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• Conferences to go to 2011 Edition

  - by Zypher

  It's that time of year to start thinking about what conferences we want to beg,plead,borrow and steal to get to go to this year. We all like a good conference, but are generally limited in the funds available to go to them - if we are provided any - so we need to be at least a little picky. What are the conferences that you are really excited about this year, and what tracks do you think will be the most beneficial to a sysadmin?

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• How to determine most stable Cisco IOS release?

  - by Chris J

  This post is about a Catalyst 4948E switch. I was looking on the download page and realized that there are no "GD" versions available. Are the "ED" versions stable? Even if you change "ED" to "GD" in the URL the IOS images are still the same. http://www.cisco.com/cisco/software/release.html?mdfid=283027810&flowid=3592&softwareid=280805680&release=15.1.1-SG2&relind=AVAILABLE&rellifecycle=ED&reltype=latest Is 15.1 as reliable as 15.0? My devices are currently on the 12.2 train. Is there anything special to upgrade to one of the 15.x trains? Are the configurations compatible.

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• Linux/hostapd: AP can ping clients, clients can access internet, can't access www@wlan1 with more than 5-6 packets at once

  - by mhambra

  Please edit the title, can't make it sound better. -- OP. Hi all, I have a Wifi USB dongle in a PC, that serves as an AP for laptop. wlan1: 192.168.2.1, netmask 255.255.255.0, routed: route add -net 192.168.2.0 netmask 255.255.255.0 gw 192.168.2.1 ping 192.168.2.2 (laptop): ping was ok for lot of packets. Now, I try to access 192.168.2.1:80/myindex.html (apache) from laptop, and can see that own 1kb test page. But, trying to access 192.168.2.1:80/my.jpg, I see the following: GET /my.jpg HTTP/1.1 200 OK <jpg header, about a kilobyte> <TCP packet retransmisson> <TCP packet retransmisson> <end of stream> It seems to be a hostapd's problem (networked stuff worked fine with Ad-Hoc), but it may be also forwarding/routing problem too. What to google for? Even more strange, SSH to that host works fine.

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• How do I get the IP Adress of my vpn server

  - by kashif

  I Connect to internet using PPTP connection type from my computer using following setting internet address: blue.connect.net.pk user id: myusername password: mypassword my problem: my dwr-112 router doesn't support internet address name, it rather supports only ip address of the server i.e I'm not able to type blue.connect.net.pk as it only supports server's ip adress. my question: How can I know the ip address of vpn server so that I can configure my dwr-112 router to connect to internet using pptp connection type

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• Killing CLOSE_WAIT sockets without killing parent process on Linux

  - by Alex Neth

  Tomcat is leaving me with CLOSE_WAIT sockets which ultimately saturate the maximum number of connections. I've tried many methods in my client and server code to get rid of these to no avail, including closing connections, calling System.gc(), etc. Now I'm trying to find a way to simply time these out quickly in the OS. I've got conntrack working, but am not sure how to use that to kill these connections. I've also set /proc/sys/net/ipv4/netfilter/ip_conntrack_tcp_timeout_close_wait to 1, which of course is too low but the connections persist. Is there a way to kill these zombie sockets? Running Ubuntu.

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• OpenVPN multiple servers on the same subnet, high availability

