Ubuntu 18.04.2 LTS
fail2ban/bionic,bionic,now 0.10.2-2 all [installed]

only changed /etc/fail2ban/jail.d/defaults-debian.conf to:
[sshd]
enabled = true
port = 22
action = iptables-multiport
logpath = /var/log/auth.log
maxretry = 2
bantime = 3600

restarted the daemon with sysctemctl
then trying to fail 2+ attempts from the same ext IP and it doesn't quite seem to work:
$:/etc/fail2ban/jail.d# fail2ban-client status sshd
Status for the jail: sshd
|- Filter
|  |- Currently failed: 0
|  |- Total failed: 0
|  `- File list:    /var/log/auth.log
`- Actions
   |- Currently banned: 0
   |- Total banned: 0
   `- Banned IP list:

log upon service restart says:
2019-04-29 15:13:33,406 fail2ban.transmitter    [2797]: WARNING Command ['status', 'ssh'] has failed. Received UnknownJailException('ssh',)
2019-04-29 15:14:46,624 fail2ban.server         [2797]: INFO    Shutdown in progress...
2019-04-29 15:14:46,624 fail2ban.server         [2797]: INFO    Stopping all jails
2019-04-29 15:14:46,625 fail2ban.filter         [2797]: INFO    Removed logfile: '/var/log/auth.log'
2019-04-29 15:14:46,984 fail2ban.actions        [2797]: NOTICE  [sshd] Flush ticket(s) with iptables-multiport
2019-04-29 15:14:46,985 fail2ban.jail           [2797]: INFO    Jail 'sshd' stopped
2019-04-29 15:14:46,985 fail2ban.database       [2797]: INFO    Connection to database closed.
2019-04-29 15:14:46,985 fail2ban.server         [2797]: INFO    Exiting Fail2ban
2019-04-29 15:14:47,114 fail2ban.server         [3075]: INFO    --------------------------------------------------
2019-04-29 15:14:47,115 fail2ban.server         [3075]: INFO    Starting Fail2ban v0.10.2
2019-04-29 15:14:47,116 fail2ban.database       [3075]: INFO    Connected to fail2ban persistent database '/var/lib/fail2ban/fail2ban.sqlite3'
2019-04-29 15:14:47,117 fail2ban.jail           [3075]: INFO    Creating new jail 'sshd'
2019-04-29 15:14:47,119 fail2ban.jail           [3075]: INFO    Jail 'sshd' uses poller {}
2019-04-29 15:14:47,119 fail2ban.jail           [3075]: INFO    Initiated 'polling' backend
2019-04-29 15:14:47,120 fail2ban.filter         [3075]: INFO      maxLines: 1
2019-04-29 15:14:47,140 fail2ban.server         [3075]: INFO    Jail sshd is not a JournalFilter instance
2019-04-29 15:14:47,140 fail2ban.filter         [3075]: INFO    Added logfile: '/var/log/auth.log' (pos = 7070725, hash = 3000f5568634f4f210c166b92c6a0e5f9047f0f3)
2019-04-29 15:14:47,140 fail2ban.filter         [3075]: INFO      encoding: UTF-8
2019-04-29 15:14:47,141 fail2ban.filter         [3075]: INFO      maxRetry: 2
2019-04-29 15:14:47,141 fail2ban.filter         [3075]: INFO      findtime: 600
2019-04-29 15:14:47,141 fail2ban.actions        [3075]: INFO      banTime: 3600
2019-04-29 15:14:47,142 fail2ban.jail           [3075]: INFO    Jail 'sshd' started

and I don't see anything in IPTABLES, well expected in this case. yet:
Chain INPUT (policy ACCEPT)
target     prot opt source               destination

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination