Hello Rene,
I was testing these two different manual tunneling types in the lab and wanted to confirm what one should see as that expected MTU for GRE vs. the manual tunnel? I know that you state GRE has a higher MTU, but that was not what I observed in the testing. Also not 100%
R6#sh int tunn0
Tunnel0 is up, line protocol is up
Hardware is Tunnel
MTU 17916 bytes, BW 100 Kbit/sec, DLY 50000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation TUNNEL, loopback not set
Keepalive not set
Tunnel linestate evaluation up
Tunnel source 10.36.36.6 (GigabitEthernet0/1), destination 10.23.23.2
Tunnel Subblocks:
src-track:
Tunnel0 source tracking subblock associated with GigabitEthernet0/1
Set of tunnels with source GigabitEthernet0/1, 1 member (includes iterators), on interface
Tunnel protocol/transport GRE/IP
Key disabled, sequencing disabled
Checksumming of packets disabled
Tunnel TTL 255, Fast tunneling enabled
Tunnel transport MTU 1476 bytes
.
.
.
vs.
R022DC3N4806#sh int tunn0
Tunnel0 is up, line protocol is up
Hardware is Tunnel
MTU 17920 bytes, BW 100 Kbit/sec, DLY 50000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation TUNNEL, loopback not set
Keepalive not set
Tunnel linestate evaluation up
Tunnel source 10.36.36.6 (GigabitEthernet0/1), destination 10.23.23.2
Tunnel Subblocks:
src-track:
Tunnel0 source tracking subblock associated with GigabitEthernet0/1
Set of tunnels with source GigabitEthernet0/1, 1 member (includes iterators), on interface
Tunnel protocol/transport IPv6/IP
Tunnel TTL 255
Tunnel transport MTU 1480 bytes
Tunnel transmit bandwidth 8000 (kbps)
Tunnel receive bandwidth 8000 (kbps)
Last input 00:00:09, output 00:00:21, output hang never
Last clearing of "show interface" counters 00:16:08
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
--More--
Also I am not seeing any association with one of my MAC addresses to the link-local address for GRE tunnel that you mention is created with EUI-64 and takes lowest numbered interface MAC address.
R6#sh ipv6 route
IPv6 Routing Table - default - 4 entries
Codes: C - Connected, L - Local, S - Static, U - Per-user Static route
B - BGP, HA - Home Agent, MR - Mobile Router, R - RIP
H - NHRP, I1 - ISIS L1, I2 - ISIS L2, IA - ISIS interarea
IS - ISIS summary, D - EIGRP, EX - EIGRP external, NM - NEMO
ND - ND Default, NDp - ND Prefix, DCE - Destination, NDr - Redirect
O - OSPF Intra, OI - OSPF Inter, OE1 - OSPF ext 1, OE2 - OSPF ext 2
ON1 - OSPF NSSA ext 1, ON2 - OSPF NSSA ext 2, la - LISP alt
lr - LISP site-registrations, ld - LISP dyn-eid, a - Application
R 2001:10:22:22::/64 [120/2]
via FE80::5287:89FF:FEB9:7460, Tunnel0
C 2001:10:66:66::/64 [0/0]
via Loopback0, directly connected
L 2001:10:66:66::66/128 [0/0]
via Loopback0, receive
L FF00::/8 [0/0]
via Null0, receive
Many thanks for your help to clarify.