Translate to different size

is possible to remove or disable by default from /opt/vyatta/share/perl5/Vyatta/SrcNatRule.pm

if (!($outside_addr_mask == $src_addr_mask)) {
  return ("\nsource address should be a subnet with the same network prefix as translation address" .
          "\nwhen translation address is defined with a prefix for static network mapping "
          , undef);
}

we need translate from /8 to /27 etc.
thank you.

You already can do this by entering IP range as translation address.
When you use network address as translation address, then VyOS trying to configure NETMAP rule (not SNAT).

IP range is problem, because vyos change translation address per connection…

OK. We understand source of your problem now. Corresponding feature request opened in Phabricator.

thank you… we use vyos NAT for 40.000 users… and this feature will be good