Input error & runts

buntschu · ‎05-02-2005

Hi, we have a Cisco 3750 connected to an Extreme Switch. The statistics on the 3750 giga port show us increasing input errors and runts (same amount).

sw1#sh int gigabitEthernet 1/0/25

GigabitEthernet1/0/25 is up, line protocol is up (connected)

Hardware is Gigabit Ethernet, address is 000f.24e8.4899 (bia 000f.24e8.4899)

Description: link B20-si

MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation ARPA, loopback not set

Keepalive set (10 sec)

Full-duplex, 1000Mb/s, link type is auto, media type is SX

output flow-control is off, input flow-control is off

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 00:14:09

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 4396000 bits/sec, 499 packets/sec

5 minute output rate 281000 bits/sec, 63 packets/sec

527195 packets input, 582404207 bytes, 0 no buffer

Received 493205 broadcasts (0 multicast)

1082 runts, 0 giants, 0 throttles

1082 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored

0 watchdog, 492202 multicast, 0 pause input

0 input packets with dribble condition detected

60062 packets output, 30733468 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

sw1#

Interesting is that when removing vlan 2 on this trunk (on the extreme side), we don't get any error on the 3750...

Any idea ??

Francois

Kevin Dorrell · ‎05-02-2005

Interesting that when you prune VLAN 2 at the far end, the runts stop. Is it still native VLAN 1?

I am going to take a complete guess here, because I do not know the Extreme switch. I am going to guess that the Extreme Switch is a cut-through switch, and that there is some host on VLAN 2 on the Extreme Switch that is generating runt frames. Because the Extreme Switch is cut-through, the runts are passed through transparently.

Why is the host generating runts? The most common reason is a duplex mismatch. If the switch port is full duplex, and the host thinks it is half duplex, then the host will interrupt a frame whenever it thinks a collision has occurred. Some of these will come out as runts. Does the Extreme Switch have a runt counter, or is that not possible with cut-through?

The most common cause of duplex mismatches, at least on Cisco switches, is where you have a host in auto duplex and the switch in configured duplex.

Hope this helps.

Kevin Dorrell

Luxembourg

alagrawa · ‎05-03-2005

Hi Francois,

Thanks for writing in. When you prune vlan 2, do you have any other vlans other than the native vlan which are active on this trunk link?

Please also check the output of 'show controller ethernet-controller fas1/0/25'. Do you see undersize packet counter incrementing?

You might be hitting bug CSCec14238: 3750 connected using dot1q cause Runts increase on interface.

http://www.cisco.com/cgi-bin/Support/Bugtool/onebug.pl?bugid=CSCec14238

Release Notes

Symptom:

When using dot1q on trunk interface on the Cat3750, runts may be seen on

show interface output because valid dot1q encapsulated packets which are

61-64 bytes including the q-tag are counted by the Cat3750 as undersized

frames, even though these packets are forwarded correctly. In addition,

these packets are not reported in the appropriate category (unicast,

multicast, broadcast) in receive statistics.

Workaround:

There is no workaround.

This bug is fixed in code 12.1(19)EA1 and 12.2(20)SE1 and above.

The following field notice also talks about this.

http://www.cisco.com/en/US/customer/products/hw/switches/ps5206/products_field_notice09186a00802cac62.shtml

Please check the code running on your 3750 switch and see if you might be affected by this bug.

Hope this helps.

warm regards

-Alok

buntschu · ‎05-03-2005

Thanks a lot for your helpful comments, it seems that we are running with this bug. We will then upgrade our switch to the latest release.

Regards

Francois