Why is a website assigned the same ip address each time?
Discuss with a suitable example whether a server can be assigned two different IP addresses.
Would appreciate some help in these two questions.
Thanks
Question #1:
Short answer: websites are assigned the same IP address so that Web clients will send requests to the proper system.
Long answer: Web clients rarely connect to servers using IP addresses directly. Instead, clients use domain names like www.google.com. DNS software then maps the name to the address.
Thus changing a Web server address should be easy - just change the name mapping. But for performance reasons, name mappings are cached. So if the mapping is changed, some caches will have the old mapping for a period of time (called the Time To Live, or TTL). So changing a Web server address isn't trivial.
Question #2:
There are a number of circumstances where a server can have more than one IP address:
The server is hosting multiple VMs. Each VM has its own IP address.
The server is hosting websites for multiple companies. Each website has its own IP address.
The server is doing routing between two subnets. It will have separate IP addresses for each subnet it is on.
Related
I am trying to get the big picture although my primary domain is not networking.
Some question's narrowed down for which I'm not getting enough/proper answers online
Is the IP that is resolved by the DNS server when I hit www.google.com is same as any of the Google router's Gateway IP?
Do bigger companies like Amazon do port forwarding?
If point 2 is true, I suppose they must be port forwarding with only 443 (https) port which means, to use multiple static IP across different data centers, they need to have that many routers. So, if they have N static IP address which resolves to a website, then they must be having N routers right? Is this a fair assumption?
A gateway IP refers to a device on a network which sends local
network traffic to other networks. it sits between you and internet,or other network . its like a watchman.
Question 1 : google.com has multiple ip addresses lets say then , Yes, that is possible, and will need to be two A records. This is called Round-Robin DNS. Clients will semi-randomly use one of the two addresses.
question2: yes port forwarding happens more often than we think. ALL VPC's (virtual private clouds like AWS , GCP , Azure etc) use this as they dont want to expose servers/internal resources to the internet.
depending on the port number , particular service is exposed to requesting client. lets say we want to make a website public , then we explicitly expose port 80(http) 443(https) so that web crawlers and users can see them.
Port forwarding, sometimes called port mapping, allows computers or
services in private networks to connect over the internet with other
public or private computers or services.
google https://www.google.com:444/ wont work because they did not expose port 444 on their cloud router
but https://www.google.com:443/ will work because the server corresponding to google.com has explicitly left it open.
How IP is resolved:
Step 1 - Send a Request to Resolve a Domain Name
When you type www.google.com into a browser, in order to load the webpage, your computer asks for the IP address. Computers do not know in advance where they can find the necessary information, so they try searching through the DNS cache and for available external source. proceed from lower level caches to root/main servers.
Step 2+3 - Try to resolve an IP Locally
Before going externally, your computer loads the local DNS cache database to see if you already requested the IP for that domain name. Every computer has a temporary cache with the most recent DNS requests and attempts to connect to online sources. if required record is present locally its called "CACHE HIT" and query stops.
However A computer’s local DNS cache database does not always contain the necessary data to resolve a domain name this is called a "CACHE MISS" . In that case, the request goes further to your Internet Service Provider (ISP) and its DNS server.
Step 4 - ISPs Ask Outside DNS Servers to Provide an IP Address iff Cache miss
ISP DNS resolvers are configured to ask other DNS servers for correct IP address mapping until they can provide data back to the requester. These are iterative DNS queries.
When a DNS client sends such a request, the first responding server does not provide the needed IP address. Instead, it directs the request to another server that is lower in the DNS hierarchy, and that one to another until the IP address is fully resolved. There are a few stops in this process.
hierarchy looks like this (just for reference):
Root domain nameservers. Root servers themselves do not map IP addresses to domain names. Instead, they hold the information about all top-level domain (TLD) nameservers and point to their location. TLD is the rightmost section of a domain name... Root servers are critical since they are the first stop for all DNS lookup requests.
TLD nameservers. These servers contain the data for second-level domains, such as ‘phoenixnap’ in phoenixnap.com. Previously, the root server pointed to the location of the TLD server. Then, the TLD server needs to direct the request toward the server that contains the necessary data for the website we are trying to reach.
Authoritative nameserver. Authoritative servers are the final destination for DNS lookup requests. They provide the website’s IP address back to the recursive DNS servers. If the site has subdomains, the local DNS server will keep sending requests to the authoritative server until it finally resolves the IP address.
Step 5 - Receive the IP Address
Once the ISP’s recursive DNS server obtains the IP address by sending multiple iterative DNS queries, it finally returns it to your computer. The record for this request now stays cached on the hard drive. The browser can then fetch this IP from the cache and connect it to the website’s server.
ALL this happens in less than 1 second, most of the times. if you just registered a new domain it might take few hours to propagate this DNS cache globally hence newly registered websites do not show up sometimes.
