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New Member

Output drops on 3560

Hi,

We have a 3560 connected via trunk to a 2950 (Both 10/100 ports), and we are seeing large amounts of output drops on the 3560 port - Ports were set to 100/FULL, now auto/auto(Negotiating to 100/FULL).

3560:

interface FastEthernet0/1
description Trunk-to-ESW01
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 1,11,12,35,103,104,106-108,112,113,115,120-123
switchport trunk allowed vlan add 156,158,206,472,473,475,478-488,590,591,957
switchport trunk allowed vlan add 970,1002-1005
switchport mode trunk
switchport nonegotiate
mls qos trust dscp
storm-control broadcast level 20.00
storm-control action trap
no cdp enable
spanning-tree bpdufilter enable
spanning-tree guard root

2950:

interface FastEthernet0/20
description trunk to esw02
switchport trunk allowed vlan 1,11,12,35,68,103,104,106-108,112,113,115
switchport trunk allowed vlan add 120-123,156,158,206,472,473,475,478-488,590
switchport trunk allowed vlan add 591,957,970
switchport mode trunk
mls qos trust dscp
storm-control broadcast level 20.00
storm-control action trap
no cdp enable
spanning-tree bpdufilter enable
spanning-tree guard root

And the drops:

3560:

FastEthernet0/1 is up, line protocol is up (connected)
  Hardware is Fast Ethernet, address is f4ac.c17d.af83 (bia f4ac.c17d.af83)
  Description: Trunk-to-ESW01
  MTU 1998 bytes, BW 100000 Kbit, DLY 100 usec,
     reliability 255/255, txload 138/255, rxload 53/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Full-duplex, 100Mb/s, media type is 10/100BaseTX
  input flow-control is off, output flow-control is unsupported
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:03, output 00:00:03, output hang never
  Last clearing of "show interface" counters 2d09h
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 150147
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 20925000 bits/sec, 4704 packets/sec
  5 minute output rate 54280000 bits/sec, 7758 packets/sec
     497109451 packets input, 293548981757 bytes, 0 no buffer
     Received 1086289 broadcasts (242554 multicasts)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 242554 multicast, 0 pause input
     0 input packets with dribble condition detected
     593084216 packets output, 451392427662 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 babbles, 0 late collision, 0 deferred
     0 lost carrier, 0 no carrier, 0 PAUSE output
     0 output buffer failures, 0 output buffers swapped out

2950:

FastEthernet0/20 is up, line protocol is up (connected)
  Hardware is Fast Ethernet, address is 0017.5af5.6694 (bia 0017.5af5.6694)
  Description: trunk to esw02
  MTU 1530 bytes, BW 100000 Kbit, DLY 100 usec,
     reliability 255/255, txload 53/255, rxload 139/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Full-duplex, 100Mb/s, media type is 100BaseTX
  input flow-control is unsupported output flow-control is unsupported
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 6d14h, output 00:00:07, output hang never
  Last clearing of "show interface" counters 6d05h
  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 54592000 bits/sec, 7789 packets/sec
  5 minute output rate 20978000 bits/sec, 7139 packets/sec
     2485643391 packets input, 596308546 bytes, 0 no buffer
     Received 491697 broadcasts (0 multicast)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 244841 multicast, 0 pause input
     0 input packets with dribble condition detected
     2517124831 packets output, 2011506627 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 babbles, 0 late collision, 0 deferred
     0 lost carrier, 0 no carrier, 0 PAUSE output
     0 output buffer failures, 0 output buffers swapped out

Next thing we would try is to replace the eth cable(It is in remote location, so is difficult) - Other than cable, what else can we test to try and identify the cause of the drops?

Thanks in advance.

4 REPLIES
Hall of Fame Super Gold

Re: Output drops on 3560

johnelliot6 wrote:

3560:

FastEthernet0/1 is up, line protocol is up (connected)
  Hardware is Fast Ethernet, address is f4ac.c17d.af83 (bia f4ac.c17d.af83)
  Description: Trunk-to-ESW01
  MTU 1998 bytes, BW 100000 Kbit, DLY 100 usec,
     reliability 255/255, txload 138/255, rxload 53/255

2950:

FastEthernet0/20 is up, line protocol is up (connected)
  Hardware is Fast Ethernet, address is 0017.5af5.6694 (bia 0017.5af5.6694)
  Description: trunk to esw02
  MTU 1530 bytes, BW 100000 Kbit, DLY 100 usec,
     reliability 255/255, txload 53/255, rxload 139/255

MTU mis-match?

New Member

Re: Output drops on 3560

Ah - Well done!

So miss-match in mtu would cause output drops?

As the 2950 only supports 1530byte mtu, is our only option to drop the 3560's mtu to match this?

Hall of Fame Super Gold

Re: Output drops on 3560

I'd try to match the MTU of both sides and try again.

New Member

Re: Output drops on 3560

As per-interface mtu setting is not supported, is there anyway workaround(mtu discovery?) - As preference would not to have to drop system mtu to match 2950+reboot switch.

Thanks.

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