Thank you for the quick answer. That explains part of it. Still, `tcp flags & (fin|syn|rst|ack) != syn` becomes `tcp != syn / fin,syn,rst,ack` and both expressions are interpreted as equal after parsing. Can you please point me to any documentation of operator expression syntax/precedence ? On Mon, Nov 6, 2023, at 08:28, Pablo Neira Ayuso wrote: > On Mon, Nov 06, 2023 at 08:11:09AM -0500, Aurel Wisse wrote: > > Hi, > > > > I am starting to learn nftables (only superficial previous experience with iptables) and I can't find certain syntax rules for expressions and operators in the wiki or the man page. > > > > I am learning by listing the rulesets of certain predefined firewalls (fw4/OpenWRT, UFW) and I notice that certain listed rules contain operators which I can guess (hopefully correctly) from context and the original syntax in the imported file, but I would like to be sure in order not to make mistakes while building my own firewall. > > > > Examples: > > > > tcp flags & (fin|syn|rst|ack) != syn jump syn_flood > > > > becomes > > > > tcp flags syn / fin,syn,rst,ack jump syn_flood > > That is a bug in nftables v1.0.2, here with recent version it shows: > > tcp flags != syn / fin,syn,rst,ack > > > So, from context, commas without spaces around them are equivalent to logical or with precedence over "/", and "/" is somehow "!=" ?? . Where did the & (logical AND?) operator go? > > > > This is just one example. I would like to learn the full operator syntax rules in nftables. Any ideas where I should look ? Do I have to dig into the source code ? > > > > Thanks > > > > Aurel > > > > nftables v1.0.2 (Lester Gooch) > > Pop-OS (6.5.6-76060506-generic) >
