[c-nsp] Large amounts of undersize packets

[Chris Griffin]

If using dot1q trunking, we saw this kind of behavior between a Cat6509 
and 2924 years ago.  It was due to the fact that the Cat6509 didn't pad 
small frames (mostly TCP acks) that would result in a minimum size frame 
after dot1q encapsulation.  The 2924 passed these but reported them as 
undersized.

Chris

Mattias Eliasson wrote:
> Hello
> 
> I have a SFP LX/LH interface in a 3560G that has no errors in "sh int" 
> but massive undersize packets (500-4000/s) in "show interface counters 
> error.
> 
> The interface is switching about 70/40Mbit of data and never more then 
> 200Mbit.
> 
> The other device is a GSR (partner) where they see giants on there port.
> 
> There is no problem with the traffic flow, no packetloss etc etc.
> 
> 
> Output
> 
> interface GigabitEthernet0/26
>   switchport trunk encapsulation dot1q
>   switchport trunk allowed vlan 15
>   switchport mode trunk
> end
> 
> GigabitEthernet0/26 is up, line protocol is up (connected)
>    Hardware is Gigabit Ethernet, address is 0016.c785.cb1a (bia 
> 0016.c785.cb1a)
>    MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,
>       reliability 255/255, txload 14/255, rxload 10/255
>    Encapsulation ARPA, loopback not set
>    Keepalive not set
>    Full-duplex, 1000Mb/s, link type is auto, media type is 1000BaseLX SFP
>    input flow-control is off, output flow-control is unsupported
>    ARP type: ARPA, ARP Timeout 04:00:00
>    Last input 26w6d, output 00:00:00, output hang never
>    Last clearing of "show interface" counters 00:21:32
>    Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
>    Queueing strategy: fifo
>    Output queue: 0/40 (size/max)
>    30 second input rate 41777000 bits/sec, 5190 packets/sec
>    30 second output rate 58074000 bits/sec, 11185 packets/sec
>       6719065 packets input, 2436706204 bytes, 0 no buffer
>       Received 0 broadcasts (0 multicast)
>       0 runts, 0 giants, 0 throttles
>       0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
>       0 watchdog, 0 multicast, 0 pause input
>       0 input packets with dribble condition detected
>       15710756 packets output, 1518701210 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
> 
> 
> 
> Port        Align-Err    FCS-Err   Xmit-Err    Rcv-Err UnderSize
> *snip*
> Gi0/26              0          0          0          0   3997338
> *snip*
> 
> What would cause this behaviour?
> 
> Mattias Eliasson
> 
> Teknikmejeriet AB
> ISP
> Sweden
> 
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-- 
Chris Griffin                                cgriffin at ufl.edu
Sr. Network Engineer - CCNP                  Phone: (352) 392-2061
Network Services / Florida LambdaRail        Fax:   (352) 392-9440
University of Florida                        Gainesville, FL 32611