In my network infrastructure I have multiple subnets intended to segregate different types of devices. I would like the ability to serve different DNS responses from different DNS servers based on the requesting subnet. For example I'd like to use Google's DNS for one subnet but say CloudFlare's anti-malware DNS for another. I would also like the ability to then further lock down by using different "address" declarations on the different subnets.
One way that some people accomplish the first part is to use the "dhcp-option" declaration to serve different server addresses to the different subnets but this kind of defeats the purpose of DNSMASQ and turns it basically into just a DHCP server and also defeats using a firewall to restrict access to port 53 to control any hard-coded dns servers.
The other option I've seen is to run 2 instances of DNSMASQ however this creates a highly customized setup which doesn't allow any of the system level configuration files or run scripts which I'd like to avoid.
So I'm hoping someone can offer a solution for this.
Thanks in advance.
Presumably you want to all of the subnets to use DNSMasq to resolve local domain names, but you want the subnets to use different recursive resolvers for Internet queries?
You should be able to do that with the DHCP settings (so that each subnet will received two DNS entries - one for DNSMasq and one for another resolver e.g. 8.8.8.8). These entries will end up in the /etc/resolv.conf for each device and will be attempted in order when the device needs to resolve DNS. If DNSMasq is set to resolve local queries only, then the device will be forced to try the second address (e.g. 8.8.8.8) to resolve Internet queries.
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Could deploy Bosh and small footprint tanzu application service(tas) in Azure, without using the domains.All Vms are running.Can i access the ccapi and apps manager with the IP address instead of the api.SYSTEMDOMAIN?
The short answer is no. You really, really want to have DNS set up properly.
Here's the long answer that is more nuanced.
All requests to your foundation go through the Gorouter. Gorouter will take the incoming request, look at the Host header and use that to determine where to send the request. This happens the same for system services like CAPI and UAA as it does for apps you deploy to the foundation.
DNS is a requirement because of the Host header. A browser trying to access CAPI or an application on your foundation is going to set the Host header based on the DNS entry you type into your browser's address bar. The cf CLI is going to do the same thing.
There are some ways to work around this:
If you are strictly using a client like curl where you can set the Host header to arbitrary values. In that way, you could set the host header to api.system_domain and at the same time connect to the IP address of your foundation. That's not a very elegant way to use CF though.
You can manually set entries in your /etc/hosts` (or similar on Windows). This is basically a way to override DNS resolution and supply your own custom IP.
You would need to do this for uaa.system_domain, login.system_domain, api.system_domain and any host names you want to use for apps deployed to your foundation, like my-super-cool-app.apps_domain. These should all point to the IP of the load balancer that's in front of your pool of Gorouters.
If you add enough entries into /etc/hosts you can make the cf CLI work. I have done this on occasion to bypass the load balancer layer for troubleshooting purposes.
Where this won't work is on systems where you can't edit /etc/hosts, like customers or external users of software running on your foundation or if you're trying to deploy apps on your foundation that talk to each other using routes on CF (because you can't edit /etc/hosts in the container). Like if you have app-a.apps_domain and app-b.apps_domain and app-a needs to talk to app-b. That won't work because you have no DNS resolution for apps_domain.
You can probably make app-to-app communication work if you are able to use container-to-container networking and the apps.internal domain though. The resolution for that domain is provided by Bosh DNS. You have to be aware of this difference though when deploying your apps and map routes on the apps.internal domain, as well as setting network policy to allow traffic to flow between the two.
Anyway, there might be other hiccups. This is just off the top of my head. You can see it's a lot better if you can set up DNS.
The most easy way to achieve a portable solution is a service like xip.io that will work out of the box. I have setup and run a lot of PoCs that way, when wildcard DNS was something that enterprise IT was still oblivious about.
It works like this (excerpt from their site):
What is xip.io?
xip.io is a magic domain name that provides wildcard DNS
for any IP address. Say your LAN IP address is 10.0.0.1.
Using xip.io,
10.0.0.1.xip.io resolves to 10.0.0.1
www.10.0.0.1.xip.io resolves to 10.0.0.1
mysite.10.0.0.1.xip.io resolves to 10.0.0.1
foo.bar.10.0.0.1.xip.io resolves to 10.0.0.1
...and so on. You can use these domains to access virtual
hosts on your development web server from devices on your
local network, like iPads, iPhones, and other computers.
No configuration required!
Google has multiple servers at multiple locations. When I search Google in my web browser, how does the DNS map this name to the corresponding IP address? Google has multiple servers in multiple locations with separate IPs. Is a load balancer used first?
A couple of different approaches are used:
Geographic DNS
When a request comes in for a domain name, the DNS server looks at the IP address making the request and returns an IP address of a nearby server.
Some complicated extensions are required to deal with large shared caching DNS servers (like ISP nameservers), but that's the general idea.
Anycast DNS
Anycast is a weird routing trick where a single IP range can be advertised by multiple ASes. This will cause requests to an IP address in that range to be routed to whichever server is closest.
If a DNS server is hosted on an anycast IP, different instances of that server can be configured to return different IPs. This can be used as a computationally easier alternative to geographic DNS.
Anycast HTTP
If anycast can be used to route DNS to the closest server, why not just go to the next step and use it to route HTTP as well?
(It turns out there's a reason why you usually don't want to do this: Routing changes can break a HTTP connection. This doesn't affect DNS as it's usually used over UDP. Cloudflare does it anyway, though, and it usually works fine… YMMV.)
In large scale reverse proxy server is usually used for this purpose and it can do various tasks including load balancing as well. To the client it appears that you connect only to one server while reverse proxy hides servers behind it.
In small scale you can do similar things just with DNS settings mapping different domain names to different IP addresses. See this article
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 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.
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.