The argument -n shows the addresses and other information that use names in numeric format. The -a argument is used to display each rule's handle (i.e., a numerical identifier).
Chains
type refers to the kind of chain to be created. Possible types are:
filter: Supported by arp, bridge, ip, ip6 and inet table families.
route: Mark packets (like mangle for the output hook, for other hooks use the type filter instead), supported by ip and ip6.
nat: In order to perform Network Address Translation, supported by ip and ip6.
hook refers to an specific stage of the packet while it's being processed through the kernel. More info in Netfilter hooks.
The hooks for ip, ip6 and inet families are: prerouting, input, forward, output, postrouting.
The hooks for arp family are: input, output.
The bridge family handles ethernet packets traversing bridge devices.
The hooks for netdev are: ingress, egress.
priority refers to a number used to order the chains or to set them between some Netfilter operations. Possible values are: NF_IP_PRI_CONNTRACK_DEFRAG (-400), NF_IP_PRI_RAW (-300), NF_IP_PRI_SELINUX_FIRST (-225), NF_IP_PRI_CONNTRACK (-200), NF_IP_PRI_MANGLE (-150), NF_IP_PRI_NAT_DST (-100), NF_IP_PRI_FILTER (0), NF_IP_PRI_SECURITY (50), NF_IP_PRI_NAT_SRC (100), NF_IP_PRI_SELINUX_LAST (225), NF_IP_PRI_CONNTRACK_HELPER (300).
policy is the default verdict statement to control the flow in the base chain. Possible values are: accept (default) and drop. Warning: Setting the policy to drop discards all packets thathave not been accepted by the ruleset.
Inserted rules are placed at the beginning of the chain, by default. However, if you specify a position handle, then the new rule is inserted just before the existing rule with that handle.
udplite sport 22udplite sport!=33-45udplite sport {33, 55, 67, 88}udplite sport {33-55 }udplite sport vmap {25:accept, 28:drop }udplite sport 1024 udplite dport 22
ct state { new, established, related, untracked }ct state!= relatedct state establishedct state 8
direction <value>
Direction of the packet relative to the connection
ct direction originalct direction!= originalct direction { reply, original }
status <status>
Status of the connection
ct status expected(ct status & expected)!= expectedct status { expected, seen-reply, assured, confirmed, snat, dnat, dying }
mark [set]
Mark of the connection
ct mark 0ct mark or 0x23== 0x11ct mark or 0x3!= 0x1ct mark and 0x23== 0x11ct mark and 0x3!= 0x1ct mark xor 0x23== 0x11ct mark xor 0x3!= 0x1ct mark 0x00000032ct mark!= 0x00000032ct mark 0x00000032-0x00000045ct mark!= 0x00000032-0x00000045ct mark { 0x32, 0x2222, 0x42de3 }ct mark { 0x32-0x2222, 0x4444-0x42de3 }ct mark set 0x11 xor 0x1331ct mark set 0x11333 and 0x11ct mark set 0x12 or 0x11ct mark set 0x11ct mark set markct mark set mark map {1: 10, 2: 20, 3: 30}
meta mark 0x4meta mark 0x00000032meta mark and 0x03== 0x01meta mark and 0x03!= 0x01meta mark!= 0x10meta mark or 0x03== 0x01meta mark or 0x03!= 0x01meta mark xor 0x03== 0x01meta mark xor 0x03!= 0x01meta mark set 0xffffffc8 xor 0x16meta mark set 0x16 and 0x16meta mark set 0xffffffe9 or 0x16meta mark set 0xffffffde and 0x16meta mark set 0x32 or 0xfffffmeta mark set 0xfffe xor 0x16
priority [set] <priority>
tc class id
meta priority nonemeta priority 0x1:0x1meta priority 0x1:0xffffmeta priority 0xffff:0xffffmeta priority set 0x1:0x1meta priority set 0x1:0xffffmeta priority set 0xffff:0xffff
statement is the action performed when the packet match the rule. It could be terminal and non-terminal. In a certain rule we can consider several non-terminal statements but only a single terminal statement.
