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How is a chain assigned a priority in nftables?
Each nftables base chain is assigned a priority that defines its ordering among other base chains, flowtables, and Netfilter internal operations at the same hook. For example, a chain on the prerouting hook with priority -300 will be placed before connection tracking operations.
How does the type statement work in nftables?
Unlike the base checks chain, in this one we tell nftables what kind of packets we would like to accept and what we would like to do with them by default. With the type statement, we tell nftables our chain will be of type filter (filtering packets), and it will do so on input packets (incoming packets).
What happens when packets are not handled in nftables?
That means all packets that are not handled are dropped by default. Packets from the loopback interface are generally safe, so just accept everything coming from there. There are two ways to move the flow of the rule processing to another chain: jump and goto.
Why are there no hooks for the Nat chain?
This means that the chain type for the specified family is not available in that hook. In the example above, the problem is that the available hooks for the NAT chain type are: prerouting, input, output and postrouting. Question 4. How do nftables and iptables interact when used on the same system?
How to create a list of nftables rules?
% nft list chain filter ouput table ip filter { chain output { type filter hook output priority 0; ip daddr 8 .8.8.8 counter packets 0 bytes 0 tcp dport ssh counter packets 0 bytes 0 } } There are plenty of output text modifiers than can be used when listing your rules, to for example, translate IP addresses to DNS names, TCP protocols, etc.
When to register a trace chain in nftables?
This example assumes you have an existing raw prerouting chain (at priority -300), hence, this is registering a trace chain right before this chain (at priority -301). Once you are done with rule tracing, you can just delete this chain to disable it:
When to use handle as reference in nftables?
If you want to add a rule at a given position, you have to use the handle as reference: % nft list table filter -n -a table filter { chain output { type filter hook output priority 0; ip protocol tcp counter packets 82 bytes 9680 # handle 8 ip saddr 127 .0.0.1 ip daddr 127 .0.0.6 drop # handle 7 } }