects, the actual process makes me cringe. To get a users name, for example, a request would go out of our box, over the LAN, back in, then run through a script which calls a method, JSON encodes the output and feeds that back. That would then need to be JSON decoded, and be presented as an array ready to use. Working with arrays, as appose to objects, makes me sad in a modern PHP framework. Their thoughts (and my responses): Having one method of doing thing keeps things simple. - You'd only do things differently if you were using a different language anyway. It will become robust. - Seeing as the API will run off the library of models, I think my option would be just as robust. What do you think? I'd be really interested to hear the thoughts of others on this, especially as opinions on both sides are not founded on any past experience.

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• Looking for an algorithm to connect dots - shortest route

  - by e4ch

  I have written a program to solve a special puzzle, but now I'm kind of stuck at the following problem: I have about 3200 points/nodes/dots. Each of these points is connected to a few other points (usually 2-5, theoretical limit is 1-26). I have exactly one starting point and about 30 exit points (probably all of the exit points are connected to each other). Many of these 3200 points are probably not connected to neither start nor end point in any way, like a separate net, but all points are connected to at least one other point. I need to find the shortest number of hops to go from entry to exit. There is no distance between the points (unlike the road or train routing problem), just the number of hops counts. I need to find all solutions with the shortest number of hops, and not just one solution, but all. And potentially also solutions with one more hop etc. I expect to have a solution with about 30-50 hops to go from start to exit. I already tried: 1) randomly trying possibilities and just starting over when the count was bigger than a previous solution. I got first solution with 3500 hops, then it got down to about 97 after some minutes, but looking at the solutions I saw problems like unnecessary loops and stuff, so I tried to optimize a bit (like not going back where it came from etc.). More optimizations are possible, but this random thing doesn't find all best solutions or takes too long. 2) Recursively run through all ways from start (chess-problem-like) and breaking the try when it reached a previous point. This was looping at about a length of 120 nodes, so it tries chains that are (probably) by far too long. If we calculate 4 possibilities and 120 nodes, we're reaching 1.7E72 possibilities, which is not possible to calculate through. This is called Depth-first search (DFS) as I found out in the meantime. Maybe I should try Breadth-first search by adding some queue? The connections between the points are actually moves you can make in the game and the points are how the game looks like after you made the move. What would be the algorithm to use for this problem? I'm using C#.NET, but the language shouldn't matter.

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• How do I server multiple domains from the same directory and codebase without my configuraton breaking when apache.conf is overwritten?

  - by neokio

  I have 20 domains on a VPS running cPanel. One public_html is filled with code, the remaining 19 are symbolic links to that one. (For example, assets is a directory within public_html ... for the 19 others, there's a symbolic link to that directory in each each accounts public_html dir.) It's all PHP / MySQL database driven, with content changing depending on the domain. It works like a charm, assuming cPanel has suExec enabled correctly, and assuming apache.conf does NOT have SymLinksIfOwnerMatch enabled. However, every few weeks, my apache.conf is mysteriously overwritten, re-enabling SymLinksIfOwnerMatch, and disabling all 19 linked sites for as long as it takes for me to notice. Here's the offending line in apache.conf: <Directory "/"> AllowOverride All Options ExecCGI FollowSymLinks IncludesNOEXEC Indexes SymLinksIfOwnerMatch </Directory> The addition of SymLinksIfOwnerMatch disables the sites in a strange way ... the html is generated correctly, but all css/js/image in the html fails to load. Clicking any link redirects to /. And I have no idea why. I do have a few things in my .htaccess, which work fine when SymLinksIfOwnerMatch is not present: <IfModule mod_rewrite.c> # www.example.com -> example.com RewriteCond %{HTTPS} !=on RewriteCond %{HTTP_HOST} ^www\.(.+)$ [NC] RewriteRule ^ http://%1%{REQUEST_URI} [R=301,L] # Remove query strings from static resources RewriteRule ^assets/js/(.*)_v(.*)\.js /assets/js/$1.js [L] RewriteRule ^assets/css/(.*)_v(.*)\.css /assets/css/$1.css [L] RewriteRule ^assets/sites/(.*)/(.*)_v(.*)\.css /assets/sites/$1/$2.css [L] # Block access to hidden files and directories RewriteCond %{SCRIPT_FILENAME} -d [OR] RewriteCond %{SCRIPT_FILENAME} -f RewriteRule "(^|/)\." - [F] # SLIR ... reroute images to image processor RewriteCond %{REQUEST_URI} ^/images/.*$ RewriteRule ^.*$ - [L] # ignore rules if URL is a file RewriteCond %{REQUEST_FILENAME} !-f # ignore rules if URL is not php #RewriteCond %{REQUEST_URI} !\.php$ # catch-all for routing RewriteRule . index.php [L] </ifModule> I also use most of the 5G Blacklist 2013 for protection against exploits and other depravities. Again, all of this works great, except when SymLinksIfOwnerMatch gets added back into apache.conf. Since I've failed to find the cause of whatever cPanel/security update is overwriting apache.conf, I thought there might be a more correct way to accomplish my goal using group permissions. I've created a 'www' group, added all accounts to the group, and chmod -R'd the code source to use that group. Everything is 644 or 755. But doesn't seem to be enough. My unix isn't that strong. Do you need to restart something for group changes to take effect? Probably not. Anyways, I'm entering unknown territory. Can anyone recommend the right way to configure a website for multiple sites using one codebase that doesn't rely on apache.conf?

