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:lastproofread: 2023-11-23
########
Firewall
########
With VyOS being based on top of Linux and its kernel, the Netfilter project
created iptables and its successor nftables for the Linux kernel to
work directly on the 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
Main points regarding this packet flow and terminology used in VyOS firewall are below:
* **Bridge Port?**: choose appropriate path based on whether interface where the
packet was received is part of a bridge, or not.
If interface where the packet was received isn't part of a bridge, then packet
is processed at the **IP Layer**:
* **Prerouting**: several actions can be done in this stage, and currently
these actions are defined in different parts in VyOS configuration. Order
is important, and all these actions are performed before any actions
defined under ``firewall`` section. Relevant configuration that acts in
this stage are:
* **Conntrack Ignore**: rules defined under ``set system conntrack ignore
[ipv4 | ipv6] ...``.
* **Policy Route**: rules defined under ``set policy [route | route6]
...``.
* **Destination NAT**: rules defined under ``set [nat | nat66]
destination...``.
* **Destination is the router?**: choose appropriate path based on
destination IP address. Transit forward continues to **forward**,
while traffic that 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 VyOS router,
such as NTP, or a response to traffic received externaly through
**inputt** (for example response to an ssh login attempt to the router).
This includes ipv4 and ipv6 filtering rules, defined in:
* ``set firewall ipv4 input filter ...``.
* ``set firewall 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 interface where the packet was received is part of a bridge, then packet
is processed at the **Bridge Layer**, which contains a basic setup for
bridge filtering:
* **Forward (Bridge)**: stage where traffic that is trespasing through the
bridge is filtered and controlled:
* ``set firewall bridge forward filter ...``.
Main structure VyOS firewall cli is shown next:
.. code-block:: none
- set firewall
* bridge
- forward
+ filter
* 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
- name
+ custom_name
* ipv6
- forward
+ filter
- input
+ filter
- output
+ filter
- ipv6-name
+ custom_name
* zone
- custom_zone_name
+ ...
Please, refer to appropiate 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
<https://wiki.nftables.org/wiki-nftables/index.php/Netfilter_hooks>`_
Zone-based firewall
^^^^^^^^^^^^^^^^^^^
.. toctree::
:maxdepth: 1
:includehidden:
zone
With zone-based firewalls a new concept was implemented, in addtion to the
standard in and out traffic flows, a local flow was added. This local was for
traffic originating and destined to the router itself. Which means 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 </configuration/firewall/zone>`
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