My application is sending reports to another application (which maintains a database of reports) on the network with simple IPv4 addresses. I can construct a valid IPAddress in two ways:
string address = "200.1.2.41";
IPAddress ip1 = IPAddress.Parse(address);
IPAddress ip2 = (Dns.GetHostEntry(address)).AddressList[0];
If address represents an IP that is reachable, both methods are quick (though IPAddress.Parse is quickest). But if address is not reachable (eg. the server is off or the user has entered the wrong IP in Settings) then Parse is lightning quick...but Dns.GetHostEntry hangs for up to 9s.
I did a parameter-by-parameter check and the final variables ip1 and ip2 are identical. Given that Parse is always quick, and that I'm using standard four-octet IPv4 addresses only, is there any compelling reason to use the Dns.GetHostEntry method? Might I need Dns.GetHostEntry if I switch to IPv6 or named hosts like FOOD.HALL.01 in future?
If you just want get an instance of IPAddress for your IP address string representation, than yes, using the DNS for that purpose is absolute overkill.
All sorts of timeouts, latencies, etc. are absolute expected. At least compared to the purely local parsing and disecting of the string representation that happens in IPAddress.Parse(). What that does is, ask the DNS server to resolve the IP address string into a hostname "entry". From that you get the IP address back that you knew all along (albeit as string and not IPAddress).
Now, if you want to be able to "convert" host names into IP addresses in the future, then yes, you need to go via DNS.
But you could always do it in that manner (conceptually):
// First see if it is a valid IP address rep - fast.
IPAddress ip;
if (!IPAddress.TryParse(address, out ip))
{
// See if it is a hostname - slower.
ip = Dns.GetHostEntry(address).AddressList[0];
}
And yes, IPAddress.TryParse() (or Parse()) can handle IPv4 and IPv6 addresses.
Related
I can't find a question or post specific to Azure for this, and I'm not sure what's different in the environment in Azure versus my testing environments that would cause this.
I've tried a few methods to get this to work but I'm not coming right. Please note this isn't Webapi, so using the HttpRequestMessage, as far as I know, is not going to work either.
Here's what I've tried so far:
Method 1:
string ipAddress = "";
IPHostEntry Host = default(IPHostEntry);
Host = Dns.GetHostEntry(System.Environment.MachineName);
ipAddress = Host.AddressList.SingleOrDefault(x => x.AddressFamily == System.Net.Sockets.AddressFamily.InterNetwork).MapToIPv4().ToString();
Method 2:
string userIP = Request.ServerVariables["HTTP_X_FORWARDED_FOR"];
if (string.IsNullOrEmpty(userIP))
{
userIP = Request.ServerVariables["REMOTE_ADDR"];
}
return userIP;
Thanks in advance.
Read the value transported in this header:
x-forwarded-for: "91.23.44.24:52623"
Note there's a source port number trailing the IP address, so parse accordingly.
Also, as #NicoD correctly points out, the header in question may contain an array of proxy servers the request traversed. For example:
x-forwarded-for: "91.23.44.24:52623, 91.23.44.155"
Syntax
X-Forwarded-For: <client>, <proxy1>, <proxy2>
<client> The client IP address
<proxy1>, <proxy2> If a request goes through multiple proxies, the IP addresses of each successive proxy is listed. This means, the right-most IP address is the IP address of the most recent proxy and the left-most IP address is the IP address of the originating client.
What about that glaring port number you ask?
From https://www.rfc-editor.org/rfc/rfc7239:
5.2. Forwarded For
[...] this parameter MAY instead contain an IP
address (and, potentially, a port number).
All client requests are terminated in the frontend layer and proxied via Application Request Routing to your web worker (hosting the MVC5 application).
I think I may be in a situation where the answer is this is not possible but in case not here goes...
I have written an ASP .NET MVC 3 application and I am using the Request.UserHostName property and then passing the value that that returns into Dns.GetHostEntry to find out all the possible IPs and the host name for the currently connected client, for example:
var clientAddress = Request.UserHostName;
var entry = Dns.GetHostEntry(clientAddress);
Generally that is fine except I have a case where I get a "host not found" SocketException from the Dns.GetHostEntry call.
The really odd thing is that the address that is returned from the Request.UserHostName property is not the public address or any of the private addresses. To prove this I ran this bit of code on the client machine in question...
var host = Dns.GetHostEntry(Dns.GetHostName());
foreach (var a in host.Aliases)
{
Console.WriteLine("alias '{0}'", a);
}
foreach (var a in host.AddressList)
{
Console.WriteLine("ip address '{0}'", a);
}
// ...from http://stackoverflow.com/a/2353177/1039947...