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• How can you know what is w3wp.exe doing? (or how to diagnose a performance problem)

  - by Daniel Magliola

  I'm having a performance problem in a site we've made, and I'm not exactly sure how to start diagnosing it. The short description is: We have a very small site (http://hearablog.com) with very little traffic, in a crappy dedicated server, CPU is always very high, sometimes it stays at 100% for minutes, and w3wp.exe is taking most of it. A typical scenario is w3wp.exe takes 60%, and SQL Server takes about 30%. Our DB is pretty small too. Long description and more details: The site is hosted in a very crappy server by Cari.Net. From the beginning we had the feeling that the server didn't quite behave correctly, like some things would take just too long, so this could be a configuration problem from the get go. It may also be that we are getting a virtual server while we're supposed to have a dedicated one, although we have no evidence that'd indicate this, except for the fact that the server tends to be quite slow. The server is Windows 2008 Standard 64-bit, with SQL 2008 Express Hardware is a Celeron 2.80 GHz, 1Gb RAM The website is developed in ASP.Net MVC, using Entity Framework for data access. Now, this is pretty crappy hardware, but i've had other servers with these guys, with equivalent (or worse) HW, and performance is much better than this one. That said, the other servers have W2003 and SQL2005, and I'm using ASP.Net "WebForms" 2.0, no MVC, no LINQ, no EF; so I'm not sure whether going to 2008 / the other stuff means a big performance penalty is expected. I'm serving MP3 files (5-20 Mb) regularly, which is a slightly unusual load, maybe that is causing some kind of problems? Would that cause w3wp to use a lot of CPU? Disk usage seems very low. Memory is usually around 90%, but disk usage seems to indicate it's not paging much. I get tons of e-mails every day about SQL timeouts, for queries taking over 30 seconds, although all our queries are pretty straightforward (or should be, but EF may be screwing it up). This is what resource monitor looks like in one of these "sprints" of 100% CPU, in case there's anything useful there. And a snapshot of some performance counters: Now, what confuses me very much is that CPU usage of w3wp is just so high. It shouldn't be doing much really... So my questions are... Is there any way of finding out "what" it is doing? Maybe even profile it? Any performance counters I should be looking at? Is this to be expected given this hardware/software configuration? Is this could be cause by some kind of configuration failure, where would you start looking? Thank you VERY much. Daniel Magliola

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• HAProxy reqrep remove URI on backend request

  - by Jim

  real quick question regarding HAProxy reqrep. I am trying to rewrite/replace the request that gets sent to the backend. I have the following example domain and URIs http://domain/web1 http://domain/web2 I want web1 to go to backend webfarm1, and web2 to go to webfarm2. Currently this does happen. However I want to strip off the web1 or web2 URI when the request is sent to the backend. Here is my haproxy.cfg frontend webVIP_80 mode http bind :80 #acl routing to backend acl web1_path path_beg /web1 acl web2_path path_beg /web2 #which backend use_backend webfarm1 if web1_path use_backend webfarm2 if web2_path default_backend webfarm1 backend webfarm1 mode http reqrep ^([^\ ]*)\ /web1/(.*) \1\ /\2 balance roundrobin option httpchk HEAD /index HTTP/1.1\r\nHost:\ example.com server webtest1 10.0.0.10:80 weight 5 check slowstart 5000ms server webtest2 10.0.0.20:80 weight 5 check slowstart 5000ms backend webfarm2 mode http reqrep ^([^\ ]*)\ /web2/(.*) \1\ /\2 balance roundrobin option httpchk HEAD /index HTTP/1.1\r\nHost:\ example.com server webtest1-farm2 10.0.0.110:80 weight 5 check slowstart 5000ms server webtest2-farm2 10.0.0.120:80 weight 5 check slowstart 5000ms If I go to http://domain/web1 or http://domain/web2 I see it in the error logs that the request on a server in each backend that the requst is for the resource /web1 or /web2 respectively. Therefore I believe there to be something wrong with my regular expression, even though I copied and pasted it from the Documentation. http://code.google.com/p/haproxy-docs/wiki/reqrep Summary: I'm trying to route traffic based on URI, however I want to strip the URI on the backend side. Go to http://domain/web1 -- backend request of / to webfarm1 Thank you! -Jim

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• RouterOS on Hyper-V (v3/2012) - any way to get it working?

  - by TomTom

  Trying to set up a small VPN point to connect into a remote Hyper-V cluster using ROuterOS. Anyone got it working ON Hyper-V with the latest builds of RouterOS? It seems the legacy network adapter is not supported anymore either (or just broken). The platform is a Windows Server 2012 RC. This is not a high performance setup - the RouterOS wont do the routing for more than the backend administrative access, and the only real traffic we will see there is when ISO images for new operating systems are uploaded. Otherwise we will have possibly RDP traffic as well as web / http traffioc, but this is internal only (dashboards, some control panel). The server has no public business. So the price for non virtualized network cards is ok for me. After hooking up - ping just does not work. After some time I see in windows (arp -a on the command line), so I know that the Hyper-V side is set up properly. Just no packets arrived. I have turned off all protection on Hyper-V (or : not turned them on), so no MAC spoofing protection etc. in the Advanced page for the legacy adapters. Unless I can get it work I will have to resort to using a windows install as router / VPN endpoint, which introduces another OS into the fabric (we run all routers etc. so far on mikrotik in hardware, which is why I want this one to be RouterOS, too). And no, putting hardware there is NOT an option - the cost would be significant.

