Hi folks,
I came across an issue today for one of our clients who is on DMVPN Phase 3. The GRE Tunnel is showing te MTU to be set at above 17000 under the 'show interface tunnel 150' command whereas the show ip interface tunnel 150 command shows the MTU to be at 1430 which is what I have configured it to be. The IOS I am using at the moment for the router is Advanced-Security-K9 and the router model is 2801 ISR. I saw the same output for another branch of the same client and the Tunnel MTU there is set at 1430 which is exactly what I have conigured it to be. Below is the edited output of the 'show interface tunnel 150' and below that is the show run output of the aforementioned tunnel that I first mentioned where I noticed the discrepancy. The physitcal interface that te tunnel is bound to is a Fast Ethernet port on a 4 port EtherSwitch which has been made a part of an access VLAN and the VLAN has been assigned an IP address for layer 3 functionality. Please do have a look and suggest what could be wrong and what are the variables that could be causing this to happen. Do let me know if you need more information please. Thanks.
Tunnel150 is up, line protocol is up
Hardware is Tunnel
Description: xxxxxx
Internet address is xxx.xxx.xxx.xxx/xx
MTU 17912 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 source xxx.xxx.xxx.xxx (Vlanxxx)
Tunnel protocol/transport multi-GRE/IP
Key 0xF3, sequencing disabled
Checksumming of packets disabled
Tunnel TTL 255
Tunnel transport MTU 1472 bytes
Tunnel transmit bandwidth 8000 (kbps)
Tunnel receive bandwidth 8000 (kbps)
Tunnel protection via IPSec (profile "xxxxx-xxxxxxx")
Last input 00:00:08, output 23:37:44, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 1518
Queueing strategy: fifo
Output queue: 0/0 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
390 packets input, 93480 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
620 packets output, 79440 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 unknown protocol drops
0 output buffer failures, 0 output buffers swapped out
Below is the Tunnel's config:
interface Tunnel150
description xxxxxxx
ip address xxx.xxx.xxx.xxx xxx.xxx.xxx.xxx
no ip redirects
ip mtu 1430
ip nhrp authentication xxxxxxxx
ip nhrp map multicast xxx.xxx.xxx.xxx
ip nhrp map xxx.xxx.xxx.xxx
ip nhrp network-id 243
ip nhrp holdtime 3600
ip nhrp nhs xxx.xxx.xxx.xxx
ip nhrp shortcut
ip tcp adjust-mss 1330
ip ospf network point-to-multipoint
ip ospf cost 10
ip ospf hello-interval 10
ip ospf priority 0
ip ospf mtu-ignore
tunnel source Vlan150
tunnel mode gre multipoint
tunnel key xxx
tunnel protection ipsec profile xxx.xxx.xxx.xxx
