Rnp - A simple cloud-friendly tool for testing network reachability.
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NOTE: This project is in early stage and might not be stable yet.
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Why Rnp?
TCP connect tool is one of the most frequently used tool for testing network reachability. And yet, we have another one here... So why?
Although there are indeed numerous tools doing tcp connect test, I wrote this new one for some specific reasons:
- Easy to deploy and run.
- Wide platform support: Windows/Linux, x86/amd64/arm64.
- Wide machine environment support: Different machines might have very different environment. Some of them might not have or cannot install any heavy runtime, like JRE/CLR.
- Be cloud-friendly:
- Fast network scan:
- Nowadays, network data path are mostly redundant, technologies like ECMP are widely used in the modern data center.
- Because of this, if one network link is having trouble, we will see intermediate packet drop/latency, instead of seeing full connectivity drop. Hence, we need a tool to help us scan all possible network paths and find out the bad links.
- Friendly to SNAT:
- If you are using load balancers in cloud for making outbound connections, you must be familiar with SNAT port allocation failure / exhaustion. It is because our backend instances are sharing the small set of public ips for making outbound connections. And the load balancer manages the port allocation on those IPs the and tracks all connections for doing SNAT.
- Since the tcp connect test tools are essentially creating new connections all the time to a unique endpoint, it can easily trigger SNAT port allocation failures.
- Whenever a connection hits port allocation failures, the packet could never go out and causing the test tools reporting timeout failures. These are purely noises and making our testing hard to do.
- Fast network scan:
- A language with light-weighted & GC-free runtime to avoid unstable measurements.
- Easy to use:
- Formatted output for offline analysis, scripting or simply information archive.
- Simple analysis and brief summary for heavy testing to help quickly troubleshoot the problems.
- ...
To help us achieve the things above, we are implementing our ping in the following way:
- Use Rust as the programming language:
- Rust is a system language with very light-weighted and GC-free runtime, which means no more random lags during our measurements, such as stop-the-world stages in GC.
- Rust has wide range of platform support and produces almost self-contained native binaries, so we can simply copy and run.
- Rust is as fast as C, while also has great support for modern age asynchronous programming. Gems like go-like mpsc channel, async/await, you can find them all in Rust.
- ...
- RST instead of FIN:
- Most of the tcp connect tools follows the regular way to disconnect the TCP connection - the 4-way handshake with FIN packet. This is great for servers, but not for testing.
- The regular disconnect leaves the ports in TIME_WAIT state and the cloud load balancers have to keep tracking the SNAT ports as well. It can easily cause SNAT port allocation error everywhere in your service, which you definitely don't want to see. And our ping will try to avoid this to happen.
- Ping as spray:
- To help us test all possible data path links, we keep rotating our source port during our ping.
- To make the ping run faster, we can change the number of pings we run in parallel as well the intervals we wait between the pings. This helps us spray all possible network paths.
- Friendly result output:
- Besides outputting the ping result in the most well-known way (just like ping), we also provided more ways to show the results, such as very compacted scatter map.
- We also support outputting the result into CSV/JSON/Text files for later analysis or scripting.
Some hard decisions:
- DNS name resolution is intentionally not supported. Using IP address is enforced when using our ping.
- This is because DNS can return different result based on geo-location. This misleads people a lot when collaborating on network issues, because it might end up with different people debugging different issues without even knowing it for long time.
- To get IP from DNS, we can run
nslookup.
Usage
Ok, let's check some real cases to get started!
The simplest case - regular TCP connect test. Works just like ping.
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Now let's make our ping faster by adding -p 10 to spawn 10 workers and -i 0 to remove the intervals we wait between each ping, then run 100 pings. And to avoid abusing our console, we disable the regular output (-q), enable the result scatter map (-r) and log the details to a json file for later use (--log-json log.json).
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We will see the test will complete almost immediately, and the details will be logged into the json file:
And now, we can see our ping failed on port 19653, then we can start a continuous ping to rerun the bad ports. And we can see a fairly high failure rate on this port as below.
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Also, we can easily try all failure ports again and see how they look like. Here is an example using powershell, and on non-windows platform, we can easily do the same thing with tools like jq:
# Extract the failure ports
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# Retry
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And rnp will start to rotate the ping within all the specified source ports for testing.
More in help
To see more on this tool, we can try --help option.
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Contributes
Thanks a lot in being interested in this project and all contributions are welcomed!
To contribute to the project, please feel free to open issues and discuss. Then submit a pull request for review and merge into main branch.
How to build
Just like the rest of Rust project, simply use cargo to build it.
To build release version:
To build other targets, such as ARM64 on windows, we can use --target to specify the target (of course, in this specific case, we need to install the msvc ARM64 toolchain from visual studio).
Future plans and issue tracking
- IPv6 (not tested)
- Maybe other protocol support? (ICMP is bad for checking all possible paths, because there are no variations for routing in the packet. And UDP has no uniformed handshake.).
- ...
Resources
- Equal-cost multi-path routing
- AWS NAT gateways and ErrorPortAllocation error
- Azure Load Balancer, SNAT port exhaustion and outbound connectivity troubleshooting
License
Apache-2.0: https://www.apache.org/licenses/LICENSE-2.0