Firewall

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Proxmox VE Firewall provides an easy way to protect your IT infrastructure. You can setup firewall rules for all hosts inside a cluster, or define rules for virtual machines and containers. Features like firewall macros, security groups, IP sets and aliases help to make that task easier.

While all configuration is stored on the cluster file system, the iptables-based firewall runs on each cluster node, and thus provides full isolation between virtual machines. The distributed nature of this system also provides much higher bandwidth than a central firewall solution.

The firewall has full support for IPv4 and IPv6. IPv6 support is fully transparent, and we filter traffic for both protocols by default. So there is no need to maintain a different set of rules for IPv6.

Zones

The Proxmox VE firewall groups the network into the following logical zones:

Host

Traffic from/to a cluster node

VM

Traffic from/to a specific VM

For each zone, you can define firewall rules for incoming and/or outgoing traffic.

Configuration Files

All firewall related configuration is stored on the proxmox cluster file system. So those files are automatically distributed to all cluster nodes, and the pve-firewall service updates the underlying iptables rules automatically on changes.

You can configure anything using the GUI (i.e. DatacenterFirewall, or on a NodeFirewall), or you can edit the configuration files directly using your preferred editor.

Firewall configuration files contains sections of key-value pairs. Lines beginning with a # and blank lines are considered comments. Sections starts with a header line containing the section name enclosed in [ and ].

Cluster Wide Setup

The cluster wide firewall configuration is stored at:

/etc/pve/firewall/cluster.fw

The configuration can contain the following sections:

[OPTIONS]

This is used to set cluster wide firewall options.

enable: <integer> (0 - N)

Enable or disable the firewall cluster wide.

policy_in: <ACCEPT | DROP | REJECT>

Input policy.

policy_out: <ACCEPT | DROP | REJECT>

Output policy.

[RULES]

This sections contains cluster wide firewall rules for all nodes.

[IPSET <name>]

Cluster wide IP set definitions.

[GROUP <name>]

Cluster wide security group definitions.

[ALIASES]

Cluster wide Alias definitions.

Enabling the Firewall

The firewall is completely disabled by default, so you need to set the enable option here:

[OPTIONS]
# enable firewall (cluster wide setting, default is disabled)
enable: 1
Important If you enable the firewall, traffic to all hosts is blocked by default. Only exceptions is WebGUI(8006) and ssh(22) from your local network.

If you want to administrate your Proxmox VE hosts from remote, you need to create rules to allow traffic from those remote IPs to the web GUI (port 8006). You may also want to allow ssh (port 22), and maybe SPICE (port 3128).

Tip Please open a SSH connection to one of your Proxmox VE hosts before enabling the firewall. That way you still have access to the host if something goes wrong .

To simplify that task, you can instead create an IPSet called “management”, and add all remote IPs there. This creates all required firewall rules to access the GUI from remote.

Host Specific Configuration

Host related configuration is read from:

/etc/pve/nodes/<nodename>/host.fw

This is useful if you want to overwrite rules from cluster.fw config. You can also increase log verbosity, and set netfilter related options. The configuration can contain the following sections:

[OPTIONS]

This is used to set host related firewall options.

enable: <boolean>

Enable host firewall rules.

log_level_in: <alert | crit | debug | emerg | err | info | nolog | notice | warning>

Log level for incoming traffic.

log_level_out: <alert | crit | debug | emerg | err | info | nolog | notice | warning>

Log level for outgoing traffic.

ndp: <boolean>

Enable NDP.

nf_conntrack_max: <integer> (32768 - N)

Maximum number of tracked connections.

nf_conntrack_tcp_timeout_established: <integer> (7875 - N)

Conntrack established timeout.

nosmurfs: <boolean>

Enable SMURFS filter.

smurf_log_level: <alert | crit | debug | emerg | err | info | nolog | notice | warning>

Log level for SMURFS filter.

tcp_flags_log_level: <alert | crit | debug | emerg | err | info | nolog | notice | warning>

Log level for illegal tcp flags filter.

tcpflags: <boolean>

Filter illegal combinations of TCP flags.

[RULES]

This sections contains host specific firewall rules.