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• Configuring VirtualBox host only networking: OSX host, Ubuntu guest

  - by Greg K

  I have a Ubuntu guest configured with two interfaces, eth0 is using NAT and works fine, I can access the net. The second interface eth1 is set to host only networking and VirtualBox has created a vboxnet0 virtual adapter on the host. I've configured vboxnet0 in VirtualBox adapter settings with the following: ip 192.168.21.20 subnet 255.255.255.0 Once the VM guest is running, ifconfig on OSX has vboxnet0 setup as: vboxnet0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500 ether 0a:00:27:00:00:00 inet 192.168.21.20 netmask 0xffffff00 broadcast 192.168.21.255 In the guest, eth0 is set to use DHCP, I've statically assigned eth1 to 192.168.21.20 (is this a mistake?): auto eth1 iface eth1 inet static address 192.168.21.20 netmask 255.255.255.0 network 192.168.21.0 broadcast 192.168.21.255 gateway 192.168.21.1 There is no device on 192.168.21.1 - what should I set my gateway to? In the guest the routes look like so: Destination Gateway Genmask Flags Metric Ref Use Iface 192.168.21.0 * 255.255.255.0 U 0 0 0 eth1 10.0.2.0 * 255.255.255.0 U 0 0 0 eth0 default 10.0.2.2 0.0.0.0 UG 100 0 0 eth0 default 192.168.21.1 0.0.0.0 UG 100 0 0 eth1 Route table on OSX: $ netstat -nr Routing tables Internet: Destination Gateway Flags Refs Use Netif Expire default 10.77.36.1 UGSc 28 0 en1 10.77.36/22 link#5 UCS 5 0 en1 10.77.39.38 127.0.0.1 UHS 1 2236 lo0 10.77.39.255 link#5 UHLWbI 1 66 en1 127 127.0.0.1 UCS 0 0 lo0 127.0.0.1 127.0.0.1 UH 1 8642 lo0 169.254 link#5 UCS 0 0 en1 192.168.21 link#7 UC 2 0 vboxnet 192.168.21.20 a:0:27:0:0:0 UHLWI 0 4 lo0 192.168.21.255 link#7 UHLWbI 2 64 vboxnet I can't SSH from the host to the guest (I used to be able to when the VM was configured with a bridged connection): $ ssh 192.168.21.20 ssh: connect to host 192.168.21.20 port 22: Connection refused What have I done wrong here? TIA

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• Configuring default gateway returned by dhcp server

  - by comp1mp

  Hello, I have a machine which connects via ethernet to a private LAN, and wireless to a network which provides internet connectivity. The private LAN uses a wireless router to perform DHCP. The problem is that the wireless and NIC adapters have different default gateways. The default gateway for the private LAN has a lower adapter metric, and is thus chosen by the routing algorithm. I am thus unable to browse the internet when connected to both adapters. The following link has a solution for manually setting the adapter metric to a high number. http://superuser.com/questions/77822/how-to-tell-windows-7-to-ignore-a-default-gateway I was hoping to find a different solution. Does any one know of a router that allows you to configure its DHCP server to return an empty default gateway? I cannot find such an option for my linksys wrt300n. Configuring a static ip address with no default gateway does work, however I would like to use DHCP if possible. Does anyone know of a different way to specify a default gateway for a windows 7 machine with multiple network adapters without mucking with the adapter metric? Thanks, Matthew

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• Connecting to ItsHidden in Ubuntu 9.10 problems

  - by Ionel Bratianu

  I try to setup a VPN connection to ItsHidden on Ubuntu 9.10. I double-checked my credentials in the VPN configuration, but I don't think that this is problem. In my syslog I got these messages: Jan 11 14:38:46 NetworkManager: Starting VPN service 'org.freedesktop.NetworkManager.pptp'... Jan 11 14:38:46 NetworkManager: VPN service 'org.freedesktop.NetworkManager.pptp' started (org.freedesktop.NetworkManager.pptp), PID 4502 Jan 11 14:38:46 NetworkManager: VPN service 'org.freedesktop.NetworkManager.pptp' just appeared, activating connections Jan 11 14:38:46 NetworkManager: VPN plugin state changed: 1 Jan 11 14:38:46 NetworkManager: VPN plugin state changed: 3 Jan 11 14:38:46 pppd[4506]: Plugin /usr/lib/pppd/2.4.5//nm-pptp-pppd-plugin.so loaded. Jan 11 14:38:46 NetworkManager: VPN connection 'ItsHidden' (Connect) reply received. Jan 11 14:38:46 pppd[4506]: pppd 2.4.5 started by root, uid 0 Jan 11 14:38:46 pppd[4506]: Using interface ppp0 Jan 11 14:38:46 NetworkManager: SCPlugin-Ifupdown: devices added (path: /sys/devices/virtual/net/ppp0, iface: ppp0) Jan 11 14:38:46 NetworkManager: SCPlugin-Ifupdown: device added (path: /sys/devices/virtual/net/ppp0, iface: ppp0): no ifupdown configuration found. Jan 11 14:38:46 pppd[4506]: Connect: ppp0 /dev/pts/1 Jan 11 14:39:06 pptp[4508]: nm-pptp-service-4502 fatal[get_ip_address:pptp.c:430]: gethostbyname 'vpn.itshidden.com': HOST NOT FOUND Jan 11 14:39:06 pppd[4506]: Modem hangup Jan 11 14:39:06 pppd[4506]: Connection terminated. Jan 11 14:39:06 NetworkManager: VPN plugin failed: 1 Jan 11 14:39:06 NetworkManager: SCPlugin-Ifupdown: devices removed (path: /sys/devices/virtual/net/ppp0, iface: ppp0) Jan 11 14:39:06 pppd[4506]: Exit. Jan 11 14:39:06 NetworkManager: VPN plugin failed: 1 Jan 11 14:39:06 NetworkManager: VPN plugin failed: 1 Jan 11 14:39:06 NetworkManager: VPN plugin state changed: 6 Jan 11 14:39:06 NetworkManager: VPN plugin state change reason: 0 Jan 11 14:39:06 NetworkManager: connection_state_changed(): Could not process the request because no VPN connection was active. Jan 11 14:39:06 NetworkManager: Policy set 'Auto eth0' (eth0) as default for routing and DNS. Jan 11 14:39:19 NetworkManager: [1263213559.003098] ensure_killed(): waiting for vpn service pid 4502 to exit Jan 11 14:39:19 NetworkManager: [1263213559.003289] ensure_killed(): vpn service pid 4502 cleaned up Because the gethostbyname is failing, I suppose that the NetworkManager doesn't know that I use proxies for accessing Internet. I'm not sure that this is the real problem. Could you tell me a solution to make gesthostbyname not failing anymore?

