Getting Started with CBR Shell: A Step-by-Step TutorialCBR Shell is a lightweight, scriptable command-line environment designed to simplify configuration, automation, and troubleshooting for systems that rely on bandwidth shaping, rate control, or capacity-based routing. This tutorial walks you through everything from installation to practical examples, helping you gain confidence using CBR Shell for real-world tasks.
What is CBR Shell?
CBR Shell is a shell tailored specifically for Capacity-Based Routing (CBR) and similar traffic-control use cases. It combines a concise command set with scripting facilities, allowing administrators and developers to define, test, and automate bandwidth policies, route selection logic, and traffic classification.
Key features:
- Declarative policy definitions for bandwidth and routing.
- Lightweight interpreter that runs on small devices and servers.
- Scriptable with functions, variables, and conditionals.
- Integration hooks for monitoring and logging systems.
- Support for emulation modes to test policies safely.
System requirements
Before installing, ensure your environment meets these minimum requirements:
- Linux (Debian/Ubuntu/CentOS) or macOS; Windows via WSL.
- 64-bit CPU with at least 1 GB RAM (2 GB recommended).
- Python 3.8+ if using the Python-based installer or extensions.
- Network utilities: iproute2, tc (for Linux), or equivalent.
Installation
- Download the latest release from the official repository or package manager. On Debian/Ubuntu:
sudo apt update sudo apt install cbr-shell - For macOS using Homebrew:
brew install cbr-shell - If no package is available, install from source:
git clone https://example.com/cbr-shell.git cd cbr-shell ./configure make sudo make install
After installation, verify with:
cbr --version You should see the installed version and build info.
Basic concepts and commands
CBR Shell introduces a few domain-specific concepts:
- Policy — a named set of rules that define how traffic is shaped or routed.
- Class — a traffic class, often associated with bandwidth limits or priorities.
- Matcher — an expression that selects packets (by IP, port, protocol, DSCP, etc.).
- Action — what to do with matched traffic (route, limit, drop, tag).
Common commands:
- cbr policy create
- cbr class add
–rate - cbr match add
–src 10.0.0.0/8 –dport 80 - cbr apply
–interface eth0 - cbr show policies
- cbr simulate
–trace flow.json
Example: create a policy and class
cbr policy create web-policy cbr class add web-policy web-traffic --rate 2000 cbr match add web-policy web-traffic --dport 80 --proto tcp cbr apply web-policy --interface eth0 A step-by-step example: Rate-limiting HTTP and prioritizing VoIP
Goal: Limit HTTP to 2 Mbps and prioritize VoIP (SIP/RTP) with guaranteed 1 Mbps and low latency.
- Create the policy:
cbr policy create office-policy - Add classes:
cbr class add office-policy voip --rate 1000 --priority high --latency low cbr class add office-policy http --rate 2000 --priority low cbr class add office-policy bulk --rate 5000 --priority best-effort - Add matchers:
cbr match add office-policy voip --proto udp --dport 5060-5061 cbr match add office-policy voip --proto udp --dport 10000-20000 cbr match add office-policy http --proto tcp --dport 80,443 cbr match add office-policy bulk --src 10.1.0.0/16 - Apply to interface:
cbr apply office-policy --interface eth1 - Verify:
cbr show policies cbr stats show --policy office-policy
Scripting with CBR Shell
CBR Shell supports simple scripts to automate tasks. Scripts use variables, conditionals, and functions.
Example script (save as manage_policy.cbr):
#!/usr/bin/env cbr policy="office-policy" if ! cbr policy exists $policy; then cbr policy create $policy cbr class add $policy voip --rate 1000 --priority high --latency low cbr class add $policy http --rate 2000 --priority low cbr match add $policy voip --proto udp --dport 5060-5061 cbr match add $policy http --proto tcp --dport 80,443 cbr apply $policy --interface eth1 else echo "Policy $policy already exists" fi Run:
chmod +x manage_policy.cbr ./manage_policy.cbr Monitoring, logging, and simulation
- Real-time stats: cbr stats show –interface eth1 –interval 5
- Logs: /var/log/cbr-shell.log (or configured syslog)
- Simulation mode: cbr simulate
–input sample-flows.json –report sim-report.json
Simulation is useful to validate behavior before applying policies on production interfaces.
Troubleshooting common issues
- “tc not found” — install iproute2 package.
- Rules not applied — confirm interface name and permissions (run with sudo).
- Unexpected matches — use cbr simulate or cbr debug trace to see which matcher matched a flow.
- Performance concerns — check CPU usage; consider offloading to hardware or simplifying match expressions.
Best practices
- Start with a simple policy, then iterate.
- Use simulation to test rules.
- Prefer broad classes with fewer matchers for performance.
- Keep critical real-time traffic in high-priority classes with explicit minimum rates.
- Version-control your policy scripts.
Further learning and resources
- Official docs and command reference (install includes man pages).
- Example policy repository with common templates.
- Community forums and mailing lists for user-contributed scripts.
CBR Shell is designed to be practical and approachable: begin with small policies, use simulation to validate, and gradually automate with scripts. The commands above give a functional starting point you can adapt to your environment.
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