VM/Container Configuration

VM firewall configuration is read from:

/etc/pve/firewall/<VMID>.fw

and contains the following data:

[OPTIONS]

This is used to set VM/Container related firewall options.

dhcp: <boolean>

Enable DHCP.

enable: <boolean>

Enable/disable firewall rules.

ipfilter: <boolean>

Enable default IP filters. This is equivalent to adding an empty ipfilter-net<id> ipset for every interface. Such ipsets implicitly contain sane default restrictions such as restricting IPv6 link local addresses to the one derived from the interface’s MAC address. For containers the configured IP addresses will be implicitly added.

log_level_in: <alert | crit | debug | emerg | err | info | nolog | notice | warning>

Log level for incoming traffic.

log_level_out: <alert | crit | debug | emerg | err | info | nolog | notice | warning>

Log level for outgoing traffic.

macfilter: <boolean>

Enable/disable MAC address filter.

ndp: <boolean>

Enable NDP.

policy_in: <ACCEPT | DROP | REJECT>

Input policy.

policy_out: <ACCEPT | DROP | REJECT>

Output policy.

radv: <boolean>

Allow sending Router Advertisement.

[RULES]

This sections contains VM/Container firewall rules.

[IPSET <name>]

IP set definitions.

[ALIASES]

IP Alias definitions.

Enabling the Firewall for VMs and Containers

Each virtual network device has its own firewall enable flag. So you can selectively enable the firewall for each interface. This is required in addition to the general firewall enable option.

The firewall requires a special network device setup, so you need to restart the VM/container after enabling the firewall on a network interface.

Firewall Rules

Firewall rules consists of a direction (IN or OUT) and an action (ACCEPT, DENY, REJECT). You can also specify a macro name. Macros contain predefined sets of rules and options. Rules can be disabled by prefixing them with |.

Firewall rules syntax
[RULES]

DIRECTION ACTION [OPTIONS]
|DIRECTION ACTION [OPTIONS] # disabled rule

DIRECTION MACRO(ACTION) [OPTIONS] # use predefined macro

The following options can be used to refine rule matches.

-dest <string>

Restrict packet destination address. This can refer to a single IP address, an IP set (+ipsetname) or an IP alias definition. You can also specify an address range like 20.34.101.207-201.3.9.99, or a list of IP addresses and networks (entries are separated by comma). Please do not mix IPv4 and IPv6 addresses inside such lists.

-dport <string>

Restrict TCP/UDP destination port. You can use service names or simple numbers (0-65535), as defined in /etc/services. Port ranges can be specified with \d+:\d+, for example 80:85, and you can use comma separated list to match several ports or ranges.

-iface <string>

Network interface name. You have to use network configuration key names for VMs and containers (net\d+). Host related rules can use arbitrary strings.

-proto <string>

IP protocol. You can use protocol names (tcp/udp) or simple numbers, as defined in /etc/protocols.

-source <string>

Restrict packet source address. This can refer to a single IP address, an IP set (+ipsetname) or an IP alias definition. You can also specify an address range like 20.34.101.207-201.3.9.99, or a list of IP addresses and networks (entries are separated by comma). Please do not mix IPv4 and IPv6 addresses inside such lists.

-sport <string>

Restrict TCP/UDP source port. You can use service names or simple numbers (0-65535), as defined in /etc/services. Port ranges can be specified with \d+:\d+, for example 80:85, and you can use comma separated list to match several ports or ranges.

Here are some examples:

[RULES]
IN SSH(ACCEPT) -i net0
IN SSH(ACCEPT) -i net0 # a comment
IN SSH(ACCEPT) -i net0 -source 192.168.2.192 # only allow SSH from 192.168.2.192
IN SSH(ACCEPT) -i net0 -source 10.0.0.1-10.0.0.10 # accept SSH for ip range
IN SSH(ACCEPT) -i net0 -source 10.0.0.1,10.0.0.2,10.0.0.3 #accept ssh for ip list
IN SSH(ACCEPT) -i net0 -source +mynetgroup # accept ssh for ipset mynetgroup
IN SSH(ACCEPT) -i net0 -source myserveralias #accept ssh for alias myserveralias

|IN SSH(ACCEPT) -i net0 # disabled rule

IN  DROP # drop all incoming packages
OUT ACCEPT # accept all outgoing packages

Security Groups

A security group is a collection of rules, defined at cluster level, which can be used in all VMs' rules. For example you can define a group named “webserver” with rules to open the http and https ports.

# /etc/pve/firewall/cluster.fw

[group webserver]
IN  ACCEPT -p tcp -dport 80
IN  ACCEPT -p tcp -dport 443

Then, you can add this group to a VM’s firewall

# /etc/pve/firewall/<VMID>.fw

[RULES]
GROUP webserver

IP Aliases

IP Aliases allow you to associate IP addresses of networks with a name. You can then refer to those names:

  • inside IP set definitions

  • in source and dest properties of firewall rules

Standard IP Alias local_network

This alias is automatically defined. Please use the following command to see assigned values:

# pve-firewall localnet
local hostname: example
local IP address: 192.168.2.100
network auto detect: 192.168.0.0/20
using detected local_network: 192.168.0.0/20

The firewall automatically sets up rules to allow everything needed for cluster communication (corosync, API, SSH) using this alias.

