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  • Ubuntu with KVM guest VM and broken bridges

    - by MadPsy
    I have an Ubuntu box with a KVM guest VM running. They use bridging so the guest VM attaches to the physical network of its host. The guest VM has 2 NICs in 2 different bridges. First NIC of the VM is tap5 and is in bridge br0 br0 8000.46720f5c572e no eth0.500 tap5 Second NIC of the VM is tap2 and is in bridge br100 br100 8000.76ad2fc96661 no eth0.100 eth0.101 eth0.103 eth0.104 eth0.105 tap2 On the host, br0 has an IP and br100 does not 21: br0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP link/ether 46:72:0f:5c:57:2e brd ff:ff:ff:ff:ff:ff inet 192.168.100.4/24 brd 192.168.10.255 scope global br0 inet6 fe80::d6ae:52ff:febe:777/64 scope link valid_lft forever preferred_lft forever On the guest, its eth0 and eth1 interfaces both have IP addresses 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000 link/ether 00:3e:61:fb:7a:da brd ff:ff:ff:ff:ff:ff inet 192.168.100.6/24 brd 192.168.100.255 scope global eth0 inet6 fe80::23e:61ff:fefb:7ada/64 scope link valid_lft forever preferred_lft forever 3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000 link/ether 00:3e:61:fb:7a:ea brd ff:ff:ff:ff:ff:ff inet 172.16.50.129/25 brd 172.16.50.255 scope global eth1 inet6 fe80::23e:61ff:fefb:7aea/64 scope link valid_lft forever preferred_lft forever On the guest VM, a tcpdump of its eth1 interface (tap2) shows traffic from its eth0 interface (tap5), as if the 2 bridges are themselves bridged. This means any interface on br100 is now bridged across to br0 - which is completely broken. root@chillispot:~# tcpdump -c 1 -n -v -i eth1 net 192.168.100.0/24 tcpdump: listening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes 16:31:24.175583 IP (tos 0x0, ttl 64, id 48054, offset 0, flags [DF], proto TCP (6), length 148) 192.168.100.6.22 > 192.168.100.4.59505: Flags [P.], cksum 0x6c2b (correct), seq 1056321648:1056321744, ack 398642983, win 1700, options [nop,nop,TS val 197473436 ecr 200655363], length 96 What could be bridging the 2 bridges, except the guest VM (which is a stock Ubuntu install)? I am at a complete loss! Thanks.

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  • What programming language best bridges the gap between pseudocode and code?

    - by Kai
    As I write code from now on, I plan to first lay out everything in beautiful, readable pseudocode and then implement the program around that structure. If I rank the languages that I currently know from easiest to most difficult to translate, I'd say: Lisp, Python, Lua, C++, Java, C I know that each language has its strength and weaknesses but I'm focusing specifically on pseudocode. What language do you use that is best suited for pseudocode-to-code? I always enjoy picking up new languages. Also, if you currently use this technique, I'd love to hear any tips you have about structuring practical pseudocode. Note: I feel this is subjective but has a clear answer per individual preference. I'm asking this here because the SO community has a very wide audience and is likely to suggest languages and techniques that I would otherwise not encounter.

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  • Diving into OpenStack Network Architecture - Part 1

