There is a lot of other answers related to this issue, however I believe this is specific.
I am using Delphi XE2 and Indy 10.5.8 and TIdUDPServer
In my local development network I have everything on the same network ip subrange and all connected to the very same Access Point (LinkSys)
I have Androids sendind UDP Broadcast to 255.255.255.255 to request the server ip address that is written in Delphi listening using TIdUDPServer on the port 44444.
The requests get there fine and I can answer back no problem. Works exactly as expected.
However I have noted that in some networks it does not work! It is always simple networks based on an access point, I am not sure but seems that where the problem happens the server PC is connect to the LAN port while the devices are using the wifi, all in the same access point.
Could be the case that the access points do not broadcast the UDP packet by the both LAN and wifi? I know that this kind of broadcast is very limited, but I have not found any information that tell me that in the same access point there is limitations like that.
Is there are ways to test, or workaround?
This solution needs to be strong enough to deal with the many AP out there.
EDIT: For those that want to get the source code for retrieving more information from the network including the broadcast ip as mentioned on the answer below follow this solution, it is all there.
http://www.code10.info/index.php?option=com_content&view=article&id=54:articleretrieve-network-adapter-information&catid=47:cat_coding_algorithms_network&Itemid=78
255.255.255.255 is not the best option for sending UDP broadcasts, and some routers/firewalls do block it unless configured otherwise. The better option is to use the NIC's actual subnet broadcast IP instead. For example, if a UDP socket is bound to local IP 192.168.0.1 with a subnet mask of 255.255.255.0, then the broadcast IP for that subnet is 192.168.0.255.
Most platforms have OS-specific APIs for retrieving a NIC's actual broadcast IP, such as getifaddrs() on POSIX systems, or at least for retrieving the NIC's subnet mask, such as GetAdaptersInfo() and GetAdaptersAddresses() on Windows, so you can calculate the broadcast IP manually.
Retrieving the local broadcast IP(s) may be added to Indy in a future version.
Related
I was quite surprised when I found out that there was a really big range of IP addresses allocated for loopback (127.x.y.z).
I didn't find much information about why it's like this, except that it could be used for testing networks and protocols locally, which got me thinking if it could be a good idea to use these addresses for IPC.
At the moment, as far as I know, IPC based on networking is usually done with TCP/UDP by opening sockets on ports which are most likely not used by any other service.
So my question is, to be even more sure that there won't be a port collision, could other loopback addresses be used instead?
For a more concrete example, could two processes communicate through sockets on address 127.31.41.59 and ports 27 and 18 (or even different loopback addresses)?
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...
In my recent app I managed to send data (mostly audio) via UDP in my local network (WiFi) to other iPhone. And now I need to do this same but in WAN. Can You guys please point me in the right direction where to start? What I need to achieve this?
I'm using GCDAsyncSocket to manage sockets. I believe that I have to got server, where I can keep IP addresses of both devices.
Also, how can I connect to device behind NAT/Firewall? I'm guessing, that I need to have public IP address (scrapped for instance from http://checkip.dyndns.com/). And then do I need to traceroute? Or NSLookup? Or piggyback? Or do I need to use UDP hole punching?
I know it's a lot of question, but if you can just point me to the right technology, I would be very grateful.
To achieve a communication between two participants behind a NAT you could use Hole-Punching like you mentioned it. This is explained quite well here: http://en.wikipedia.org/wiki/UDP_hole_punching#Flow
Basically a Server with a Public IP and Port is used to share the Port-numbers of the iPhones.
But a NAT may use a different Port for every different IP the iPhone talks to. So if iPhone1 sends data to the server the NAT uses port X, but if iPhone1 wants to send data to a different IP the NAT may choose port Y. (See http://en.wikipedia.org/wiki/Network_address_translation#Symmetric_NAT)
To overcome this problem there is a protocol called UPnP and the lesser known NAT Port Mapping Protocol.
I am not well versed in UPnP but maybe someone else can provide some information on that.
The protocol NAT-PMP enables you to dynamically request an external port to be forwarded to your device. See http://en.wikipedia.org/wiki/NAT_Port_Mapping_Protocol, RFC 6886 .
This allows you to "predict" your external port and establish connections over NAT.
I would like to do a scan in a LAN network to find devices linked.
I'm developping an app in IOS for IPAD
How do I do???
Because those are mobile devices I will assume you want to find devices on a wireless network. Theoretically, since wifi uses shared medium for communication, you can passively listen for traffic flowing through the network and collect data about client without sending any packets. This is something that is commonly referred to as a promiscuous mode. In practice there is 99% chance that the network adapter driver will allow you only to get traffic destined for your MAC address. In that case you will need to resort to actively scanning the network subnet which is not 100% accurate and depending on how the network is implemented can be considered as a possible attack.
The simple way of scanning is sending ICMP requests (ping) to every IP address in the subnet and collecting data from those who send back the echo reply. This is not reliable because some hosts won't respond to ICMP echo request even if they are active. First thing you need is to find out your own IP address and the subnet mask, and calculate the range of possible addresses in your subnet. The range is obtained by using logical AND operator where operands are binary values of your IP address and subnet mask. This is an example from the program that calculates this for typical 192.168.1.1 subnet with 255.255.255.0 subnet mask (192.168.1.1/24 in CIDR notation):
Address: 192.168.1.1 11000000.10101000.00000001 .00000001
Netmask: 255.255.255.0 = 24 11111111.11111111.11111111 .00000000
Wildcard: 0.0.0.255 00000000.00000000.00000000 .11111111
Network: 192.168.1.0/24 11000000.10101000.00000001 .00000000
Broadcast: 192.168.1.255 11000000.10101000.00000001 .11111111
HostMin: 192.168.1.1 11000000.10101000.00000001 .00000001
HostMax: 192.168.1.254 11000000.10101000.00000001 .11111110
Then you would iterate through the range and ping every address. Another thing you can consider is listening for broadcast traffic such as ARP and collecting some of the information that way. I don't know what are you trying to make but you can't get many useful information this way, except for vendor of a host's network adapter.
Check my LAN Scan on Github. It does exactly what you want.
I recently used MMLANScan that was pretty good. It discovers IP, Hostname and MAC Address.
Bonjour have been around since 2002, have a look at it!
I mean, just look at their current tagline:
Bonjour, also known as zero-configuration networking, enables automatic discovery of devices and services on a local network using industry standard IP protocols. Bonjour makes it easy to discover, publish, and resolve network services with a sophisticated, yet easy-to-use, programming interface that is accessible from Cocoa, Ruby, Python, and other languages.
Writing WinXPe NDIS 5.1 device driver. Started with Intel E100 driver source from DDK and adapting to Altera triple-speed ethernet core. Receive packet through scatter gather DMA working well, can see good data. Transmit packet through separate scatter gather DMA claims to be working well. Problem is that ipconfig shows IPv6 only IP address for the NIC. Control Panel, Network Configuration, Internet Protocol, has set static IPv4 IP address and no DHCP. But ipconfig doesn't see it. Can't find any OIDs which appear to tell WinXPe anything about IPv6 versus IPv4. Control Panel, Network Configuration correctly updates itself for ethernet connect and disconnect, but nothing seems to please ipconfig. Where is ipconfig getting its IPv6 information, and how can the driver affect it? Thanks.
The problem was an incomplete implementation of OID_GEN_CURRENT_PACKET_FILTER which inhibited the higher level driver from passing IPv4 packets to/from the driver. Although none of the flag bits in OID_GEN_CURRENT_PACKET_FILTER appears relevant to IPv4 [or IPv6], it mattered. Took a call to Microsoft on my MSDN account to resolve this.