Firewall Rules
The Cumulus Linux default firewall rules protect the switch control plane and CPU from DOS and other potentially malicious network attacks.
In Cumulus Linux 5.8 and earlier, the set of default firewall rules are more open; Cumulus Linux accepts packets from all addresses and protocols. Cumulus Linux 5.9 and later provides a set of default firewall rules that allows only specific addresses and ports, and drops disallowed packets.
The default set of firewall rules consists of IP and transport level rules. To block specific layer 2 packets such as ARP, LLDP, or STP or any packets sent to the CPU as part of generic traps, you must configure separate rules using control plane ACLs in the INPUT or OUTPUT chain of ebtables. See Access Control List Configuration.
Default Firewall Rule Files without NVUE
Cumulus Linux enables the default firewall rules on the switch even before you apply NVUE configuration for the first time. The default firewall rules are in the 01control_plane.rules and 98control_plane_whitelist.rules files in the /etc/cumulus/acl/policy.d/ directory.
If you prefer to configure the switch by editing Linux files instead of running NVUE commands, you can make changes to these files to add additional rules.
DoS Rules
DoS rules protect the switch control plane and CPU from DOS attacks. Cumulus Linux provides firewall DoS rules to:
- Allow only internal traffic to the loopback interfaces.
- Accept already established connections and outbound traffic.
- Set the
- allowoption to color the packets from a specific interface. You can set this option if you need to apply different policies for differentethinterfaces. - Drop packets if the first TCP segment is not SYN.
- Drop fragmented IP packets.
- Drop Christmas tree packets; packets with all TCP flags set.
- Drop NULL packets.
- Drop invalid packets.
- Drop strange MSS values.
- Provide brute-force protection.
- Drop packets with routing Header Type 0.
- Drop packets with a hop limit greater than 1.
- Limit excessive TCP reset packets.
- Protect against SYN flood.
- Rate limit new TCP connections for each IP address.
- Log all remaining packets, then drop them.
Whitelist Rules
Whitelist rules specify the services or application ports enabled on the switch. Cumulus Linux provides firewall whitelist rules to enable TCP ports and UDP ports.
The following table lists the ports that Cumulus Linux enables by default.
| Protocol | Port | Application |
|---|---|---|
| TCP | 22 | SSH |
| TCP | 179 | BGP |
| UDP | 68 | DHCP Client |
| UDP | 67 | DHCP Server |
| UDP | 123 | NTP |
| UDP | 323 | Chrony |
| UDP | 161 | SNMP |
| UDP | 6306 | A multicast socket used internally. |
| UDP | 69 | TFTP |
| TCP/UDP | 389 | LDAP |
| UDP | 1812,1813 | RADIUS |
| TCP/UDP | 49 | TACACS |
| TCP/UDP | 53 | DNS |
| TCP | 8765 | NVUE NGINX |
| UDP | 6343, 6344 | sFlow |
| UDP | 514 | remote syslog |
| UDP | 3786 | BFD |
| UDP | 4784 | Multi-Hop BFD |
| TCP | 5342 | MLAG |
| UDP | 4789 | VXLAN |
| UDP | 319,320 | PTP |
| TCP | 443 | HTTPS |
| TCP | 9339 | gNMI |
| TCP | 31980,31982 | NETQ Agent |
| OSPF | NA | NA |
| UDP | 53 (SPORT) | DNS response packets |
| TCP | 9999 | XMLRPC |
| ICMP | NA | Ping |
| PIM | NA | NA |
| IGMP | NA | NA |
| VRRP | NA | NA |
| TCP | 639 | MSDP |
Unset the Default Firewall Rules
To unset the default firewall rules and use the setting in Cumulus Linux 5.8 and earlier that accepts packets from all addresses and protocols:
cumulus@switch:~$ nv unset system control-plane acl acl-default-dos
cumulus@switch:~$ nv unset system control-plane acl acl-default-whitelist
cumulus@switch:~$ nv config apply
To set the firewall rules back to the default setting:
cumulus@switch:~$ nv set system control-plane acl acl-default-dos inbound
cumulus@switch:~$ nv set system control-plane acl acl-default-whitelist inbound
cumulus@switch:~$ nv config apply
Add Firewall Rules
You cannot modify the acl-default-dos and acl-default-whitelist rules. However, you can append or insert additional rules. Additionally, you can add your own ACLs and apply them on the control plane; control plane ACLs take precedence over acl-default-whitelist rules when the default firewall rules are enabled.