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• Existing open source software for wireless mesh networking?

  - by user70352

  Hello! My goal: Build a wireless mesh network with some ALIX 2D2 (500 MHz AMD Geode LX800 x86 CPU, 256MB RAM, Atheros wireless card) Aside from working like a normal wireless mesh network users should be able to read/write data from/to the ALIX Boxes and the ALIX boxes should be able to process data. Questions: Should I try to flash dd-wrt x86, voyage linux (linux.voyage.hk) or something else? What (open source) software should I look into before I start? Should I use a 'server' for data storage and processing instead of the ALIX boxes? Is it even possible to use the ALIX boxes for routing AND data storage and processing? Final notes: Data can be anything, for example, I want to setup a wireless mesh using the OLSRD protocol so my whole town gets wifi and can access songs on the network. It's not for that, but that's the idea. I'm not afraid of programing, compiling or working with *nix. This is mostly 'for fun' rather than for practicality. Thanks in advance for any feedback.

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• Avoiding DNS timeouts when a dns server fails

  - by user65124

  Hi there. We have a small datacenter with about a hundred hosts pointing to 3 internal dns servers (bind 9). Our problem comes when one of the internal dns servers becomes unavailable. At that point all the clients that point to that server start performing very slowly. The problem seems to be that the stock linux resolver doesn't really have the concept of "failing over" to a different dns server. You can adjust the timeout and number of retries it uses, (and set rotate so it will work through the list), but no matter what settings one uses our services perform much more slowly if a primary dns server becomes unavailable. At the moment this is one of the largest sources of service disruptions for us. My ideal answer would be something like "RTFM: tweak /etc/resolv.conf like this...", but if that's an option I haven't seen it. I was wondering how other folks handled this issue? I can see 3 possible types of solutions: Use linux-ha/Pacemaker and failover ips (so the dns IP VIPs are "always" available). Alas, we don't have a good fencing infrastructure, and without fencing pacemaker doesn't work very well (in my experience Pacemaker lowers availability without fencing). Run a local dns server on each node, and have resolv.conf point to localhost. This would work, but it would give us a lot more services to monitor and manage. Run a local cache on each node. Folks seem to consider nscd "broken", but dnrd seems to have the right feature set: it marks dns servers as up or down, and won't use 'down' dns servers. Any-casting seems to work only at the ip routing level, and depends on route updates for server failure. Multi-casting seemed like it would be a perfect answer, but bind does not support broadcasting or multi-casting, and the docs I could find seem to suggest that multicast dns is more aimed at service discovery and auto-configuration rather than regular dns resolving. Am I missing an obvious solution?

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• Cannot connect to a VPN server - authentication failed with error code 691

  - by stacker

  When trying to connect to a VPN server, I get the 691 error code on the client, which say: Error Description: 691: The remote connection was denied because the user name and password combination you provided is not recognized, or the selected authentication protocol is not permitted on the remote access server. I validated that the username and password are correct. I also installed a certification to use with the IKEv2 security type. I also validated that the VPN server support security method. But I cannot login. In the server log I get this log: Network Policy Server denied access to a user. The user DomainName\UserName connected from IP address but failed an authentication attempt due to the following reason: The remote connection was denied because the user name and password combination you provided is not recognized, or the selected authentication protocol is not permitted on the remote access server. Any idea of what can I do? Thanks in advance! Log Name: Security Source: Microsoft-Windows-Security-Auditing Date: 12/29/2010 7:12:20 AM Event ID: 6273 Task Category: Network Policy Server Level: Information Keywords: Audit Failure User: N/A Computer: VPN.domain.com Description: Network Policy Server denied access to a user. Contact the Network Policy Server administrator for more information. User: Security ID: domain\Administrator Account Name: domain\Administrator Account Domain: domani Fully Qualified Account Name: domain.com/Users/Administrator Client Machine: Security ID: NULL SID Account Name: - Fully Qualified Account Name: - OS-Version: - Called Station Identifier: 192.168.147.171 Calling Station Identifier: 192.168.147.191 NAS: NAS IPv4 Address: - NAS IPv6 Address: - NAS Identifier: VPN NAS Port-Type: Virtual NAS Port: 0 RADIUS Client: Client Friendly Name: VPN Client IP Address: - Authentication Details: Connection Request Policy Name: Microsoft Routing and Remote Access Service Policy Network Policy Name: All Authentication Provider: Windows Authentication Server: VPN.domain.home Authentication Type: EAP EAP Type: Microsoft: Secured password (EAP-MSCHAP v2) Account Session Identifier: 313933 Logging Results: Accounting information was written to the local log file. Reason Code: 16 Reason: Authentication failed due to a user credentials mismatch. Either the user name provided does not map to an existing user account or the password was incorrect.

