For example, I've a server hosted at my home with 2 NICs for redundancy obviously.
NIC1 has been assigned with the public IP 103.204.82.22 from ISP1
NIC2 has been assigned with the public IP 144.110.12.64 from ISP2
I can access the server with both IP as usual.
Now, I have a domain acme.com. I've created a subdomain server.acme.com. I want to point server.acme.com to both the IPs so that in case one ISP fails to provide connectivity my server still remains online with the other one.
I've already tried with A and CNAME records. But it isn't working. It's working with A record if I use only one IP for the subdomain.
Can anyone tell me what and how can I point both the IPs to the single subdomain?
Thanks in advance
What you are describing is called DNS round robin, but that won't give you your expected outcome.
Anything you do with DNS if one ISP connection is down, traffic will still go there.
You may have your terminology mixed up a little to start with.
in this case, I suspect you really mean that server.acme.com is a host record, rather than a subdomain. (A subdomain would mean that the server address would be at servername.server.acme.com)
If you create an A record, and put both IP addresses in, and keep the TTL (time to live) short, then when a client wants to contact your machine it will randomly pick one of the addresses. If that address is unavailable, it will move on to the next. If that address stops working, it will keep trying it for the 'TTL' time.
Presuming that the IP addresses don't change, which would be a different problem altogether, then this provide basic load balancing and failover to both connections.
Amazon provide a more advanced type of DNS, that will actively monitor your connections and only provide responses that are live. - https://docs.aws.amazon.com/Route53/latest/DeveloperGuide/routing-policy.html
Related
We ordered a dedicated server for our website example.com and expected to have 2 IPs - one for ns1.example.com and one for ns2.example.com. But the provider has allocated the same IP for both ns1.example.com and ns2.example.com giving us a spare IP address that we can use for something else. They have offered to change it to two IPs but now we're not sure which is better.
Nobody is using our site right now but we hope it will be very popular in the future and we don't want anything to hold us back. So what are the pros and cons of having one IP address or two? Which is better for us going forward?
Thanks
From Loadbalancing point of view - If both IP addresses are given to same server, than it doesn't serve the purpose.
Just curious in era of cloud, why use dedicated server? Any specific reason.
I'm trying to get all the domains linked to a record like here
http://viewdns.info/reverseip/?host=23.227.38.68&t=1 but I'm getting no luck with dig 23.227.38.68 or nslookup 23.227.38.68. Any idea what I'm doing wrong?
The design of DNS does not support discovering every domain associated with a certain IP address. You may be able to retrieve one or more DNS names associated with the IP address through reverse IP lookup (PTR records), but does not necessarily give you all domains. In fact, it rarely will.
This is because the information you seek is scattered throughout the global DNS network and there is no single authoritative node in the network that has this information. If you think about it, you can point the DNS A record of your own domain to the IP of stackoverflow.com and that's perfectly valid, but anyone seeking to know this would have to find your DNS servers to figure this out. DNS does not provide any pointers for this, though.
Yet, certain "passive DNS" services (probably including viewdns.info) seem to overcome this limitation. These services all work by aggregating DNS data seen in the wild one way or another. At least one of these services works by monitoring DNS traffic passing through major DNS resolvers, building a database from DNS queries. For instance, if someone looks up yourdomain.com that points to 1.2.3.4 and the DNS query happens to pass through the monitored resolver, they take note of that. If a query for anotherdomain.com is seen later and it also resolves to 1.2.3.4, now they have two domains associated with 1.2.3.4, and so on. Note that due to the above, none of the passive DNS services are complete or real-time (they can get pretty close to either, though).
I have a more specific DNS situation than it is usually asked, and have extinguished reading resources already. At this point I'm pretty desperate. Here is the scenario
Get a computer with OLD IP (let's call it that) for a new domain. Set up for the first time its own ns1.mydomain and ns2.mydomain successfully. They had propagated and all was fine whether you entered mydomain.com or www.mydomain.com
Fast forward a few months, and have to upgrade to new machine, with NEW IP. Soon, I will no longer have access to OLD IP machine. I make an exact copy (went over it many, many times) of the DNS configuration from the old machine on the new one, replacing OLD IP with NEW IP
Since the old machine is still running, I change its DNS records to point to the new IP instead, because I figured it would help 'transfer the authoritative dns' to the new machine. Of course, I have no real grasp of how the authoritative dns is set, even with all my reading.
What followed is that after a few hours (it has been more than a day already by now), typing mydomain.com points to the new IP, while typing www.mydomain.com will keep pointing to the same old one. On the domain.com.zone file, on both OLD IP and NEW IP computers, I have a record for www IN CNAME domain.com.
Also, going to http://www.intodns.com will say "Looks like the A records (the GLUE) got from the parent zone check are different than the ones got from your nameservers".
Doing a nslookup, will say that the authoritative answers can be found at my nameservers, but they still point to the OLD IP
Finally, still after 24h, if I do a service named stop on the OLD IP computer and go to http://www.internetsupervision.com, it will fail finding the DNS for mydomain.com or www.mydomain.com. Yet, if I turn named service back on, it will find it again immediately.
I believe my lack of understanding of the authoritative DNS is preventing me from making a new IP machine start broadcasting the new DNS records. As I've said, I still have access to the old machine, but only for a few more days.
