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d987e155ea
Instead of checking only sslip.io, we expand our [4-times-per-day] nameserver checks to include nip.io. This is a component of the long-running campaign to promote the nip.io domain to full citizenship.
171 lines
6.2 KiB
Markdown
171 lines
6.2 KiB
Markdown
# sslip.io
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[](https://github.com/cunnie/sslip.io/actions/workflows/nameservers.yml)
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[](https://github.com/cunnie/sslip.io/actions/workflows/ci-tests.yml)
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_sslip.io_ is a DNS server that maps specially-crafted DNS A records to IP
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addresses (e.g. "127-0-0-1.sslip.io" maps to 127.0.0.1). It is similar to, and
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inspired by, [xip.io](http://xip.io/).
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If you'd like to use sslip.io _as a service_, refer to the website
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([sslip.io](https://sslip.io)) for more information. This README targets
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developers; the website targets users.
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## Quick Start
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```bash
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git clone https://github.com/cunnie/sslip.io.git
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cd sslip.io
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go mod tidy
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sudo go run main.go
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# sudo is required on Linux, but not on macOS, to bind to privileged port 53
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```
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In another window:
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```bash
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dig @localhost 192.168.0.1.sslip.io +short
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# should return "192.168.0.1"
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```
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### Quick Start Tests
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```bash
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go mod tidy
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go generate
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ginkgo -r -p .
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```
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## Running Your Own Nameservers
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We can customize our nameserver and address records (NS, A, and AAAA), which
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can be particularly useful in an internetless (air-gapped) environment. This can
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be done with a combination of the `-nameservers` flag and the `-addresses` flag.
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For example, let's say we're the DNS admin for pivotal.io, and we'd like to
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have a subdomain, "xip.pivotal.io", that does sslip.io-style lookups (e.g.
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"127.0.0.1.xip.pivotal.io" would resolve to "127.0.0.1"). Let's say we have two
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servers that we've set aside for this purpose:
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- ns-sslip-0.pivotal.io, 10.8.8.8 (IPv4)
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- ns-sslip-1.pivotal.io, fc88:: (IPv6)
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First, we delegate the subdomain "xip.pivotal.io" to our two nameservers, and
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then we run the following command run on each of the two servers:
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```bash
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# after we've cloned our repo & cd'ed into it
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go run main.go \
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-nameservers=ns-sslip-0.pivotal.io,ns-sslip-1.pivotal.io \
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-addresses ns-sslip-0.pivotal.io=10.8.8.8,ns-sslip-1.pivotal.io=fc88::
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```
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**Note: These nameservers are not general-purpose nameservers; for example,
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they won't look up google.com. They are not recursive.** Don't ever configure a
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machine to point to these nameservers.
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### Running with Docker
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Probably the easiest way to run the nameserver is with the official Docker
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image,
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[cunnie/sslip.io-dns-server](https://hub.docker.com/r/cunnie/sslip.io-dns-server):
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```bash
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docker run \
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-it \
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--rm \
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-p 53:53/udp \
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cunnie/sslip.io-dns-server
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```
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If we see the error, "`Error starting userland proxy: listen udp4 0.0.0.0:53:
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bind: address already in use.`", we turn off the systemd resolver: `sudo
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systemctl stop systemd-resolved`
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Let's try a more complicated setup: we're on our workstation, jammy.nono.io,
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whose IP addresses are 10.9.9.114 and 2601:646:0100:69f0:0:ff:fe00:72. We'd like
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our workstation to be the DNS server:
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```bash
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docker run \
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-it \
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--rm \
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-p 53:53/udp \
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cunnie/sslip.io-dns-server \
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-nameservers jammy.nono.io \
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-addresses jammy.nono.io=10.9.9.114,jammy.nono.io=2601:646:100:69f0:0:ff:fe00:72
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```
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From another machine, we look up the DNS NS record for "127.0.0.1.com", and we
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see the expected reply:
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```bash
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dig ns 127.0.0.1.com @jammy.nono.io +short
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...
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;; ANSWER SECTION:
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127.0.0.1.com. 604800 IN NS jammy.nono.io.
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;; ADDITIONAL SECTION:
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jammy.nono.io. 604800 IN A 10.9.9.114
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jammy.nono.io. 604800 IN AAAA 2601:646:100:69f0:0:ff:fe00:72
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```
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The Docker image is multi-platform, supporting both x86_64 architecture as well
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as ARM64 (AWS Graviton, Apple M1/M2).
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## Command-line Flags
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- `-port` overrides the default port, 53, which the server binds to. This can
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be especially useful when running as a non-privileged user, unable to bind to
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privileged ports (<1024) ("`listen udp :53: bind: permission denied`"). For
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example, to run the server on port 9553: `go run main.go -port 9553`. To
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query, `dig @localhost 127.0.0.1.sslip.io -p 9553`
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- `-nameservers` overrides the default NS records `ns-do-sg.sslip.io`,
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`ns-gce.sslip.io`, `ns-hetzner.sslip.io`, and `ns-ovh.sslip.io`; flag, e.g.
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`go run main.go -nameservers ns1.example.com,ns2.example.com`). If you're
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running your own nameservers, you probably want to set this. Don't forget to
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set address records for the new name servers with the `-addresses` flag (see
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below). Exception: `_acme-challenge` records are handled differently to
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accommodate the procurement of Let's Encrypt wildcard certificates; you can
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read more about that procedure [here](docs/wildcard.md)
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- `-addresses` overrides the default A/AAAA (IPv4/IPv6) address records. For
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example, here's how we set the IPv4 record & IPv6 record for our nameserver
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(in the `-nameservers` example above), ns1.example.com: `-addresses
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ns1.example.com=10.8.8.8,ns1.example.com=fc::8888`. Note that you can set
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many addresses for a single host, e.g.
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`ns1.example.com=1.1.1.1,ns1.example.com=8.8.8.8,ns1.example.com=9.9.9.9`
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- `-blocklistURL` overrides the default block list,
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(<https://raw.githubusercontent.com/cunnie/sslip.io/main/etc/blocklist.txt>).
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It's not necessary to override this if you're in an internetless environment:
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if the DNS server can't download the blocklist, it prints out a message and
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continues to serve DNS queries
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## DNS Server Miscellany
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- it binds to both UDP and TCP.
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- The SOA record is hard-coded except the _MNAME_ (primary master name server)
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record, which is set to the queried hostname (e.g. `dig big.apple.com
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@ns.sslip.io` would return an SOA with an _MNAME_ record of
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`big.apple.com.`
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- The MX records are hard-coded to the queried hostname with a preference of 0,
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except `sslip.io` itself, which has custom MX records to enable email
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delivery to ProtonMail
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- There are no SRV records
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## Directory Structure
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- `spec/` contains the tests for the production nameservers. To run
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the tests locally:
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```bash
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DOMAINS=nip.io,sslip.io rspec --format documentation --color spec
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```
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- `k8s/document_root_sslip.io/` contains the HTML content of the sslip.io
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website.
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### Acknowledgements
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- Sam Stephenson (xip.io), the late Roopinder Singh (nip.io), and the other DNS
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developers out there
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- The contributors (@normanr, @jpambrun come to mind) who improved sslip.io
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- Let's Encrypt for bumping our rate limits
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