About companies owning multiple IPs
Big companies have pool of IPs reserved for example 123.234.xxx.xxx which means a company has reserved 255*255 ips. they are mapped on a VPC(virtual private cloud)
and accessible vis a subnet masking and CIDR feature, like your EC2 instances on AWS
Is the IP that is resolved by the DNS server when I hit www.google.com is same as any of the Google router's Gateway IP?
For sure it should, but it is mostly a Google management question that only they will be able to answer right. The thing is that we must understand how DNS query's work for this.
Let's take a look of it:
Device A requests the IP address through a DNS query of the device B.
To do this, it uses the network port 53 (Domain) on which it will ask, depending on which DNS server is being used at the time, which is usually the home router. Then the router will ask the ISP's DNS server, which will respond with a cached response, or the query with another server on top of it if it does not have one; All this process is followed until a reliable cache response is reached or until the authoritative response server is reached, that is, the name server that manages the domain in question.
Only the authoritative response server contains the reliable information of which IP of the domain which is going to be reached.
I suppose that within Google's servers and its network they use Google's own DNS servers, which are 8.8.8.8 and 8.8.4.4 where the DNS records are obtained and consulted by caching from many sites.
In general terms Google's IP will change depending on where you are, I made a DIG query to Google's authoritative servers, however, I received a result based on location to improve the route and loading time of the site which was 142.250.73.238.
Do bigger companies like Amazon do port forwarding?
Yes, they do. To handle queries with load balancers or similar and even for caching dns requests.
If point 2 is true, I suppose they must be port forwarding with only 443 (https) port which means, to use multiple static IP across different data centers, they need to have that many routers. So, if they have N static IP address which resolves to a website, then they must be having N routers right? Is this a fair assumption?
This has multiple answers. By the way, they actually can do a secure DNS query.
if they have N static IP address which resolves to a website, then they must be having N routers right?
They don't have to, but if they want to they can.
"Is this a fair assumption?"
No, the IP's doesn't depend on a router, the router only routes to a computer/server which can have multiple IP's. By the other hand, each thing (computer, server, etc... must have an IP which can be also a WAN IP).
I am now just starting to understand Httpcontexts and server side logic. Total beginner.
I have understood how to read the http requests from a client and get the remote IP etc.
I came across the hostname property.
I believe hostname and domain are completely different.
My undersanding is that stackoverflow is the domain name.
Given its widespread reach, stackoverflow can have multiple servers and hence multiple ip addresses.
So is there a way to determine to which server a client is requesting to in asp.net core 2.0?
You are correct that stackoverflow.com is a domain name. A domain name points to an IP address. That's called DNS. stackoverflow.com points to one single IP address not multiple. There's probably a load balancer at that IP address which then points you to an available server, which is internal you can't see that, but that's another story.
If you ping stackoverflow.com you get:
The whole point of DNS is to not use IP address but a domain name.
I'm not sure why you would want to see the IP. Maybe this stackoverflow question can help: Resolve HostName to IP
I'm a little confused about IP addresses.
I know that every web domain has an ip address.
Does the IP address represent the physical machine / host the website files are stored on?
Therefore when DNS lookup is performed, the domain's IP address is returned to the client. The client then uses this ip to contact the server that the web files reside on.
Is my understanding correct?
Many thanks
You are correct.
It is kind of like how some companies may say Dial PIZZAHUT instead of saying, Dial 74992488. PIZZAHUT is easier to remember, but you actually are dialling the number.
You're talking about HTTP protocol. Yes, FQDN (web domain) is resolved to IP address by DNS server. Client will connect to server IP address. Since you're probably using HTTP 1.1, HTTP request will contain also FQDN. This information is used by web server to perform several checks, like SSL certificate validation or Virtualhost management (several domains on a single IP address).
Pretext: There is a ABC company providing Virtual Private Server for $xx, which includes features like blah1, blah2, blah3 and 1 dedicated IP address.
I have my home FiOS internet connection.
I have serverA, serverB, serverC running at my home.
Let's assume ServerA is a web server.
Scenario 1:
To access this web serve from outside my LAN, I would type "myDynamicIPAddress", we are assuming it still has the same lease token, and get access to my website successfully.
Scenario 2:
I am at my school/work(I work at a corporate office). I would type "myDynamicIPAddress" to access my web server. Since my IP address is dynamic/residential, it is blocked(All residential IP are blocked by default, to reduce the chance of them getting infected and sending out spams).
My question:
Is there any way to connect my home network to the VPS that I purchased(the one with dedicated IP, remember?), so that I can use that dedicated IP address to connect to my web server from my school/work where residential IP address are blocked(this also means no Dyndns.com/no-ip.com).
I hope I explained my question correctly and I posted it in the right section.
Thank You in advance.
EDIT1: I found this one question, but I want to do the exact opposite of what the user in this question is asking for.
https://superuser.com/questions/498529/is-it-possible-to-use-a-static-ip-assigned-by-my-isp-for-an-offsite-web-server-o
The answer is the same as the other question, for the same reasons. The IP address is routed to the owning network prefix so it can't be used at a different location without changing the Internet routing tables to point the overall prefix to route to a different place. Since you don't own the network prefix, you can't do that.
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.