I'm working with Microchip's TCP/IP stack and the host name of my device is not being broadcasted, although I can access it using its DHCP assigned IP.
So the question is, what is the protocol that a network device uses to broadcast its host name, so that when I see a list of devices in a network I can identify it by name?
Is it the NetBIOS name service or something else? Thanks in advance.
The most network-agnostic way to specify a hostname for a host on the network is through DNS, which your device itself cannot control, but all is not lost.
In most environments, the DHCP and DNS servers are tied (AD in Windows networks, DNSMasq on linux, etc...) so your best option is to rely on this behaviour. When you request an IP using DHCP, the DHCP protocol allows you to specify the hostname you'd like to use and if the network is set up to allow DNS entries to be created and maintained by the DNS server, the hostname you send during your DHCP request will typically be used.
The DHCP parameter is called 'Hostname'. The Network protocol documentation for this parameter is located in RFC 2132, and explained here.
There is WINS (based on NetBIOS) that supports this functionality.
There is ZeroConf/Bonjour that offer a "service advertisement" protocol but I am guessing that's not what you are after here.
In "normal" IP based networks, name resolution would go through a DNS layer: the DNS servers propagate their databases (if instructed too of course) but there is no concept of "broadcasting" at this layer.
I guess you've solved this by now but I modified the dchp.c file in the Microchip stack and added the following to the options part of _DHCPSend().
// host name
i = strlen(AppConfig.NetBIOSName);
UDPPut(12); //host name code
UDPPut(i); //length
UDPPutString(AppConfig.NetBIOSName);
This worked for me.
Related
In http the client supplies the hostname it used to connect to the service with. Now, for bare TCP connections, is there something similar one can do? My scenario is I have a service that has multiple open TCP ports and that works fine, but for convenience I would like to use the same port and subdomains. Is there any layer I can add on top (like a load balancer), or change the service? I have control over most things, basically anything goes.
Example:
Today I can connect to two TCP services like so: foobar.com:1001 and foobar.com:1002. Is it possible to have e.g. service-1.foobar.com:1000 go to foobar.com:1001 and service-2.foobar.com:1000 go to foobar.com:1002.
Different services can bind to same port but on different IP. Hence different domains shall resolve to different IPs : Port combination [where Port is same for all services]. And you can use Proxy service as from HA Proxy to route connections to final destination.
If I understand your question correctly based on your example then no it is not possible. In this case, there is no difference between an HTTP and TCP connection.
In both cases, the hostname is simply resolved to an ip address. If you setup DNS resolution for foobar.com, service-1.foobar.com, service-2.foobar.com to point to the same ip address then they will all go to the same machine.
I have at times needed to have a service running on a different port internally than it is accessible externally. For that, if you are running on Linux, you can simply use iptables to do the port forwarding.
You can find other stack overflow questions/answers for setting up the port forwarding.
https://serverfault.com/questions/140622/how-can-i-port-forward-with-iptables
I've a VPS with IPv6 and a IPv4 NAT - so I have access to the server through IPv4 with a port range for my service.
The ideal use for the server would be a mail server and DNS records (specifically MX records) cannot take a port.
Is there anyway to access this server without having to declare the port, for example through a domain like example.com being mapped to 192.168.1.1:200?
IP does know nothing about "ports". It is a network layer protocol that is responsible for addressing and routing. Look closer to OSI model, for example here: OSI
Any service you run is situated above this layer. It hard to understand what do you mean under "access the server"? If you think about SSH or RDP -- you can't reach them without port definition. If you think about exchanging information between client and server without specifing the port -- it is possible. For example by using ICMP for data exchange though it is not meant for that.
Every service need a port.
DNS need to run under a port 53(or not)..
MX record is not a service.
You need to know what is a service and the relation of a service and ports
I have a server and a few clients, software-wise, and I want the client to figure out the IP address of the server without actually referring to a specific database.
I had a misconception about UDP up until now that UDP only used the Port as a common identifier between servers and clients, but I was wrong apparently.
Requirement:
I want my server to broadcast a message to ALL devices on the network, once every 5 seconds or so.
That message will contain the IP of the server.
Software using such technique already:
A photo transfering app for iOS, called "Photo Transfer App" is really easy to use because it basically tells you to open the app on your Mac and on your iPhone, and then you press "Discover", and BAM! your devices have found each other.
But how?