    - by Ronen Kofman
    v\:* {behavior:url(#default#VML);} o\:* {behavior:url(#default#VML);} w\:* {behavior:url(#default#VML);} .shape {behavior:url(#default#VML);} rkofman Normal rkofman 83 3045 2014-05-23T21:11:00Z 2014-05-27T06:58:00Z 3 1883 10739 Oracle Corporation 89 25 12597 12.00 140 Clean Clean false false false false EN-US X-NONE HE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin-top:0in; mso-para-margin-right:0in; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0in; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:Arial; mso-bidi-theme-font:minor-bidi; mso-bidi-language:AR-SA;} Before we begin OpenStack networking has very powerful capabilities but at the same time it is quite complicated. In this blog series we will review an existing OpenStack setup using the Oracle OpenStack Tech Preview and explain the different network components through use cases and examples. The goal is to show how the different pieces come together and provide a bigger picture view of the network architecture in OpenStack. This can be very helpful to users making their first steps in OpenStack or anyone wishes to understand how networking works in this environment.  We will go through the basics first and build the examples as we go. According to the recent Icehouse user survey and the one before it, Neutron with Open vSwitch plug-in is the most widely used network setup both in production and in POCs (in terms of number of customers) and so in this blog series we will analyze this specific OpenStack networking setup. As we know there are many options to setup OpenStack networking and while Neturon + Open vSwitch is the most popular setup there is no claim that it is either best or the most efficient option. Neutron + Open vSwitch is an example, one which provides a good starting point for anyone interested in understanding OpenStack networking. Even if you are using different kind of network setup such as different Neutron plug-in or even not using Neutron at all this will still be a good starting point to understand the network architecture in OpenStack. The setup we are using for the examples is the one used in the Oracle OpenStack Tech Preview. Installing it is simple and it would be helpful to have it as reference. In this setup we use eth2 on all servers for VM network, all VM traffic will be flowing through this interface.The Oracle OpenStack Tech Preview is using VLANs for L2 isolation to provide tenant and network isolation. The following diagram shows how we have configured our deployment: This first post is a bit long and will focus on some basic concepts in OpenStack networking. The components we will be discussing are Open vSwitch, network namespaces, Linux bridge and veth pairs. Note that this is not meant to be a comprehensive review of these components, it is meant to describe the component as much as needed to understand OpenStack network architecture. All the components described here can be further explored using other resources. Open vSwitch (OVS) In the Oracle OpenStack Tech Preview OVS is used to connect virtual machines to the physical port (in our case eth2) as shown in the deployment diagram. OVS contains bridges and ports, the OVS bridges are different from the Linux bridge (controlled by the brctl command) which are also used in this setup. To get started let’s view the OVS structure, use the following command: # ovs-vsctl show 7ec51567-ab42-49e8-906d-b854309c9edf     Bridge br-int         Port br-int             Interface br-int type: internal         Port "int-br-eth2"             Interface "int-br-eth2"     Bridge "br-eth2"         Port "br-eth2"             Interface "br-eth2" type: internal         Port "eth2"             Interface "eth2"         Port "phy-br-eth2"             Interface "phy-br-eth2" ovs_version: "1.11.0" We see a standard post deployment OVS on a compute node with two bridges and several ports hanging off of each of them. The example above is a compute node without any VMs, we can see that the physical port eth2 is connected to a bridge called “br-eth2”. We also see two ports "int-br-eth2" and "phy-br-eth2" which are actually a veth pair and form virtual wire between the two bridges, veth pairs are discussed later in this post. When a virtual machine is created a port is created on one the br-int bridge and this port is eventually connected to the virtual machine (we will discuss the exact connectivity later in the series). Here is how OVS looks after a VM was launched: # ovs-vsctl show efd98c87-dc62-422d-8f73-a68c2a14e73d     Bridge br-int         Port "int-br-eth2"             Interface "int-br-eth2"         Port br-int             Interface br-int type: internal         Port "qvocb64ea96-9f" tag: 1             Interface "qvocb64ea96-9f"     Bridge "br-eth2"         Port "phy-br-eth2"             Interface "phy-br-eth2"         Port "br-eth2"             Interface "br-eth2" type: internal         Port "eth2"             Interface "eth2" ovs_version: "1.11.0" Bridge "br-int" now has a new port "qvocb64ea96-9f" which connects to the VM and tagged with VLAN 1. Every VM which will be launched will add a port on the “br-int” bridge for every network interface the VM has. Another useful command on OVS is dump-flows for example: # ovs-ofctl dump-flows br-int NXST_FLOW reply (xid=0x4): cookie=0x0, duration=735.544s, table=0, n_packets=70, n_bytes=9976, idle_age=17, priority=3,in_port=1,dl_vlan=1000 actions=mod_vlan_vid:1,NORMAL cookie=0x0, duration=76679.786s, table=0, n_packets=0, n_bytes=0, idle_age=65534, hard_age=65534, priority=2,in_port=1 actions=drop cookie=0x0, duration=76681.36s, table=0, n_packets=68, n_bytes=7950, idle_age=17, hard_age=65534, priority=1 actions=NORMAL As we see the port which is connected to the VM has the VLAN tag 1. However the port on the VM network (eth2) will be using tag 1000. OVS is modifying the vlan as the packet flow from the VM to the physical interface. In OpenStack the Open vSwitch agent takes care of programming the flows in Open vSwitch so the users do not have to deal with this at all. If you wish to learn more about how to program the Open vSwitch you can read more about it at http://openvswitch.org looking at the documentation describing the ovs-ofctl command. Network Namespaces (netns) Network namespaces is a very cool Linux feature can be used for many purposes