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• How ISP or dns server find the nameserevr [on hold]

  - by IT researcher

  I saw some articles about how DNS propagation happens.I know that ISP or DNS server(such as google public dns) cache the ip address of website which it uses to convert domain name to ip address. But my doubt is from where these ISP or dns serevr know which nameserver to go for particular domain name. for example a domain.com has two name servers ns1.domain.com and ns2.domain.com. But how the ISP server or dns server know that it uses these name server and i have to send request to this name server.So where does this record mainatined?

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• Distributed development staff needing a common IP range

  - by bakasan

  I work on a development staff that is geographically distributed, mostly all throughout the state of CA, but several key members also must travel frequently. We rely quite heavily on a 3rd party provider API for a great deal of our subsystems (can't get into who it is or what they do). The 3rd party however is quite stringent on network access and have no notion of a development sandbox. Access is restricted to 2, 3 IP numbers and that's about it. Once we account for our production servers, that leaves us with an IP or two to spare for our dev team--which is still problematic as people's home IP changes, people travel, we have more than 2 devs, etc. Wide IP blocks are not permitted by the 3rd party. Nor will they allow dynamic DNS type services. There is no simple console to swap IPs on the fly either (e.g. if a dev's IP at home changes or they are on the road). As none of us are deep network experts, I'm wondering what our viable options are? Are there such things as 3rd party hosts to VPNs? Generally I think of a VPN as a mechanism to gain access to a home office, but the notion would be a 3rd party VPN that we'd all connect to and we'd register this as an IP origin w/ our 3rd party. We've considered using Amazon EC2 to effectively host a dev environment for each dev and using that to connect. Amazon only gives you so many static IPs however (I believe 5?) so this would only be a stop gap solution until our team size out strips our IP count at Amazon. Those were the only viable thoughts that I had, but again, I'm far from a networking guy. Tried searching for similar threads, but I'm not even sure I know the right vernacular to look around for.

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• Apache2: not defined domains directing to the same virtual host

  - by rafaame

  I have Apache2 configured in a debian box with virtual hosts. I have several domains pointing to the box's IP address. The domains whose virtual hosts are configured works perfectly. But if I type in the browser a domain that is pointing to the box but whose the virtual host is not configured, I get to a random virtual host of another domain in the box. Not a random, but one of the virtual hosts (always the same) but I dunno why it is it. The correct would be that the domains that are not configured as virtual hosts return a hostname error or something, right? Does someone know how to fix the problem? One of my virtual hosts config file: <VirtualHost *:80> ServerAdmin [email protected] ServerName dl.domain.com DocumentRoot /var/www/dl.domain.com/public_html/ <Directory /> Options FollowSymLinks AllowOverride None </Directory> <Directory /var/www/dl.domain.com/public_html/> Options Indexes FollowSymLinks MultiViews AllowOverride All Order allow,deny allow from all </Directory> ScriptAlias /cgi-bin/ /usr/lib/cgi-bin/ <Directory "/usr/lib/cgi-bin"> AllowOverride None Options +ExecCGI -MultiViews +SymLinksIfOwnerMatch Order allow,deny Allow from all </Directory> ErrorLog /var/log/apache2/error.log # Possible values include: debug, info, notice, warn, error, crit, # alert, emerg. LogLevel warn CustomLog /var/log/apache2/access.log combined Alias /doc/ "/usr/share/doc/" <Directory "/usr/share/doc/"> Options Indexes MultiViews FollowSymLinks AllowOverride None Order deny,allow Deny from all Allow from 127.0.0.0/255.0.0.0 ::1/128 </Directory> </VirtualHost> My apache2.conf http://www.speedyshare.com/files/29107024/apache2.conf Thanks for the help

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• VSFTPD does not allow upload with virtual users

