We have email validation tool which tell, is valid or invalid by checking MX record ect.
It is working fine in my old server. Same build which i have deployed in another server Windows 2012, is not working, may be fire wall is blocking ?
I have opened port 25 in both InBound and OutBound
What i need to do ?
In that tool, which query MxRecords DnsQuery
Your issue is that you've confused the port for SMTP (25) with the port for DNS (53). Open 53 and you should find that your queries work. Note that you will need to open it for both TCP and UDP; packets at or below 512 bytes use UDP, above that use TCP.
More information can be found on Wikipedia.
Related
I have created a test account to IOThub and pulled down the azure-iot-sdks git archive to test with.
I have added my connection string to both the iothub_client_sample_http and iothub_client_sample_mqtt .c files.
When I run the iothub_client_sample_http I see a couple of network packets sent and acked before I get a segmentation violation in pthread_mutex_lock called from PR_lock. I will track this down and fix it.
More importantly, I want to use the MQTT protocol. When I execute the iothub_client_sample_mqtt app I get a timeout in the connect code. I have looked at the packets with wire shark and what I see is:
TCP 74 33226 > secure-mqtt [SYN] Seq=0 Win=29200 Len=0 MSS=1460 SACK_PERM=1 TSval=81898578 TSecr=0 WS=128
Then two more packets going out the same with retransmission. I never see any reply packets.
Is there something I need to enable at the IOThub to allow using MQTT?
I actually want to use mosquitto in the product and I get the same scenario from my code.
Thanks for any help.
You can also use MQTT over WebSockets which uses 443 port instead of 8883.
See more details from https://learn.microsoft.com/en-us/azure/iot-hub/iot-hub-mqtt-support
Thanks for the answer. It turns out the company was filtering all packets to port 8883 and that was my issue.
MQTT has some particular advantages over other protocols to the hub. As it becomes more popular IT organizations will need to change this type of thing.
Thanks again.
Short version: How would you recommend going about connecting a client to a server that are on the same local network, without manually entering the ip, when broadcast is disabled?
Further details: I am working on an educational multiplayer game for children. Many schools appear to be blocking broadcasting for security reasons. The children will be rather young, so it could be difficult for them and error-prone to have to enter the IP manually. They will all be in the same room and will all see the server screen. The game is made in Unity (C#).
Potential solutions: Here's what I thought about:
Connecting both the local server and clients to an external server, communicating the local server ip through the clients through the external server, then connecting directly and disconnect from the server. Not ideal because of the extra hosting costs.
Send a regular UDP message periodically to all ips on the subnet? This will probably be picked up by any decent firewall and blocked though, right?
Putting a QR code on the server that kids would take a picture of with the client app and have it connect that way? May be more of a hassle.
Having the server play random tones corresponding to numbers that the client is listening for? (Speakers may not always work though)
Sounds like the first one is the most sane and easy solution. Do you have any other ideas on what someone in this situation could try?
Is UDP multicast possible?
If yes then a common solution is that all participants join the same multicast group and the server listens on a well known port. If a client wants to know the address of the server it sends a packet to the multicast group, which is received by the client and answered with another packet, which then can be used by the client to determine the servers address.
In addition to that servers can also announce their presence in regular intervals by sending a suitable message to the multicast group.
What I can think of is an ad-hoc communication protocol between all the devices. Say you have 1 server and 10 clients. All the devices should run a service(say server-discovery) that binds to a fixed port say 9999. Now any time the client wants to connect to the server and doesn't know the IP, it starts a scan. Loops through different IPs and tries to connect to 9999. If it manages to hit, it asks for the server IP. In case it manages to hit the server it will get the IP since the server knows it's own IP and the client will maintain the server IP in a cache. If the client hits another client. It can ask for the server IP. It the other client knows the IP it will share the info else decline.
I agree there is a lot of overhead, but I think this will be robust unlike sound and would reduce cost of printing QRs everytime.
on the local network the traffic is direct from host to host.
I don't understand which devices is blocking local broadcasts.
if there aren't too many peers on the LAN ( less then 100 ), I think udp broadcasts work fine and you dont pollute the network.
to have an idea of your "pond", I suggest you to sniff your local traffic.
there are many broadcasts : arp, windows, ipp, dropbox...
I'm building a chat server with .NET. I have tried opening about 2000 client connections and my Linksys WRT54GL router (with tomato firmware) drops dead each time. The same thing happens when I have several connections open on my Azureus bit-torrent client.
I have three questions:
Is there a limit on the number of open sockets I can have in Windows Server 2003?
Is the Linksys router the problem? If so is there better hardware recommended?
Is there a way to possibly share sockets so that I can handle more open client connections with fewer resources?
