I have a series of routers (Cisco ISR 1811) that has defaulted to an MTU size of 17867. This only happens on tunnel interfaces, and seems to happen for all tunnel interfaces on that series router. The MTU on my 2811 & 2821 all default to MTU 1514 bytes.
There is no MTU manully configured. I have searched and can't find what would cause this.
Any thoughts?
Thank You
Tunnel1 is up, line protocol is up
Hardware is Tunnel
Description: Tunnel Holly
Internet address is z.z.z.z/30
MTU 17867 bytes, BW 1500 Kbit/sec, DLY 50000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation TUNNEL, loopback not set
Keepalive not set
Tunnel source y.y.y.y, destination x.x.x.x
Tunnel protocol/transport IPSEC/IP
Tunnel TTL 255
Tunnel transport MTU 1427 bytes
Tunnel transmit bandwidth 8000 (kbps)
Tunnel receive bandwidth 8000 (kbps)
Tunnel protection via IPSec (profile "Crytp_Profile_1")
Last input never, output never, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/0 (size/max)
5 minute input rate 2000 bits/sec, 2 packets/sec
5 minute output rate 2000 bits/sec, 2 packets/sec
25658 packets input, 2909400 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
26567 packets output, 3632936 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 unknown protocol drops
0 output buffer failures, 0 output buffers swapped out