  - by Mr. Squig

  I am attempting to setup VSFTPD with virtual users on a server running Ubuntu 12.04. I have configured the server to allow for virtual users to login, but I am having trouble getting it to allow uploads. My vsftpd.conf is as follows: listen=YES anonymous_enable=NO local_enable=YES write_enable=YES local_umask=022 anon_upload_enable=YES dirmessage_enable=YES use_localtime=YES xferlog_enable=YES connect_from_port_20=YES chroot_local_user=YES virtual_use_local_privs=YES guest_enable=YES guest_username=virtual user_sub_token=$USER local_root=/var/www/$USER hide_ids=YES secure_chroot_dir=/var/run/vsftpd/empty pam_service_name=vsftpd rsa_cert_file=/etc/ssl/private/vsftpd.pem /etc/pam.d/vsftpd contains: auth required pam_pwdfile.so pwdfile /etc/vsftpd.passwd crypt=hash account required pam_permit.so crypt=hash I have two virtual users set up, one of which has the same name as a local user. They each have a directory in /var/www/ owned by 'virtual'. As I understand it, when a virtual user logs in this way they will appear to the system as the user virtual. Using this configuration user can log on, but cannot upload files. The error given in /var/log/vsftpd.log is: Tue Nov 20 19:49:00 2012 [pid 2] CONNECT: Client "96.233.116.53" Tue Nov 20 19:49:07 2012 [pid 1] [zac] OK LOGIN: Client "96.233.116.53" Tue Nov 20 19:49:11 2012 [pid 2] CONNECT: Client "96.233.116.53" Tue Nov 20 19:49:11 2012 [pid 1] [zac] OK LOGIN: Client "96.233.116.53" Tue Nov 20 19:49:11 2012 [pid 3] [zac] FAIL CHMOD: Client "96.233.116.53", "/test.ppm 644" I have tried changing the permissions of these directories in all sorts of ways, but nothing seem to work. I have a feeling that it is something simple related to permissions. Any ideas?

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• BSOD trying to migrate Windows XP from a physical to a virtual machine

  - by pauldoo

  I am attempting to migrate a Windows XP Home installation from a physical machine to a virtual machine. The physical machine has two hard disks; the first is 250GB containing the "C:", the second is 1TB containing "D:". I'd like to create a new virtual machine stored on the D:, which is a copy of the Windows XP Home installation that is currently on the C:. (This will leave the 250GB drive clear for me to install a fresh copy of Windows 7, and still be able to access the old XP installation if necessary.) The first method I tried was to follow the instructions here: http://www.virtualbox.org/wiki/Migrate_Windows I booted up from an Ubuntu Live CD in order to execute the Linux commands whilst the Windows system wasn't running. With this method the virtual machine would always blue screen on startup with a "STOP 0x0000007B" message. The instructions above say to try a "repair install" using the Windows XP disc. Unfortunately for me my XP disc is scratched and will not boot so I was unable to try a repair install. The second method I tried was to use "VMWare Converter Standalone Client". This tool executed without any errors, but again produced a virtual machine that blue screens on startup with the same "STOP" message. Are there any other methods to move the Windows XP installation into a virtual machine? I think next I will try some more manual process to create the cloned virtual machine. I think I will try installing a fresh copy of Windows XP to a virtual machine, then once that is booting OK I will ntfsclone the source C: partition over the top. Perhaps this will fix the booting problems if the issue is related to the MBR or partition table in some way.

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• Which IP should I use for my nameserver

  - by Luke Bream

  Sorry to ask whats probably very obvious question. I have just got a new server that is fantastically cheap but unfortunatly doesnt come with any technical support and Im very out of my depth ! My hosting company has provided the following information... Below you will find your additional IP addresses added to the server 5.9.36.51 Please note that you can use the subnet only for this server. IP: 5.9.225.64 /27 Mask: 255.255.255.224 Broadcast: 5.9.225.95 Useable IP addresses: 5.9.225.65 to 5.9.225.94 It has cPanel with WHM and im going through the setup... I have a number of questions... my domian is purchased from godaddy and I want to use it as the name server. Question 1: Which IP or IP's do I enter into the godaddy interface for ns1.mydomian.com ns2.mydomain.com Question 2: In the WHM nameserver setup what do I enter for... Please enter an IP address for each of your nameservers. ns1.mydomain.com ?????? ns2.mydomain.com ?????? Add "A Entries" for Hostname IP for Entry: ????????? Thanks for aany help you can give Luke

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• Possible to IPSec VPN Tunnel Public IP Addresses?