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• ADSIEdit Cleanup After Exchange 2003 Crash During Transition To Exchange 2010

  - by ThaKidd

  Hello all. I would value some input from a few Exchange 2010 experts. I have almost completed the transition from Exchange 2003 Standard to Exchange 2010 Standard. Everything went smoothly until I tried to uninstall Exchange 2003. At that point the server bit the dust and died completely. I now have NO access to the old Exchange System Management MMC as I am running Windows 2008 SR2 and Windows 7 only. I can only fix this with ADSIEdit, EMShell, and EMConsole. I have used the 2010 shell to move/remove/verify that all mailboxes, public folders and OAB are hosted on Exchange 2010. I also verified that the routing connector has been deleted. The only two things that were not done was to remove the Recipient Update Service and actually perform the removal of the 2003 software. I have spent a lot of time going through ASDIedit and have located the old Administrative Group and the Exchange 2003 server listed under it. I also located the Recipient Update Service which includes two entries; Enterprise and my domain name. I have read that it is an unwise idea to remove the old administrative group so I won't bother messing with that. I am repeatedly getting three warnings in the Application Log. Both are from MSExchangeTransport EventID 5006 (Cannot find route to Mailbox Server OLDSERVER) and 5020 (The topology doesn't contain a route to Exchange 2000 Server or Exchange Server 2003) So my questions are: To clean out AD of the old Exchange 2003 info, can I delete the server name folder (Configuration - Services - Microsoft Exchange - ExchOrg - Administrative Groups - First Administrative Group - Servers - Old Server) and also delete the Update Recipient Service (Enterprise) and Update Recipient Service (DOMAIN) containers safely? Are there any additional items I need to address to ensure the AD is clean? Thanks in advance for your help!

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• pfSense Firewall or Linsys/Cisco router for small offices

  - by Tim Meers

  I'm about to start switching some networks around for multiple small offices. Each office has about 10 to 15 users and 10 to 15 computers. Each office has a spread of generic routers and access points. The routers vary from being used as routers, to just being an access point for wireless. Nothing formal has really ever beem implemented for each of the 10 offices. What I'm wanting is to set up a pfSense box for each office to configure things like: traffic shaping (for VoIP QOS) URL Filtering DHCP static routing multiple VLANs I'll then use some of the existing hardware for wireless. Maybe even integrate the wireless right into the firewall depending on the office layout. So my question, would this be better to do a full blown firewall box, or but a new business class or high end consumer class Linksys router to do the URL filtering, QOS and DHPC? Each option could allow for remote access and VPN for remote maintnance and each would only cost a nominal about of money for something decent, i.e. under $250.

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• How can I forward an application with X11 in grayscale

  - by ??????? ???????????

  I am trying to run a graphical application at home and display it on a it on a laptop which is located about six routing hops away. The problem is that the connection is so slow (or rather there is so much GOOEY being transfered) that the mouse is unresponsive and it takes a "long time" to redraw the window even at a resolution of 800x600 pixels. The connection speeds are 10MBit up at home and about 1MBit down on the laptop, which I think should be sufficient for looking at some GUI in (almost) real time. Since this traffic is sent over over a secure shell, I have enabled Compression with highest CompressionLevel along with Ciphers set to blowfish-cbc. This has substantially improved the responsiveness of the application, making it nearly usable. However, my goal is to improve the performance even further by sacrificing colors and even frame rate. The application to be displayed a Qemu SDL window with a graphically-oriented OS in it. This is not strictly relevant, but perhaps there are options to tweak the SDL output which I am not aware of. A possible workaround would be to run the application in a "hidden" X server and enabling TigerVNC on that X server. This would automatically give me the benefits of an optimized VNC viewport, but the goal is to do without (reduce complexity). The question I'm asking is what are my options for reducing the data-rate generated on the server in order to make the graphical application more usable on the client. As mentioned, colors are not important and I could probably work with 5-16 fps. Both machines are running Gentoo with the software in question being: workstation X.Org X Server 1.10.4 OpenSSH_5.8p1-hpn13v10, OpenSSL 1.0.0e QEMU emulator version 0.15.1 (qemu-kvm-0.15.1) laptop X.Org X Server 1.12.2 OpenSSH_5.8p1-hpn13v10lpk, OpenSSL 1.0.0j

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• ASDIEdit Cleanup After Exchange 2003 Crash During Transition To Exchange 2010

