There were some similiar bugs, but all of them seem fixed and all of them doesn't relate to TrueNAS 12 so I opened up this new one.

IPv6 stopped working for my jails. Originally jail was set to autoconf but somehow wasn't reachable any more so I set it to static configuration for testing. Eversince I did this, jail cannot be started, saying the default gateway wasn't reachable. I double checked the coorect IP settings. This is the error, which is only shown, when I start jail from command line:

root@filer[~]# iocage start syncthing

• Starting syncthing
  + Started OK
  + Using devfs_ruleset: 1002 (iocage generated default)
  + Configuring VNET FAILED
  route: writing to routing socket: Network is unreachable
  add net default: gateway 2001:xxxx:28d4:1b::1 fib 0: Network is unreachable

This is my forum thread:

https://www.ixsystems.com/community/threads/jail-networking-issue-in-12-0-beta-2-1.87373/

My Host:

Asrock Taichi X470 Ultimate
Ryzen 7 3700X
64 GB RAM
6 x 6 TB RaidZ2 SATA
1 x 100 GB SSD SATA Boot Drive
2 x 500 GB NVMe SSD Mirror for iocage and bhyve guests
Mellanox ConnectX-3 10G / VLAN 802.1Q / Bridges

Network config on host is:

root@filer[~]# ifconfig
igb0: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> metric 0 mtu 1500
description: connected to aruba
options=8120b8<VLAN_MTU,VLAN_HWTAGGING,JUMBO_MTU,VLAN_HWCSUM,WOL_MAGIC,VLAN_HWFILTER>
ether 70:85:c2:8d:38:62
media: Ethernet autoselect (1000baseT <full-duplex&gt
status: active
nd6 options=9<PERFORMNUD,IFDISABLED>
lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> metric 0 mtu 16384
options=680003<RXCSUM,TXCSUM,LINKSTATE,RXCSUM_IPV6,TXCSUM_IPV6>
inet6 ::1 prefixlen 128
inet6 fe80::1%lo0 prefixlen 64 scopeid 0x2
inet 127.0.0.1 netmask 0xff000000
groups: lo
nd6 options=21<PERFORMNUD,AUTO_LINKLOCAL>
pflog0: flags=0<> metric 0 mtu 33160
groups: pflog
mlxen0: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> metric 0 mtu 9000
description: connected to aruba
options=8d00b8<VLAN_MTU,VLAN_HWTAGGING,JUMBO_MTU,VLAN_HWCSUM,VLAN_HWFILTER,VLAN_HWTSO,LINKSTATE>
ether f4:52:14:55:3b:d0
media: Ethernet autoselect (10Gbase-CX4 <full-duplex,rxpause,txpause&gt
status: active
nd6 options=9<PERFORMNUD,IFDISABLED>
vlan5: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> metric 0 mtu 1500
description: oldlan vlan
options=80000<LINKSTATE>
ether f4:52:14:55:3b:d0
groups: vlan
vlan: 5 vlanpcp: 0 parent interface: mlxen0
media: Ethernet autoselect (10Gbase-CX4 <full-duplex,rxpause,txpause&gt
status: active
nd6 options=9<PERFORMNUD,IFDISABLED>
vlan13: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> metric 0 mtu 1500
description: DMZ vlan
ether 70:85:c2:8d:38:62
groups: vlan
vlan: 13 vlanpcp: 0 parent interface: igb0
media: Ethernet autoselect (1000baseT <full-duplex&gt
status: active
nd6 options=9<PERFORMNUD,IFDISABLED>
bridge5: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
description: oldlan bridge
ether 02:8b:c9:1a:01:05
inet6 fe80::8b:c9ff:fe1a:105%bridge5 prefixlen 64 scopeid 0x7
inet6 2001:xxxx:28d4:1b:21b:21ff:fec1:a8c0 prefixlen 64
inet 10.10.101.101 netmask 0xffffff00 broadcast 10.10.101.255
id 00:00:00:00:00:00 priority 32768 hellotime 2 fwddelay 15
maxage 20 holdcnt 6 proto stp-rstp maxaddr 2000 timeout 1200
root id 00:00:00:00:00:00 priority 32768 ifcost 0 port 0
member: vnet0.3 flags=143<LEARNING,DISCOVER,AUTOEDGE,AUTOPTP>
ifmaxaddr 0 port 10 priority 128 path cost 2000
member: vnet0.1 flags=143<LEARNING,DISCOVER,AUTOEDGE,AUTOPTP>
ifmaxaddr 0 port 9 priority 128 path cost 2000
member: vlan5 flags=143<LEARNING,DISCOVER,AUTOEDGE,AUTOPTP>
ifmaxaddr 0 port 5 priority 128 path cost 55
groups: bridge
nd6 options=21<PERFORMNUD,AUTO_LINKLOCAL>
bridge13: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
description: DMZ bridge
ether 02:8b:c9:1a:01:0d
id 00:00:00:00:00:00 priority 32768 hellotime 2 fwddelay 15
maxage 20 holdcnt 6 proto stp-rstp maxaddr 2000 timeout 1200
root id 00:00:00:00:00:00 priority 32768 ifcost 0 port 0
member: vlan13 flags=143<LEARNING,DISCOVER,AUTOEDGE,AUTOPTP>
ifmaxaddr 0 port 6 priority 128 path cost 55
groups: bridge
nd6 options=9<PERFORMNUD,IFDISABLED>

I disabled hardware offload for both physical NICs.