AS I've mentioned before, Raymond Chen has good advice on this sort of question: If you have to ask about OS limits, you're probably doing something wrong. The IP protocol only allows for a maximum of 65535 ports and many of these are reserved and not available for general use. I would suggest that your messaging protocols need to be thought out in more detail so that OS limits are not an issue. I'm sure there are many good resources describing such systems, and there are certainly people here that would have good ideas about it.
EDIT: I'm going to put some thoughts about implementing a scalable chat server.
First off, designate a single port on the server for clients to communicate through. Whenever a client needs to update the chat state (a new user message for example) do the following:
create message packet
open port to server
send packet
close port
The server then does the following:
connection request received
get packet
close connection
process packet
for each client that requires updating
open connection to clients
send update packet
close connection
When a new chat session is started, the client starting the session sends a 'new session' message to the server with the clients user details and IP address for responses. The server creates a new chat session and responds with the session ID. The client then sends packets containing the messages the user types, the server processes them and forwards the message to other clients in the same session. When a client leaves the chat, it sends a 'end session' message to the server. The server removes the client from the session and destroys the session when there are no more clients in the session.
Hope that gets you thinking.
i have found some answers to this that i feel i should share:
Windows 2003 server has a limit on the number of ports that may be used. but this is configurable via a registry tweak to change the MaxUSerPort setting from 5000 to say, 64k( max).
Exploring further, i realize that the 64k port restriction is actually per IP address, hence a single server can easily attain much more ports, and hence TCP connections by either installing multiple network cards, or binding more than one IP address to a network card. that way, you can scale your system to handle n x 64k ports.
Had for days a problem with the available sockets on my Window 7 machine. After reading some articles about socket leaks in Win 7, I applied a Windows patch - nothing changed.
Below there is an article describing windows connection problems in great detail:
http://technet.microsoft.com/en-us/magazine/2007.12.network.aspx
For me it worked the following:
Open Regedit
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\Tcpip\Parameters: Create TcpNumConnections, REG_DWORD, decimal value 500 (this can be set according to your needs); EnableConnectionRateLimiting, REG_DWORD, value 0;
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\Tcpip: Create MaxUserPort, REG_DWORD, decimal value 65534
Restart Windows
I spent the last two days reading each StackOverflow questions and answers (and googling of course) about Indy TCP and UDP protocol in order to decide which one should I use in my communication method between my User Application and my Windows Service.
From what I saw so far, UDP is the easiest and the only one I managed to work to receive broadcast messages from TidUDPClient (I did not testes the response back yet). And I also noticed that TCP is a bit more complicated with it's thread loop.
But since everywhere I am told UDP is not reliable, UDP is not reliable... I begin to wonder if it's not better to use TCP anyway.
My User Application will be running on many machines, and the Service will be running in one of them, sharing one IP with a Client, or in a dedicated machine, depending on my client's funds. So, should I really be worried about UDP data loss possibilities?
I need broadcast capabilities so my server advises all clients at once about Application updates, and of course, if my the Client Application does not know in which IP the Service/Server is, it will send a broadcast call to be told where the server is. Is that applicable to TCP?
The messages I am sending are requests for users access confirmation, users privileges, and application executable file updates, since the main application can't update itself.
Those messages are encrypted like below, and they might bet bigger sometimes.
e86c6234bf117b97d6d4a0c5c317bbc75a3282dfd34b95446fc6e26d46239327f2f1db352b2f796e95dccd9f99403adf5eda7ba8
I decided to use them both!
Simple use case:
In order to communicate with TCP prococol you have to establish a connection which you can have only if you know IP and Port on both ends.
If you do not have that information when you load your Application, then you use the UDP to Broadcast your IP address and your intention to find the/a Server. You may try about 5 times before you raise the user an error telling that you did not find the Server or that the Server is down.
Sending that message in UDP will (one time or other) reach the UDP ear of the Server, which will now know the IP from the lonely Client's IP and will now begin a proper connection via TCP to be read talk about the critical messages of the Application.
What do you think of that approach?
I recently found the ping command on the mac. I used to it casually ping my rails heroku app. I was wondering if this type of ping, from the terminal, increases the total number of hits the website gets (obviously not unique hits).
ping is a network command not using the port 80 or http protocol.
So there's no way it can count towards a rails application hit.
More info :
http://wiki.answers.com/Q/Which_port_is_used_by_Ping_command
The ping command only pings the host, it is a network tool to check connectivity between machines, it is a different protocol from HTTP, please read this, it may help you understand a bit better what is ping http://en.wikipedia.org/wiki/Ping_%28networking_utility%29 and what is his uses.
Cheers
What Anthony said above is true. Ping uses ICMP which is lower in the stack than an http request going over port 80. Ping only sends a single packet, expecting a single packet in response which is rather small (I think 64bytes round trip).
This can however generate load on the box running your server. So be wary of excess use as you could inadvertently cause a denial of service :)