  - by ThaKidd

  Hello all. I would value some input from a few experts. I have almost completed the transition from Exchange 2003 Standard to Exchange 2010 Standard. Everything went smoothly until I tried to uninstall Exchange 2003. At that point the server bit the dust and died completely. I now have NO access to the old Exchange System Management MMC as I am running Windows 2008 SR2 and Windows 7 only. I can only fix this with ASDIEdit, EMShell, and EMConsole. I have used the 2010 shell to move/remove/verify that all mailboxes, public folders and OAB are hosted on Exchange 2010. I also verified that the routing connector has been deleted. The only two things that were not done was to remove the Recipient Update Service and actually perform the removal of the 2003 software. I have spent a lot of time going through ASDIedit and have located the old Administrative Group and the Exchange 2003 server listed under it. I also located the Recipient Update Service which includes two entries; Enterprise and my domain name. I have read that it is an unwise idea to remove the old administrative group so I won't bother messing with that. I am repeatedly getting three warnings in the Application Log. Both are from MSExchangeTransport EventID 5006 (Cannot find route to Mailbox Server OLDSERVER) and 5020 (The topology doesn't contain a route to Exchange 2000 Server or Exchange Server 2003) So my questions are: To clean out AD of the old Exchange 2003 info, can I delete the server name folder (Configuration - Services - Microsoft Exchange - ExchOrg - Administrative Groups - First Administrative Group - Servers - Old Server) and also delete the Update Recipient Service (Enterprise) and Update Recipient Service (DOMAIN) containers safely? Are there any additional items I need to address to ensure the AD is clean? Thanks in advance for your help!

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• Inserting and Deleting Sub Rows in GridView

  - by Vincent Maverick Durano

  A user in the forums (http://forums.asp.net) is asking how to insert  sub rows in GridView and also add delete functionality for the inserted sub rows. In this post I'm going to demonstrate how to this in ASP.NET WebForms.  The basic idea to achieve this is we just need to insert row data in the DataSource that is being used in GridView since the GridView rows will be generated based on the DataSource data. To make it more clear then let's build up a sample application. To start fire up Visual Studio and create a WebSite or Web Application project and then add a new WebForm. In the WebForm ASPX page add this GridView markup below:   1: <asp:gridview ID="GridView1" runat="server" AutoGenerateColumns="false" onrowdatabound="GridView1_RowDataBound"> 2: <Columns> 3: <asp:BoundField DataField="RowNumber" HeaderText="Row Number" /> 4: <asp:TemplateField HeaderText="Header 1"> 5: <ItemTemplate> 6: <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox> 7: </ItemTemplate> 8: </asp:TemplateField> 9: <asp:TemplateField HeaderText="Header 2"> 10: <ItemTemplate> 11: <asp:TextBox ID="TextBox2" runat="server"></asp:TextBox> 12: </ItemTemplate> 13: </asp:TemplateField> 14: <asp:TemplateField HeaderText="Header 3"> 15: <ItemTemplate> 16: <asp:TextBox ID="TextBox3" runat="server"></asp:TextBox> 17: </ItemTemplate> 18: </asp:TemplateField> 19: <asp:TemplateField HeaderText="Action"> 20: <ItemTemplate> 21: <asp:LinkButton ID="LinkButton1" runat="server" onclick="LinkButton1_Click" Text="Insert"></asp:LinkButton> 22: </ItemTemplate> 23: </asp:TemplateField> 24: </Columns> 25: </asp:gridview>   Then at the code behind source of ASPX page you can add this codes below:   1: private DataTable FillData() { 2:   3: DataTable dt = new DataTable(); 4: DataRow dr = null; 5:   6: //Create DataTable columns 7: dt.Columns.Add(new DataColumn("RowNumber", typeof(string))); 8:   9: //Create Row for each columns 10: dr = dt.NewRow(); 11: dr["RowNumber"] = 1; 12: dt.Rows.Add(dr); 13:   14: dr = dt.NewRow(); 15: dr["RowNumber"] = 2; 16: dt.Rows.Add(dr); 17:   18: dr = dt.NewRow(); 19: dr["RowNumber"] = 3; 20: dt.Rows.Add(dr); 21:   22: dr = dt.NewRow(); 23: dr["RowNumber"] = 4; 24: dt.Rows.Add(dr); 25:   26: dr = dt.NewRow(); 27: dr["RowNumber"] = 5; 28: dt.Rows.Add(dr); 29:   30: //Store the DataTable in ViewState for future reference 31: ViewState["CurrentTable"] = dt; 32:   33: return dt; 34:   35: } 36:   37: private void BindGridView(DataTable dtSource) { 38: GridView1.DataSource = dtSource; 39: GridView1.DataBind(); 40: } 41:   42: private DataRow InsertRow(DataTable dtSource, string value) { 43: DataRow dr = dtSource.NewRow(); 44: dr["RowNumber"] = value; 45: return dr; 46: } 47: //private DataRow DeleteRow(DataTable dtSource, 48:   49: protected void Page_Load(object sender, EventArgs e) { 50: if (!IsPostBack) { 51: BindGridView(FillData()); 52: } 53: } 54:   55: protected void LinkButton1_Click(object sender, EventArgs e) { 56: LinkButton lb = (LinkButton)sender; 57: GridViewRow row = (GridViewRow)lb.NamingContainer; 58: DataTable dtCurrentData = (DataTable)ViewState["CurrentTable"]; 59: if (lb.Text == "Insert") { 60: //Insert new row below the selected row 61: dtCurrentData.Rows.InsertAt(InsertRow(dtCurrentData, row.Cells[0].Text + "-sub"), row.RowIndex + 1); 62:   63: } 64: else { 65: //Delete selected sub row 66: dtCurrentData.Rows.RemoveAt(row.RowIndex); 67: } 68:   69: BindGridView(dtCurrentData); 70: ViewState["CurrentTable"] = dtCurrentData; 71: } 72:   73: protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e) { 74: if (e.Row.RowType == DataControlRowType.DataRow) { 75: if (e.Row.Cells[0].Text.Contains("-sub")) { 76: ((LinkButton)e.Row.FindControl("LinkButton1")).Text = "Delete"; 77: } 78: } 79: }   As you can see the code above is pretty straight forward and self explainatory but just to give you a short explaination the code above is composed of three (3) private methods which are the FillData(), BindGridView and InsertRow(). The FillData() method is a method that returns a DataTable and basically creates a dummy data in the DataTable to be used as the GridView DataSource. You can replace the code in that method if you want to use actual data from database but for the purpose of this example I just fill the DataTable with a dummy data on it. The BindGridVew is a method that handles the actual binding of GridVew. The InsertRow() is a method that returns a DataRow. This method handles the insertion of the sub row. Now in the LinkButton OnClick event, we casted the sender to a LinkButton to determine the specific object that fires up the event and get the row values. We then reference the Data from ViewState to get the current data that is being used in the GridView. If the LinkButton text is "Insert" then we will insert new row to the DataSource ( in this case the DataTable) based on the rowIndex if not then Delete the sub row that was added. Here are some screen shots of the output below: On initial load:   After inserting a sub row:   That's it! I hope someone find this post useful!   Technorati Tags: ASP.NET,C#,GridView

