Firewall
Overview
VyOS makes use of Linux netfilter for packet filtering.
The firewall supports the creation of groups for ports, addresses, and networks (implemented using netfilter ipset) and the option of interface or zone based firewall policy.
Note
Important note on usage of terms: The firewall makes use of the terms in, out, and local for firewall policy. Users experienced with netfilter often confuse in to be a reference to the INPUT chain, and out the OUTPUT chain from netfilter. This is not the case. These instead indicate the use of the FORWARD chain and either the input or output interface. The INPUT chain, which is used for local traffic to the OS, is a reference to as local with respect to its input interface.
Global settings
Some firewall settings are global and have an affect on the whole system.
By default, when VyOS receives an ICMP echo request packet destined for itself, it will answer with an ICMP echo reply, unless you avoid it through its firewall.
With the firewall you can set rules to accept, drop or reject ICMP in, out or local traffic. You can also use the general firewall all-ping command. This command affects only to LOCAL (packets destined for your VyOS system), not to IN or OUT traffic.
Note
firewall all-ping affects only to LOCAL and it always behaves in the most restrictive way
set firewall all-ping enable
When the command above is set, VyOS will answer every ICMP echo request addressed to itself, but that will only happen if no other rule is applied dropping or rejecting local echo requests. In case of conflict, VyOS will not answer ICMP echo requests.
set firewall all-ping disable
When the command above is set, VyOS will answer no ICMP echo request addressed to itself at all, no matter where it comes from or whether more specific rules are being applied to accept them.
This setting enable or disable the response of icmp broadcast messages. The following system parameter will be altered:
net.ipv4.icmp_echo_ignore_broadcasts
This setting handle if VyOS accept packets with a source route option. The following system parameter will be altered:
net.ipv4.conf.all.accept_source_routenet.ipv6.conf.all.accept_source_route
enable or disable of ICMPv4 or ICMPv6 redirect messages accepted by VyOS. The following system parameter will be altered:
net.ipv4.conf.all.accept_redirectsnet.ipv6.conf.all.accept_redirects
enable or disable ICMPv4 redirect messages send by VyOS The following system parameter will be altered:
net.ipv4.conf.all.send_redirects
enable or disable the logging of martian IPv4 packets. The following system parameter will be altered:
net.ipv4.conf.all.log_martians
Set the IPv4 source validation mode. The following system parameter will be altered:
net.ipv4.conf.all.rp_filter
Enable or Disable if VyOS use IPv4 TCP SYN Cookies. The following system parameter will be altered:
net.ipv4.tcp_syncookies
Enable or Disable VyOS to be RFC 1337 conform. The following system parameter will be altered:
net.ipv4.tcp_rfc1337
Set the global setting for an established connection.
Groups
Firewall groups represent collections of IP addresses, networks, or ports. Once created, a group can be referenced by firewall rules as either a source or destination. Members can be added or removed from a group without changes to, or the need to reload, individual firewall rules.
Groups need to have unique names. Even though some contain IPv4 addresses and others contain IPv6 addresses, they still need to have unique names, so you may want to append “-v4” or “-v6” to your group names.
Address Groups
In an address group a single IP address or IP address ranges are defined.
Define a IPv4 or a IPv6 address group
set firewall group address-group ADR-INSIDE-v4 address 192.168.0.1
set firewall group address-group ADR-INSIDE-v4 address 10.0.0.1-10.0.0.8
set firewall group ipv6-address-group ADR-INSIDE-v6 address 2001:db8::1
Network Groups
While network groups accept IP networks in CIDR notation, specific IP addresses can be added as a 32-bit prefix. If you foresee the need to add a mix of addresses and networks, the network group is recommended.
Define a IPv4 or IPv6 Network group.
set firewall group network-group NET-INSIDE-v4 network 192.168.0.0/24
set firewall group network-group NET-INSIDE-v4 network 192.168.1.0/24
set firewall group ipv6-network-group NET-INSIDE-v6 network 2001:db8::/64
Port Groups
A port group represents only port numbers, not the protocol. Port groups can be referenced for either TCP or UDP. It is recommended that TCP and UDP groups are created separately to avoid accidentally filtering unnecessary ports. Ranges of ports can be specified by using -.
Define a port group. A port name can be any name defined in /etc/services. e.g.: http
set firewall group port-group PORT-TCP-SERVER1 port http
set firewall group port-group PORT-TCP-SERVER1 port 443
set firewall group port-group PORT-TCP-SERVER1 port 5000-5010
Rule-Sets
A rule-set is a named collection of firewall rules that can be applied to an interface or a zone. Each rule is numbered, has an action to apply if the rule is matched, and the ability to specify the criteria to match. Data packets go through the rules from 1 - 999999, at the first match the action of the rule will be executed.
This set the default action of the rule-set if no rule matched a packet criteria.
Use this command to enable the logging of the default action.
This required setting defines the action of the current rule.
Provide a description for each rule.
Enable or disable logging for the matched packet.
If you want to disable a rule but let it in the configuration.
Matching criteria
There are a lot of matching criteria against which the package can be tested.
