Cisco ISR 2901

My first thought is that you have MTU issue, i.e. you have packet larger than your port GigabitEthernet0/1 can accommodate. If you do "Show interface GigabitEthernet0/1", you will see that MTU is 1500. You should also see that you the giant counter will be incrementing.  You may want to try adjusting the MTU on port GigabitEthernet0/1.

Second thought, you may be hitting a bug - see also https://supportforums.cisco.com/thread/2110260

Alternatively, you can keep the new IOS but adjust buffer size - see also https://supportforums.cisco.com/thread/2215525

I tried the following config on the router: ip virtual-reassembly in max-fragments 64 max-reassemblies 1024

I have seen no difference. The error still comes up and i cannot cannot access anything from the outside of the network.


I did a sh int gi 0/1 and got the following:


GigabitEthernet0/1 is up, line protocol is up
  Hardware is CN Gigabit Ethernet, address is c067.af7a.cec1 (bia c067.af7a.cec1)
  Description: -INSIDE-
  MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation 802.1Q Virtual LAN, Vlan ID  1., loopback not set
  Keepalive set (10 sec)
  Full Duplex, 1Gbps, media type is RJ45
  output flow-control is XON, input flow-control is XON
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:00, output 00:00:00, 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: 0/40 (size/max)
  5 minute input rate 2802000 bits/sec, 425 packets/sec
  5 minute output rate 2789000 bits/sec, 402 packets/sec
     21041859 packets input, 4181740538 bytes, 0 no buffer
     Received 1352453 broadcasts (0 IP multicasts)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 2876 multicast, 0 pause input
     19640306 packets output, 4086524617 bytes, 0 underruns
     0 output errors, 0 collisions, 2 interface resets
     2237 unknown protocol drops
     0 babbles, 0 late collision, 0 deferred
     1 lost carrier, 0 no carrier, 0 pause output
     0 output buffer failures, 0 output buffers swapped out

These are only suggestions:

(1) try changing MTU size using command "ip mtu" - check if maximum configurable MTU is enough to cover 3994 bytes, e.g. 4000 bytes - see also http://www.cisco.com/en/US/docs/ios/12_2/ipaddr/command/reference/1rfip2.html

(2) Check if the packets coming to the router, have DF (Do not Fragment) set. If DF is set, then the packets cannot be broken. I don't think that is the issue, but it is worth checking. You can use a packet analyser like WireShark for this. If the DF flag is set, try taking it off if possible.

(3) Try ping with different packet sizes

(4) Reload router

(5) Try another IOS, the very latest if possible - if you have CCO account, you should be able to download IOS.

(6) If everything fails, raise a TAC case with Cisco - this must be the last resort, as it could take some time to get to the bottom of the problem.

This experts-exchange post, mentions possible IOS bug.

http://www.experts-exchange.com/Hardware/Networking_Hardware/Routers/Q_28171813.html

I restarted next hop and that fixed the issue