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• Site to Site VPN with Fault Tolerence

  - by Nordberg

  Hello, I have a situation where I require an IPSEC tunnel between two sites. Site 2 is a small branch office with basic (ADSL) connectivity and Site 1 is the "main" office with SDSL and ADSL for redundancy should the SDSL fail. From Site 1, all traffic bound for the 172.0.0.0 network will then be sent down another IPSEC tunnel to a supplier's Remote Server. See this page for the basic premise (this is a rough idea and things can be moved about etc...) I am considering specifying Cisco ASA devices as the firewalls for both sites for all connections. Would it be possible to employ something like HSRC to provide a backup at Site 1 should the SDSL go down? I suppose the key aims here are that Site 2 can somehow failover to initiate a VPN to the ASA behind the ADSL at Site 1. I will have a 21 subnet mask on all internet connections so can play with Class C routing if need be... If I'm barking up the wrong tree with HSRC, is there another way I can acheive this without massive expenditure on Barracuda routers et al? Many Thanks.

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• IPCop Packet Mangling

  - by Zenham

  I've found myself in a pickle replacing an old firewall for a client this afternoon. I'm configuring their new IPCop firewall (1.4.21), Zerina OpenVPN addon is installed. What I need to do: There are three network interfaces, currently set up as red (WAN), green (LAN, 192.168.20.0/24) and orange (remote network 10.1.20.0/24). The orange interface is a direct fiber link to another organization. Simple description: Traffic and networks appear to be properly configured at this point, but I have many (150+) specific IPs on the LAN which, when accessing the resources on the 10.1.20.x network, need to be mangled to appear to be coming from the 10.1.20.0/24 network (and return traffic properly delivered). The routing on the far side was configured earlier and should be fine, but I need to redirect any packets coming across destined for those IPs to end up at their proper destination. The addressing is fixed and predictable (ie. 192.168.20.125 - 10.1.20.125). I need to insert whatever rules I have into the IPCop ruleset through /etc/rc.local I know, I'm just not sure about how I should structure this. There's CUSTOMOUTPUT and CUSTOMINPUT targets, both which currently just consist of the single rule redirecting packets to the OVPNOUTPUT/OVPNINPUT targets, so I'm guessing I should insert a rule matching outbound packets destined for the 10.1.20.x network and redirecting to a new target (maybe called TO-ORANGE) and a rule at the top of CUSTOMINPUT which redirects to a FROM-ORANGE target. Under those targets, I would have rules which do the IP matching and mangling. Am I approaching this right? If so, I'm not very familiar with mangle, and would appreciate seeing examples of how to write that source-IP rewrite. If not, how would you suggest doing this? TIA! edit: I notice additionally that the nat table has CUSTOMPREROUTING and CUSTOMPOSTROUTING targets, I guess I could alternatively post the rules in there....

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• Windows Server 2008 DHCP with RRAS

  - by Guillermo Prandi

  I have a Windows Server 2008 R2 which is a member of a domain, but is placed in a remote location. The server is directly connected to Internet. Clients need to access a particular insecure TCP service in this server (ports 9730 and 9731). Since clients have dynamic IP addresses I cannot know in advance, I thought it would be nice to have them connected through a VPN in order to access the insecure service, but ONLY to access that service, like this: Client ------> VPN TUNNEL ------> (Insecure service at Server) | \----> (Normal internet access) I'd enable the insecure ports in the firewall only from VPN accesses. For this I configured RRAS in the server and gave it a static IP address range (172.19.1.2 through 172.19.1.254) to serve the clients. First I thought I could use DHCP to assign the addresses, but I cannot use DHCP in my LAN connection (not allowed by the hosting service). I tried configuring DHCP binding it to a Microsoft Loopback Adapter, but that's not supported as a DHCP source by RRAS. What I want to accomplish is to send specific DHCP options to the client (network mask, routing table, etc.). In particular: Prevent the client from having the server as default router (without changing the client's "use default gateway in remote network"). Have it as a route for the server's internal RRAS address only (172.19.1.1). Prevent the client from using a 255.255.0.0 mask for the 172.19.x.x network (a 255.255.255.0 mask would be better). Can I do that with RRAS only? How? Currently, the only solution I can think of is to use DHCP in the LAN adapter, but filter DHCP packets so they don't reach the provider's network. However, I'm not sure if that will work. Any suggestions are welcomed! Guille