Verdict statements
The verdict statement alters control flow in the ruleset and issues policy decisions for packets. The valid verdict statements are:
accept: Accept the packet and stop the remain rules evaluation.
drop: Drop the packet and stop the remain rules evaluation.
queue: Queue the packet to userspace and stop the remain rules evaluation.
continue: Continue the ruleset evaluation with the next rule.
return: Return from the current chain and continue at the next rule of the last chain. In a base chain it is equivalent to accept
jump <chain>: Continue at the first rule of <chain>. It will continue at the next rule after a return statement is issued
goto <chain>: Similar to jump, but after the new chain the evaluation will continue at the last chain instead of the one containing the goto statement
group <value> [queue-threshold <value>] [snaplen <value>] [prefix "<prefix>"]
log prefix aaaaa-aaaaaa group 2 snaplen 33log group 2 queue-threshold 2log group 2 snaplen 33
Reject
The default reject will be the ICMP type port-unreachable. The icmpx is only used for inet family support.
More information on the Rejecting_traffic page.
reject statement
with <protocol> type <type>
rejectreject with icmp type host-unreachablereject with icmp type net-unreachablereject with icmp type prot-unreachablereject with icmp type port-unreachablereject with icmp type net-prohibitedreject with icmp type host-prohibitedreject with icmp type admin-prohibitedreject with icmpv6 type no-routereject with icmpv6 type admin-prohibitedreject with icmpv6 type addr-unreachablereject with icmpv6 type port-unreachablereject with icmpx type host-unreachablereject with icmpx type no-routereject with icmpx type admin-prohibitedreject with icmpx type port-unreachableip protocol tcp reject with tcp reset
The nftables wiki has to say: The priority can be used to order the chains or to put them before or after some Netfilter internal operations. For example, a chain on the prerouting hook with the priority -300 will be placed before connection tracking operations.
Nftables doesn't have any default tables. Without a table being built, nftables will not filter network traffic. Note: adding rules to a running nftables can cause loss of connectivity to the system.
Basic Configuration. Initially, nftables starts with a completely empty ruleset; there are no predefined tables, chains, or rules. As a user (or admin), you first create the tables, add chains to the tables that hook into the Linux kernel as netfilter hooks, and then fill the chains with the appropriate rules.
nftables provides a simpler, more efficient alternative to iptables, with unified IPv4/IPv6 handling. Features like rule tracing and multi-action rules in nftables enhance network management. Transitioning to nftables offers better performance and simplicity, supported by tools like iptables-translate.
In the minimum slack rule, when two or more tasks compete with each other, one should choose the task with minimum total slack. and the best overall priority rule should be based on the minimum slack rule.
nftables utilizes the building blocks of the Netfilter infrastructure, such as the existing hooks into the networking stack, connection tracking system, userspace queueing component, and logging subsystem.
#netfilter (webchat) nftables is the successor to iptables. It replaces the existing iptables, ip6tables, arptables, and ebtables framework. It uses the Linux kernel and a new userspace utility called nft. nftables provides a compatibility layer for the iptables/ip6tables and framework.
A table for fail2ban needs to be added to nftables. An ip table is used to support both IPv4 and IPv6. The priority for the table is set high to reject connections before other rules are evaluated.
Ufw stands for Uncomplicated Firewall, and is a program for managing a netfilter firewall. It provides a command line interface and aims to be uncomplicated and easy to use. Note: It should be noted that UFW can use either iptables or nftables as the back-end firewall.
The principle of priority states simply that the earliest name applied properly to a taxon of animals is the correct scientific name, with the date of publication determined by the stated date on the publication or by other means if that information is not reliable.
Priority Sequencing Rules provide the guidance for the order in which the jobs are to be processed at a workstation. The application of different priority rules in job shop scheduling gives different order of scheduling.
Priority—Matching precedence of the flow entry. When a packet is matched with the flow table, only the highest priority flow entry that matches the packet is selected. Counters—Counts of the packets and bytes that match the flow entry.
Introduction: My name is Van Hayes, I am a thankful, friendly, smiling, calm, powerful, fine, enthusiastic person who loves writing and wants to share my knowledge and understanding with you.
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