jails jail: dns: jail_set: Invalid argument

[Ferocious1881]

When I try jail -crm -f dns.conf, where dns.conf is the following

dns {
exec.start = "/bin/sh /etc/rc";
exec.stop = "/bin/sh /etc/rc.shutdown";
exec.consolelog = "/var/log/jail_console_${name}.log";

allow.raw_sockets;
exec.clean;
mount.devfs;
enforce_statfs = 5;
devfs_ruleset = 5;

path = "/jails/${name}";
host.hostname = "${name}";

$unterid = "3";
$id = "${unterid}";
$ip = "192.168.0.${unterid}/24";
$gateway = "192.168.0.1";
$bridge = "bridge0";
$epair = "epair${id}";

vnet;
vnet.interface = "${epair}b";

exec.prestart  = "/sbin/ifconfig ${epair} create up";
exec.prestart += "/sbin/ifconfig ${epair}a up descr jail:${name}";
exec.prestart += "/sbin/ifconfig ${bridge} addm ${epair}a up";
exec.prestart += "/sbin/ifconfig ${epair}a ether 02:16:b1:a5:e9:0a";
exec.prestart += "/sbin/ifconfig ${epair}b ether 02:16:b1:a5:e9:0b";
exec.start    += "/sbin/ifconfig ${epair}b ${ip} up";
exec.start    += "/sbin/route add default ${gateway}";
exec.poststop = "/sbin/ifconfig ${bridge} deletem ${epair}a";
exec.poststop += "/sbin/ifconfig ${epair}a destroy";
}

I get the following:

jail: dns: jail_set: Invalid argument

I already destroyed the network device, before creating, and put a fresh bsdinstall jail in the jail's root.