  - by andre

  Hey everyone. Let me start by saying that my Linux experience isn't super awesome but I can usually find my way around things easily. Over at work we have an OpenVPN setup that's been due for some improvement for a while now. The main server (tap mode) runs in our office, behind a rather slow DSL connection. The main problem is that, since I'm usually out of the office, every time I want to access something on the virtual network I have to go through that server to get anywhere else. We have two servers up on 100 Mbit connections that we use for development and production purposes, about 3 more servers in the office (one of them behind a different T1 line for VOIP) and about two dozen clients who use the network on a daily basis from various locations. We've had situations where network routing (outside of our control) would not allow people to reach our main OpenVPN server whilst the other locations were connectable. Also any time someone outside the office wants to fetch something from any of the servers (say, a 500 MB code repository), a whopping 20 KB/s download speed is just unacceptable these days (did I mention slow DSL? ok). We had to implement traffic shaping on this server since maxing out this connection was fairly trivial. I had the thought of running two (or more) OpenVPN servers in the network. These would have to have the same subnet though, as our application relies on virtual network's IP addresses for some of its core functionality. The clients would also preferably retain the same IP addresses but that's not vital. For simplicity, lets call the current server office and the second server I'm setting up, cloud. Call the server on the T1 phone. This proved to be rather complex because as soon as I connect to cloud, I cannot see office. Any routes to a server that would go through office also do not work while I'm connected to cloud (no ping, nothing) and vice-versa. There's no rules for iptables that would be blocking the traffic either. Recently I came across this article on linuxjournal but the solution they provide seems to only cover the use of two servers and somewhat outdated (can't even find much documentation, their wiki is offline). They also state that adding more servers would be a complex task. Ideally I would like to keep the existing server office running the virtual network and also run the OpenVPN daemon on the cloud and phone servers (100 Mbit and very reliable connection, respectively) so that we're on safe ground in case of a hardware failure, DSL failure, etc. So, in essence, I'm looking for a highly available OpenVPN solution (fix, patch, hack, tweak, whatever you want to call it) that will accept connections on multiple hosts (2 or more) whilst keeping the same IP address subnet regardless of the server to which you connect to. Thanks for reading and sorry for the long post, I hope it gets the point across :P

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• Standards for documenting/designing infrastructure

  - by Paul

  We have a moderately complex solution for which we need to construct a production environment. There are around a dozen components (and here I'm using a definition of "component" which means "can fail independently of other components" - e.g. an Apache server, a Weblogic web app, an ftp server, an ejabberd server, etc). There are a number of weblogic web apps - and one thing we need to decide is how many weblogic containers to run these web apps in. The system needs to be highly available, and communications in and out of the system are typically secured by SSL Our datacentre team will handle things like VLAN design, racking, server specification and build. So the kinds of decisions we still need to make are: How to map components to physical servers (and weblogic containers) Identify all communication paths, ensure all are either resilient or there's an "upstream" comms path that is resilient, and failover of that depends on all single-points of failure "downstream". Decide where to terminate SSL (on load balancers, or on Apache servers, for instance). My question isn't really about how to make the decisions, but whether there are any standards for documenting (especially in diagrams) the design questions and the design decisions. It seems odd, for instance, that Visio doesn't have a template for something like this - it has templates for more physical layout, and for more logical /software architecture diagrams. So right now I'm using a basic Visio diagram to represent each component, the commms between them with plans to augment this with hostnames, ports, whether each comms link is resilient etc, etc. This all feels like something that must been done many times before. Are there standards for documenting this?

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• File property information (last write time and file size) in explorer out of date by hours over netw

  - by David L Morris

  An application is running on a windows XP prof machine picking up file from a network share from another windows machine. It detects that the file has been updated (by date and time or optionally file size) and reads it for any new data. Most of the time the last write time and file size, seems to be up to date. Occasionally, this information stops being updated, even though the file is growing (intermittently during the day) with appended content, so that the last write time and file size remain fixed at some arbitrary moment. This is visible in explorer, where it shows a fixed last write time on the reading machine. Just opening the file to edit it in notepad, immediately refreshes the file properties, and the other application picks up where it left of. The file location can't be changed, nor the location of the relevant applications. Any solutions to resolve this problem?

