I have question on DHCP server in home router. I have founded, that I have same IP address in my notebook for some time. I don't know, how long it last, but it is probably few weeks at least. Will DHCP server ever change my local IP if i will still connecting to that Wi-Fi?
I am asking, because I am working on home automation system and I don't know if i had to keep care about checking if my devices has same IP...Because there will be server, which will remember IP of its clients (lets say ESP8266 modules). Must I periodically check IP address (in my modules) and send new IP to server (in case of change)? Or DHCP server will not change IP address of my modules, connected to that DHCP server? And what about situation when ESP8266 module will disconnect (lets say it will be off for few days) - is it common to get different or same IP from DHCP after connection again?
Thanks!
Simple solution would be reserving IP address for your ESP8266 modules in your DHCP server that they always receive the same IPs.
With regards to your questions:
My routers DHCP server saves clients and keep information about them unless it is deleted explicitly or number of saved clients gets larger than number of addresses available. It serves always the same IP to saved clients. Obviously it depends on the router and might be different in your case.
I'd not check for IPs manually, I'd rather reserve the IPs for the modules as said above.
If your DHCP server stores client information it will give the same IPs to your modules upon reconnect. Otherwise not it won't be necessary the case.
If you use or consider using MQTT server (my preferred way :) ) for your home automation (it has integration in many systems like e.g. Home Assistant) you won't need to care about IP addresses of your modules at all you'd only need to fix IP of the MQTT server.
Another option can be addressing your modules (or/and server) using host name instead of IPs. If you develop n Arduino this GitHub thread might be helpful.
Related
I have an embedded webserver running on a device. Now I want a smartphone app to connect to the webserver. They are on the same wifi network but they don't know each others IP addresses.
I understand that this problem is often solved by implementing the mDNS protocol on the server. But are there any alternatives? Can the server maybe ask for specific IP address or similar?
If it has to be entirely automated, such that the embedded webserver is discoverable, perhaps scan the entire netblock looking for the correct response "http://[IP_address]/yes-im-the-one" from your embedded webserver?
Although beware, some network monitors may then consider the IP of your smartphone/device that does that scan "dangerous" and cut it off from the network - this is probably only a "big enterprise" problem.
...after you "find" your server, perhaps the application should cache/remember this, so it doesn't have to scan next time.
Other things you could do: give your embedded webserver a static IP on the LAN, either by setting this on the device itself, or via a DHCP reservation from whatever is the local DHCP server on the LAN.
What allot of emended devices do is come delivered with a static LAN IP already set on it, then it's up to the sysadmin to change their computer's IP temporarily to be in the same range, then they can visit the webserver or telnet into the default IP, and change it to what they want (to match their network's IP range)
I'm making an XNA game. When I started, I had a broadband connection with real IP, so I could host servers of any kind without any problem, but now I don't have that connection any more and I want to be able to let players from outside my local network connect to my server again. How do I do that? How do big guys at studios do that?
Cheap option:
Configure your home router (it does have real, but probably dynamic, IP address) to forward connections on some port of your liking to your server on the local network. Read up on Network Address Translation - that's the trick routers use to hide a network behind a single routable IP.
Setup a DDNS account somewhere, so people can find your game server by name instead of changing IP address.
Expensive options:
Buy static IP package from your ISP (not always available).
Deploy your game at a Hosting Service.
Generally there are two ways to connect two clients:
Give each client other client's IP address and let them connect to each other.
Give each client a mid-server's IP address and tunnel the traffic through it.
First way assumes each client has a real IP address and they both can be a server to one another. Second way is for when one or both clients don't have real IP address.
I am developing a networked application that runs on a few different computers on a LAN. One of the core needs is for the app to maintain a list of peers on the LAN with which it has communicated in the past, so that it can restore previous sessions. The naive solution would be to just remember the IP and store it in a table, but what happens when the IP of a peer changes?
Instead, I thought I'd store the hostname of the peers so even if the IP changes they will still be reachable via their hostname. (I know hostnames can change as well but that is good enough).
So my question is what exactly is needed to make hostname resolution work on a LAN with mixed Windows/Mac/Linux clients?
