Provided by: iptables_1.8.7-1ubuntu6_amd64 bug


       xtables-legacy — iptables using old getsockopt/setsockopt-based kernel api


       xtables-legacy  are  the original versions of iptables that use old getsockopt/setsockopt-
       based kernel interface.  This kernel interface has some  limitations,  therefore  iptables
       can  also  be used with the newer nf_tables based API.  See xtables-nft(8) for information
       about the xtables-nft variants of iptables.


       The xtables-legacy-multi binary can be linked to the traditional names:

            /sbin/iptables -> /sbin/iptables-legacy-multi
            /sbin/ip6tables -> /sbin/ip6tables-legacy-multi
            /sbin/iptables-save -> /sbin/ip6tables-legacy-multi
            /sbin/iptables-restore -> /sbin/ip6tables-legacy-multi

       The iptables version string will indicate whether the legacy API (get/setsockopt)  or  the
       new nf_tables API is used:
            iptables -V
            iptables v1.7 (legacy)


       When  inserting  a rule using iptables -A or iptables -I, iptables first needs to retrieve
       the current active ruleset, change it to include the new rule, and then  commit  back  the
       result.  This means that if two instances of iptables are running concurrently, one of the
       updates might be lost.  This can be worked around partially with the --wait option.

       There is also no method to monitor changes to the  ruleset,  except  periodically  calling
       iptables-legacy-save and checking for any differences in output.

       xtables-monitor(8)  will  need  the  xtables-nft(8)  versions  to  work, it cannot display
       changes made using the iptables-legacy tools.


       xtables-nft(8), xtables-translate(8)


       Rusty Russell originally wrote iptables, in early consultation with Michael Neuling.

                                            June 2018                           XTABLES-LEGACY(8)