How can my requirement be achieved?
EDIT
I googled a bit. Could server host on 255.255.255.255and clients connect to that address solve my problem?
According to this Wikipedia article, 255.255.255.255 is used for broadcasting.
Can someone confirm?
If you will use broadcast address (255.255.255.255) or network broadcast (like 192.168.1.255 for network 192.168.1.xxx or in the prefix notation 192.168.1.0/24). You will get essential limitation: your broadcast will NEVER leave that network. So all host inside the LAN will see your broadcast message but nobody else.
Multicast as mentioned by null is better because it can leave your network and pass through the IP routers. But this is feasible only by special network settings on that routers (and require multicast routing capability on that routers).
Another technology without such limitation can be use is dynamic DNS (server will register itself via DNS).
Multicast would be better than broadcast. See also: Bonjour, multicast DNS & SSDP.
More information on Bonjour is available here.
I am at a large University, with servers set up on the Univeristy network. The network has internal (10...) IP addresses, and external (129...) IP addresses. I have a ColdFusion-based business process which FTP's data from an external server.
The server on which the ColdFusion instance is based has several (about 10) IP addresses associated with it, both internal and external. It has one primary address, which has been, until recently, external.
Using Wireshark, we have been able see which IP is used, and it is never the primary, but other than that, does not seem to follow any logic.
We recently changed the primary IP for the server to an internal address, to comply with new University-wide security policies, and the FTP connection from Coldfusion stopped working. Using Wireshark, we've confirmed it is going out on one of the internal (10...*) IP addresses (not the primary).
Is there a way to control which IP ColdFusion uses for an FTP connection, either through system configuration, or programmatically?
Code for the FTP call:
var ftpService= new ftp(
username = partnerConfig.sftpLogin,
connection = "MyConnection",
password = partnerConfig.sftpPw,
fingerprint = partnerConfig.sftpFingerprint,
server = partnerConfig.sftpServer,
secure = "yes"
);
var result=ftpService.open();
var result2=ftpService.listdir(directory = partnerConfig.inFolder, name="dirlist");
var result3=result2.getResult();
EDIT: My server guy tells me that this University is fairly unique in how it configures the subnets. NO firewall exceptions are allowed from the 10.* subnet. The "Public" IP's are not public by default, simply the ones which are capable of having exceptions.
FURTHER EXPLANATION: It comes down to the Rules and IP addresses the main IT org at the university set up. the 10.x.x.x IPs are never allowed access outside the university ("internal"). 129.x.x.x IP, may have firewall exceptions ("external"). If I type ipconfig (it's Windows), I see about 10 static IP addresses, half of which are 10.x.x.x, and half of which are 129.x.x.x. When the "primary" IP for the machine was a 129.x.x.x address, Coldfusion chose one of the OTHER 129.x.x.x addresses for the outgoing IP for the connection. With the "primary" IP switched to a 10.x.x.x IP, ColdFusion is choosing one of the OTHER 10.x.x.x addresses for the outgoing connection. My choices, as far as I can tell are 1) Switch the primary back to a 129.x.x.x for the server; 2) Move the site to a different server with a primary of 129.x.x.x, and keep other sites on the server in compliance with the new policy; 3)See if I can figure out how to control which IP Coldfusion chooses from the 10 static IPs on the server.
Our admin figured it out. We needed to add a static route to the server, so that whenever ColdFusion (or any application) tries to connect to the specific destination we were FTPing to, it goes through a specific outgoing IP address.
This was not something I was familiar with, but a quick search gives the basics: http://technet.microsoft.com/en-us/library/dd469825.aspx
You have an internal IP address and you are not sure what the external is? This sound like a network bridge issue. What you are looking for is FTP proxy or some tool that associates an externally assigned IP to an internally assigned IP for port 22 (or whatever you set your port to). Look at: http://wiki.squid-cache.org/Features/FtpGateway
FTP reverse proxy
It sounds like your IPs (even internally may not be static)...or maybe it just feels that way. Make sure your internal IP is static.
Read about FTP port forwarding: Here are some port forwarding guides.
Other keywords FTP bridge, FTP one-to-one mapping, among others.
Good luck.
I had a similar question regarding the cfmail tag:
Force cfmail tag to send from a specfic server IP address
Unfortunately, I didn't get an answer that worked. ColdFusion seems to pick (seemingly at random) which source IP address is used.
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.