In ower system we have two machines which connected by MSMSQ. one machine contains two static ip addresses (each ip belongs to other lan) and the second one using one ip address. We have a proccedure which change the ip address of the machine with one ip address to ip belongs to the lan of one of the ip address of the machine contains two ip address. the problem is that each time after changing the ip MSMQ connect after 15 minutes. On xp it was immidate.
What can couse this?
The Windows 7 situation sounds 'normal'. MSMQ relies on TCP/IP name resolution. If you change the IP address of a PC, other machines don't immediately know about it until cached information is replaced with new.
The Windows XP situation implies that the way MSMQ uses the cached information, or the way the PC caches information, was tweaked.
MSMQ and cached IP addresses
http://geekswithblogs.net/Plumbersmate/archive/2011/08/19/msmq-and-cached-ip-addresses.aspx
You will need the Wayback Machine for the KB article I reference
https://web.archive.org/web/20100212070948/http://support.microsoft.com/kb/833512
Related
My Raspberry Pi 4 B is connected (for the first time) to the WiFi of my PC (running Windows). Then the raspberry(ip) showed up in the list in Network Scanner of MobaXterm. What surprised me is that the list also shows the name of my Pi. And ping -a ip also shows the name.
How does this work?
When the Raspberry Pi connects to your WiFi it doesn't just get an IP address assigned. It also gets a host name assigned. It either sends its own host name to the DHCP server or the DHCP server assigns a host name.
Now, when you have an IP address, you can do a reverse search. Usually DNS works in the way that you give it a name and it returns the IP address. But there is also reverse search, give it an IP address and get a name back.
In your local network the DHCP server and your DNS resolver work together. Whenever a reverse search for a local IP address is made, the answer is fetched from the DHCP server. And the DHCP server answers with the host name from step one.
In most WiFi routers dnsmasq does this for you, on a Windows machine it is built into Windows.
So I am kind of new to networking and I'm just interested in the client/server architecture. Let's say you developed a program and the client version ran on a computer and the server version on the server(obviously). In order for the client to connect to the server, it would have to know the ip address of the server (and the port attached so it can be routed to the correct computer/program). Does that mean that the server's ip address can not change? Would you have to specifically tell your ISP to keep the ip address static? Because if both the client and server ip addresses change, then they would have no way to connect and the program wouldn't work... in other words there has to be one constant. When you sign up for a VPS do they give you a static ip address you can bind to from the client version? Thanks!
In order for the client to connect to the server, it would have to know the ip address of the server (and the port attached so it can be routed to the correct computer/program).
Correct.
Does that mean that the server's ip address can not change?
No. In fact, IPs can change at any time. Most servers that are exposed to the public Internet have a static domain name registered in the Internet's DNS system. A client asks DNS to resolve the desired domain name to its current IP address, and then the client can connect to it. But even in private LANs, most routers act as a local DNS server, allowing machines on the same network to discover each other's IP by machine name.
The OS typically handles DNS for you. A client can simply call gethostbyname() or prefferably getaddrinfo(), and the OS will perform DNS queries as needed on the client's behalf and return back the reported IP(s).
Would you have to specifically tell your ISP to keep the ip address static?
You can, but that usually costs extra. And it is not necessary if your server is registered in DNS. And there are free/cheap DNS systems that work with servers that do not have a static IP.
Because if both the client and server ip addresses change, then they would have no way to connect and the program wouldn't work...
That is where DNS comes into play.
in other words there has to be one constant.
A registered domain name that can be resolved by DNS.
When you sign up for a VPS do they give you a static ip address you can bind to from the client version?
It depends on the VPS service, but a more likely scenario would be you are assigned a static sub-domain within the VPS service's main domain. For example, myserver.thevps.com. Or, if you buy your own domain (which can be done very cheaply from any number of providers), you can usually link it to the DNS server operated by your VPS service.
How to retrieve virtual machine data such as ip address on the HOST .
I've created virtual machines using qemu-system-x86_64.
At time of asking, it was not possible to query the guest IP address from virsh. Modern libvirt though supports the "domifaddr" command in virsh which lets you query the DHCP assigned IP address for guests that are connected to libvirt's "default" network. It does not work for guests using direct bridging to the LAN.
Second, there is now also the ability to setup an NSS module on the host, so you can login to guests based on their hostname, instead of raw IP. Again this works for guests using the default network
I'm using ZeroMQ on Windows, using C#, and am confused by a very basic networking question. I set up simplistic sample programs, one to PUBlish messages, the others use a SUB socket to receive them (the SUBscriber programs).
Works fine when both are on the same box. I used endpoint tcp://127.0.0.1:5000
As the next step, I put the SUBscriber program on a separate virtual machine (VM), to simulate using separate computers. I ran ipconfig to get it's IP address (on the guest os), 192.168.92.136
The host os has several network interfaces, one of which is the VMware Network Adapter VMnet1, with IP 192.168.92.1
On the host os, I ran the PUB program and connected the socket to 192.168.92.136, the IP address of the guest os.
On the guest os, I ran the SUB program and connected the socket to the IP of the host os. Did not work.
Then I changed the SUB program on the guest os to make it connect it to it's own IP address, ie that of the guest os - 192.168.92.136. Now it works!
Question: Why? I'm confused. But in a way it sort of makes sense: if that socket is for a service that attends to various clients that dynamically come and go, it doesn't know the IP address of each client. Therefore what the heck do you specify as the IP address for the SUB socket?! So connecting it to it's own host IP address does solve that concern. But the ZeroMQ Guide doesn't say this anywhere!
A related question is: if your host has multiple network interfaces, and each has it's own IP address, then if you connect your socket to some other host using the IP address of that other host - do you not need to specify which of those network interfaces you want to connect through? If so, how?
Incidentally, only one subscriber program seems to be able to connect at a time. The 2nd program to attempt to connect to it's SUB socket to the local IP address always gets a "Address is in use" error-message. I'm trying to make progress in small steps and learn this as I go.
Thanks for any help or advice.
James Hurst, JamesH at Designforge dot com
According to http://www.cisco.com/en/US/solutions/collateral/ns340/ns517/ns224/ns892/ns894/white_paper_c11-525307.html
Each virtual machine is given a dedicated network interface card. My question is, how do a server containing about 10 virtual machines, ever support 10 NIC's ?
Those NICs are probably virtual. Packets from them are routed to the physical NIC(s) and the other way around. It's pretty much the same thing as you get in modern WiFi routers: at home you only have one Ethernet port from your Internet Service Provider, it's in the modem. You connect your router to it, but your router may have 2+ Ethernet ports to which you can connect multiple PCs.
They can be physical too and either be directly accessible to VMs or indirectly.