The user can overwrite these values in the cluster.fw alias section. If you use a single host on a public network, it is better to explicitly assign the local IP address

#  /etc/pve/firewall/cluster.fw
[ALIASES]
local_network 1.2.3.4 # use the single ip address

IP Sets

IP sets can be used to define groups of networks and hosts. You can refer to them with ‘+name` in the firewall rules’ source and dest properties.

The following example allows HTTP traffic from the management IP set.

IN HTTP(ACCEPT) -source +management

Standard IP set management

This IP set applies only to host firewalls (not VM firewalls). Those IPs are allowed to do normal management tasks (PVE GUI, VNC, SPICE, SSH).

The local cluster network is automatically added to this IP set (alias cluster_network), to enable inter-host cluster communication. (multicast,ssh,…)

# /etc/pve/firewall/cluster.fw

[IPSET management]
192.168.2.10
192.168.2.10/24

Standard IP set blacklist

Traffic from these IPs is dropped by every host’s and VM’s firewall.

# /etc/pve/firewall/cluster.fw

[IPSET blacklist]
77.240.159.182
213.87.123.0/24

Standard IP set ipfilter-net*

These filters belong to a VM’s network interface and are mainly used to prevent IP spoofing. If such a set exists for an interface then any outgoing traffic with a source IP not matching its interface’s corresponding ipfilter set will be dropped.

For containers with configured IP addresses these sets, if they exist (or are activated via the general IP Filter option in the VM’s firewall’s options tab), implicitly contain the associated IP addresses.

For both virtual machines and containers they also implicitly contain the standard MAC-derived IPv6 link-local address in order to allow the neighbor discovery protocol to work.

/etc/pve/firewall/<VMID>.fw

[IPSET ipfilter-net0] # only allow specified IPs on net0
192.168.2.10

Services and Commands

The firewall runs two service daemons on each node:

  • pvefw-logger: NFLOG daemon (ulogd replacement).

  • pve-firewall: updates iptables rules

There is also a CLI command named pve-firewall, which can be used to start and stop the firewall service:

# pve-firewall start
# pve-firewall stop

To get the status use:

# pve-firewall status

The above command reads and compiles all firewall rules, so you will see warnings if your firewall configuration contains any errors.

If you want to see the generated iptables rules you can use:

# iptables-save

Tips and Tricks

How to allow FTP

FTP is an old style protocol which uses port 21 and several other dynamic ports. So you need a rule to accept port 21. In addition, you need to load the ip_conntrack_ftp module. So please run:

modprobe ip_conntrack_ftp

and add ip_conntrack_ftp to /etc/modules (so that it works after a reboot).

Suricata IPS integration

If you want to use the Suricata IPS (Intrusion Prevention System), it’s possible.

Packets will be forwarded to the IPS only after the firewall ACCEPTed them.

Rejected/Dropped firewall packets don’t go to the IPS.

Install suricata on proxmox host:

# apt-get install suricata
# modprobe nfnetlink_queue

Don’t forget to add nfnetlink_queue to /etc/modules for next reboot.

Then, enable IPS for a specific VM with:

# /etc/pve/firewall/<VMID>.fw

[OPTIONS]
ips: 1
ips_queues: 0

ips_queues will bind a specific cpu queue for this VM.

Available queues are defined in

# /etc/default/suricata
NFQUEUE=0

Notes on IPv6

The firewall contains a few IPv6 specific options. One thing to note is that IPv6 does not use the ARP protocol anymore, and instead uses NDP (Neighbor Discovery Protocol) which works on IP level and thus needs IP addresses to succeed. For this purpose link-local addresses derived from the interface’s MAC address are used. By default the NDP option is enabled on both host and VM level to allow neighbor discovery (NDP) packets to be sent and received.

Beside neighbor discovery NDP is also used for a couple of other things, like autoconfiguration and advertising routers.

By default VMs are allowed to send out router solicitation messages (to query for a router), and to receive router advertisement packets. This allows them to use stateless auto configuration. On the other hand VMs cannot advertise themselves as routers unless the “Allow Router Advertisement” (radv: 1) option is set.

As for the link local addresses required for NDP, there’s also an “IP Filter” (ipfilter: 1) option which can be enabled which has the same effect as adding an ipfilter-net* ipset for each of the VM’s network interfaces containing the corresponding link local addresses. (See the Standard IP set ipfilter-net* section for details.)

Ports used by Proxmox VE

  • Web interface: 8006

  • VNC Web console: 5900-5999

  • SPICE proxy: 3128

  • sshd (used for cluster actions): 22

  • rpcbind: 111

  • corosync multicast (if you run a cluster): 5404, 5405 UDP