  - by caleban

  A customer uses an IBM SAS product over the internet. Traffic flows from the IBM hosting data center to the customer network through Juniper VPN appliances. IBM says they're not tunneling private IP addresses. IBM says they're tunneling public IP addresses. Is this possible? What does this look like in the VPN configuration and in the packets? I'd like to know what the source/destination ip/ports would look like in the encrypted tunneled IPSec Payload and in the IP packet carrying the IPSec Payload. IPSec Payload: source:1.1.1.101:1001 destination:2.2.2.101:2001 IP Packet: source:1.1.1.1:101 destination:2.2.2.1:201 Is it possible to send public IP addresses through an IPSec VPN tunnel? Is it possible for IBM to send a print job from a server on their network using the static-nat public address over a VPN to a printer at a customer network using the printer's static-nat public address? Or can a VPN not do this? Can a VPN only work with interesting traffic from and to private IP addresses?

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• pptpd-logwtmp.so config wrong ip address

  - by rgc

  i have setup a pptp vpn on ubuntu 10.04, and i config local ip address , remote ip address as following: local IP address 10.0.30.100 remote IP address 192.168.13.100 after i use windows to connect to vpn server in windows , i only could send packets, can not receive any packets. i also check the pptp log in ubuntu server, and find this strange thing rcvd [IPCP ConfAck id=0x1 <compress VJ 0f 01> <addr 10.0.30.100>] rcvd [IPCP ConfReq id=0x2 <compress VJ 0f 01> <addr 192.168.13.100> <ms-dns1 202.119.32.6> <ms-dns2 202.119.32.12>] sent [IPCP ConfAck id=0x2 <compress VJ 0f 01> <addr 192.168.13.100> <ms-dns1 202.119.32.6> <ms-dns2 202.119.32.12>] Cannot determine ethernet address for proxy ARP local IP address 10.0.30.100 remote IP address 192.168.13.100 pptpd-logwtmp.so ip-up ppp0 **172.25.146.174** i did not set 172.25.146.174, it should be 192.168.13.100, can anyone tell me what should i do to fix this problem?

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• Domain names timing out after VPS IP change

  - by Fourjays

  I rent a CentOS 5 VPS from a UK-based provider, with DirectAdmin also installed. On Thursday night, they carried out planned maintenance to changed the two IPs I had been assigned to two new ones. On Friday, after the change had taken place, I updated my domain name records to reflect the IP change. Since then, all of the domains pointing to the VPS are timing out. Additionally, DirectAdmin was also not responding, but was was resolved by running the ipswap scripts as found in the DirectAdmin knowledgebase. It did not fix my domains though. I have contacted the VPS provider but I have been waiting for a response for some time now. I have checked again, and again, and all the IPs referenced in DirectAdmin are correct. If I go to the server IP in my browser it responds with "Apache is functioning normally." Email accounts on the server are also functioning correctly. But if I access a domain itself, it times out. Running a ping and a DNS look-up, I can confirm the nameserver IPs are correct. If I run a trace route it reaches an IP that is similar to my VPS IPs (last 2 blocks are different) before timing out (it never shows my server IP). I am relatively new to VPS management so don't have a vast wealth of experience with troubleshooting problems on them. I have checked all of the httpd configuration files, which don't seem to have any IP references in them at all. Looking in the Apache error logs, what errors there are do not coincide with times I have tried to access the site. Is this issue at my provider's end? Is there anything else I can check or test, to rule out post-IP-change problems with my server configuration? It was all running fine prior to the IP change.

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• Possible to IPSec VPN Tunnel Public IP Addresses?

  - by caleban

  A customer uses an IBM SAS product over the internet. Traffic flows from the IBM hosting data center to the customer network through Juniper VPN appliances. IBM says they're not tunneling private IP addresses. IBM says they're tunneling public IP addresses. Is this possible? What does this look like in the VPN configuration and in the packets? I'd like to know what the source/destination ip/ports would look like in the encrypted tunneled IPSec Payload and in the IP packet carrying the IPSec Payload. IPSec Payload: source:1.1.1.101:1001 destination:2.2.2.101:2001 IP Packet: source:1.1.1.1:101 destination:2.2.2.1:201 Is it possible to send public IP addresses through an IPSec VPN tunnel? Is it possible for IBM to send a print job from a server on their network using the static-nat public address over a VPN to a printer at a customer network using the printer's static-nat public address? Or can a VPN not do this? Can a VPN only work with interesting traffic from and to private IP addresses?

