sslip.io

Test Type	Status
Production Nameservers
DNS Server Unit Tests

sslip.io is a DNS server that maps specially-crafted DNS A records to IP addresses (e.g. "127-0-0-1.sslip.io" maps to 127.0.0.1). It is similar to, and inspired by, xip.io.

If you'd like to use sslip.io as a service, refer to the website (sslip.io) for more information. This README targets developers; the website targets users.

• src/ contains the source code to the DNS server.
• ci/ contains the Concourse continuous integration (CI) pipeline and task.
• spec/ contains the tests for the production nameservers. To run the tests locally:

  DOMAIN=sslip.io rspec --format documentation --color spec/

• k8s/document_root/ contains the HTML content of the sslip.io website. Please run tidy -im -w 120 k8s/document_root/index.html before submitting pull requests.
• bosh-release/ contains the BOSH release. BOSH is the mechanism we use to deploy the servers, and the sslip.io BOSH release is a packaging of the DNS server (analogous to a .msi, .pkg, .deb or .rpm)
• conf/sslip.io+nono.io.yml (deprecated) contains the PowerDNS's pipe backend's configuration in YAML format for use with BOSH. The pdns_pipe key is the pipe backend script, and pdns_pipe_conf is its configuration file.

DNS Server

The DNS server is written in Golang and is not configurable without modifying the source:

• it binds to port 53 (you can't change it)
• it only binds to UDP (no TCP, sorry)
• The SOA record is hard-coded with the exception of the MNAME (primary master name server) record, which is set to the queried hostname (e.g. dig big.apple.com @ns-aws.nono.io would return an SOA with an MNAME record of big.apple.com.
• The NS records are hard-coded
• The MX records are hard-coded to the queried hostname with a preference of 0, with the exception of sslip.io itself, which has custom MX records to enable email delivery to ProtonMail.
• No TXT records are returned with the exception of sslip.io, which has custom records to enable email delivery
• There are no SRV records

To run the unit tests:

cd src
go get github.com/onsi/ginkgo/ginkgo
go get github.com/onsi/gomega/...
ginkgo -r .

To run the server on, say, a Mac, you must first start the server:

cd src
go run main.go

And then, in another window, run a query, e.g.:

dig +short 127.0.0.1.sslip.io @localhost

Which will return the expected IP address:

127.0.0.1

You will also see a log message in the server window, similar to the following:

2020/11/22 03:45:44 ::1.62302 TypeA 127.0.0.1.sslip.io. ? 127.0.0.1

Acknowledgements

• Sam Stephenson (xip.io), Roopinder Singh (nip.io), and the other DNS developers out there
• The contributors (@normanr, @jpambrun come to mind) who improved sslip.io
• Jenessa Petersen of Let's Encrypt who bumped the rate limits
• Natalia Ershova of JetBrains who provided a free license for open source development