and is heavily used in OpenStack networking. Network namespaces are isolated containers which can hold a network configuration and is not seen from outside of the namespace. A network namespace can be used to encapsulate specific network functionality or provide a network service in isolation as well as simply help to organize a complicated network setup. Using the Oracle OpenStack Tech Preview we are using the latest Unbreakable Enterprise Kernel R3 (UEK3), this kernel provides a complete support for netns. Let's see how namespaces work through couple of examples to control network namespaces we use the ip netns command: Defining a new namespace: # ip netns add my-ns # ip netns list my-ns As mentioned the namespace is an isolated container, we can perform all the normal actions in the namespace context using the exec command for example running the ifconfig command: # ip netns exec my-ns ifconfig -a lo        Link encap:Local Loopback           LOOPBACK  MTU:16436 Metric:1           RX packets:0 errors:0 dropped:0 overruns:0 frame:0           TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0           RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b) We can run every command in the namespace context, this is especially useful for debug using tcpdump command, we can ping or ssh or define iptables all within the namespace. Connecting the namespace to the outside world: There are various ways to connect into a namespaces and between namespaces we will focus on how this is done in OpenStack. OpenStack uses a combination of Open vSwitch and network namespaces. OVS defines the interfaces and then we can add those interfaces to namespace. So first let's add a bridge to OVS: # ovs-vsctl add-br my-bridge Now let's add a port on the OVS and make it internal: # ovs-vsctl add-port my-bridge my-port # ovs-vsctl set Interface my-port type=internal And let's connect it into the namespace: # ip link set my-port netns my-ns Looking inside the namespace: # ip netns exec my-ns ifconfig -a lo        Link encap:Local Loopback           LOOPBACK  MTU:65536 Metric:1           RX packets:0 errors:0 dropped:0 overruns:0 frame:0           TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0           RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b) my-port   Link encap:Ethernet HWaddr 22:04:45:E2:85:21           BROADCAST  MTU:1500 Metric:1           RX packets:0 errors:0 dropped:0 overruns:0 frame:0           TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0           RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b) Now we can add more ports to the OVS bridge and connect it to other namespaces or other device like physical interfaces. Neutron is using network namespaces to implement network services such as DCHP, routing, gateway, firewall, load balance and more. In the next post we will go into this in further details. Linux Bridge and veth pairs Linux bridge is used to connect the port from OVS to the VM. Every port goes from the OVS bridge to a Linux bridge and from there to the VM. The reason for using regular Linux bridges is for security groups’ enforcement. Security groups are implemented using iptables and iptables can only be applied to Linux bridges and not to OVS bridges. Veth pairs are used extensively throughout the network setup in OpenStack and are also a good tool to debug a network problem. Veth pairs are simply a virtual wire and so veths always come in pairs. Typically one side of the veth pair will connect to a bridge and the other side to another bridge or simply left as a usable interface. In this example we will create some veth pairs, connect them to bridges and test connectivity. This example is using regular Linux server and not an OpenStack node: Creating a veth pair, note that we define names for both ends: # ip link add veth0 type veth peer name veth1 # ifconfig -a . . veth0     Link encap:Ethernet HWaddr 5E:2C:E6:03:D0:17           BROADCAST MULTICAST  MTU:1500 Metric:1           RX packets:0 errors:0 dropped:0 overruns:0 frame:0           TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000           RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b) veth1     Link encap:Ethernet HWaddr E6:B6:E2:6D:42:B8           BROADCAST MULTICAST  MTU:1500 Metric:1           RX packets:0 errors:0 dropped:0 overruns:0 frame:0           TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000           RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b) . . To make the example more meaningful this we will create the following setup: veth0 => veth1 => br-eth3 => eth3 ======> eth2 on another Linux server br-eth3 – a regular Linux bridge which will be connected to veth1 and eth3 eth3 – a physical interface with no IP on it, connected to a private network eth2 – a physical interface on the remote Linux box connected to the private network and configured with the IP of 50.50.50.1 Once we create the setup we will ping 50.50.50.1 (the remote IP) through veth0 to test that the connection is up: # brctl addbr br-eth3 # brctl addif br-eth3 eth3 # brctl addif br-eth3 veth1 # brctl show bridge name     bridge id               STP enabled     interfaces br-eth3         8000.00505682e7f6       no              eth3                                                         veth1 # ifconfig veth0 50.50.50.50 # ping -I veth0 50.50.50.51 PING 50.50.50.51 (50.50.50.51) from 50.50.50.50 veth0: 56(84) bytes of data. 64 bytes from 50.50.50.51: icmp_seq=1 ttl=64 time=0.454 ms 64 bytes from 50.50.50.51: icmp_seq=2 ttl=64 time=0.298 ms When the naming is not as obvious as the previous example and we don't know who are the paired veth interfaces we can use the ethtool command to figure this out. The ethtool command returns an index we can look up using ip link command, for example: # ethtool -S veth1 NIC statistics: peer_ifindex: 12 # ip link . . 12: veth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000 Summary That’s all for now, we quickly reviewed OVS, network namespaces, Linux bridges and veth pairs. These components are heavily used in the OpenStack network architecture we are exploring and understanding them well will be very useful when reviewing the different use cases. In the next post we will look at how the OpenStack network is laid out connecting the virtual machines to each other and to the external world. @RonenKofman

