Netiscope

A simple command line (CLI) tool to check network connectivity.

Netiscope is meant to be a helper tool to be used in case the network doesn't seem to be working properly, and can give hints about what's going wrong. There is not a lot of secret sauce to this tool: a seasoned user can do these check themselves with various tools to determine the root cause of a problem. However, Netiscope may make this task simpler.

Netiscope is open source and can be extended with more checks.

Quick Start Guide

In order to compile, you need to install Golang. Then, to get the source for Netiscope:

mkdir -p ~/go/src/
cd ~/go/src/
git clone https://github.com/robert-kisteleki/netiscope.git

There are a few Go packages that are required to compile:

go get github.com/miekg/dns
go get github.com/fatih/color
go get github.com/sparrc/go-ping
go get gopkg.in/ini.v1

Now you're ready to compile and run:

cd ~/go/src/netiscope/
go build netiscope
./netiscope -v -color

On Linux, the ping functionality may need '"unprivileged" ping via UDP" permission:

sudo sysctl -w net.ipv4.ping_group_range="0   2147483647"

Checks

Netiscope executes a series of checks, each tailored to discover if a particular networking function is working properly or not.

The default output contains lines of [timestamp, check, level, details].

1. Local network interfaces

Check if any routable addresses are present. Current unicast IPv4 and IPv6 addresses are evaluated on each interface. Special addresses (such as RFC1918) are marked.

2. Local DNS resolvers

Check if DNS resolvers are defined, reachable and if they work properly. Each resolver defined in resolv.conf is pinged and a series of DNS lookups (for well known targets such as google.com) are executed against them. The results are matched against a known-good list of potential responses (see CIDR list).

3. Open DNS resolvers

Check if well-known open DNS resolvers are reachable. "Well-known" includes:

• 1.1.1.1 (Cloudflare)
• 8.8.8.8 (Google)
• 9.9.9.9 (Quad9)

Like with the local DNS resolvers, each one is pinged and a series of DNS lookups (for well known targets such as google.com) are executed against them. The results are matched against a known-good list of potential responses (see CIDR list).

X. Future checks

The checks could also include:

• (TODO, possible) Wifi signal/noise/channel/rate/packet loss/...
• (TODO, possible) Check of DoT (DNS over TLS) or DoH (DNS over HTTPS) or DNSSEC validation are available and working
• (TODO, possible) Query root name servers and/or traceroute to them
• (TODO, possible) Traceroute to known targets (M-Lab, RIPE Atlas anchors, ...)
• (TODO, possible) Detect presence of a captive portal
• (TODO, possible) Availability of popular services (google, facebook, ...), perhaps including:
  • IP based (as opposed to DNS based) to detect DNS censorship
  • verification of TLS certificates
  • sanity check of responses
  • whether protocols such as QUIC can be used
• (TODO, possible) IPv6 PMTUD to various targets
• (TODO, possible) Check ability to spoof packets / BCP38 compliance
• (TODO, possible) Measure upstream/downstream bandwidth
• (TODO, possible) Outbound port filtering
• (TODO, possible) User defined check: favourite VPN, personal webserver, ... using ping/HTTPS/etc

Configuration

See netiscope.ini for details. This configuration is loaded on start. It can be explicitly specified via the -c parameter, from ./netiscope.ini, or from ~/.config/netiscope.ini.

Notable command line options:

• -c CONFIG specifies a config file
• -C CIDRFILE specifies a provider CIDR list file
• -s SECTION specifies a configuration section list sthe checks to execute instead of checks
• -skip4 and -skip6 disable IPV4/IPv6 checks, respectively
• -force4 and -force6 enforce IPV4/IPv6 checks, respectively, even if no useful network interfaces are found
• -l LEVEL sets the log level. LEVEL can be detail, info (default), warning or error
• -v is a shorthand to increase logging to detail level
• -color enables (ANSI) output colors

The configuration file has several sections:

• The main section has basic options, many which can also be set on the command line:
  • loglevel
  • color
  • skip_ipv4 and skip_ipv6
  • force_ipv4 and force_ipv6
  • ping_packets
• The checks section lists the checks to execute
  • Each check has (or can have) its own section defining options for the particular check
• The CIDRFILE contains the list of CIDR blocks for (some) providers. This allows checking if the IP address used (or looked up) for that provider is in this "known good" list. This file is looked up using the -C option, or where the main config file is.
• See the sections and comments in the supplied config file for more details, examples and default settings

Author

Robert Kisteleki (kistel@gmail.com)

License and Feedback

The code is open sourced under GPLv3 license. It is available at https://github.com/robert-kisteleki/netiscope/.