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• Virtual Machine Network Architecture, Isolating Public and Private Networks

  - by Mark

  I'm looking for some insight into best practices for network traffic isolation within a virtual environment, specifically under VMWARE ESXi. Currently I have (in testing) 1 hardware server running ESXi but i expect to expand this to multiple pieces of hardware. The current setup is as follows: 1 pfsense VM, this VM accepts all outside (WAN/internet) traffic and performs firewall/port forwarding/NAT functionality. I have multiple public IP addresses sent to the this VM that are used for access to individual servers (via per incoming IP port forwarding rules). This VM is attached to the private (virtual) network that all other VMs are on. It also manages a VPN link into the private network with some access restrictions. This isn't the perimeter firewall but rather the firewall for this virtual pool only. I have 3 VMs that communicate with each other, as well as have some public access requirements: 1 LAMP server running an eCommerce site, public internet accessible 1 accounting server, access via windows server 2008 RDS services for remote access by users 1 inventory/warehouse management server, VPN to client terminals in warehouses These servers constantly talk with each other for data synchronization. Currently all the servers are on the same subnet/virtual network and connected to the internet through the pfsense VM. The pfsense firewall uses port forwarding and NAT to allow outside access to the servers for services and for server access to the internet. My main question is this: Is there a security benefit to adding a second virtual network adapter to each server and controlling traffic such that all server to server communication is on one separate virtual network, while any access to the outside world is routed through the other network adapter, through the firewall, and on the the internet. This is the type of architecture i would use if these were all physical servers, but i'm unsure if the networks being virtual changes the way i should approach locking down this system. Thank you for any thoughts or direction to any appropriate literature.

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• Getting a domain sub-directory url for a new server

  - by Xianlin

  I have an web application server running tomcat and i need to publish my APIs to internet users. However I don't have a domain name for this server and I can only put the ip address of this server (e.g. 145.XXX.XXX.XXX) to point out where my API xml files are located. I have another web server running with a domain name "http://www.webserver.com" registered on the internet and I want to make use of its domain name to server my web application server API xml files location. How can I do that? using "www.webserver.com/api" or using "api.webserver.com"? which is better? Also I wonder if I want to publish a "rstp://145.XXX.XXX.XXX" web link for video streaming purpose, can I use "rstp://www.webserver.com/api" to replace it and how to do it? I always thought the url contain domain sub-directory name cannot point to another IP address, it only can point to another folder location on the webserver itself.

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• IP queue buffer

  - by summerbulb

  I seem to have an issue with IP queue. I have a linux machine that I am using to run some experiments. The linux machine is configured to be a router, having two NICs, connecting two other computers, and managing their network traffic. All incoming packages are captured, using iptables, and analyzed by a C application. The application analyzing the packets has a built-in delay, as part of the experiment. So I have one very fast computer sending packets through my linux-router and a (relatively) slow linux-router that analyses and deals with the packets, one by one. This situation leads to the fact that when I fire up a sender application on one of the computers connected to the linux-router, my IP queue on the linux-router gets filled up (almost) instantaneously. The IP queue's max length is currently set to 1024, and if it overflows, the packets are dropped. This is expected and i'm OK with it. But, (and this is where it gets interesting), every now and then I get the following error: "Failed to receive netlink message: No buffer space available" At start, I thought this was due to the IP queue overflow, but after some analysis i found that sometimes I get the error even if the IP queue buffer did not overflow, and sometime I DON'T get the message even though the buffer DID overflow. When I run > cat /proc/net/ip_queue, I get the following table (also used to monitor the IP queue overflow): Peer PID : 27389 Copy mode : 2 Copy range : 65535 Queue length : 0 Queue max. length : 1024 Queue dropped : 1166875 Netlink dropped : 2916 Looking at the last two values, Queue dropped seems to refer to packets that did not manage to get into the IP queue because the buffer was full. I can see this value rise as I bombard the linux-router. Netlink dropped ( as it's name implies :) ) seems to have to do with the error i'm getting. I did my best to search for material on this error, but wasn't able to find anything that seemed to point me in the required direction. Bottom line: Why am I getting this error and what can I do to avoid it?