String direction = "";
WebRequest request = WebRequest.Create("http://checkip.dyndns.org/");
using (WebResponse response = request.GetResponse())
{
using (var stream = new StreamReader(response.GetResponseStream()))
{
direction = stream.ReadToEnd();
}
}
int first = direction.IndexOf("Address: ") + 9;
int last = direction.LastIndexOf("</body>");
direction = direction.Substring(first, last - first);
Console.WriteLine("Public IP: '{0}'", direction);
It prints three IP addresses (::1, one private and one public) but none of them are the address that is returned from Request.UserHostName.
If I pass in any of the addresses printed from the above test application into the Dns.GetHostEntry method I get a sensible value back.
So, is there any way that I could get from this strange IP address that is not the public nor any of the privates, to one where I could get the host entry for it without an exception (and what is this address)?
By the way, there is no X_FORWARD_FOR header or anything else that I may be able to identify the client with, as far as I can tell, in the HTTP message?
Background to the Question
So it was pointed out (thanks Damien) that if I explained why I am asking this perhaps someone can provide an alternative approach so here is some background...
I have a requirement that the administrator of the application should be allowed to specify in the configuration a single machine that is allowed to view the page - IP address or machine name - I can probably get the machine name requirement removed but even if they specify the IP address in the configuration it will still not match the IP address that is returned from the UserHostName property since they will use the IP address that is returned when they ping the machine name.
My thinking, therefore, was that if I take whatever is sent in the HTTP header and pass that into GetHostEntry then take all the possible results from that (all the IPs and the host name) and see if any of them match the configured value I could say "allow" otherwise "disallow" (I was going to remove the part of the host name before the first dot too, to cover that eventuality). That scheme has been blown out of the water by this situation I have where the IP address is not at all what I would expect.
The host name of the client is not normally known because it is not transmitted at the HTTP level. The server cannot know it. Look at the HTTP requests with Fiddler to see for yourself that there is not a lot of information available to the server (and the client can forge all request contents of course).
Use the UserHostAddress property to get the IP address. That is the most you can reliably find out. Once you have that you can try to reverse the IP to a host name but that is not always possible.
I have a more specific answer to your question. By examining the source code for HttpRequest.UserHostName here, I found that it maps to a IIS server variable named REMOTE_HOST which is described here. The property will return the IP adddress of the client, unless you have configured IIS in the way described, in which case IIS will do a reverse DNS lookup to attempt to return the name associated with the IP.
Make sure you read the Remarks section at Dns.GetHostEntry on the many cases it can (partially) fail:
Remarks
The GetHostEntry method queries a DNS server for the IP
address that is associated with a host name or IP address.
If an empty string is passed as the hostNameOrAddress argument, then this method
returns the IPv4 and IPv6 addresses of the local host.
If the host name could not be found, the SocketException exception is returned
with a value of 11001 (Windows Sockets error WSAHOST_NOT_FOUND). This
exception can be returned if the DNS server does not respond. This
exception can also be returned if the name is not an official host
name or alias, or it cannot be found in the database(s) being queried.
The ArgumentException exception is also returned if the
hostNameOrAddress parameter contains Any or IPv6Any.
The GetHostEntry method assumes that if an IP literal string is passed in the
hostNameOrAddress parameter that the application wants an IPHostEntry
instance returned with all of the properties set. These properties
include the AddressList, Aliases, and HostName. As a result, the
implementation of the GetHostEntry method exhibits the following
behavior when an IP string literal is passed:
The method tries to parse the address. If the hostNameOrAddress parameter contains a legal IP string literal, then the first phase succeeds.
A reverse lookup using the IP address of the IP string literal is attempted to obtain the host name. This result is set as the HostName property.
The host name from this reverse lookup is used again to obtain all the possible
IP addresses associated with the name and set as the AddressList
property.
For an IPv4 string literal, all three steps above may
succeed. But it is possible for a stale DNS record for an IPv4 address
that actually belongs to a different host to be returned. This may
cause step #3 to fail and throw an exception (there is a DNS PTR
record for the IPv4 address, but no DNS A record for the IPv4
address).
For IPv6, step #2 above may fail, since most IPv6
deployments do not register the reverse (PTR) record for an IPv6
address. So this method may return the string IPv6 literal as the
fully-qualified domain (FQDN) host name in the HostName property.
The GetHostAddresses method has different behavior with respect to IP
literals. If step #1 above succeeds (it successfully parses as an IP
address), that address is immediately returned as the result. There is
no attempt at a reverse lookup.
IPv6 addresses are filtered from the results of the GetHostEntry method if the local computer does not have IPv6 installed. As a result, it is possible to get back an empty
IPHostEntry instance if only IPv6 results where available for the
hostNameOrAddress.parameter.
