Troubleshoot giants

khuysmans · ‎01-06-2006

Hello,

I have noticed that on the Vlan1 interface of one of my switches there are giants being received (about 1 each second). I have the impression the broadcasts are incrementing at the same rate as the giants.

The interface output:

#sh int vlan1

VLAN1 is up, line protocol is down

Hardware is CPU Interface, address is 0006.d792.4cc0 (bia 0006.d792.4cc0)

MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec,

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

Encapsulation ARPA, loopback not set

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 1d01h

Queueing strategy: fifo

Output queue 0/40, 0 drops; input queue 0/75, 0 drops

5 minute input rate 12000 bits/sec, 1 packets/sec

5 minute output rate 0 bits/sec, 0 packets/sec

189714 packets input, 149843962 bytes, 0 no buffer

Received 97383 broadcasts, 0 runts, 92566 giants, 0 throttles

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

0 input packets with dribble condition detected

95933 packets output, 10965800 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 output buffer failures, 0 output buffers swapped out

I am trying to figure out what is causing this phenomenon.

There are no interfaces assigned to Vlan1.

I have disabled STP (since this is a standalone switch).

Any ideas on how to troubleshoot this will be greatly appreciated.

With kind regards,

Kevin Huysmans

spremkumar · ‎01-06-2006

Hi

first thing would be ur VLAN interface itself is down but giants are basically referred to as frames more than 1500Bytes in size which will be of around 1522Bytes.

You can enable the support for giants in ur switch by using mtu 1522 in the global mode.

Also clear the counters in u switch using clear counters and check the same.

regds

khuysmans · ‎01-06-2006

Thank you for your response, spremkumar.

I know that the VLAN interface is down, that doesn't trouble me all that much.

I am not interested in actually allowing the giants, I want to know what is causing them.

I have just cleared the counters and here's how it looks now:

#sh int vlan1

VLAN1 is up, line protocol is down

Hardware is CPU Interface, address is 0006.d792.4cc0 (bia 0006.d792.4cc0)

MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec,

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

Encapsulation ARPA, loopback not set

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 00:00:23

Queueing strategy: fifo

Output queue 0/40, 0 drops; input queue 0/75, 0 drops

5 minute input rate 12000 bits/sec, 4 packets/sec

5 minute output rate 2000 bits/sec, 2 packets/sec

85 packets input, 40028 bytes, 0 no buffer

Received 29 broadcasts, 0 runts, 24 giants, 0 throttles

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

0 input packets with dribble condition detected

50 packets output, 11360 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 output buffer failures, 0 output buffers swapped out

kind regards,

Kevin Huysmans

mheusinger · ‎01-08-2006

Hello,

there can be serveral reasons for Giants.

First they are occuring in your native VLAN (I assume). They could be sent by a host with MTU set to larger values than 1500. F.e. GE interfaces have MTU sizes up to 9216 Bytes supported and sometimes servers are using larger values to improve throughput.

Second you might have MPLS enabled between two routers connected to the switch, which also could result in giants.

The probability of option 1) is considerably higher than the one for option 2).

So the first thing I would do is to check MTU settings of attached hosts (especially servers), because this is a standalone switch.

Did this help? Please rate all posts.

Martin

khuysmans · ‎01-09-2006

Hello Martin,

What you explain with regard to GE interfaces makes sense to me.

I am wondering though. Say a server using a GE interface is connected to the FE interface of this switch and the server is actually sending giants. Why would this show up on my VLAN1 interface and not on the respective port?

VLAN1 is indeed my native VLAN.

with regards,

Kevin

rdboyd · ‎01-08-2006

There is a bug with CEF for the CAT 6500. Please upgrade to 12.2(18)SXF for the fix. I am sure there are other code versions that will have the fix also. Make sure no user data is being sent over VLAN 1 as this should be reserved for ONLY switch management traffic.

regards

Ricky Boyd

www.hypernetworks.net

khuysmans · ‎01-09-2006

Ricky,

I am running: IOS (tm) C3500XL Software (C3500XL-C3H2S-M), Version 12.0(5.3)WC(1)

There should be no traffic going over VLAN1, I have my management traffic on interface VLAN10.

There are no interfaces assigned to VLAN1, so I am assuming no user data can be sent over that VLAN.

What can I check to make sure?

I am still having trouble understanding how VLAN1 can be seeing giants if it is not being used.

With kind regards,

Kevin