01 Mar

Encrypted DNS using DNSCrypt

Writing this post from my hotel room in Kathmandu. I found that many of the servers appear to be DNS resolvers which is unusual.

E.g:

 

This seems unusual and is the result of basically port 53 DNS hijack. Let’s try to verify it using popular “whoami.akamai.net” query.

So clearly something in middle is hijacking DNS queries and no matter whichever DNS resolver I try to use, the queries actually hit authoritative DNS via 202.79.32.164. This belongs to WorldLink Communications (ISP here in Nepal) and I am just 5 hops away from it.

 

So what can be done about these cases? Well, one way is VPN of course but with a setup where VPN server’s IP address is hardcoded in the client and not using DNS. It works and does the task but performance can vary greatly depending on how far is the tunnel server. A better and more modern way out of it is by using encryption in DNS by using a protocol named “DNSCrypt“. DNSCrypt offers to encrypt of DNS queries from clients to the DNS resolvers. (Beyond that resolver still, follow usual non-encrypted root chain to reach authoritative DNS servers).

 

So how does it work?

There’s no integrated support of DNSCrypt in OS’es at this time. There are number of projects like dnscrypt-osxclient available on GitHub which enable this support.  Once configured, the client changes system’s DNS resolver to a local IP which listens for port 53 (regular/non-encrypted) requests.

The client often offers support of various open resolvers like OpenDNS, Quad9 etc.

 

 

Here it shows that DNS resolver in my case happens to be Cisco’s OpenDNS. As soon as the client gets port 53 DNS queries, it encrypts it and sends via UDP port 443 (UDP or TCP depending on provider and client configuration). The encyption is based on trusted root CA’s and associated chain as popularly used in HTTPS. This is also one of reasons why DNSCrypt is also known as DNS over HTTPS.

 

Here’s an example of a DNS query to resolve A record of google.com while running tcpdumps in parallel:

This shows request went in clear text to 127.0.0.54 which is configured on loopback. While in parallel if I watch for traffic towards OpenDNS public IPs, I get:

Thus all that appears here is just an encrypted packet to Cisco OpenDNS over UDP port 443.

I ran another query and saved it in pcap file. Here’s how it looks like in wireshark:

 

 

 

That’s all about it for now. I am going to keep encryption enabled especially when travelling from now onwards. Time to get some sleep. 🙂

 

Useful Links:

  1. dnscrypt-osxclient – https://github.com/alterstep/dnscrypt-osxclient
  2. DNSCrypt Wikipedia – https://en.wikipedia.org/wiki/DNSCrypt
  3. DNS Over HTTPS (Google Public DNS) – https://developers.google.com/speed/public-dns/docs/dns-over-https
  4. DNS over TLS (Quad9) – https://quad9.net/faq/#Does_Quad9_support_DNS_over_TLS
27 Apr

Cloudflare hosting F root server

A few days some folks in internet community noticed Cloudflare AS13335 announcing F root server’s routes covering prefix 192.5.5.0/24.

 

 

Above tweet shows that case is clearly not a mistake but rather some sort of arrangement between Cloudflare and ISC (which is responsible for F-root). There was another discussion on DNS-OARC mailing list here.

From our bgp.he.net tool, one can analyse route propagation for F root’s AS3557.

 

Here we can see that routes are visible from AS13335 to Telefonica AS13335. One can safely assume that AS12956 (considered to be a Tier1 / transit free network as per list here) is not a customer of Cloudflare. So the fact that still route is being announced to Telefonica gives an impression that AS3557 is downstream of Cloudflare.

It’s hard to say on the kind of arrangement as I still see many of instances of F-root are being hosted directly by ISC from hostname.bind query triggered via local RIPE Atlas probes in those regions. It could be that Cloudflare is hosting a part of this setup say in developing region where they have their caching PoPs. Yet to see a detailed blog post from Cloudflare about it. (I like their detailed blog!)

 

Update: 2nd April 2017 

Henry from Cloudflare pointed me to their official announcement blog post written after around 5 months of this post. You can find their official announcement here.