Without the use of a central authority the only reliable way to achieve this is through the use of zerconfiguration name resolution. This means that without a multicast router you will only be able to dynamically resolve peers on the same subnet as the resolving host. You could use something like bonjour for mac, netbios or ssdp for windows or avahi for linux but you can't assume that these are enabled. I may be overlooking some more popular protocols that perform this function well but I would personally throw together a quick udp broadcast name resolution protocol for your application. Take a look at these for some more ideas:
Zeroconf Name resolution
Universal local network name resolution method without DNS?
http://en.wikipedia.org/wiki/Zero_configuration_networking#Name_resolution
http://en.wikipedia.org/wiki/Broadcast_address#IP_networking
I would pick a specific udp port to listen on (lets say 12000) and then when you're ready to resolve hosts send a "hello" udp packet out to 255.255.255.255 on port 12000 and all of the other hosts on your network running your app should reply with a packet containing their hostname, possibly other information.
I made a program many years ago, that connects to a SQL Server database (port 1433), and I no longer have the code for this application, but I need to know whether it is trying to connected to the domain name exampleDomain.com or if it is connecting directly to the IP address, xxx.xxx.xxx.xxx.
I need to find this out because I want to switch hosting providers, but cannot let this application stop working, so I'm not sure if changing the IP Address of the SQL server will affect the program.
Is there a way I can tell what this program is connecting to? The raw IP Address or the domain Name?
thanks.
Use wireshark. http://www.wireshark.org/
It's free, easy to use, and very powerful.
You can monitor all traffic coming out of your PC and you can filter the traffic by type. So first I would look for any DNS communication that has MyDoman.com and then look at TCP connections.
Some background first. I have a .net client agent installed on each of the machines in the lan. They are interacting with my central server [website] also on the same lan.
It is important for my website to figure out which of the machines can talk to each other. For example, machines of one subnet cannot directly talk to machines of another subnet without configuring the routers and such. But machines in the same subnet should be able to talk to each other directly.
The problem I am facing is when the lan setup is like in Figure 1.
Because Comp1, Comp2 and Comp3 are behind a router, they have got the ipaddress 192.168.1.2 till 192.168.1.4. My client agent on these machines report the same ipaddress back to the server. However, machines Comp4, Comp5 also have the same ipaddresses.
Thus, as far as my server is concerned, there are 2 machines with the same ipaddress. Not just that, because the subnet mask is 255.255.255.0 for all machines, my server is fooled into thinking that Comp1 can directly talk to Comp5, which is not possible.
So, how do I solve this? What do I need to change in my client or in my server, so that I can support this scenario. These two are the only things in my control.
EDIT: Seems that the network diagram
is over simplified and there could be
multiple router/subnet levels. My
original answer will not handle this
scenario. Also, with the restriction
of modifying only the client app or server
app and not tampering with the
routers and firewalls makes
it more difficult.
EDIT2: Using 'arp -a' you can extract
the MAC address of the router. If the
client apps can manage to do this then
the puzzle is solved!
The client app knows the local machine address and passes it to the server app.
The server app knows the remote address when a connection comes in. This would be machine address or a router address.
From these two values you can work out what you ask.
For example:
Server app receives connection from 10.10.10.2 with client supplying 192.168.1.2
Server app receives connection from 10.10.10.3 with client supplying 192.168.1.3
The 'remote address' distinguishes the subnets.
So, all you need to figure out is how to extract the remote address of a client connection. If you are using any of the popular web technologies for your server app then this is very easy.
One approach is for the individual client machines to determine who they can see using a broadcast message. Have each client listen on some particular UDP port, and each client broadcast its presence to whatever the local broadcast domain is. When clients can see each other in this way, they can probably also make TCP connections to each other.
If the server needs to know which clients can talk to each other, just have the clients tell the server.
If the network diagram is complicated enough I think if would be very difficuilt to find what you need.
You should also take into account that Comp1 can establish direct connection to Comp6.
The solution I can suggest is probing. Client receives list of all other clients from server and tries to establish connection to each of them. I think that would be the only way to know which clients are REALLY accessible assuming any number of routers/firewalls/NATs in the network. Doesn'r scale much for a big number of computers of course.