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• Windows Server 2008 R2 Virtual Network Setup

  - by jpearl01

  Hi all, Some background: I'm very much new to networking in general, and virtualization in particular. I'm trying to set up a series of VMs as we are transitioning to a thin client setup. I have been supplied a limited number of static ip addresses. The server is located in an offsite building which houses the network we use to connect to the internet, share folders etc. The setup I've been trying to go for is this: The host OS (Windows Server 2008 R2) is bound to one nic using one of the static ips (say, Nic1 and ip 10.255.6.61). I've set up another external virtual network attached to another physical nic , and a virtual private network attached to no nic. There is one VM running the same os (as the host). This VM is connected to both the external virtual network (and uses another static ip say Nic2 and ip 10.255.6.62) and also to the virtual private network (I gave it a static random ip 192.168.88.1 subnet mask 255.255.255.0). This virtual private network is connected to all the other VMs. I'd like to share the internet connection with all the other VMs on the private virtual network, and so I installed the RRAS role on the server connected to Nic2, and selected the option to share the internet over the vpn. I've run through the RRAS wizard a few times, trying different configurations, but none of them seem to be letting the other vms connect to the 'net. The vms seem to connect to the virtual private network fine, they are assigned an ip address and everything, but no internet, and no rest of the network either. The other problem is in general I connect to the vms with RDP. Will that be possible with a setup like this? i.e. will the vms show up as computers on the network? If not, what are my other options? Thanks! ~josh

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• Transferring an SQL Processor License to a virtual hosted environment

  - by Andrew Shepherd

  My company is currently hosting a service in-house, and we want to move to an externally hosted environment. We would then be using a virtual server. I understand that this might be spread across multiple machines, but from my perspective as a customer, this layer is abstracted away - I shouldn't know or care about the hardware that the OS is hosted on. We have a licensed edition of SQL Server 2008. This is one Processor license. Will it be a violation of the licensing agreement to use this in a virtual environment. From the reference guide here it says When licensed Per Processor With Workgroup, Web, and Standard editions, for each server to which you have assigned the required number of per processor licenses, you may run, at any one time, any number of instances of the server software in physical and virtual operating system environments on the licensed server. However, the total number of physical and virtual processors used by those operating system environments cannot exceed the number of software licenses assigned to that server For enterprise edition there is an added option: if all physical processors in a machine have been licensed, then you may run unlimited instances of SQL server 2008 in one physical and an unlimited number of virtual operating environments on that same machine. I'm having trouble getting my head around this. Would I theoretically have to get a license for every processor in this virtual environment (which is effectively impossible because I have no way of knowing how many processors there actually are)? Or can I just say that it's hosted on one "virtual" server, so that's OK?

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• A record point not working

  - by Peter

  I'm trying to do an A record point to transfer the hosting of a domain from one provider to another. I don't want to change the nameservers as this will result in emails going down. The output when I dig for the domain shows the correct IP (78.46.63.87) for the new host. I know A records can take a while to propagate but Its been over 36hrs now and I still keep getting this error(below) when I try to pull the domain through as an addon domain via Cpanel on the new host. Are the old nameservers conflicting with the A record point? here's the error: Using nameservers with the following IPs: 208.80.125.4,208.80.126.4,208.80.124.4,208.94.148.4 Sorry, the domain is already pointed to an IP address that does not appear to use DNS servers associated with this server. Please transfer the domain to this servers nameservers or have your administrator add one of its nameservers to /etc/ips.remotedns and make the proper A entries on that remote nameserver.

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• Windows Server 2008 R2 Virtual Network Setup