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• setting up my own name server

  - by mmokh

  I'm in the process of setting up my own name servers using BIND9, however I want to visualize the name server setup in relation to registrars and other name servers. Say I have a domain www.mydomain.com I setup my 2 name servers: ns1.mydomain.com - 192.168.0.1 ns2.mydomain.com - 192.168.0.2 1) How does the world know that my name servers are now at ns1.mydomain and ns2.mydomain. I read about setting up glue records at my registrar. Could you please elaborate on this, i.e. once i setup these glue records, can I now use my name servers in NS records for any other domain? For e.g. NS records for www.otherdomain.com - ns1.mydomain.com/ns2.mydomain.com 2) Given I setup the glue records as mentioned above, do I "have to" update mydomain.com NS records to point to my name servers? Can I keep mydomain.com NS records pointing to my registrars name servers, however use ns1.mydomain.com/ns2.mydomain.com as name servers for any other domain I own? Thanks

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• MacBook Air Keeps dropping Wi-Fi

  - by Robert Patrick

  So my MacBook Air keeps dropping Wi-Fi for some reason. It happens ONLY on my home network, and ONLY to my computer. I'm using a Linksys WRT54G router. I'm the only Mac on the network. Every other Wi-Fi network is perfectly fine, and every other computer on this network is fine. Many things can happen. It could say it's connected, but not be able to access the internet (whether it tells me that there's no internet access or not). It may just drop Wi-Fi altogether, and refuse to connect. Generally, if I unplug the router and plug it back in, it's all good. It also works if I restart my computer. This happens multiple times a day. Yesterday I did everything I know to get it to connect (restart router many times, restart my MacBook), and nothing worked. Eventually it just magically worked. How can I stop this from happening? We got a notice from Comcast a while ago saying that a bot called DNS Changer was detected on one or more machines on the network. I'm assuming that this can't be me, right?

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• How to force Windows 7 to ask for a "fresh" IP address from DHCP server?

  - by haimg

  I'm troubleshooting a certain issue with my DHCP configuration, and need my Windows machine to ask for a "fresh" IP address, so I can see which address DHCP server gives by default. When I do ipconfig /release followed by ipconfig /renew, Windows "proposes" its old IP address to the DHCP server (just checked with Wireshark, initial "DHCP Discover" message has Option-50 (requested IP address) with Windows machine's old IP). Tried disabling/enabling network adapter. Same behavior. Question: How can I force Windows to just ask for a new IP address, without proposing its old IP address.

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• Very High Network out in ec2 instance

  - by Jatin

  I launched an ubuntu-14.04-64bit instance in Amazon EC2 two days back. And I started Tomcat 7.0.54 in that instance and deployed my application war files. It has no other software installed other than tomcat and the default ones. In the past 2 days, its shows 858 GB of Data Transfer(Network Out) from that instance. I have attached a graph of Amazon CloudWatch Metric "Network Out" My application does not do any data download/upload. Its a Java Spring application and the front end is in HTML&Javascript. My application traffic was very low (less than 20 hits) in those 2 days. Is there a way to find out why these data transfers happened and also to find what data has been transferred. If you can see in graph, network out was 20gb per minute. Some more info: Network in was negligible CPU Utilization was very high Everything else was low

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• Transient network dropout for Xen DomU's

  - by Stephen C

  We've got a CentOS server running a cluster of virtuals. Occasionally the cluster's internal network drops out for a minute or so ... and then comes back. The problem is somehow related to the actual network traffic, but it is not a simple load issue. (The system is generally lightly loaded, and the problem occurs irrespective of actual load.) The setup: CentOS 5.6 on Dom0, various CentOS on the DomU's Hardware - a Dell R710 with a BroadCom NextXpress 2 NIC (sigh) using the latest drivers for the NIC from BroadCom Xen configured to use network-bridge and vif-bridge Some iptable tweaks to route an unrelated port to one of the virtuals. The system has one externally visible IP address, and Dom0 runs an Apache httpd configured with a number of virtual hosts each of which reverse proxies to web servers running on the virtuals. (The virtuals have to be NAT'ed, primarily because we don't have enough allocated public IP addresses.) The symptoms: Works fine most of the time. When someone tries to UPLOAD a large file to one virtuals, the internal network drops out ... for all virtuals: The Dom0 httpd sees a network timeout talking to the backend server on the virtual and reports a 502. A previously established ssh connection from Dom0 to any of the DomU's freezes. Our monitoring shows ping failures for traffic between virtuals. The Xen consoles to the DomU's do not freeze. No log messages in any log files that I can see, on either Dom0 or the DomU's ... apart from the Dom0 httpd logs. After a minute or so, the problem clears by itself. This is 100% reproducible. What we've tried: Downloading, building and installing the latest BNX2 driver on Dom0 Turning off MSI on the NIC - adding "options bnx2 disable_msi=1" to /etc/modprobe.conf Turning off tcp segmentation offload - "ethtool -K eth0 tso off". Sacrificing a black rooster at midnight. I've exhausted all my options apart from switching to KVM ... or slaughtering more roosters. Any suggestions?

