slodns

Slodns is a forwarding DNS server to simulate slow, jittery, or problematic DNS implementations. It is able to add a uniform or dynamic delay upon DNS datagrams, or drop them at a pre-defined rate. It is useful for validating DNS failure handling.

$ dig speedtest.net @8.8.8.8 | grep "Query time"
;; Query time: 12 msec

$ slodns 
Request: speedtestnet
Response: speedtestnet delay 1000 ms

$ dig speedtest.net @127.0.0.1 -p 5053 | grep "Query time"
;; Query time: 1028 msec

Installation

Requrirements

Python 2.7 is required to run slodns. No external python resources are required.

Root is not required if you run on the default port. If you want to run on port 53, then you will need to run as root or use iptables.

Supported Platforms

slodns has been tested on the following platforms:

1. MacOS 10.12 (Sierra)
2. Debian 7/8
3. Ubuntu 14.04/16.04
4. Freebsd 9/10
5. PfSense 2.3

It will probably work on other platforms as well, feel free to let me know!

Installation via Git

wget https://raw.githubusercontent.com/brennentsmith/slodns/master/slodns
chmod +x slodns

Usage

usage: A forwarding DNS server to simulate slow, jittery, or problematic DNS implementations.
       [-h] [-i INTERFACE] [-p PORT] [-u UPSTREAM_SERVER]
       [-q UPSTREAM_SERVER_PORT] [-d DELAY] [-l LOSS] [-j JITTER]

optional arguments:
  -h, --help            show this help message and exit
  -i INTERFACE, --interface INTERFACE
                        interface for server to bind to. Defaults to
                        localhost.
  -p PORT, --port PORT  port for server to listen on. Defaults to 5053.
  -u UPSTREAM_SERVER, --upstream-server UPSTREAM_SERVER
                        upstream nameserver. Defaults to 8.8.8.8.
  -q UPSTREAM_SERVER_PORT, --upstream-server-port UPSTREAM_SERVER_PORT
                        upstream nameserver port. Defaults to 53.
  -d DELAY, --delay DELAY
                        delay of requests in milliseconds. Defaults to 1000ms.
  -l LOSS, --loss LOSS  percent of requests which will be 'lost'. Defaults to
                        0
  -j JITTER, --jitter JITTER
                        quantity of random variation +/- base in ms. Defaults
                        to 0 (no jitter). Should not be larger than delay.

Examples

Share slodns to machines on the LAN on port 53.

$ sudo slodns -i 0.0.0.0 -p 53

Use a local DNS server with a 2 second simulated delay and 0.5s jitter.

$ slodns -u 192.168.2.1 -d 2000 -j 500

Simulate a lossy network with 500ms delay, 100ms jitter (400 - 600ms), and 25% request loss.

$ slodns -u 192.168.2.1 -d 500 -j 100 -l 25

Running on Privileged Ports

As binding to ports <= 1024 require root execution, you have two choices for slodns. The first is to use sudo and run slodns as root.

$ sudo slodns -i 0.0.0.0 -p 53

The other option is to enable port forwarding within the kernel and use iptables - an example rule is below:

iptables -t nat -A PREROUTING -s 127.0.0.1 -p udp --dport 53 -j REDIRECT --to 5053`
iptables -t nat -A OUTPUT -s 127.0.0.1 -p udp --dport 53 -j REDIRECT --to 5053`