The Aliases property of the IPHostEntry instance returned is not populated by this method and will always be empty.
How can I get all of the IP addresses attached to the machine that my application (C# NET Console app) is running on? I need to bind a WCF service to the primary IP address, and return a list of the full IP address list.
using System.Net;
string myHostName = Dns.GetHostName().ToString();
string ipAddress = Dns.Resolve(HostName).AddressList[0].ToString();
This is what I am using right now to get the Primary IP address, but I can't figure out how to get the rest to return them.
If I bind a WCF service to localhost:8000, will that expose it on the primary?
The DNS variants work across the network, but one DNS entry can have many IP addresses and one IP address can have many DNS entries.
More importantly, an address needn't be bound to a DNS entry at all.
For the local machine try this:
foreach (NetworkInterface netInterface in
NetworkInterface.GetAllNetworkInterfaces())
{
Console.WriteLine("Name: " + netInterface.Name);
Console.WriteLine("Description: " + netInterface.Description);
Console.WriteLine("Addresses: ");
IPInterfaceProperties ipProps = netInterface.GetIPProperties();
foreach (UnicastIPAddressInformation addr in ipProps.UnicastAddresses)
{
Console.WriteLine(" " + addr.Address.ToString());
}
Console.WriteLine("");
}
I think this example should help you.
// Get host name
String strHostName = Dns.GetHostName();
// Find host by name
IPHostEntry iphostentry = Dns.GetHostByName(strHostName);
// Enumerate IP addresses
foreach(IPAddress ipaddress in iphostentry.AddressList)
{
....
}
Edit:
"There's no such thing as a "primary" IP address.
The routing table determines which outward-facing IP address is used depending on the destination IP address (and by extension, the network interface, which itself can be virtual or physical)."
Why not just bind to 0.0.0.0 ?
That way you listen on all ips
You should probably bind to 0.0.0.0:8000, that will expose it on all available IP addresses and only bind to a particular IP address if the user/administrator demands so.
IPAddress[] localIPs = Dns.GetHostAddresses(Dns.GetHostName());
I think the OP is asking about how to get all addresses on a local NIC, not just those addresses known to DNS.
By primary he probably means the main address under "use the following IP address" in the adapter properties, and by "the rest" he probably means those listed in Advanced > (Additional) IP Addesses.
DNS will not necessarily know those.
I have managed to get the connected clients IP with the code below but can't seem to get the hostname.
Globals.connectedIPAddress = "" + IPAddress.Parse(((
IPEndPoint)_client.Client.RemoteEndPoint).Address.ToString());
Well, not every IP address has a name. However, given the IPAddress you can use Dns.GetHostEntry to try to resolve it. Also note that if it's being a NAT router, you'll be getting the router's IP address rather than their actual machine.
And just to address the point in the comments, I agree that there's no point in ToString/Parse/ToString:
IPAddress address = ((IPEndPoint)_client.Client.RemoteEndPoint).Address;
Globals.connectedIPAddress = address.ToString();
How do you get the ipaddress and location of every website vistor of your website through Asp.Net?
Thanks
To get the user's IP use:
Request.UserHostAddress
You can use this webservice to get their geographic location.
http://iplocationtools.com/ip_location_api.php
string VisitorIPAddress = Request.UserHostAddress.ToString();
and based on the ipaddress you can narrow down the location: find the geographical location of a host
Request.UserHostAddress won’t work if you're behind a proxy. Use this code:
public static String GetIPAddress()
{
String ip = HttpContext.Current.Request.ServerVariables["HTTP_X_FORWARDED_FOR"];
if (string.IsNullOrEmpty(ip))
ip = HttpContext.Current.Request.ServerVariables["REMOTE_ADDR"];
else
ip = ip.Split(',')[0];
return ip;
}
Note that HTTP_X_FORWARDED_FOR should be used BUT as it can return multiple IP addresses separated by a comma you need to use the Split function. See this page for more info.
Well the following property should give you the IP Address of teh client (or the clients proxy server)
Request.UserHostAddress
As for location, you'd need to use some GeoIP/GeoLocation plugin like MaxMind to figure that out.
http://www.maxmind.com/
To get the IP do:
Request.UserHostAddress
And you can map IP to location using a webservice (slower) or a database (faster) like this:
http://ip-to-country.webhosting.info/node/view/5
It's server technology-agnostic, but I'd recommend piggy-backing on Google's AJAX loader: http://code.google.com/apis/ajax/documentation/#ClientLocation
It's in Javascript and will even give you the person's city/state/country (well, it takes a guess based on IP address). Post it back to the server and it's available to you in ASP.NET or whatever.