DNS for Developers - NDC Oslo 2016

Editor's Notes

1. Run command line nslookup www.google.comNote that the response is from an unauthoritative server (meaning it is served from a cache somewhere in between our PC and the Internet) Dig provides us more info about how the name resolution happensdig A www.google.com +trace
2. Maybe visit the site and look at a few of the servers – there are tonnes of them!
3. Browser makes a request to a non-existent hostname Our DNS resolver learns that ns1.google.com is in an IP address that we own Our OS (or worse, our recursive DNS) caches this, I own Google on your machine 
4. Open 02 CachePoisoning demo Walk through the code, explain the redirects that happen (our custom domain says it’s in Google’s DNS, for which we send the IP address in the response) Set machine’s nameserver to 127.0.0.1 Visit the custom HTML page Visit www.google.com Ping www.google.com and note the IP address is wrong
5. Create new Traffic Manager endpoint in new portal (maartenba.trafficmanager.net) Set DNS TTL to 30 seconds to make the talk more enjoyable Add external endpoints: www.bing.com www.google.com Run nslookup set type=CNAME maartenba.trafficmanager.net See result, wait 30 seconds and try again See different result We can do this failover, round-robin, or “performance”
6. Mention CDN’s exist with both approaches. Both have own advantages. No logic = no logic, just route. Logic = be smart, eg Cedexis does multi-CDN, picks host based on all kinds of parameters, uses monitoring, …
7. Open 03 ConfigurationSample demo Explain ConfigurationServer class – it adds an entry per configuration value we want to store and serves it up as a TXT record Explain we could have multiple of the same, the client would just get multiple entries instead of one. Useful for failover scenarios etc. Show server Program.cs where we store some values, then run it Show client Program.cs where we fetch values, then run it Explain we could have multiple servers, to which we can recurse for shared settings across environments
8. You are probably already using this today! (Office 365? Apple Bonjour)
9. Open 04 ServiceDiscovery Run ServiceDiscovery.Client and see if there are any printers (or other) on the local network. Probably not but let’s check anyway. Open ServiceDiscovery.SampleService, explain what we are doing here We have a simple OWIN Web API running, nothing fancy Now let’s publish this service! ZeroconfService package from NuGet using (var service = new ZeroconfService.NetService( "local.", "_webapi._tcp", "Maarten's awesome API", 9999)) { service.Publish(); Console.ReadLine(); } Run the client again, see that our service is now discovered – zero configuration! The service tells everyone else where it lives and what it does.
10. Open 05 HTTP over DNS Demonstrate the server – run the server project Use nslookup set type=TXT Query for www.google.com See that we get back a number of chunks – we need this as the DNS response can only contain a limited amount of data Get a chunk, 1.www.google.com Get another, 2.www.google.com Now look at the server code – Open HttpProxyingDnsServer Important work is in “ResolveLocal” Explain the code – we check if we request a chunk or not. If not, calculate number of chunks and return it as a TXT If we do want a chunk, fetch the chunk and the next chunks, return TXT records for each Now look at the custom client we created Create a DNS client Get the value for number of chunks Get the chunks and concatenate them Run the client as well, see what it does…