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  • httpd running as _www instead of www as it used to

    - by Ethon Bridges
    OSX Mountain Lion and Apache 2.2.22. I have always had the httpd.conf set as: User www Group www and it was running as such. Until today. Rebooted the server for another reason and when I tried to make some changes to a website via FTP this evening, it said access denied. Got to looking at the processes and httpd is now running as _www. WTH? Now of course all of my users are getting denied messages I assume because they were all created and permitted with the www user, not _www. Any idea why this happened or what I may have done to cause it?

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  • Apache virtual server httpd-vhosts undocumented issue

    - by Ethon Bridges
    I have read the Apache documentation on the https-vhosts.conf file and after a couple of hours fighting this problem, figured it out on my own. Here's the situation: We have a domain that ends in a .ws Apparently you can't do this in the conf file. You MUST use the ? wildcard or it will not work. The * wildcard will not work either. Further, in the ServerAlias directive, anything past the first entry will not work if the first entry in the ServerAlias directive is not correct. Here is an example of an entry that does NOT work. Note that anotherdomain.com and yetanotherdomain.com will fail because thedomain.ws is not configured correctly: <VirtualHost *:80> DocumentRoot /opt/local/apache2/sites/ourdomain ServerName www.thedomain.ws ServerAlias thedomain.ws another domain.com yetanotherdomain.com <Directory /opt/local/apache2/sites/ourdomain> allow from all </Directory> </VirtualHost> Here is an example of our working entry: <VirtualHost *:80> DocumentRoot /opt/local/apache2/sites/ourdomain ServerName www.thedomain.ws? ServerAlias thedomain.ws? another domain.com yetanotherdomain.com <Directory /opt/local/apache2/sites/ourdomain> allow from all </Directory> </VirtualHost> If there is documentation of this, I sure didn't see it.

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  • Would knowing Python help with creating iPhone applications?

    - by Josh
    Here is what the apple site says: With Snow Leopard, Mac OS X makes it easy to use scripting languages as full application development tools. Snow Leopard ships with support for the RubyCocoa Bridge and the PyObjC bridge. These two bridges give developers access not only to system APIs, but to Cocoa frameworks such as AppKit and Core Data, enabling you to build fully native Mac OS X applications in Ruby or Python. The RubyCocoa and PyObjC bridges allow you to freely mix code written in Objective-C with code written in the scripting language. You can quickly build prototypes and then optimise by implementing performance-critical pieces in Objective-C. How could Python help in this case?

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  • Friday Fun: Dynamite Train

    - by Asian Angel
    This week’s game involves an ‘explosive’ combination of trains, bridges, and dynamite! Your mission is to stop these trains from crossing the various bridges using ingenuity and a limited supply of explosives. Can you destroy all the bridge designs and building materials you encounter or will your carefully thought out plans of destruction fail? HTG Explains: Is ReadyBoost Worth Using? HTG Explains: What The Windows Event Viewer Is and How You Can Use It HTG Explains: How Windows Uses The Task Scheduler for System Tasks

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  • Integrating Java webapps with Adobe Professional: Resources?

    - by Steve
    I'm interested in learning what resources there are for integrating Java and Adobe Professional, in general. If it helps, my projects already use the Spring Framework. My boss is particularly interested in being able to fill out a PDF form from within a Java webapp and have that data go directly to our database. She mentioned that .net had a lot of bridges to Adobe Professional. I would rather new projects be in Java so I am eager to find if there are any easy bridges between Java and Adobe Professional. Thanks in advance for any information. So far a Google search on "Java Adobe Professional" didn't turn up anything, so I thought I would ask here. Thanks.

