RESCACHED(1) Manual Page

NAME

rescached - DNS resolver cache daemon.

Table of Contents

SYNOPSIS
OPTIONS
DESCRIPTION
BUILDING
CONFIGURATION
WEB USER INTERFACE
EXIT STATUS
FILES
NOTES
BUGS
AUTHOR
LICENSE
LINKS
SEE ALSO

SYNOPSIS

rescached [-config 'rescached.cfg']

OPTIONS

rescached.cfg is rescached configuration, usually it reside in /etc/rescached/rescached.cfg.

DESCRIPTION

rescached is a daemon that caching internet name and address on local memory for speeding up DNS resolution.

rescached is not a reimplementation of DNS server like BIND.

rescached primary goal is only to caching DNS queries and answers, used by personal or small group of users, to minimize unneeded traffic to outside network.

FEATURES

List of current features,

Enable to handle request from UDP and TCP connections
Enable to forward request using UDP or TCP
Load and serve addresses and host names in /etc/hosts
Load and serve hosts formatted files inside directory /etc/rescached/hosts.d/
Blocking ads and/or malicious websites through host list in /etc/rescached/hosts.d/
Support loading and serving zone file format from /etc/rescached/zone.d
Integration with openresolv
Support DNS over TLS (DoH) (RFC 7858)
Support DNS over HTTPS (DoH) (RFC 8484)

BEHIND THE DNS

When you open a website, let say 'kilabit.info', in a browser, the first thing that browser do is to translate name address 'kilabit.info' into an internet address (for example to 18.136.35.199) so browser can make a connection to 'kilabit.info' server.

How browser do that?

First, it will send query to one of DNS server listed in your system configuration (for example, /etc/resolv.conf in Linux). Then, if your DNS server also "caching" the name that you requested, it will reply the answer (internet address) directly, if it is not then it will ask their parent DNS server.

+----+      +----------------+      +------------------+
| PC | <==> | ISP DNS Server | <==> | Other DNS Server | <==> ...
+----+      +----------------+      +------------------+

If you browsing frequently on the same site, hitting the refresh button, opening another page on the same website, etc; this procedures will always repeated every times, not including all external links like ads, social media button, or JavaScript from an other server.

To make this repetitive procedures less occurred, you can run rescached in your personal computer. The first time the answer is received in your local computer, rescached will saved it in computer memory and any subsequent request of the same address will be answered directly by rescached.

+----+      +----------------+      +------------------+
| PC |      | ISP DNS Server | <==> | Other DNS Server | <==> ...
+----+      +----------------+      +------------------+
  ^^             ^^
  ||             ||
  vv             ||
+-----------+    ||
| rescached | <==//
+-----------+

The only request that will be send to your DNS server is the one that does not already exist in rescached cache.

HOW CACHE WORKS

This section explain the simplified version of how internal program works.

Each DNS record in cache have the time last accessed field, which defined how the cache will be ordered in memory. The last queried host-name will be at the bottom of cache list, and the oldest queried host-name will at the top of cache list.

The following table illustrate list of caches in memory,

+---------------------+------------------+
| Accessed At         | host-name        |
+---------------------+------------------+
| 2018-01-01 00:00:01 | kilabit.info     |
+---------------------+------------------+
| 2018-01-01 00:00:02 | www.google.com   |
+---------------------+------------------+
|         ...         |        ...       |
+---------------------+------------------+
| 2018-01-01 00:01:00 | www.kilabit.info |
+---------------------+------------------+

Every cache.prune_delay (let say every 5 minutes), rescached will try to pruning old records from cache. If the accessed-at value of record in cache is less than,

current-time + cache.threshold

(remember that "cache.threshold" value must be negative) it will remove the record from cache.

BUILDING

PREREQUISITES

Go compiler
git, version control system
asciidoc, to generate manual pages
systemd or system V init tool for service on Linux

COMPILING

Steps to compile from source,

$ go get -u github.com/shuLhan/rescached-go
$ cd ${GOPATH}/src/github.com/shuLhan/rescached-go
$ go build ./cmd/rescached

The last command will build binary named rescached in current directory.