This is similar to the network groups part, but here you are able to negate the matching addresses.
set firewall name WAN-IN-v4 rule 100 source address 192.0.2.10-192.0.2.11
# with a '!' the rule match everything except the specified subnet
set firewall name WAN-IN-v4 rule 101 source address !203.0.113.0/24
set firewall ipv6-name WAN-IN-v6 rule 100 source address 2001:db8::202
Only in the source criteria, you can specify a mac-address.
set firewall name LAN-IN-v4 rule 100 source mac-address 00:53:00:11:22:33
set firewall name LAN-IN-v4 rule 101 source mac-address !00:53:00:aa:12:34
A port can be set with a port number or a name which is here
defined: /etc/services.
set firewall name WAN-IN-v4 rule 10 source port '22'
set firewall name WAN-IN-v4 rule 11 source port '!http'
set firewall name WAN-IN-v4 rule 12 source port 'https'
Multiple source ports can be specified as a comma-separated list. The whole list can also be “negated” using ‘!’. For example:
set firewall ipv6-name WAN-IN-v6 rule 10 source port '!22,https,3333-3338'
Use a specific address-group. Thes can also be “negated” using ‘!’. For Example
set firewall name WAN-IN-v4 rule 20 source group address-group '!TRUSTED-HOSTS'
Use a specific network-group
Use a specific port-group
Match a protocol criteria. A protocol number or a name which is here
defined: /etc/protocols.
Special names are all for all protocols and tcp_udp for tcp and udp
based packets. The ! negate the selected protocol.
set firewall name WAN-IN-v4 rule 10 protocol tcp_udp
set firewall name WAN-IN-v4 rule 11 protocol !tcp_udp
set firewall ipv6-name WAN-IN-v6 rule 10 protocol tcp
Allowed values fpr TCP flags: SYN, ACK, FIN, RST, URG,
PSH, ALL When specifying more than one flag, flags should be comma
separated. The ! negate the selected protocol.
set firewall name WAN-IN-v4 rule 10 tcp flags 'ACK'
set firewall name WAN-IN-v4 rule 12 tcp flags 'SYN'
set firewall name WAN-IN-v4 rule 13 tcp flags 'SYN,!ACK,!FIN,!RST'
Applying a Rule-Set to an Interface
A Rule-Set can be applied to every interface:
in: Ruleset for forwarded packets on an inbound interfaceout: Ruleset for forwarded packets on an outbound interfacelocal: Ruleset for packets destined for this router
Here are some examples for applying a rule-set to an interface
set interface ethernet eth1 vif 100 firewall in name LANv4-IN
set interface ethernet eth1 vif 100 firewall out name LANv4-OUT
set interface bonding bond0 firewall in name LANv4-IN
set interfaces openvpn vtun1 firewall in name Lanv4-IN
Note
As you can see in the example here, you can assign the same rule-set to several interfaces. An interface can only have one rule-set per chain.
Zone-based Firewall Policy
As an alternative to applying policy to an interface directly, a zone-based firewall can be created to simplify configuration when multiple interfaces belong to the same security zone. Instead of applying rule-sets to interfaces, they are applied to source zone-destination zone pairs.
An basic introduction to zone-based firewalls can be found here, and an example at Zone-Policy example.
Define a Zone
To define a zone setup either one with interfaces or a local zone.
Set interfaces to a zone. A zone can have multiple interfaces. But an interface can only be a member in one zone.
Define the zone as a local zone. A local zone has no interfaces and will be applied to the router itself.
Change the default-action with this setting.
Applying a Rule-Set to a Zone
Before you are able to apply a rule-set to a zone you have to create the zones first.
You apply a rule-set always to a zone from an other zone, it is recommended to create one rule-set for each zone pair.
set zone-policy zone DMZ from LAN firewall name LANv4-to-DMZv4
set zone-policy zone LAN from DMZ firewall name DMZv4-to-LANv4
Operation-mode Firewall
Rule-set overview
This will show you a basic firewall overview
[email protected]:~$ show firewall
------------------------
Firewall Global Settings
------------------------
Firewall state-policy for all IPv4 and Ipv6 traffic
state action log
----- ------ ---
invalid accept disabled
established accept disabled
related accept disabled
-----------------------------
Rulesets Information
-----------------------------
--------------------------------------------------------------------------
IPv4 Firewall "DMZv4-1-IN":
Active on (eth0,IN)
rule action proto packets bytes
---- ------ ----- ------- -----
10 accept icmp 0 0
condition - saddr 10.1.0.0/24 daddr 0.0.0.0/0 LOG enabled
10000 drop all 0 0
condition - saddr 0.0.0.0/0 daddr 0.0.0.0/0 LOG enabled
--------------------------------------------------------------------------
IPv4 Firewall "DMZv4-1-OUT":
Active on (eth0,OUT)
rule action proto packets bytes
---- ------ ----- ------- -----
10 accept tcp_udp 1 60
condition - saddr 0.0.0.0/0 daddr 0.0.0.0/0 match-DST-PORT-GROUP DMZ-Ports /*
DMZv4-1-OUT-10 */LOG enabled
11 accept icmp 1 84
condition - saddr 0.0.0.0/0 daddr 0.0.0.0/0 /* DMZv4-1-OUT-11 */LOG enabled
10000 drop all 6 360
condition - saddr 0.0.0.0/0 daddr 0.0.0.0/0 LOG enabled
--------------------------------------------------------------------------
IPv4 Firewall "LANv4-IN":
Inactive - Not applied to any interfaces or zones.
