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https://github.com/Fusion/kittendns


https://github.com/Fusion/kittendns

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# What is this?



A toy DNS for hobbyists and worried people.



Mission Statement:



- No fat. Fast.



Features:



- Really easy to configure (toml syntax)

- Rule engine to rewrite/deny queries

- Plugins support



But also:



- RFC2136 and LetsEncrypt compatibility, use as a DNS endpoint to obtain certificates

- Configuration auto-update



# Configuration, Documentation



    

Take a look at the content of the `config.toml.template` file. Copy it to `config.toml` and run.



Read the [CONCISE DOCUMENTATION](https://github.com/Fusion/kittendns/wiki) 📖



# DNS Synchronization



There is currently no notion of primary and secondary DNS. All your DNS instances are equal. It would be fairly easy to implement `IXFR/AXFR` but unless it becomes a mandatory feature, this seems to go against my "no fat/easy to configure" goals. With this being said, you could use something like [Syncthing](https://syncthing.net/) to keep `config.toml` current.



# Tell me more about the DNS repository



In the `github.com/miekg/dns` repository, there was a pull request allowing code using that library to retrieve additional information about the requesting socket. This includes source IP, which can be convenient in a split horizon environment. It lives in this directory (slightly adapted)



# Performance testing



The tests below are performed using authoritative (local) records as my main goal is to offer a server that can survive a brutal assault serving cloud endpoints. Performing the same test against recursed hosts offers similar performance, simply because I am not querying 1M different hosts and the server efficiently`*` caches responses (while respecting their TTL)



These tests are run locally on a 2020 Macbook M1 Pro and jMeter is using as much CPU as it dares to, while kittendns doesn't even appear in my top output.



`*` dumbly



## jMeter stress testing



1. Run Wireshark to capture a DNS query. In the details window, select the Domain Name System layer, right-click, copy as a hex stream.

2. In jMeter, paste in the "Request Data" area



The jMeter test plan is stored in `KittenDNS jMeter Test Plan.jmx`



Since we are testing DDoS-type scenarios, we are not going to allow any ramp-up. All clients will be hitting the servers from the beginning.



Results:



|Scenario|Queries/Minute|Queries/Second|

|-|-|-|

|1M queued queries for locally resolved hosts|1.3M|21,666|

|1M queued queries for locally resolved, CNAME'd hosts|1.276M|21,417|

|1M queries, but by 100 users, no ramp-up|4.599M|76,650|

|1M queries, 100 users, flattening enabled|4.623M|77,050|

|1M queries, bump to 1,000 users|3.2M|53,333|



Observations:

- If we distribute across 1000 users rather than 100, threading starts degrading.

- Flattening doesn't provide the expected level of improvement.



![](assets/jmeter-kittendns.png)



Latency is pretty good, too.



## Mig testing



https://github.com/infobloxopen/dnstools/tree/master/mig



```

./mig -s 192.168.1.189 -n 1000000 -d domains.lst -o perf.json

python2 ../analyser/fit.py results/perf.json

```



Results:



|Rule Engine|Queries/Minute|Queries/Second|

|-|-|-|

|Enabled|6.7M|111,677|

|Disabled|6.79M|113,181|



Again, a somewhat unexpected result: a lightly loaded rule engine has almost no impact on the server's performance.



# Todo



## Cache improvements



- If flattening is enabled, we should cache the flattened version.

- When flattening, what about recursed and fragmented answers?



## Circuit Breaker (when recursing)/Rate Limiter



Because, realistically, it is better to fail some queries if this will allow them to succeed later.



Rate Limiter: should be limiting some misbehaving clients. Problem: how do we identify a "Client?"

- Is a client a single IP address? If it's a site DNS proxying to us, then it may be allowed higher traffic levels

- Should we throttle a combination of source + queries?



# FAQ



Q: I noticed that you are storing similar records in separate structures. For instance, there is one entry for a A (v4) record,

and another entry for its AAAA (v6) counterpart. This is wasteful!



A: You are correct. However, I should not store both entries using the same key because they can both be capitalized differently.

And, little known fact, capitalization in DNS can be a security feature.



Q: What's that about capitalization?



A: KittenDNS makes sure that the response to a query returns the host capitalized exactly as it was in the query.

This is a protection scheme against DNS poisoning, known as the '0x20' trick.



# Misc



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