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• How to add a broadcast address to loopback with ifconfig on a OS/X?

  - by chrisapotek

  I am trying to use ifconfig to turn on broadcast on my loopback interface. It currently reads: lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384 As you can see, no broadcast address! :( :( :( I tried this on OS/X but it did not work and it did not give any error or feedback: ifconfig lo0 broadcast 127.255.255.255 Any guru would know that? I have one server that sends one packet. I have two clients running on the same machine as the server. I need them to pick up the packet WITHOUT having to force the server to send it twice.

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• Why does my Intel Tolapai network chip not transmit packets?

  - by Hanno Fietz

  I'm trying to deploy an embedded system (NISE 110 by Nexcom) based on the Intel EP80579 (Tolapai) chip. Tolapai apparently integrates controllers for Ethernet etc. on a single chip (Intel homepage). The machine can't get a network connection. Diagnosis as far as I could manage: Drivers drivers from Intel compiled and installed without problems (version 1.0.3-144). Kernel version and Linux distribution (CentOS 5.2, 2.6.18) match the driver's installation instructions. drivers are loaded and show up in lsmod (module names are gcu and iegbe) interfaces eth0 and eth1 show up in ifconfig ifconfig I can bring up the interfaces with fixed IP pinging the interface locally works ifconfig shows flag UP but not RUNNING Link ethtool shows "Link detected: no", "Speed: unknown (65536)" and "Duplex: unknown (255)" Link LED is on on the other side of the cable, ethtool shows "Link detected: yes" and reports a speed of 1000 Mbps, which has allegedly been auto-neogotiated with the problematic device. Network traffic analysis the device does not reply on ARP, ICMP echo or anything else (iptables is down) when trying to send ICMP or DHCP requests, they never reach the other end activity LED is off on the device, on at the other end. I tried the following without any effect: Different cables (2 straight, one crossed), I get the link LED lit up on each. Three different devices on the other end (one PC, one netbook, one router) Fixed ARP table entries on both sides Connecting both network ports of the machine with each other, won't ping through the cable, but will ping locally. Tried straight and crossed cables for that.

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• Slow LAN transfer from 3rd party computer

  - by Chris

  Hi Everyone, I've got an odd problem that I'm not really sure where to start the troubleshooting process. I have a 'server' with Windows Server 2008R2 (64-bit) installed and it has a couple of hard drives. If I Remote Desktop into the server and transfer files from one HD to the other, all it fine. If however, I use my workstation (Windows 7 64bit) and open up a shared resource on the server and transfer a file from one hard drive on the server to another HD on the server (not using Remote Desktop, just Windows explorer/Network places), the transfer crawls... It takes about 5mins to discover files/calculate the transfer and then starts transferring at speeds like 56KB/s - 200KB/s. Both machines have Marvel GigE network ports with a TrendNet 8-port green GigE switch. I've set Jumbo packets to 9K on both machines...

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• How do I keep a bridge enabled on a bonded interface?