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  • Brainstorming - MIDI over LAN

    - by Hunter Bridges
    I'm planning out a summer coding project for myself. I work with a lot of MIDI and have been researching it a lot. I know it's an old technology, but it works with a lot of music hardware/software so in my eyes, it's still viable. Anyway, I haven't ever worked with writing drivers or anything, so I don't know where I would start with this. So, provided I have MIDI data already being sent over LAN to a server (I know how to do that part), what steps would it take for the server to channel those received messages to an emulated MIDI device, that could then be accessed in music software and so on? Also, what would it take to also send MIDI data back through the LAN to be received by the device that originally received the message? I'm not really looking for too specific a solution. Really I am just trying to come up with a game plan right now and I need to figure out where/what to research.

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  • iPhone: In landscape-only, after first addSubview, UITableViewController doesn't rotate properly

    - by Clay Bridges
    A minimal illustrative Xcode project for this is available on github. On my UIWindow, when I add second (and subsequent) UITableView's as subviews, they do not rotate properly, and thus appear sideways. This is only tested in the Simulator. Here's a little code for you: - (void)applicationDidFinishLaunching:(UIApplication *)application { ShellTVC* viewA = [[ShellTVC alloc] initWithTitle:@"View A"]; ShellTVC* viewB = [[ShellTVC alloc] initWithTitle:@"View B"]; // The first subview added will rotate to landscape correctly. // Any subsequent subview added will not. // You may try this by various commentings and rearranging of these two statements. [window addSubview:[viewA tableView]]; [window addSubview:[viewB tableView]]; [window makeKeyAndVisible]; } viewB appears sideways. Comment out the addSubview for viewB, and viewA appears correctly. Do that for viewA only, and viewB appears correctly. I am not creating these UITableViewControllers via NIBs, though the UIWindow is. In case you are wondering, ShellTVC is-a UITableViewController, and implements this method: - (BOOL) shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation { return (interfaceOrientation == UIInterfaceOrientationLandscapeLeft); } Also, I have set the UIInterfaceOrientation in the plist file to UIInterfaceOrientationLandscapeLeft. Probably related -- and unanswered -- SO questions here and here.

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  • Facebook Connect iPhone API logout not working

    - by Hunter Bridges
    I am attempting to write a Facebook integration in an iPhone app I'm working on. I have it logging in just fine, but I don't like the idea of being able to turn a feature on without being able to turn it off. So, in working on the logout functionality, I have been caught in a snag. - (IBAction) logoutClicked:(id)sender { if (fbLoggedIn) { FBSession * mySession = [FBSession session]; [mySession logout]; } } - (void)sessionDidLogout:(FBSession*)session { NSLog(@"Session logged out."); [theLoginButton setTitle:@"Facebook Time!" forState:UIControlStateNormal]; fbLoggedIn = FALSE; theLogoutButton.enabled = NO; theLogoutButton.alpha = 0; } The logoutClicked method responds to a button in my xib. The delegate method is not getting called. I have tried setting the Facebook session as a property in my ViewController in order to store/access the data across methods, but that didn't seem to work either. Anybody have any solutions?

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  • .NET 3.5 SP1 prerequisite, MS giving the clients 4.0

    - by Matt Bridges
    I have been using an MSI to install a WPF application using the .NET Framework 3.5 SP1. I have set up .NET 3.5 as a prerequisite in the MSI, and what has been happening for ages is that when the user does not have .NET 3.5 SP1, the MSI first has them download and install that before resuming the installation of my application. Since yesterday when MS released .NET 4.0, when users don't have .net 3.5 SP1, the MSI is directing them to install 4.0 instead. What happens though, is that after they finish installing 4.0, the MSI still detects that they don't have 3.5, and directs them to the 4.0 install site again. So the user has 4.0, but the MSI doesn't ever get to installing my application. What do I have to change in my application? This seems like an error with how MS is handling the prerequisites either on their server or in the MSI in VS 2008.