  - by jpearl01

  Some background: I'm very much new to networking in general, and virtualization in particular. I'm trying to set up a series of VMs as we are transitioning to a thin client setup. I have been supplied a limited number of static ip addresses. The server is located in an offsite building which houses the network we use to connect to the internet, share folders etc. The setup I've been trying to go for is this: The host OS (Windows Server 2008 R2) is bound to one nic using one of the static ips (say, Nic1 and ip 10.255.6.61). I've set up another external virtual network attached to another physical nic , and a virtual private network attached to no nic. There is one VM running the same os (as the host). This VM is connected to both the external virtual network (and uses another static ip say Nic2 and ip 10.255.6.62) and also to the virtual private network (I gave it a static random ip 192.168.88.1 subnet mask 255.255.255.0). This virtual private network is connected to all the other VMs. I'd like to share the internet connection with all the other VMs on the private virtual network, and so I installed the RRAS role on the server connected to Nic2, and selected the option to share the internet over the vpn. I've run through the RRAS wizard a few times, trying different configurations, but none of them seem to be letting the other vms connect to the 'net. The vms seem to connect to the virtual private network fine, they are assigned an ip address and everything, but no internet, and no rest of the network either. The other problem is in general I connect to the vms with RDP. Will that be possible with a setup like this? i.e. will the vms show up as computers on the network? If not, what are my other options? Thanks! ~josh

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• IP Masquerade and forwarding

  - by poelinca

  Hi all , i got a dedicated server running ubuntu server 10.10 with 3 ip adresses on the same eth card ( example: eth0 192.168.0.1 , eth0:0 188.78.45.0 , eth0:1 ... ) with a 3 virtual machines running ( virtualization technologi used is lxc but i don't think this matters too much ) . Now i need to redirect all ports opened ( using ufw to close/open ports ) from the ip 188.78.54.0 ( eth0:0 ) to a virtual machine ip ( let's say for example 192.168.2.3 ) , all requests made by a virtual machine should be redirected back to the virtual machine that made the request ( in this example 192.168.2.3 ) . Lets say the second vm has the ip 192.168.2.4 now i need to redirect all opened ports to from eth0:1 to this ip and viceversa . And so on and so on , what are the iptables/ufw rules to get this done ? and where to save them ( witch config file ) so they stay the same after reboot . In a few words redirect all requests comming from/to eth0:0 to a certan ip , all requests comming from/to eth0:1 to another ip ... Remember i'm saying all ports opened becouse they might be dynamicly changed . p.s. please excuse my bad english

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• iptables, forward traffic for ip not active on the host itself

  - by gucki

  I have kvm guest which's netword card is conntected to the host using a tap device. The tap device is part of a bridge on the host together with eth0 so it can access the public network. So far everything works, the guest can access the public network and it can be accessed from the public network. Now the kvm process on the host provides a vnc server for the guest which listens on 127.0.0.1:5901 on the host. Is there any way to make this vnc server accessible by the ip address which the guest is using (ex. 192.168.0.249), without interrupting the guest from using the same ip (port 5901 is not used by the guest)? It should also work when the guest is not using any ip address at all. So basically I just want to fake IP xx is on the host and only answer/ forward traffic to port 5901 to the host itself. I tried using this NAT rule on the host, but it doesn't work. Ip forwarding is enabled at the host. iptables -t nat -A PREROUTING -p tcp --dst 192.168.0.249 --dport 5901 -j DNAT --to-destination 127.0.0.1:5901 I assume this is because the IP 192.168.0.249 is not not bound to any interfaces and so no ARP requests for it get answered and so no packets for this IP arrive at the host. How can make it work? :)

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• How do you find a functions virtual call address in assembly?

  - by Daniel

  I've googled around but i'm not sure i am asking the right question or not and i couldn't find much regardless, perhaps a link would be helpful. I made a c++ program that shows a message box, then I opened it up with Ollydbg and went to the part where it calls MessageBoxW. The call address of MessageBoxW changes each time i run the app as windows is updating my Imports table to have the correct address of MessageBoxW. So my question is how do i find the virtual addres of MessageBoxW to my imports table and also how can i use this in ollydbg? Basically I'm trying to make a code cave in assembly to call MessageBoxW again. I got fairly close once by searching the executable with a hex editor and found the position of the call, and I think I found the virtual address. But when i call that virtual address in olly and saved it to the executable, the next time i opened it the call was replaced with a bunch of DB xyz (which looked like the virtual address but why did the call get removed? Sorry if my terminology is off as i'm new to this so i'm not quite sure what to call things.

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• iptables not allowing mysql connections to aliased ips?

