:lastproofread: 2024-08-05 ######## Firewall ######## .. warning:: Due to a race condition that can lead to a failure during boot process, all interfaces are initialized before firewall is configured. This leads to a situation where the system is open to all traffic, and can be considered as a security risk. As VyOS is based on Linux it leverages its firewall. The Netfilter project created iptables and its successor nftables for the Linux kernel to work directly on packet data flows. This now extends the concept of zone-based security to allow for manipulating the data at multiple stages once accepted by the network interface and the driver before being handed off to the destination (e.g., a web server OR another device). A simplified traffic flow diagram, based on Netfilter packet flow, is shown next, in order to have a full view and understanding of how packets are processed, and what possible paths traffic can take. .. figure:: /_static/images/firewall-gral-packet-flow.png The main points regarding this packet flow and terminology used in VyOS firewall are covered below: * **Bridge Port?**: choose appropriate path based on whether interface where the packet was received is part of a bridge, or not. If the interface where the packet was received isn't part of a bridge, then packet is processed at the **IP Layer**: * **Prerouting**: All packets that are received by the router are processed in this stage, regardless of the destination of the packet. Starting from vyos-1.5-rolling-202406120020, a new section was added to the firewall configuration. There are several actions that can be done in this stage, and currently these actions are also defined in different parts of the VyOS configuration. Order is important, and the relevant configuration that acts in this stage are: * **Firewall prerouting**: rules defined under ``set firewall [ipv4 | ipv6] prerouting raw...``. All rules defined in this section are processed before connection tracking subsystem. * **Conntrack Ignore**: rules defined under ``set system conntrack ignore [ipv4 | ipv6] ...``. Starting from vyos-1.5-rolling-202406120020, configuration done in this section can be done in ``firewall [ipv4 | ipv6] prerouting ...``. For compatibility reasons, this feature is still present, but it will be removed in the future. * **Policy Route**: rules defined under ``set policy [route | route6] ...``. * **Destination NAT**: rules defined under ``set [nat | nat66] destination...``. * **Destination is the router?**: choose an appropriate path based on destination IP address. Transit forward continues to **forward**, while traffic where the destination IP address is configured on the router continues to **input**. * **Input**: stage where traffic destined for the router itself can be filtered and controlled. This is where all rules for securing the router should take place. This includes ipv4 and ipv6 filtering rules, defined in: * ``set firewall ipv4 input filter ...``. * ``set firewall ipv6 input filter ...``. * **Forward**: stage where transit traffic can be filtered and controlled. This includes ipv4 and ipv6 filtering rules, defined in: * ``set firewall ipv4 forward filter ...``. * ``set firewall ipv6 forward filter ...``. * **Output**: stage where traffic that originates from the router itself can be filtered and controlled. Bear in mind that this traffic can be a new connection originated by a internal process running on the VyOS router such as NTP, or a response to traffic received externally through **input** (for example response to an ssh login attempt to the router). This includes ipv4 and ipv6 rules, and two different sections are present: * **Output Prerouting**: ``set firewall [ipv4 | ipv6] output filter ...``. As described in **Prerouting**, rules defined in this section are processed before connection tracking subsystem. * **Output Filter**: ``set firewall [ipv4 | ipv6] output filter ...``. * **Postrouting**: as in **Prerouting**, several actions defined in different parts of VyOS configuration are performed in this stage. This includes: * **Source NAT**: rules defined under ``set [nat | nat66] destination...``. If the interface where the packet was received is part of a bridge, then the packet is processed at the **Bridge Layer**: * **Prerouting (Bridge)**: all packets that are received by the bridge are processed in this stage, regardless of the destination of the packet. First filters can be applied here, and/or also configure rules for ignoring connection tracking system. The relevant configuration that acts in: * ``set firewall bridge prerouting filter ...``. * **Forward (Bridge)**: stage where traffic that is trespassing through the bridge is filtered and controlled: * ``set firewall bridge forward filter ...``. * **Input (Bridge)**: stage where traffic destined for the bridge itself can be filtered and controlled: * ``set firewall bridge input filter ...``. * **Output (Bridge)**: stage where traffic that originates from the bridge itself can be filtered and controlled: * ``set firewall bridge output filter ...``. The main structure of the VyOS firewall CLI is shown next: .. code-block:: none - set firewall * bridge - forward + filter - input + filter - output + filter - prerouting + filter - name + custom_name * flowtable - custom_flow_table + ... * global-options + all-ping + broadcast-ping + ... * group - address-group - ipv6-address-group - network-group - ipv6-network-group - interface-group - mac-group - port-group - domain-group * ipv4 - forward + filter - input + filter - output + filter + raw - prerouting + raw - name + custom_name * ipv6 - forward + filter - input + filter - output + filter + raw - prerouting + raw - ipv6-name + custom_name * zone - custom_zone_name + ... Please, refer to appropriate section for more information about firewall configuration: .. toctree:: :maxdepth: 1 :includehidden: global-options groups bridge ipv4 ipv6 flowtables .. note:: **For more information** of Netfilter hooks and Linux networking packet flows can be found in `Netfilter-Hooks `_ Zone-based firewall ^^^^^^^^^^^^^^^^^^^ .. toctree:: :maxdepth: 1 :includehidden: zone With zone-based firewalls a new concept was implemented, in addition to the standard in and out traffic flows, a local flow was added. This local flow was for traffic originating and destined to the router itself. Which means that additional rules were required to secure the firewall itself from the network, in addition to the existing inbound and outbound rules from the traditional concept above. To configure VyOS with the :doc:`zone-based firewall configuration ` As the example image below shows, the device now needs rules to allow/block traffic to or from the services running on the device that have open connections on that interface. .. figure:: /_static/images/firewall-zonebased.png