If anyone has any insight to help me in this case, I appreciate. I really don't know what to do any more and have nobody to turn to. Why is my new, updated DNS IP not propagating properly?
The servers telling the world where to go to find authoritative data for your domain are the servers for the parent domain of your domain. That is, if you want to change the IP addresses of the name servers for mydomain.com, you need to change those addresses both on your own servers and the servers for .com. The latter is typically done via an interface (usually web) provided by the people you pay to get the domain in the first place.
Apologies if this is too basic, but you don't mention changing your delegation anywhere in your question.
Reading a lot about servers, load balancing and similar topics, a question came to mind.
DNS servers are servers which gives you the IP for a given domain name. Is there a "dictator" knowing all the valid DNS servers in the world? If I want to make a DNS server, and someone requests a website it doesn't have. How would it know which other DNS to redirect the request to? What if I tell facebook.com to have a spoof IP, and everyone getting the IP from my DNS server would be communicating with a spoof facebook server? Obviously, this isn't how it works (at least not at a big degree), because then someone would have done it already to attack hundreds of people.
When one registers a domain, one has to specify the name server for that domain. What happens during this process? Is a request sent to this DNS server to notify it there is a new domain to save in the database? If so, how can anyone own the top domains like .com? And why cannot I for example make my own top domain name if I can make my own DNS server?
After looking at nginx as a load balancing system, I'm starting to wonder a bit. Is it so that a request to http://www.google.com/ works like this? The computer asks a DNS server for the IP address for google.com, and then requests it? This will only be one IP, and all requests to Google ends up at this one server? And then this IP will be connected to a nginx server, or a more basic hardware unit to route the request internally to other servers? So all requests go to one server before it redirects the request to a data center?
After looking up google.com, it says the name servers are ns1.google.com etc.. But what is the point of them, if you need a different name server to get to ns1.google.com in the first place?
Obviously what I've written doesn't make sense, because if it were true, the web as a whole would be unusable because of people exploiting the possibilities for malicious causes. And I can't imagine how ONE server could handle ALL the requests thrown at google.com.
I've tried searching Google, but all I get is theoretical explanations that led me to where I am now. It would have been great if someone would point me to some articles that explain this thoroughly, and hopefully a lot of other people will find this question useful.
Anyone can run a DNS server, but the challenge is getting someone to use it. Normally the DNS server IP is provided as a DHCP option or is statically assigned. If you can get someone to use your server, you can return any IP for any hostname, including creating new top-level domains (subject to any filtering at the client, of course. Web browsers might have difficulty with a new TLD, for example). Note that with DNSSEC, this will eventually change, as the name record will be digitally signed and your server won't be able to fake the signature exactly.
DNS servers operate in a tree. When one server receives a request for a domain it does not control, it forwards the request on to another DNS server. The other DNS server may be the one which returns the IP (this is called the authoritative server), or it may return a NS record which points to another server which then must be queried. The DNS root servers provide for resolving TLDs.
A DNS server does not need to always return the same IP for a given name. It may choose to return a different IP based on region, client IP, or even per-request. This is the most typical way to load balance. Multiple DNS servers can also load balance the DNS requests by using anycast routing, where many servers share the same public IP and traffic is routed to them randomly by publishing multiple routes for the same IP.
I have a couple EC2 instances behind an Elastic Load Balancer. These instances serve HTTP requests for a single web site. I recently started looking at the HOST header of the traffic, because I am planning to split my app into virtual hosts.
With some regularity (dozens of times a day), I log a request for a host name that is totally unrelated to my servers. As a couple examples, today I saw requests with the host names ad.adserverplus.com and r1---sn-upfn-hp5e.c.youtube.com. I looked these up and the IP addresses are not the same as any of my servers, nor of the ELB, so I am trying to develop a theory as to how this happens.
I realize that someone could be spoofing the host header, but it happens often enough that I am pretty sure this is not what is going on. My other idea is that somehow there is stale DNS data that just happens to resolve one of those hosts to my IP address, but again this seems like it could happen once in a great while but not regularly. What are some other possibilities, and how might I verify / discredit them?
EDIT
I looked at some of the unexpected host names today, and it seems that they actually do resolve to an IP that is one of the possible IPs that my domain apex resolves to. I use Route 53 for DNS, and I have the zone apex pointed to the ELB, so when I query the IP address for my domain, I get different answers depending on when I ask. So this makes me very curious, how do these IP addresses get assigned to me and how does EC2 make sure they are not co-opting an IP address that someone else is already using.
There are any number of reasons for this. First you should understand that the public host name for your EC2 instances and load balancers have likely been used before. If you have an elastic IP associated with your load balancer, it has also probably been used before.
As such you can get traffic to your servers that is intended for a previous tenant of that hostname of IP address that you are currently using.
One thing you can do is to configure your web servers to reject traffic (respond with 403) to traffic that is not arriving with the proper hostname specified or that comes from a specific external host.
Your IP or your ELBs IP may have at one point in time been an open proxy. meaning that someone is hoping that you would forward the requests on to their intended destination.
but in general open port 80 to the internet and all kinds of bots and zombies will visit you with a pretty constant flow of dodgy requests. I would imagine though that the \ec2 IP ranges would be a particularly juicy range to search for poorly patched websites to exploit.