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pcn-iptables: a clone of iptables based on eBPF

Polycube includes the pcn-iptables standalone application, a stateful firewall whose syntax and semantic are compatible with the well-known iptables Linux tool.

The frontend provides the same CLI of iptables; users can set up security policies using the same syntax by simply executing pcn-iptables instead of iptables. The backend is based on eBPF programs, more efficient classificaiton algorithms and runtime optimizations; the backend runs as a dedicated service in Polycube.

Supported features

Currently supported features:

  • Support for INPUT, OUTPUT, FORWARD chains
  • Support for ip, protocol, ports, tcp flags, interfaces
  • Support for connection tracking
  • Support for bpf TC and XDP mode

Detailed supported parameters

  • -s source IP
  • -d destination IP
  • -p l4 protocol
  • --sport source port
  • --dport destination port
  • --tcpflags tcp flags
  • -i input interface
  • -o output interface
  • -m conntrack --ctstate conntrack module

Detailed supported targets

  • -j ACCEPT accept traffic
  • -j DROP drop traffic

Detailed supported commands

  • -S Show rules
  • -L List rules
  • -A Append rule
  • -I Insert rule
  • -D Delete rule
  • -P <CHAIN> DROP/ACCEPT Setup default policy for <CHAIN>
  • -F <CHAIN> Flush policies for <CHAIN>

Limitations

  • No support for multiple chains
  • No support for SNAT, DNAT, MASQUESRADE
  • -S -L generate an output slightly different from iptables

Install

Prerequisites

pcn-iptables comes as a component of polycube framework. Refer to :doc:`polycube install guide<../../../installation>` for dependencies, kernel requirements and basic checkout and install guide.

Install Steps

To compile and install pcn-iptables, you should enable the ENABLE_PCN_IPTABLES flag in the polycube CMakeFile, which is set to OFF by default; this allows to compile the customized version of iptables used to translate commands, and install in the system pcn-iptables-init pcn-iptables and pcn-iptables-clean utils.

Note: The ENABLE_SERVICE_IPTABLES flag, which is set to ON by default, is used to compile and install the libpcn-iptables.so service (like other polycube services: bridge, router, ..). This flag is required to be enabled as well, but it comes by default.

cd polycube

# Note: ensure git submodules are updated
# git submodule update --init --recursive

mkdir -p build
cd build
cmake .. -DENABLE_PCN_IPTABLES=ON
make -j`nproc` && sudo make install

Run

1. Initialize pcn-iptables

# Start polycubed, in other terminal (or background)
sudo polycubed --daemon
# Initialize pcn-iptables
pcn-iptables-init

2. Use pcn-iptables

pcn-iptables provides same iptables syntax. Please refer to iptables online docs for more info. Following are just few examples of available commands.

# E.g.
pcn-iptables -A INPUT -s 10.0.0.1 -j DROP # Append rule to INPUT chain
pcn-iptables -D INPUT -s 10.0.0.1 -j DROP # Delete rule from INPUT chain
pcn-iptables -I INPUT -s 10.0.0.2 -j DROP # Insert rule into INPUT chain

# Example of a complex rule
pcn-iptables -A INPUT -s 10.0.0.0/8 -d 10.0.0.2 -p tcp --sport 9090 --dport 80 --tcpflags SYN,ACK ACK -j DROP

# Example of a conntrack rule
pcn-iptables -A OUTPUT -m conntrack --ctstate=ESTABLISHED -j ACCEPT

# Show rules
pcn-iptables -S # dump rules
pcn-iptables -L INPUT # dump rules for INPUT chain

pcn-iptables -P FORWARD DROP # set default policy for FORWARD chain

NOTE: do not use use sudo pcn-iptables ...

3. Stop pcn-iptables

# Stop and clean pcn-iptables
pcn-iptables-clean

# Execute the below command to validate if cleanup is successful.
pcn-iptables -S
``Note:  On successful cleanup, you should receive "No cube found named pcn-iptables"``

Advanced Features

XDP mode

pcn-iptables can also be run in XDP mode. This mode comes with performance gain, especially when policy are configured to DROP traffic.

pcn-iptables-init-xdp

Limitations

  • pcn-iptables operates only on interfaces that support XDP native mode
  • traffic is not filtered on interfaces that support only eBPF TC programs.

pcn-iptables components

iptables submodule

A customized fork of iptables is included as submodule under :scm_web:`src/components/iptables/iptables <src/components/iptables>`. We customized this version of iptables in order not to inject iptables command into netfilter, but convert them, after a validation step, into polycube syntax.

scripts folder

Scripts are used as a glue logic to make pcn-iptables run. Main purpose is initialize, cleanup and run pcn-iptables, pass pcn-iptables parameters through iptables (in charge of converting them), then pass converted commands to pcn-iptables service. Scripts are installed under /usr/local/bin.

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