INSTALLATION

After program successfully build, you can install it manually by copying to system binary directory.

MANUAL INSTALLATION

Copy rescached configuration to system directory. We use directory "/etc/rescached" as configuration directory.

$ sudo mkdir -p /etc/rescached
$ sudo cp cmd/rescached/rescached.cfg /etc/rescached/

Copy rescached program to your system path.

$ sudo cp -f rescached /usr/bin/

Create system startup script.

If you want your program running each time the system is starting up you can create a system startup script (or system service). For OS using systemd, you can see an example for systemd service in scripts/rescached.service. For system using launchd (macOS), you can see an example in scripts/info.kilabit.rescached.plist.

This step could be different between systems, consult your distribution wiki, forum, or mailing-list on how to create system startup script.

AUTOMATIC INSTALLATION ON LINUX

Automatic installation on Linux require systemd. Run the following command

$ sudo make install

to setup and copies all required files and binaries to system directories. You can then start the rescached service using systemd,

$ sudo systemctl start rescached

AUTOMATIC INSTALLATION ON MACOS

Run the following command

$ sudo make install-macos

to setup and copies all required files and binaries to system directories. You can then load the rescached service using launchd,

$ sudo launchctl load info.kilabit.rescached

POST INSTALLATION

Set your parent DNS server.

Edit rescached configuration, /etc/rescached/rescached.cfg, change the value of parent based on your preferred DNS server.
Set the cache prune delay and threshold

Edit rescached configuration, /etc/rescached/rescached.cfg, change the value of cache.prune_delay and/or cache.threshold to match your needs.

Set your system DNS server to point to rescached.

In UNIX system,

$ sudo mv /etc/resolv.conf /etc/resolv.conf.org
$ sudo echo "nameserver 127.0.0.1" > /etc/resolv.conf

If you use systemd, run rescached service by invoking,
```
$ sudo systemctl start rescached.service
```
and if you want rescached service to run when system startup, enable it by invoking,
```
$ sudo systemctl enable rescached.service
```

CONFIGURATION

All rescached configuration located in file /etc/rescached/rescached.cfg. See manual page of rescached.cfg(5) for more information.

ZONE FILE

Rescached support loading zone file format. Unlike hosts file format, where each domain name is only mapped to type A (IPv4 address), in zone file, one can define other type that known to rescached. All files defined zone.d configuration are considered as zone file and will be loaded by rescached only if the configuration is not empty.

Example of zone file,

$ORIGIN my-site.vm.
$TTL    3600

; resource record (RR) address
@ A 192.168.56.10

; resource record alias
dev CNAME @

; resource record address for other sub-domain
staging A 192.168.100.1

; resource record address for other absolute domain.
my-site.com A 10.8.0.1

Here we defined the variable origin for root domain "my-site.vm." with minimum time-to-live (TTL) to 3600 seconds. If no "$ORIGIN" variable is defined, rescached will use the file name as $ORIGIN’s value.

The "@" character will be replaced with the value of $ORIGIN.

The first resource record (RR) is defining an IPv4 address for "my-site.vm." to "192.168.56.10".

The second RR add an alias for relative subdomain "dev". Domain name that does not terminated with "." are called relative, and the origin will be appended to form the absolute domain "dev.my-site.vm". In this case IP address for "dev.my-site.vm." is equal to "my-site.vm.".

The third RR define a mapping for another relative subdomain "staging.my-site.vm." to address "192.168.100.1".

The last RR define a mapping for absolute domain "my-site.com." to IP address "10.8.0.1".

For more information about format of zone file see RFC 1035 section 5.

INTEGRATION WITH OPENRESOLV

Rescached can detect change on file generated by resolvconf. To use this feature unset the "file.resolvconf" in configuration file and set either "dnsmasq_resolv", "pdnsd_resolv", or "unbound_conf" in "/etc/resolvconf.conf" to point to file referenced in "file.resolvconf".

For more information see rescached.cfg(5).

INTEGRATION WITH DNS OVER HTTPS

DNS over HTTPS (DoH) is the new protocol to query DNS through HTTPS layer. Rescached support serving DNS over HTTPS or as client to parent DoH nameservers. To enable this feature rescached provided TLS certificate and private key.