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  • Forwarding wifi traffic to wired pc

    - by brydgesk
    I'm trying to play around with Wireshark on my home network, and was wondering if there is a way to create a new connection on my PC that receives all wifi packets on the network. The PC is a wired Windows 7 machine, and I'm using DD-WRT on an Asus RT-N16 router. I'm not trying to hack anything, I have full admin access to the router itself. My searching has led me to articles about client bridges and repeater bridges, but none of them seemed to apply entirely to my situation. I'd like to continue using my standard wifi connection, but make my PC act as a repeater that receives all wifi traffic. Again, the PC has no wireless connection. I've used tcpdump which is installed on the router itself, but I'd be more comfortable analyzing the packets in Windows, as I'm trying to learn Wireshark. Thanks

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  • Building Cocoa UIs for OS X with C# and Mono

    - by Antony Perkov
    Has anyone spent any time comparing the various Objective C bridges and associated Cocoa wrappers for Mono? I want to port an existing C# application to run on OS X. Ideally I'd run the application on Mono, and build a native Cocoa UI for it. I'm wondering which bridge would be the best choice. In case it's useful to anyone, here are some links to bridges I've found so far: CocoSharp - distributed with Mono on OS X - www.cocoa-sharp.com Monobjc - better documentation than the others (in my opinion) - www.mono-project.com/CocoaSharp and www.monobjc.net NObjective - (apparently) faster than the others - code.google.com/p/nobjective MObjc / MCocoa - code.google.com/p/mobjc and code.google.com/p/mcocoa ObjC# - www.mono-project.com/ObjCSharp

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  • Neighbour table overflow on Linux hosts related to bridging and ipv6

    - by tim
    Note: I already have a workaround for this problem (as described below) so this is only a "want-to-know" question. I have a productive setup with around 50 hosts including blades running xen 4 and equallogics providing iscsi. All xen dom0s are almost plain Debian 5. The setup includes several bridges on every dom0 to support xen bridged networking. In total there are between 5 and 12 bridges on each dom0 servicing one vlan each. None of the hosts has routing enabled. At one point in time we moved one of the machines to a new hardware including a raid controller and so we installed an upstream 3.0.22/x86_64 kernel with xen patches. All other machines run debian xen-dom0-kernel. Since then we noticed on all hosts in the setup the following errors every ~2 minutes: [55888.881994] __ratelimit: 908 callbacks suppressed [55888.882221] Neighbour table overflow. [55888.882476] Neighbour table overflow. [55888.882732] Neighbour table overflow. [55888.883050] Neighbour table overflow. [55888.883307] Neighbour table overflow. [55888.883562] Neighbour table overflow. [55888.883859] Neighbour table overflow. [55888.884118] Neighbour table overflow. [55888.884373] Neighbour table overflow. [55888.884666] Neighbour table overflow. The arp table (arp -n) never showed more than around 20 entries on every machine. We tried the obvious tweaks and raised the /proc/sys/net/ipv4/neigh/default/gc_thresh* values. FInally to 16384 entries but no effect. Not even the interval of ~2 minutes changed which lead me to the conclusion that this is totally unrelated. tcpdump showed no uncommon ipv4 traffic on any interface. The only interesting finding from tcpdump were ipv6 packets bursting in like: 14:33:13.137668 IP6 fe80::216:3eff:fe1d:9d01 > ff02::1:ff1d:9d01: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff1d:9d01, length 24 14:33:13.138061 IP6 fe80::216:3eff:fe1d:a8c1 > ff02::1:ff1d:a8c1: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff1d:a8c1, length 24 14:33:13.138619 IP6 fe80::216:3eff:fe1d:bf81 > ff02::1:ff1d:bf81: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff1d:bf81, length 24 14:33:13.138974 IP6 fe80::216:3eff:fe1d:eb41 > ff02::1:ff1d:eb41: HBH ICMP6, multicast listener reportmax resp delay: 0 addr: ff02::1:ff1d:eb41, length 24 which placed the idea in my mind that the problem maybe related to ipv6, since we have no ipv6 services in this setup. The only other hint was the coincidence of the host upgrade with the beginning of the problems. I powered down the host in question and the errors were gone. Then I subsequently took down the bridges on the host and when i took down (ifconfig down) one particularly bridge: br-vlan2159 Link encap:Ethernet HWaddr 00:26:b9:fb:16:2c inet6 addr: fe80::226:b9ff:fefb:162c/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:120 errors:0 dropped:0 overruns:0 frame:0 TX packets:9 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:5286 (5.1 KiB) TX bytes:726 (726.0 B) eth0.2159 Link encap:Ethernet HWaddr 00:26:b9:fb:16:2c inet6 addr: fe80::226:b9ff:fefb:162c/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:1801 errors:0 dropped:0 overruns:0 frame:0 TX packets:20 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:126228 (123.2 KiB) TX bytes:1464 (1.4 KiB) bridge name bridge id STP enabled interfaces ... br-vlan2158 8000.0026b9fb162c no eth0.2158 br-vlan2159 8000.0026b9fb162c no eth0.2159 The errors went away again. As you can see the bridge holds no ipv4 address and it's only member is eth0.2159 so no traffic should cross it. Bridge and interface .2159 / .2157 / .2158 which are in all aspects identical apart from the vlan they are connected to had no effect when taken down. Now I disabled ipv6 on the entire host via sysctl net.ipv6.conf.all.disable_ipv6 and rebooted. After this even with bridge br-vlan2159 enabled no errors occur. Any ideas are welcome.

