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Output drops on non-congested DMVPN tunnel???

Hello all,

I have an issue which I hope somebody can help me out with.

The issue is on a Cisco 3925E router running IOS 15.1(4)M3. I've never used the 'E' variant of this router or this IOS so I'm wondering if what I'm seeing is simply an IOS bug where it's reporting something that is not actually happening.

My router is connected to a service provider managed MPLS cloud. It's a 50meg circuit connected to the router with Ethernet handoff.

Gig0/2 is the physical interface. I'm running BGP across the cloud to my other WAN routers.

Tunnel 1202 is DMVPN tunnel. I'm running EIGRP inside the tunnels to route between all my sites.

Everything appears to be working but the router is reporting output drops on the tunnel interface. The physical interface is fine - no errors or drops.

The link is not congested. Infact it rarely goes above 2meg in or out.

In around 6 hours, the tunnel has reported over 3,600 output drops. However, "show ip traffic" shows 0 files that could not be fragmented and only 205 ICMP unreachables so I don't think MTU and fragmentation is at fault here. For info we set the MTU of the tunnel to 1400 and use "ip tcp adjust-mss 1360" on the tunnel and the LAN facing interfaces.

As well as the obvious output drops on the tunnel, the other strange thing I'm seeing is the MTU is reported as being 17854 bytes??? However, further down the "show interface Tu1202" output, it states the tunnel transport MTU to be 1414 bytes.

For clarity I've included the "show run int tu1202" and "show int tu1202".

Please let me know if you have any clues as this is doing my head in!!!!!!

Thanks very much,


Router01#sh run int tu1202
Building configuration...

Current configuration : 864 bytes
interface Tunnel1202
description *** DMVPN Tunnel ***
bandwidth 51200
ip address x.x.x.x
no ip redirects
ip mtu 1400
ip pim sparse-dense-mode
ip bandwidth-percent eigrp 1 75
ip hello-interval eigrp 1 15
ip hold-time eigrp 1 45
ip flow ingress
ip nhrp authentication XXXXXXXX
ip nhrp map multicast x.x.x.x
ip nhrp map x.x.x.x x.x.x.x
ip nhrp map multicast x.x.x.x
ip nhrp map x.x.x.x x.x.x.x
ip nhrp network-id xxxx
ip nhrp holdtime 300
ip nhrp nhs x.x.x.x
ip nhrp nhs x.x.x.x
ip tcp adjust-mss 1360
ip summary-address eigrp 1 x.x.x.x
tunnel source GigabitEthernet0/2
tunnel mode gre multipoint
tunnel protection ipsec profile AES_SHA
hold-queue 1000 in
hold-queue 1000 out

Router01#sh int tu1202
Tunnel1202 is up, line protocol is up
  Hardware is Tunnel
  Description: *** DMVPN Tunnel ***
  Internet address is x.x.x.x/24
  MTU 17854 bytes, BW 51200 Kbit/sec, DLY 50000 usec,
     reliability 255/255, txload 5/255, rxload 6/255
  Encapsulation TUNNEL, loopback not set
  Keepalive not set
  Tunnel source x.x.x.x (GigabitEthernet0/2)
   Tunnel Subblocks:
         Tunnel1202 source tracking subblock associated with GigabitEthernet0/2
          Set of tunnels with source GigabitEthernet0/2, 1 member (includes iterators), on interface <OK>
  Tunnel protocol/transport multi-GRE/IP
    Key disabled, sequencing disabled
    Checksumming of packets disabled
  Tunnel TTL 255, Fast tunneling enabled
  Tunnel transport MTU 1414 bytes
  Tunnel transmit bandwidth 8000 (kbps)
  Tunnel receive bandwidth 8000 (kbps)
  Tunnel protection via IPSec (profile "AES_SHA")
  Last input 00:00:00, output never, output hang never
  Last clearing of "show interface" counters 05:21:06
  Input queue: 0/1000/0/0 (size/max/drops/flushes); Total output drops: 3341
  Queueing strategy: fifo
  Output queue: 0/1000 (size/max)
  5 minute input rate 1311000 bits/sec, 247 packets/sec
  5 minute output rate 1065000 bits/sec, 228 packets/sec
     15465701 packets input, 3786181722 bytes, 0 no buffer
     Received 0 broadcasts (0 IP multicasts)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     14299240 packets output, 4160770083 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 unknown protocol drops
     0 output buffer failures, 0 output buffers swapped out

Everyone's tags (6)
New Member

Can anyone already have an

Can anyone already have an idea to solve this problem?

New Member

same issue here, using 15.1(4

same issue here, using 15.1(4)M4

- but, these are "fake"-drops => no dataplane loss at all as far as i see.

did you change the IOS-Release in the meantime?

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