  - by jlawer

  I'm working on setting up a pair of CentOS 6.3 servers that will run a couple of KVM vms and have come across a problem setting up a bridge on a bond. I am using Mode 4 (802.3ad) bonding on a pair of stacked Dell Powerconnect 5524 switches connecting to R320 servers. There are 2 links (1 to each switch) that form a Link Aggregation Group (802.3ad / LACP bonding). On top of the bond I have VLAN Tagging. I've verified this is a problem on multiple other bonding modes so it isn't just a mode 4 issue. I am testing what happens when 1 link is dropped (ie switch dies, cable breaks, etc). If I don't have a bridge (for KVM), everything works fine, failover happens as expected. If I have the bridge enabled, it works fine until failover (unplugging a cable). When failover happens /var/log/messages shows the slave link going down, followed within a second by: kernel: br1: port 1(bond0.8) entering disabled state The thing is /proc/net/bonding/bond0 shows the link is up as expected (simply with only 1 slave instead of 2). If I plug the cable back in it recovers and brings the bridge back to an enabled state. I actually have tested this while a ping is occuring and if the timing is right a packet will actually leave the system after the link is lost, but before the disabled message occurs. This disabled state I assumed was STP, but I have disabled STP on the bridge configuration and this issue still occurs. brctl showstp br1 still shows the link as disabled when it is running without a slave. I also switched between the nics in the server (I have 2x Broadcom & 4x intel). It doesn't matter which configuration I have. Does anyone know of a way to force the bridge to stay enabled or why its detecting the bond as disabled, when it isn't?

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• TC hashing filters - single rule deletion

  - by exa

  For traffic shaping I'm currently using a setup that looks exactly like the setup from LARTC, on this page: http://lartc.org/howto/lartc.adv-filter.hashing.html I have a simple problem with that - everytime I want to modify something in the hash table (like assign a IP to different flowid), I need to delete the whole filter table and add it again filter by filter. (I actually don't do it by hand, I have a nice program that does it for me... but still...) There is a problem - I got roughly 10k filters allocated this way and deleting and refilling the whole filtertable can get pretty lengthy, which is not exactly good for traffic shaping. My program could easily manage to delete only the rules that need to be deleted (thus reducing the whole problem to several commands and miliseconds), but I simply don't know the command that deletes only the one hashing rule. My tc filter show: filter parent 1: protocol ip pref 1 u32 filter parent 1: protocol ip pref 1 u32 fh 2: ht divisor 256 filter parent 1: protocol ip pref 1 u32 fh 2:a:800 order 2048 key ht 2 bkt a flowid 1:101 match 0a0a0a0a/ffffffff at 16 filter parent 1: protocol ip pref 1 u32 fh 2:c:800 order 2048 key ht 2 bkt c flowid 1:102 match 0a0a0a0c/ffffffff at 16 filter parent 1: protocol ip pref 1 u32 fh 800: ht divisor 1 filter parent 1: protocol ip pref 1 u32 fh 800::800 order 2048 key ht 800 bkt 0 link 2: match 00000000/00000000 at 16 hash mask 000000ff at 16 The wish: 'tc filter del ...' command that removes only one specific filter (for example the 0a0a0a0a IP match (IP address 10.10.10.10)). Removal of some small subgroup would also be good - for example I could still recreate a bucket (bkt a) pretty fast. My attempts: I tried to number all the filters using prio, but with no help -- they just create something unusuable (but deletable) below, but the bucketed filters remain there after that gets deleted. Any ideas? edit - I'm adding a simplified tl;dr description of the problem: I created hash filter on some interfce just like in this http://lartc.org/howto/lartc.adv-filter.hashing.html I want to find a command that deletes one rule (e.g. 1.2.1.123) from the table, leaving the rest untouched and working.

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• SCP command Clarification

  - by david.colais

  I'm using the scp commands to pull some files from the remote server and one variation of the command is not working. I have 2 files names one.xml and two.xml in a remote server and I'm pulling these two files into the current dir using the following command: scp [email protected]:/student/class/Intermediate/one.xml . scp [email protected]:/student/class/Intermediate/two.xml . The above command works fine but if I use wildcards to pull all the xml files in a single shot as shown below it returns scp: No match. scp [email protected]:/student/class/Intermediate/*.xml . Why is it working if I pull the files individually and not working if I try to pull using wildcards.