If you use non-default ports for an application, NVIDIA recommends that you add a whitelist rule for the non-default port. For example, if you use ports 3020 and 3022 for radius server accounting and authentication instead of 1812 and 1813, you can add the following whitelist rules:
cumulus@switch:~$ nv set acl acl-default-whitelist rule 73 match ip udp source-port 3020
cumulus@switch:~$ nv set acl acl-default-whitelist rule 73 match ip connection-state new
cumulus@switch:~$ nv set acl acl-default-whitelist rule 73 match ip connection-state established
cumulus@switch:~$ nv set acl acl-default-whitelist rule 73 action permit
cumulus@switch:~$ nv set acl acl-default-whitelist rule 74 match ip udp source-port 3022
cumulus@switch:~$ nv set acl acl-default-whitelist rule 74 match ip connection-state new
cumulus@switch:~$ nv set acl acl-default-whitelist rule 74 match ip connection-state established
cumulus@switch:~$ nv set acl acl-default-whitelist rule 74 action permit
cumulus@switch:~$ nv config apply
Hashlimit and Recent List Match
For firewall IPv4 type ACLs on the control plane, you can match on hashlimit and recent list. These matches are not supported for data plane ACLs, which get installed in hardware.
Cumulus Linux provides the following commands for matching on hashlimit.
| Command | Description |
|---|---|
nv set acl <acl> rule <rule> match ip hashlimit name |
The hashlimit name. |
nv set acl <acl> rule <rule> match ip hashlimit mode |
The hashlimit mode. You can specify src-ip or dst-ip. |
nv set acl <acl> rule <rule> match ip hashlimit burst |
The hashlimit burst rate; the maximum number of packets to match in a burst. You can specify a value between 1 and 4294967295. |
nv set acl <acl> rule <rule> match ip hashlimit rate-above |
The limit rate. You can specify <integer/second>, <integer/min>, or <integer/hour>. The maximum rate is 1000000/second. |
nv set acl <acl> rule <rule> match ip hashlimit expire |
The number of milliseconds after which hash entries expire. |
nv set acl <acl> rule <rule> match ip hashlimit source-mask |
The source address grouping prefix length. |
nv set acl <acl> rule <rule> match ip hashlimit destination-mask |
The destination address grouping prefix length. |
The following example shows an ACL that drops packets when matching on hashlimit.
To configure the hashlimit match, you must set the hashlimit name, mode, expiration, burst, and rate; the source mask and destination mask settings are optional.
cumulus@switch:~$ nv set acl EXAMPLE1 type ipv4
cumulus@switch:~$ nv set acl EXAMPLE1 rule 10 match ip protocol tcp
cumulus@switch:~$ nv set acl EXAMPLE1 rule 10 match ip source-ip 10.0.14.2/32
cumulus@switch:~$ nv set acl EXAMPLE1 rule 10 match ip hashlimit name ssh
cumulus@switch:~$ nv set acl EXAMPLE1 rule 10 match ip hashlimit mode src-ip
cumulus@switch:~$ nv set acl EXAMPLE1 rule 10 match ip hashlimit expire 100
cumulus@switch:~$ nv set acl EXAMPLE1 rule 10 match ip hashlimit burst 100
cumulus@switch:~$ nv set acl EXAMPLE1 rule 10 match ip hashlimit rate-above 100/second
cumulus@switch:~$ nv set acl EXAMPLE1 rule 10 match ip hashlimit source-mask 32
cumulus@switch:~$ nv set acl EXAMPLE1 rule 10 action deny
cumulus@switch:~$ nv set interface swp1 acl EXAMPLE1 inbound control-plane
cumulus@switch:~$ nv config apply
NVUE writes this rule in the /etc/cumulus/acl/policy.d/50_nvue.rules file:
cumulus@switch:~$ sudo cat /etc/cumulus/acl/policy.d/50_nvue.rules
[iptables]
## ACL EXAMPLE1 in dir inbound on interface swp1 ##
# rule-id #10: #
-A INPUT -i swp1 -m comment --comment rule_id:10,acl_name:EXAMPLE1,dir:inbound,interface_id:swp1 -s 10.0.14.2/32 -p tcp -m hashlimit --hashlimit-name ssh --hashlimit-mode srcip --hashlimit-htable-expire 100 --hashlimit-burst 100 --hashlimit-above 100/second --hashlimit-srcmask 32 -j DROP
You can also show the ACL settings with the nv show acl <acl> command:
cumulus@switch:~$ nv show acl EXAMPLE1
applied
---- -------
type ipv4
rule
=======
Number Summary
------ ------------------------------------------
10 match.ip.hashlimit.burst: 100
match.ip.hashlimit.expire: 100
match.ip.hashlimit.mode: src-ip
match.ip.hashlimit.name: ssh
match.ip.hashlimit.rate-above: 100/second
match.ip.hashlimit.source-mask: 32
match.ip.protocol: tcp
match.ip.source-ip: 10.0.14.2/32
Cumulus Linux provides the following commands to match on recent list.