  - by Curtis

  I have a fairly simple iptables firewall on a server that provides MySQL services, but iptables seems to be giving me very inconsistent results. The default policy on the script is as follows: iptables -P INPUT DROP I can then make MySQL public with the following rule: iptables -A INPUT -p tcp --dport 3306 -j ACCEPT With this rule in place, I can connect to MySQL from any source IP to any destination IP on the server without a problem. However, when I try to restrict access to just three IPs by replacing the above line with the following, I run into trouble (xxx=masked octect): iptables -A INPUT -p tcp --dport 3306 -m state --state NEW -s 208.XXX.XXX.184 -j ACCEPT iptables -A INPUT -p tcp --dport 3306 -m state --state NEW -s 208.XXX.XXX.196 -j ACCEPT iptables -A INPUT -p tcp --dport 3306 -m state --state NEW -s 208.XXX.XXX.251 -j ACCEPT Once the above rules are in place, the following happens: I can connect to the MySQL server from the .184, .196 and .251 hosts just fine as long as am connecting to the MySQL server using it's default IP address or an IP alias in the same subnet as the default IP address. I am unable to connect to MySQL using IP aliases that are assigned to the server from a different subnet than the server's default IP when I'm coming from the .184 or .196 hosts, but .251 works just fine. From the .184 or .196 hosts, a telnet attempt just hangs... # telnet 209.xxx.xxx.22 3306 Trying 209.xxx.xxx.22... If I remove the .251 line (making .196 the last rule added), the .196 host still can not connect to MySQL using IP aliases (so it's not the order of the rules that is causing the inconsistent behavior). I know, this particular test was silly as it shouldn't matter what order these three rules are added in, but I figured someone might ask. If I switch back to the "public" rule, all hosts can connect to the MySQL server using either the default or aliased IPs (in either subnet): iptables -A INPUT -p tcp --dport 3306 -j ACCEPT The server is running in a CentOS 5.4 OpenVZ/Proxmox container (2.6.32-4-pve). And, just in case you prefer to see the problem rules in the context of the iptables script, here it is (xxx=masked octect): # Flush old rules, old custom tables /sbin/iptables --flush /sbin/iptables --delete-chain # Set default policies for all three default chains /sbin/iptables -P INPUT DROP /sbin/iptables -P FORWARD DROP /sbin/iptables -P OUTPUT ACCEPT # Enable free use of loopback interfaces /sbin/iptables -A INPUT -i lo -j ACCEPT /sbin/iptables -A OUTPUT -o lo -j ACCEPT # All TCP sessions should begin with SYN /sbin/iptables -A INPUT -p tcp ! --syn -m state --state NEW -j DROP # Accept inbound TCP packets (Do this *before* adding the 'blocked' chain) /sbin/iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT # Allow the server's own IP to connect to itself /sbin/iptables -A INPUT -i eth0 -s 208.xxx.xxx.178 -j ACCEPT # Add the 'blocked' chain *after* we've accepted established/related connections # so we remain efficient and only evaluate new/inbound connections /sbin/iptables -N BLOCKED /sbin/iptables -A INPUT -j BLOCKED # Accept inbound ICMP messages /sbin/iptables -A INPUT -p ICMP --icmp-type 8 -j ACCEPT /sbin/iptables -A INPUT -p ICMP --icmp-type 11 -j ACCEPT # ssh (private) /sbin/iptables -A INPUT -p tcp --dport 22 -m state --state NEW -s xxx.xxx.xxx.xxx -j ACCEPT # ftp (private) /sbin/iptables -A INPUT -p tcp --dport 21 -m state --state NEW -s xxx.xxx.xxx.xxx -j ACCEPT # www (public) /sbin/iptables -A INPUT -p tcp --dport 80 -j ACCEPT /sbin/iptables -A INPUT -p tcp --dport 443 -j ACCEPT # smtp (public) /sbin/iptables -A INPUT -p tcp --dport 25 -j ACCEPT /sbin/iptables -A INPUT -p tcp --dport 2525 -j ACCEPT # pop (public) /sbin/iptables -A INPUT -p tcp --dport 110 -j ACCEPT # mysql (private) /sbin/iptables -A INPUT -p tcp --dport 3306 -m state --state NEW -s 208.xxx.xxx.184 -j ACCEPT /sbin/iptables -A INPUT -p tcp --dport 3306 -m state --state NEW -s 208.xxx.xxx.196 -j ACCEPT /sbin/iptables -A INPUT -p tcp --dport 3306 -m state --state NEW -s 208.xxx.xxx.251 -j ACCEPT Any ideas? Thanks in advance. :-)

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• What are the advantages and disadvantages of the various virtual machine image formats?

