Information
Chains are containers for rules. They exist in two kinds, base chains and regular chains. A base chain is an entry point for packets from the networking stack, a regular chain may be used as jump target and is used for better rule organization.
Note: - IF - Firewalld is in use, this recommendation can be skipped.
If a base chain doesn't exist with a hook for input, forward, and delete, packets that would flow through those chains will not be touched by nftables.
Solution
- IF - NFTables utility is in use on your system:
Run the following command to create the base chains:
# nft create chain inet <table name> <base chain name> { type filter hook <(input|forward|output)> priority 0 ; }
Example:
# nft create chain inet filter input { type filter hook input priority 0 ; }
# nft create chain inet filter forward { type filter hook forward priority 0 ; }
# nft create chain inet filter output { type filter hook output priority 0 ; }
Note: use the add command if the create command returns an error due to the chain already existing.
Impact:
If configuring over ssh, creating a base chain with a policy of drop will cause loss of connectivity.
Ensure that a rule allowing ssh has been added to the base chain prior to setting the base chain's policy to drop