Example configuration in rescached.cfg,

[dns "server"]
parent = https://kilabit.info/dns-query
tls.certificate = /etc/rescached/localhost.cert.pem
tls.private_key = /etc/rescached/localhost.key.pem
tls.allow_insecure = false

If the parent nameserver is using self-signed certificate, you can set "tls.allow_insecure" to true.

Using the above configuration, rescached will serve DoH queries on https://localhost/dns-query on port 443 and UDP queries on port 53. All queries to both locations will be forwarded to parent nameserver.

This feature can be tested using Firefox Nightly by updating the configuration in "about:config" into,

network.trr.bootstrapAddress;127.0.0.1
network.trr.mode;3
network.trr.uri;https://localhost/dns-query

Since we are using mode=3, the network.trr.bootstrapAddress is required so Firefox Nightly can resolve "localhost" to "127.0.0.1". If you use the provided self-signed certificate, you must import and/or enable an exception for it manually in Firefox Nightly (for example. by opening https://localhost/dns-query in new tab and accept security risk).

To check if DoH works, first, set the debug option to 1, and restart the rescached. Open a new terminal and run sudo journalctl -xf, to show current system log. Run Firefox Nightly and open any random website. At the terminal you will see output from rescached which looks like these,

... rescached[808]: dns: ^ DoH https://kilabit.info/dns-query 41269:&{Name:id.wikipedia.org Type:A}
... rescached[808]: dns: < UDP 45873:&{Name:id.wikipedia.org Type:AAAA}
... rescached[808]: dns: + UDP 41269:&{Name:id.wikipedia.org Type:A}

If you see number "4" in request line, "< request: 4", thats indicated that request is from HTTPS connection and its working.

WEB USER INTERFACE

The rescached service provide a web user interface that can be accessed at http://127.0.0.1:5380.

Screenshot of front page

The front page allow user to monitor active caches, query the caches, and removing the caches.

Screenshot of Environment page

The Environment page allow user to modify the rescached configuration on the fly.

Screenshot of Hosts Blocks page

The Hosts Blocks page allow user to enable or disable the external sources of hosts blocks list.

Screenshot of Hosts.d page

The Hosts.d page allow user to manage hosts file, creating new hosts file, create new record, or delete a record.

Screenshot of Zone.d page

The Zone.d page allow user manage zone file, creating new zone file, adding or deleting new resource record in the zone file.

EXIT STATUS

Upon success, rescached will return 0, or 1 otherwise.

FILES

/etc/rescached/rescached.cfg: The rescached main configuration. This configuration will be read when program started.
/usr/share/rescached/COPYING: License file for this software.
/var/run/rescached.pid: File where process ID of rescached will be saved when running.

NOTES

This program developed with references to,

RFC1034: Domain Names - Concepts and Facilities.
RFC1035: Domain Names - Implementation and Specification.
RFC1886: DNS Extensions to support IP version 6.
RFC2782: A DNS RR for specifying the location of services (DNS SRV)
RFC8484: DNS Queries over HTTPS (DoH)

BUGS

rescached only know specific DNS record type,

A	A host address in IPv4
NS	An authoritative name server
CNAME	A canonical name for an alias
SOA	Start of [a zone of] authority record
MB	Mail box
MG	Mail group
NULL	Placeholders for experimental extensions
WKS	Record to describe well-known services supported by a host
PTR	Pointer to a canonical name.
HINFO	Host information
MINFO	Mail information
MX	Mail exchange
TXT	Text record
AAAA	A host address in IPv6
SRV	Service locator
OPT	This is a "pseudo DNS record type" needed to support EDNS

rescached only run and tested in Linux and macOS system. Technically, if it can compiled, it will run in any operating system.

AUTHOR

rescached is developed by Shulhan ([email protected]).

LICENSE

Use of this source code is governed by a GPL 3.0 license that can be found in the COPYING file.

LINKS

The repository for this software is available at https://github.com/shuLhan/rescached-go.

For request of features and/or bugs report please submitted through web at https://github.com/shuLhan/rescached-go/issues.

shuLhan/rescached-go

shuLhan

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