  - by Matt

  Xen and Virtualbox etc both support a range of different virtual machine image formats. These are: vmdk, vdi, qcow & qcow2, hdd & vhd. Without any bias toward a particular product, I'm wanting to know what are the advantages and disadvantages of the various formats both from a features perspective, robustness and speed? One piece of info I discovered in a forum post was this: "The major difference is that VDI uses relatively large blocks (1MB) when growing an image, and thus has less overhead for block pointers etc. but isn't ultimately space efficient in the sense that if a single byte is non-zero in such a 1MB block the entire space is used. VMDK in contrast uses 64K blocks, and thus has more management overhead and generally a bit less disk space consumption What offsets this is that VDI is more efficient when it comes to snapshots." You might be thinking, I want to know this because I want to know which format to choose? Not exactly, I'm developing some software which utilises these formats and want to support one or more of them. Simplicity, large disks and ease of development are my main drivers.

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• Does migrating 2 domain controllers between 2 datacentre requires both virtual machines to be shut down at the same time?

  - by Imagineer

  I was attempting to migrate 2 virtual machines that are domain controllers between 2 datacentres running ESX 3.5 and ESX 4.1. I was advised to shut down both domain controller at the same time during the migration process. This is to avoid USN Rollback and other replication issues. The following are the steps that I was planning to perform: 1. Shutdown both DC. 2. Copy both VMs files across to new datacentre using Veeam FastSCP (connection to both vCentre through IP address instead of hostname) 3. Power them up at new datacentre. 4. Configure Network interface/DNS/DHCP for both DCs in new datacentre I have tried to use Veeam FastSCP rather than VMware Standalone Converter is because its copying rather than converting. Someone also suggested that I use backup and restore app like Veeam backup and replication software. Sounds like a simple job, but after shutting down both DCs, the transfer rate using FastSCP is so slow registering only 1KB/s as oppose to the normal 1MB/s (or more). When that attempt to transfer failed, I tried to cold clone both DCs resulted in the both ESX hosts get disconnected. I have tried troubleshooting by referring to this - VMware KB - Diagnosing an ESX Server that is Disconnected or Not Responding in VirtualCenter It seems that the DNS being down is the caused of all unusual occurrence. The moment I powered up the DCs via VMware console command, the ESX host were able to connect to the vCentre again. How can I avoid such a pitfall again? Am I doing it correctly? Any help would be greatly appreciated! Thank you.

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• Azure Virtual Machines - what fault tolerance do they provide?

  - by Borek

  We are thinking about moving our virtual machines (Hyper-V VHDs) to Windows Azure but I haven't found much about what kind of fault tolerance that infrastructure provides. When I run VHD in Azure, I've got two questions: Is my VHD and all the data in it safe? I think that uploaded VHDs use the "Storage" infrastructure so they should be automatically replicated to multiple disks and geographically distributed but should I still make a full-image backup just to be safe? (Note that of course I will be backing up the actual data inside VMs that I care about; I just want to know if there is a chance greater than 0.0000001% that one day I will receive an email from Microsoft telling me that my VM is gone and that I should create or restore it from scratch). Do I need to worry about other things regarding the availability of my VMs? I mean, when I have an on-premise server I need to worry about the hardware itself, about the host operating system, what would happen if my router failed, if my Hyper-V's C: drive failed etc. Am I right in thinking that with Azure, their infrastructure takes care of all of this? Thanks.

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• Is there such a thing as a virtual COM port receipt printer?

  - by Blorgbeard

  I'm debugging some code that writes directly to a COM port in order to print receipts on a receipt printer. The printer model is something like an Epsom TM-88. Instead of printing reams of thermal paper while debugging this code, it would be nice if I could use some kind of virtual printer. Like PDFCreator or FinePrint, but with a virtual COM port instead of a virtual windows printer. Does anyone know of such a thing? Edit: The code sends control characters to get bold text and other formatting. I'd like to see this in the output if possible.

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