Re: Dropping packets

On 19 Nov, 04:08, "flamer die.s...@xxxxxxxxxxx" <die.s...@xxxxxxxxxxx>
wrote:
I have a cisco 3400 ME switch which is dropping a lot of packets on
one of its uplinks and customers are noticing the packet loss.

the switch has two gig uplinks, one has a tx/rx combined rate of
445Mbps which never drops a packet, the other has a combined tx/rx
throughput of 607mbps (give or take) and drops 100's of packets a
second. i think the issue may be caused by the 3400 configured for
jumbo frames and the 4507 running an MTU of 1500.

However lookign at the traffic patterns there is a huge difference in
data transmitted than received, so what is the best way to check for
loops on the switch? since the 3400 doesnt support STP on the UNI
ports, what is th ebest way to check for loops? I have checked the mac
table and there is no dupes, is there any other methods for tracking
them down?

GigabitEthernet0/13 is up, line protocol is up (connected)
  Hardware is Gigabit Ethernet, address is 0021.d7ed.e60d (bia
0021.d7ed.e60d)
  Description: xx
  MTU 9000 bytes, BW 1000000 Kbit, DLY 10 usec,
     reliability 255/255, txload 154/255, rxload 4/255
  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 00:00:00, output 00:00:00, output hang never
  Last clearing of "show interface" counters 8w5d
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops:
151923763
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 16614000 bits/sec, 13486 packets/sec
  5 minute output rate 605606000 bits/sec, 118387 packets/sec
     81890216650 packets input, 16901966809462 bytes, 0 no buffer
     Received 149312500 broadcasts (148384638 multicasts)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 148384638 multicast, 0 pause input
     0 input packets with dribble condition detected
     508715659366 packets output, 360874240939303 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

I am not familiar with this switch but I am familiar with
the related 2950 and 3550.

Regarding loops.
If your design allows customers to create loops then
this would seem to be a bit of a problem.

Some switches log 'suspicious' mac address to port
changes. i.e. they log cases where mac adresses move
from one port to another.

You could use snmp to log the stats (drops, bytes
in and bytes out) for all ports. Then you might be able to
see a pattern.

Note that most cisco kit these days seems to
only update the snmp counters every 15 or 20 seconds.

At present your rate stats are being recorded with
a time constant of 5 mins. This can be changed
down to 30 secs with

conf t
int x
load-interval 30


Maybe you need to see if you can apply QoS to
some of your clients?

There is no way for the 4500 to tell the 3400
that the MTU is inconsistent. If big frames are
present in the network the 3400 will
just transmit them and the 4500
will just drop them. This can not be instrumental
in your output drops.

Ideally you want to get mrtg or something like that going
but a quick and dirty free snmp client is getif.exe.
I have recently pointed to it on this list.
roughly www.snmpc4pc.something
It is pretty clunky and limited but with a small mumber of
ports such as you have then it will get the job done just
about. hmmm maybe not - the 16 bit counters will wrap
pretty quickly and I am pretty sure it wont handle the 64bit ones.
It does not handle overflows very gracefully.

what speed are your customer links?
what model is your switch?
what software is it running?


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