| Command | Description |
|---|---|
nv set acl <acl> rule <rule> match ip recent-list name |
The recent module name. |
nv set acl <acl> rule <rule> match ip recent-list action |
The recent action. You can specify set or update. |
nv set acl <acl> rule <rule> match ip recent-list hit-count |
The number of hits in an interval. You can specify a value between 1 and 4294967295. |
nv set acl <acl> rule <rule> match ip recent-list update-interval |
The update interval. You can specify a value between 1 and 4294967295. |
The following example shows an ACL that drops packets when matching on recent-list.
To configure the recent module match, you must set the recent list name and action; other recent-list settings are optional.
cumulus@switch:~$ nv set acl EXAMPLE1 type ipv4
cumulus@switch:~$ nv set acl EXAMPLE1 rule 10 match ip protocol tcp
cumulus@switch:~$ nv set acl EXAMPLE1 rule 10 match ip source-ip 10.0.14.2/32
cumulus@switch:~$ nv set acl EXAMPLE1 rule 10 match ip recent-list name bruteforce
cumulus@switch:~$ nv set acl EXAMPLE1 rule 10 match ip recent-list action set
cumulus@switch:~$ nv set acl EXAMPLE1 rule 10 match ip recent-list hit-count 5
cumulus@switch:~$ nv set acl EXAMPLE1 rule 10 match ip recent-list update-interval 3600
cumulus@switch:~$ nv set acl EXAMPLE1 rule 10 action deny
cumulus@switch:~$ nv set interface swp1 acl EXAMPLE1 inbound control-plane
cumulus@switch:~$ nv config apply
NVUE writes this rule in the /etc/cumulus/acl/policy.d/50_nvue.rules file:
cumulus@switch:~$ sudo cat /etc/cumulus/acl/policy.d/50_nvue.rules
[iptables]
## ACL EXAMPLE1 in dir inbound on interface swp1 ##
# rule-id #10: #
-A INPUT -i swp1 -m comment --comment rule_id:10,acl_name:EXAMPLE1,dir:inbound,interface_id:swp1 -s 10.0.14.2/32 -p tcp -m recent --name bruteforce --set --hitcount 5 --seconds 360 -j DROP
You can also show the ACL settings with the NVUE nv show acl <acl> command.
Show Firewall Rules
To show the DoS rules, run the nv show acl acl-default-dos command:
cumulus@switch:~$ nv show acl acl-default-dos
applied pending
---- ------- -------
type ipv4 ipv4
rule
=======
Number Summary
------ ----------------------------------------
30 match.ip.protocol: tcp
40 match.ip.protocol: tcp
41 match.ip.protocol: tcp
42 match.ip.protocol: tcp
50
60 match.ip.protocol: tcp
70 match.ip.protocol: tcp
80 match.ip.protocol: tcp
90 match.ip.protocol: tcp
match.ip.tcp.all-mss-except: 536-65535
100 match.ip.recent-list.action: set
match.ip.tcp.dest-port: 22
110 match.ip.recent-list.action: update
match.ip.recent-list.hit-count: 50
match.ip.recent-list.update-interval: 60
match.ip.tcp.dest-port: 22
120 match.ip.hashlimit.burst: 2
match.ip.hashlimit.expire: 30000
match.ip.hashlimit.mode: src-ip
match.ip.hashlimit.name: TCPRST
match.ip.hashlimit.rate-above: 5/min
match.ip.hashlimit.source-mask: 32
match.ip.protocol: tcp
130 match.ip.hashlimit.burst: 30
match.ip.hashlimit.expire: 30000
match.ip.hashlimit.mode: src-ip
match.ip.hashlimit.name: TCPGENERAL
match.ip.hashlimit.rate-above: 50/second
match.ip.hashlimit.source-mask: 32
match.ip.protocol: tcp
Run the nv show acl acl-default-dos --rev=applied -o json command to show additional information, such as the connection state, hit count and update interval:
cumulus@switch:~$ nv show acl acl-default-dos --rev=applied -o json
{
"rule": {
"100": {
"action": {
"recent": {}
},
"match": {
"ip": {
"connection-state": {
"new": {}
},
"recent-list": {
"action": "set"
},
"tcp": {
"dest-port": {
"22": {}
}
}
}
}
},
"110": {
"action": {
"deny": {}
},
"match": {
"ip": {
"connection-state": {
"new": {}
},
"recent-list": {
"action": "update",
"hit-count": 50,
"update-interval": 60
},
"tcp": {
"dest-port": {
"22": {}
}
}
}
}
},
...
