Almost done, also implemented 'random' flag, looks ok? or change name? for example - flag, or flags

random: randomize source port mapping.

description main
nat-flags {
   persistent
   random
}
outbound-interface bond1
source {
    address 0.0.0.0/0
}
translation {
    address 10.10.10.5-10.10.10.20
}

Created pull request

https://github.com/vyos/vyatta-nat/blob/current/scripts/vyatta-update-src-nat.pl#L159

Can we add checks?

set nat source rule 10 translation address 1.1.1.50-1.1.120 persistent

If string contain "persistent" or node set to persistent; then

$cmd = "$IPTABLES -t nat -I $chain_name $ipt_rulenum " ."$rule_str" --persistent;

I don't know how it do with perl, it their documentations it's function names "index, rindex"
index - find a substring within a string
rindex - right-to-left substring search

It would be great if someone writes this check.

Since we had to revert to the old NAT implementation due to kernel issues, this had to be back-back-ported to the old Perl code as well.

Some implementation notes that the new version from current should account for:

• The port-mapping option should only be in source NAT because it's not available for --to-destination target.
• The port-mapping option is only valid for masquerade rules.
• Since kernel 5.0, there's no distinction between --random and --random-fully, so there's no reason to provide --random.
• The address-mapping option is only valid for non-masquerade rules but works for both SNAT and DNAT.

I also wonder if they should be boolean options since post-5.0 they both can have only two values. However, kernel authors may introduce new states, so maybe keep them as is for now.