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  • Leaving a SQL Server DBA Job Gracefully

    You’re leaving your current employer for a new opportunity and want to make the move as smooth as possible. You don’t want to burn your bridges and want to make sure that everything you’ve left behind can be managed by the people you’ve left behind or the DBA who is replacing you. So, you’ve done your handover documentation and trained up the new guy. You definitely don’t want to be that DBA who is cursed the week after they leave when their network account is disabled and a bunch of stuff ‘breaks’.

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  • GDL Presents: Creative Sandbox | Geo API

    GDL Presents: Creative Sandbox | Geo API Tune in to hear about two cool, innovative campaigns that use the Geo API, Nature Valley Trail View and Band of Bridges, from the core creative teams at McCann Erickson NY, Goodby Silverstein & Partners and Famous Interactive in conversation with a Google Maps product expert. They'll talk about how they pushed the possibilities of the Geo API - and will inspire you to do the same. From: GoogleDevelopers Views: 23 1 ratings Time: 52:32 More in Science & Technology

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  • ASP.NET MVC for the Rest of Us Videos now available

    - by Jim Duffy
    Microsoft Senior Program Manager, Joe Stagner, has released his first 3 ASP.NET MVC for the Rest of Us Videos. I like the way he helps you learn ASP.NET MVC by building bridges between ASP.NET MVC concepts & ideas and ASP.NET WebForms concepts & ideas which you may already be comfortable working with. Good job Joe. Have a day. :-|

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  • GDL Presents: Creative Sandbox | Geo API

    GDL Presents: Creative Sandbox | Geo API Tune in to hear about two cool, innovative campaigns that use the Geo API, Nature Valley Trail View and Band of Bridges, from the core creative teams at McCann Erickson NY, Goodby Silverstein & Partners and Famous Interactive in conversation with a Google Maps product expert. They'll talk about how they pushed the possibilities of the Geo API - and will inspire you to do the same. From: GoogleDevelopers Views: 0 0 ratings Time: 01:00:00 More in Science & Technology

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  • Western Digital HDD disappears and reappears in BIOS

    - by tbkn23
    I know many people asked about similar problems, but I have a very specific case where I can't understand what's going on... I have a 3TB Western Digital Caviar Green disk connected in my Desktop, that also has a seagate 1.5TB disk and 2 SSD drives (OCZ and Sandisk). After working fine for quite some time (probably more than a year), suddenly my Caviar Green drive disappeared from windows. I checked the BIOS, and it wasn't there either. I opened my PC, played with the connectors, power, etc, but nothing helped. Even tried switching connectors with those of the 1.5TB disk, and nothing changed, the 1.5TB seagate was there, but the 3TB WD was not. Ok, now for the strange part. I have another desktop at home, so I took out my 3TB drive, connected it there, and it worked fine! I copied the most important files out of it, and then made another attempt in the original desktop. Surprise! It now appeared in the BIOS and worked fine! I even ran the SMART test with the WD tools and it said everything was intact. It doesn't end here. After leaving it overnight in the original desktop, it disappeared again in the morning. I repeated the entire process, connecting it to the second desktop, and there it is again working fine. Now for my question... Whats going on? The disk seems to be appearing on/off in my original Desktop, while other drives there work fine. SMART test says the disk is fine. Any ideas? Is the disk defective and should be replaced? Or maybe there's a problem with the controller in the desktop? I'm using a Gigabyte GA-880GA-UD3H motherboard and tried connecting the drive to both bridges (SATA2 and SATA3 bridges). Thanks EDIT: Power options are set never to turn off hard drives:

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