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• how to change interface ip in ifconfig with /etc/network/interfaces

  - by user2478348

  Hi everybody when modifiying /etc/network/interfaces, saving it and then executing ifconfig i can't see the modification i made..for example here is part of my /etc/network/interfaces: auto wlan1 iface wlan1 inet static address 192.168.0.60 netmask 255.255.255.0 gateway 192.168.0.61 you can see that the IP address of my wlan1 is 192.168.0.60 but when typing ifconfig i have this: wlan1 Link encap:Ethernet HWaddr 00:19:70:0f:c2:9c inet adr:192.168.0.1 Bcast:192.168.0.255 Masque:255.255.255.0 adr inet6: fe80::219:70ff:fe0f:c29c/64 Scope:Lien UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 Packets reçus:758 erreurs:0 :0 overruns:0 frame:0 TX packets:610 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 lg file transmission:1000 Octets reçus:73490 (73.4 KB) Octets transmis:127883 (127.8 KB) (the inet adr:192.168.0.1 and not 198.168.0.60)..if someone can help me I'll be very thankful :)

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• TCP video streaming: TCP throughput(rate) and RTT

  - by misteryes

  we know that a rough estimation of TCP rate is: WINDOW/RTT, where WINDOW is the min(CWIN, RWIN), CWIN is the congestion window size of the sender, while RWIN is the receiving window. nowadays, the encoding rate of videos may be 1000KB/s(8000kbit/s), if RTT is 500ms, it needs the window size to be 2000KB. But we know that usually the receiving window size is below 64KB, there is a big gap. so if RTT is too large, TCP streaming is not possible? Is my understanding right? thanks!

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• How to connect 2 routers (Asmax and D-link)

  - by piobyz

  I just bought a new router, D-link DSL 2641B and want to connect it to another one, provided by my ISP, Asmax AR 804MP. Previously, I had Linksys WRT350N, and there was no problem, while I had Ethernet cable plugged in to one of LAN ports in Asmax and INTERNET(RJ45) port in Linksys, connection used PPPoE protocol -- worked OK. D-link has DSL(RJ11) port (which I don't want to use as Asmax replacement, while there is a separate Ethernet cable with a TV plugged to Asmax, which I don't want to configure from scratch on D-link). How should I connect my new D-link to work with Asmax? Via DSL port? Via one of the LAN ports (in which case I probably should change the purpose of this port in the config, I guess?). I tried connecting D-link both ways: LAN(ASMAX) to LAN(DLINK) LAN(ASMAX) to DSL(DLINK) (using RJ11 - RJ45 cable) I hope there is some setting in the DLINK's config that I overlooked. I haven't tried to see what's in ASMAX's config, but I guess I don't need to change anything there, while Linksys worked just fine? The only difference I see, is that D-link has RJ11 DSL port as WAN, and Linksys has RJ45 (called by them INTERNET) as a main WAN port.

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• How to reliably keep an SSH tunnel open?

  - by Peltier

  I use an SSH tunnel from work to go around various idotic firewalls (it's ok with my boss :)). The problem is, after a while the ssh connection usually hangs, and the tunnel is broken. If I could at least monitor the tunnel automatically, I could restart the tunnel when it hangs, but I haven't even figured a way of doing that. Bonus points for the one who can tell me how to prevent my ssh connection from hanging, of course!

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• Looking for a reliable Personal VPN Service

  - by user38673

  I am looking for a reliable personal VPN service so that I can access sites like Pandora or Hulu even when I am not physically in the US. I have been using StrongVPN but their service is not reliable. Here are some of my key requirements: Fast Reliable I don't mind paying a reasonable fee Unlimited traffic I just need PPTP support US IP addresses No software installation needed Supports Mac Any recommendations? Thanks.

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• win32, multiple nic, different dns per nic, how gethostbyname() behaves ?

  - by dweeves

  Hello SF, On a win32 multiple nic computer, how to force DNS resolving through gethostbyname() on a specific nic if all nics have different DNS configured and have the same metric ? Otherwise, how to know which DNS will be used to resolve names each time a gethostbyname() call will be performed by the application ?

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