What are sit0 and gre0?

Host initiated restart worked this time.

The Job Entered time was 01/01/1974 12:00:00 AM though.

From my console log:````
--- 8><----- --- 8><----- --- 8><----- --- 8><----- --- 8><-----
Cleaning /tmp /var/run /var/lock.
Setting up networking…done.
Setting up IP spoofing protection: rp_filter.
Configuring network interfaces…Internet Systems Consortium DHCP Client V3.0.1
Copyright 2004 Internet Systems Consortium.
All rights reserved.
For info, please visit http://www.isc.org/products/DHCP

ip6tnl0: unknown hardware address type 769
sit0: unknown hardware address type 776
gre0: unknown hardware address type 778
ip6tnl0: unknown hardware address type 769
sit0: unknown hardware address type 776
gre0: unknown hardware address type 778
Listening on LPF/eth0/fe:fd:40:3e:be:51
Sending on LPF/eth0/fe:fd:40:3e:be:51
Sending on Socket/fallback
DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 6
DHCPOFFER from 66.220.1.7
DHCPREQUEST on eth0 to 255.255.255.255 port 67
DHCPACK from 66.220.1.7
bound to 64.62.190.81 -- renewal in 40798 seconds.
done.

Setting the System Clock using the Hardware Clock as reference…
--- 8><----- --- 8><----- --- 8><----- --- 8><----- --- 8><-----
````

What are sit0 and gre0?