To show the whitelist rules, run the nv show acl acl-default-whitelist command:
cumulus@switch:~$ nv show acl acl-default-whitelist
applied pending
---- ------- -------
type ipv4 ipv4
rule
=======
Number Summary
------ -------------------------------------------------
5 match.ip.protocol: tcp
match.ip.tcp.dest-port: ssh
10 match.ip.protocol: tcp
match.ip.tcp.dest-port: bgp
15 match.ip.protocol: tcp
match.ip.tcp.dest-port: ldap
20 match.ip.protocol: tcp
match.ip.tcp.dest-port: 8765
25 match.ip.protocol: tcp
match.ip.tcp.dest-port: https
30 match.ip.protocol: tcp
match.ip.tcp.dest-port: clag
35 match.ip.protocol: tcp
match.ip.tcp.source-port: 49
40 match.ip.protocol: udp
match.ip.udp.dest-port: dhcp-client
45 match.ip.protocol: udp
match.ip.udp.dest-port: dhcp-server
50 match.ip.protocol: udp
match.ip.udp.dest-port: ntp
55 match.ip.protocol: udp
match.ip.udp.dest-port: 323
60 match.ip.protocol: udp
match.ip.udp.dest-port: snmp
65 match.ip.protocol: udp
match.ip.udp.dest-port: tftp
70 match.ip.protocol: udp
match.ip.udp.dest-port: ldap
75 match.ip.protocol: udp
match.ip.udp.source-port: 1812
80 match.ip.protocol: udp
match.ip.udp.source-port: 1813
85 match.ip.protocol: udp
match.ip.udp.dest-port: 6343
90 match.ip.protocol: udp
match.ip.udp.dest-port: 6344
95 match.ip.protocol: udp
match.ip.udp.dest-port: 514
100 match.ip.protocol: udp
match.ip.udp.dest-port: bfd
105 match.ip.protocol: udp
match.ip.udp.dest-port: bfd-multihop
110 match.ip.protocol: udp
match.ip.udp.dest-port: 4789
115 match.ip.protocol: udp
match.ip.udp.dest-port: 319
120 match.ip.protocol: udp
match.ip.udp.dest-port: 320
125 match.ip.protocol: tcp
match.ip.tcp.dest-port: 9339
130 match.ip.protocol: tcp
match.ip.tcp.dest-port: 31980
match.ip.tcp.dest-port: 31982
135 match.ip.protocol: tcp
match.ip.tcp.dest-port: 639
140 match.ip.protocol: udp
match.ip.udp.source-port: 53
145 match.ip.protocol: tcp
match.ip.tcp.dest-port: 9999
150 match.ip.protocol: ospf
155 match.ip.protocol: pim
160 match.ip.protocol: vrrp
165 match.ip.protocol: igmp
170 match.ip.protocol: icmp
9999 Log Level: 3
action.log.log-prefix: IPTables-Dropped-<Domain>:
Log Rate: 1
Run the nv show acl acl-default-whitelist --rev=applied -o json command to show additional information, such as the connection state:
cumulus@switch:~$ nv show acl acl-default-whitelist --rev=applied -o json
{
"rule": {
"10": {
"action": {
"permit": {}
},
"match": {
"ip": {
"connection-state": {
"established": {},
"new": {}
},
"protocol": "tcp",
"tcp": {
"dest-port": {
"bgp": {}
}
}
}
}
},
"100": {
"action": {
"permit": {}
},
"match": {
"ip": {
"connection-state": {
"established": {},
"new": {}
},
"protocol": "udp",
"udp": {
"dest-port": {
"bfd": {}
}
}
}
}
...
To show information about a specific rule, run the nv show acl acl-default-dos rule <rule> command:
cumulus@switch:~$ nv show acl acl-default-dos rule 30
applied pending
------------ ------- -------
match
ip
protocol tcp tcp
Run the nv show acl acl-default-dos rule <rule> --rev=applied -o json command to see additional information, such as the connection state:
cumulus@switch:~$ nv show acl acl-default-dos rule 30 --rev=applied -o json
{
"action": {
"permit": {}
},
"match": {
"ip": {
"connection-state": {
"established": {},
"related": {}
},
"protocol": "tcp"
}
}
}
syslog Messages
Default firewall rules include a log rule for packets that arrive in the control plane and do not match user defined or default firewall rules. The switch generates a log message in /var/log/syslog for packets that match the log rule.