rule action proto packets bytes
---- ------ ----- ------- -----
10 accept all 0 0
condition - saddr 0.0.0.0/0 daddr 0.0.0.0/0 /* LANv4-IN-10 */
10000 drop all 0 0
condition - saddr 0.0.0.0/0 daddr 0.0.0.0/0
This will show you a summary of rule-sets and groups
[email protected]:~$ show firewall summary
------------------------
Firewall Global Settings
------------------------
Firewall state-policy for all IPv4 and Ipv6 traffic
state action log
----- ------ ---
invalid accept disabled
related accept disabled
established accept disabled
------------------------
Firewall Rulesets
------------------------
IPv4 name:
Rule-set name Description References
------------- ----------- ----------
DMZv4-1-OUT (eth0,OUT)
DMZv4-1-IN (eth0,IN)
------------------------
Firewall Groups
------------------------
Port Groups:
Group name Description References
---------- ----------- ----------
DMZ-Ports DMZv4-1-OUT-10-destination
Network Groups:
Group name Description References
---------- ----------- ----------
LANv4 LANv4-IN-10-source,
DMZv4-1-OUT-10-source,
DMZv4-1-OUT-11-source
This command will give an overview of a rule in a single rule-set
Overview of defined groups. You see the type, the members, and where the group is used.
[email protected]:~$ show firewall group DMZ-Ports
Name : DMZ-Ports
Type : port
References : none
Members :
80
443
8080
8443
[email protected]:~$ show firewall group LANv4
Name : LANv4
Type : network
References : LANv4-IN-10-source
Members :
10.10.0.0/16
This will show you a rule-set statistic since the last boot.
Zone-Policy Overview
Use this command to get an overview of a zone.
[email protected]:~$ show zone-policy zone DMZ
-------------------
Name: DMZ
Interfaces: eth0 eth1
From Zone:
name firewall
---- --------
LAN DMZv4-1-OUT
Show Firewall log
Note
At the moment it not possible to look at the whole firewall log with VyOS
operational commands. All logs will save to /var/logs/messages.
For example: grep '10.10.0.10' /var/log/messages
Example Partial Config
firewall {
all-ping enable
broadcast-ping disable
config-trap disable
group {
network-group BAD-NETWORKS {
network 198.51.100.0/24
network 203.0.113.0/24
}
network-group GOOD-NETWORKS {
network 192.0.2.0/24
}
port-group BAD-PORTS {
port 65535
}
}
name FROM-INTERNET {
default-action accept
description "From the Internet"
rule 10 {
action accept
description "Authorized Networks"
protocol all
source {
group {
network-group GOOD-NETWORKS
}
}
}
rule 11 {
action drop
description "Bad Networks"
protocol all
source {
group {
network-group BAD-NETWORKS
}
}
}
rule 30 {
action drop
description "BAD PORTS"
destination {
group {
port-group BAD-PORTS
}
}
log enable
protocol all
}
}
}
interfaces {
ethernet eth1 {
address dhcp
description OUTSIDE
duplex auto
firewall {
in {
name FROM-INTERNET
}
}
}
}
TCP-MSS Clamping
As Internet wide PMTU discovery rarely works, we sometimes need to clamp our TCP MSS value to a specific value. This is a field in the TCP Options part of a SYN packet. By setting the MSS value, you are telling the remote side unequivocally ‘do not try to send me packets bigger than this value’.
Starting with VyOS 1.2 there is a firewall option to clamp your TCP MSS value for IPv4 and IPv6.
Note
MSS value = MTU - 20 (IP header) - 20 (TCP header), resulting in 1452 bytes on a 1492 byte MTU.
IPv4
Use this command to set the maximum segment size for IPv4 transit packets on a specific interface (536-65535 bytes).
Instead of a numerical MSS value clamp-mss-to-pmtu can be used to automatically set the proper value.
Example
Clamp outgoing MSS value in a TCP SYN packet to 1452 for pppoe0 and 1372 for your WireGuard wg02 tunnel.
set firewall options interface pppoe0 adjust-mss '1452'
set firewall options interface wg02 adjust-mss '1372'
IPv6
Use this command to set the maximum segment size for IPv6 transit packets on a specific interface (1220-65535 bytes).
Instead of a numerical MSS value clamp-mss-to-pmtu can be used to automatically set the proper value.
Example
Clamp outgoing MSS value in a TCP SYN packet to 1280 for both pppoe0 and wg02 interface.
set firewall options interface pppoe0 adjust-mss6 '1280'
set firewall options interface wg02 adjust-mss6 '1280'
Hint
When doing your byte calculations, you might find useful this Visual packet size calculator.