for a research project I want to get the IP addresses of millions of domains. I don't want to overload a single DNS server of course. My idea would be to distribute the queries to a (few) hundred or so open dns resolvers (i.e. from http://public-dns.tk/). How can I do this? Would it be enough to install dnsmasq and add the 100 or so DNS servers to /etc/resolv.conf or would dnsmasq only query the first/second entry of the list? Caching doesn't matter since every domain is only once in the list.
I guess installing a full blown dns server with querying the root server directly is not a good idea?
You can specify the IP/address of DNS server in the dig query, that you fire:
dig #<IP_OF_DNS_SERVER> www.google.com
Example, below queries go against OpenDNS, and Google DNS respectively:
dig #208.67.222.222 www.manish-m.com
dig #8.8.8.8 stackoverflow.com
Related
I am having a bit of a head ache trying to setup my own HA solution with docker and nginx in the front acting as a load balancer.
They are actually configured by now. But as a fallback if the main node shuts down, I want to use another one since the nginx configuration for load balancing is replicated.
I thought that if I have two nodes, both set up with PowerDNS (alongside with nginx and docker), and I set those DNS servers to one of my domains, when a node shuts down, since the node is carrying the DNS server, subsequent requests will fetch the info from the other DNS server, in which the A record is configured to point to the local IP (and that way, points to the other load balancer).
Seems like I can't make that work.
Given that I have the following servers:
server_1 IP = 1.1.1.1
server_2 IP = 1.1.2.2
Each of them have a DNS server set up with PowerDNS (and fully functional, according to dig and other tests).
I got my domain DNS servers pointing to them:
ns1.example.com ---> 1.1.1.1
ns2.example.com ---> 1.1.2.2
ns1.example.com DNS server has:
example2.com A 1.1.1.1
ns2.example.com DNS server has:
example2.com A 1.1.2.2
So. Shouldn't example2.com point to 1.1.1.1/1.1.2.2 when both servers are running, but when the first server is not available, point to 1.1.2.2?
Well. When I shut down the first server and try, it gives me the IP of the first server instead of the second.
Even dig example2.com #ns2.example.com is giving me the IP defined in the A record for example2.com in the first DNS server.
Am I wrong, or there's something weird here?
I don't know where you got the idea that name servers are listed in some sort of priority order, but it's just plain wrong. All name servers authoritative for a zone are expected to have exactly the same content. Resolvers chose name servers to ask at random, to spread the load between them. Providing the authoritative servers with differing contents will only give the end users inconsistent results, not anything useful.
Also, you have forgotten that resolvers cache the answers they get. Even if DNS had worked as you thought (which is doesn't), it would have taken a resolver minutes or hours to notice the "failover".
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).
When troubleshooting DNS issues (specifically whether a domain is resolving), what is the proper way to check so that you get accurate results? DNS info is cached throughout the internet, and different machines (like local machine) or service (like pingdom) has different results.
How to check the DNS so that you know what you will get after it propagates?
Working with Heroku and CloudFlare.
In most common cases you can use tools such as: dig or host. Both tools are made for query name servers to retrieve info. You can also use a simple "ping something.domain.com" in order to see if IP has changed. But I suggest you to use different DNS's on the computer you're using to test. Actually Google DNS replicate so fast ( 8.8.8.8 ).
Not on purpose DNS poisoning: Keep in mind if you're pinging something that is recently configured/changed on your name server and still not propagated you'll "poison" the DNS's cache and this data is going to expire, but later...( Always depending on domain name TTL's of course ).
Using a new DNS wich never has known that domain you're sure the request is made for the first time and it's going to be made without asking any cache.
Example:
To get all the DNS servers for domain.com:
$ host -t ns domain.com
domain.com name server ns2.domain.com.
domain.com name server ns3.domain.com.
To ask a domain name for something.domain.com:
$ dig #nameserver something.domain.com
You can also ask for TXT, CNAME types and so on...
Examples:
AXFR retrieval test:
$ dig #domainname domain.com AXFR
Or get all Mail Exchange (MX) server for a domain:
$ host -t MX domain.com
domain.com mail is handled by 10 smtp.godo.com.
domain.com mail is handled by 20 smtp2.godo.com.
Hope it helps.
Cheers! :)
http://en.wikipedia.org/wiki/Nslookup
To get a "Non-authoritative" answer from your local name server that would be e.g.:
nslookup test.com
To check the name server where the domain is listed that would be e.g.:
nslookup test.com nameServerOfTest.com
I have configured a set of DNS records at a new DNS provider. The configuration is complex, with load-balancing, SSL, etc, there are things that could go wrong.
I want to test this configuration before changing the namespace records at registrar.
Is there any way to locally provide my machine with the new nameserver for the domain?
Are there any tools that might help with this?
Please note: I don't want to just update the A records (e.g. in /etc/hosts) - I want to specifically check the nameserver is returning the A and CNAME records.
If you're on a *nix system, you should be able to use either nslookup or dig. With both of those commands you can specify what server you would like to query. Simply use your new nameserver as the server. With dig, the query would look something like
dig #<your-nameserver> <hostname-to-look-up>
So, if you wanted to query google's public dns server and ask it about the address www.google.com, you'd use
dig #8.8.8.8 www.google.com
which, amongst other things, would tell you that www.google.com is an alias for www.l.google.com -- and then would give you a bunch of IP address (A records) for that name.
For both Windows and my remote Linux(CentOS) servers I use nslookup tool which works on both platforms:
nslookup new-sub.domain.com 8.8.8.8
// and for more details:
nslookup -debug new-sub.domain.com 8.8.8.8
So, I'm on day 3...
I am running an Ubuntu.64-based distribution on a VirtualBox. I have the need to access both external ISP DNS servers, as well as "internal" DNS servers through an OpenVPN connection. At times I need to query the external DNS(#host example.com) through the eth0 interface; sometimes I need to query the VPN "internal" DNS (#host internal.local) through the tap0 interface.
My question is: how do I configure my system to query the correct nameserver-- the ISP DNS or the VPN DNS (for attempting zone transfers, for example)?
I've tried editing resolv.conf to include both external and internal nameservers/domains, with no luck (obviously). I've also tried mitigating the situation with dnsmasq. That got me close (I think).
I realize I can use dig to set the [#server] based on individual queries, but I would appreciate a systemic resolution.
Any help would be appreciated.
I've used the PowerDNS recursor for exactly this situation before; it is in the package pdns-recursor, if you wish to try it. You'll want to set your /etc/resolv.conf to query only 127.0.0.1 should you choose to try this approach.
The forward-zones directive lets you specify which servers to contact for which zones:
forward-zones= ds9a.nl=213.244.168.210, powerdns.com=127.0.0.1
It does look a little strange, since it is one configuration setting that takes multiple values, but you do get to specify exactly which servers are going to provide answers for which domains.