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• SQL Server 2008 R2 transactional replication over VPN

  - by enashnash

  I'm having difficulty setting up replication over a VPN. I have a SQL Server 2008 R2, Enterprise Edition database on a Windows 2008 R2 Server. SQL Server is running on a non-standard port. I have set it up so that it is acting as its own distributor and have configured a publisher on this server. It is set as an updatable transational publication (yes, this is necessary). On this server, I have Routing and Remote Access enabled in order to be able to establish VPN connections. It is configured with a static IP address pool, of which the first in the range is always assigned to the server. I have assigned a test user a static address within this range (I don't know if this is necessary or not). All clients will be 2008 R2 versions, but could be SQL Express or standalone developer instances of the full product. I can establish a VPN connection from the client without problems and can see that the correct IP addresses are allocated. After connecting to the database to test that I can establish a connection, I realised that I needed to be able to connect to the database using the server name rather than an IP address - required for replication - which wouldn't work initially. I created an entry in the hosts file for the server on the client using the NETBIOS name of the server, and now I can connect to the server, from the client, using the SERVER\INSTANCE, PORT syntax, over the VPN. As it is the default instance on the server, I can also connect with simply SERVER, PORT syntax. After all that, I still get the following dreaded error: SQL Server replication requires the actual server name to make a connection to the server. Connections through a server alias, IP address, or any other alternate name are not supported. Specify the actual server name, 'SERVER\INSTANCE'. (Replication.Utilities). What have I missed? How do I get this to work? TIA

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• How much network latency is "typical" for east - west coast USA?

  - by Jeff Atwood

  At the moment we're trying to decide whether to move our datacenter from the west coast (Corvallis, OR) to the east coast (NY, NY). However, I am seeing some disturbing latency numbers from my location (Berkeley, CA) to the NYC host. Here's a sample result, retrieving a small .png logo file in Google Chrome and using the dev tools to see how long the request takes: Berkeley to NYC server: 215 ms latency, 46ms transfer time, 261ms total Berkeley to Corvallis server: 114ms latency, 41ms transfer time, 155ms total some URLs if you want to try yourself: http://careers.stackoverflow.com/content/cso/img/logo.png (NY, NY) http://serverfault.com/cache/logo.png (Corvallis, OR) It makes sense that Corvallis, OR is geographically closer to Berkeley, CA so I expect the connection to be a bit faster.. but I'm seeing an increase in latency of +100ms when I perform the same test to the NYC server. That seems .. excessive to me. Particularly since the time spent transferring the actual data only went up 10%, yet the latency went up ten times as much! That feels... wrong... to me. I found a few links here that were helpful (through Google no less!) ... http://serverfault.com/questions/63531/does-routing-distance-affect-performance-significantly http://serverfault.com/questions/61719/how-does-geography-affect-network-latency http://serverfault.com/questions/6210/latency-in-internet-connections-from-europe-to-usa ... but nothing authoritative. So, is this normal? It doesn't feel normal. What is the "typical" latency I should expect when moving network packets from the east coast <--> west coast of the USA?

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• Cisco SG200 vlan issue in ESXi VSA cluster

  - by George

  I have three Cisco SG200-26 switches, and I also have two ESXi hosts that I have connected like shown in the below "best practice" map by VMware: http://communities.vmware.com/servlet/JiveServlet/previewBody/17393-102-1-22458/VSA_networking_map.pdf Even though I created the VLANs in the SG200 and I set the two VLANs (508 and 608) as allowed for these untagged ports (where my ESX NIC's are connected), I can not ping from host 1 to host 2 when configuring the NIC's to use 608 VLAN. Am I missing something? my IP's are all in the 192.168. range, and the only reason I need the VLANs is to isolate the traffic of VSA back-end internally, only the two hosts will be using the VLANs. So I think I do not have to create virtual interfaces on my router since that's the case, is my understanding correct? Also sending my switch config screenshot below.. all 3 switches have the latest firmware (it seems these were originally linksys and got rebranded as cisco after the acquisition) http://img31.imageshack.us/img31/2503/switch.gif Any ideas what to change on the Cisco SG200 to make this work , would be appreciated! The second VLAN (608) only needs two IP's: 192.168.0.1 and 192.168.0.2 The first VLAN (508) will have about 15 IP's for ESXi Management and VSA cluster service, I could use either 192.168.1.xx or 10.0.1.xx The rest of my network (about 50 clients) is in 192.168.1.xx range VMware also states that the VLAN protocol on the physical switch must be 802.1Q, not ISL, anyone knows which of the two my SG200-26 uses? In addition to that, the only requirement from VSA is that my two hosts: -Are in the same subnet. -Have static IP addresses set. -Have the same Default Gateway configured. If I need inter-vlan routing for this, I suppose I have to create virtual interfaces on my sonicwall, and assign an IP for each VLAN, and then set routes between them? Thank you for your time!

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