Cisco 3850 interface reliability and output drops

[carl_townshend]

Hi All

We have an issue with a 100Mbit connection to our other site.

We have a 100Mbit ethernet circuit plugged into a 3850-24 port switch.

On the interface I can see the reliability drops to 180/255, the interface also has output drops incrementing as well as output errors, the values on these are the same, how come the output errors are the same as the drops?

I am guessing the drops are due to congestion? but why has the reliability dropped? we have changed the port and cable to the NTE but it is still not reliable.

Also could I reconfigure to help the output drops? maybe increase the queue-limit / buffers?

Any ideas?

[Seb Rupik]

Hi there,

What is the output of  sh int gi<x/x/x> controller ?

The reliability figure is a function of total input/output errors divided by total number of frames.

To resolve the congestion you are right about using QoS. Either configure it for congestion management to prioritise certain classes of traffic above others or tune for avoidance and intentionally drop packets which pass certain thresholds.

Cheers,

Seb.

[carl_townshend]

EUUK-HWE2-SERVER-SW#sh int gig 1/0/1 controller
GigabitEthernet1/0/1 is up, line protocol is up (connected)
  Hardware is Gigabit Ethernet, address is 70d3.79f3.b981 (bia 70d3.79f3.b981)
  Description: CONNECTION TO HQ
  MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec,
     reliability 255/255, txload 16/255, rxload 178/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Full-duplex, 100Mb/s, media type is 10/100/1000BaseTX
  input flow-control is off, output flow-control is unsupported
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:00, output never, output hang never
  Last clearing of "show interface" counters 00:57:27
  Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 1702202
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  30 second input rate 70122000 bits/sec, 7041 packets/sec
  30 second output rate 6548000 bits/sec, 4619 packets/sec
     17439006 packets input, 19162442720 bytes, 0 no buffer
     Received 305355 broadcasts (172434 multicasts)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 172434 multicast, 0 pause input
     0 input packets with dribble condition detected
     12587226 packets output, 3887351551 bytes, 0 underruns
     1702202 output errors, 0 collisions, 0 interface resets
     0 unknown protocol drops
     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
Transmit                  GigabitEthernet1/0/1          Receive
  18024346637 Total bytes                 46074275904 Total bytes
     38009670 Unicast frames                 45762009 Unicast frames
  18024112349 Unicast bytes               45949039438 Unicast bytes
         1288 Multicast frames                 466532 Multicast frames
       234288 Multicast bytes                94338473 Multicast bytes
            0 Broadcast frames                 353625 Broadcast frames
            0 Broadcast bytes                30897993 Broadcast bytes
            0 System FCS error frames               0 IpgViolation frames
            0 MacUnderrun frames                    0 MacOverrun frames
            0 Pause frames                          0 Pause frames
            0 Cos 0 Pause frames                    0 Cos 0 Pause frames
            0 Cos 1 Pause frames                    0 Cos 1 Pause frames
            0 Cos 2 Pause frames                    0 Cos 2 Pause frames
            0 Cos 3 Pause frames                    0 Cos 3 Pause frames
            0 Cos 4 Pause frames                    0 Cos 4 Pause frames
            0 Cos 5 Pause frames                    0 Cos 5 Pause frames
            0 Cos 6 Pause frames                    0 Cos 6 Pause frames
            0 Cos 7 Pause frames                    0 Cos 7 Pause frames
            0 Oam frames                            0 OamProcessed frames
            0 Oam frames                            0 OamDropped frames
      9595444 Minimum size frames             4927956 Minimum size frames
      2024065 65 to 127 byte frames           1398173 65 to 127 byte frames
     14451104 128 to 255 byte frames          6712427 128 to 255 byte frames
      2014649 256 to 511 byte frames          3131193 256 to 511 byte frames
       755908 512 to 1023 byte frames         1213867 512 to 1023 byte frames
      9169788 1024 to 1518 byte frames       29198525 1024 to 1518 byte frames
            0 1519 to 2047 byte frames             26 1519 to 2047 byte frames
            0 2048 to 4095 byte frames              0 2048 to 4095 byte frames
            0 4096 to 8191 byte frames              0 4096 to 8191 byte frames
            0 8192 to 16383 byte frames             0 8192 to 16383 byte frames
            0 16384 to 32767 byte frame             0 16384 to 32767 byte frame
            0 > 32768 byte frames                   0 > 32768 byte frames
            0 Late collision frames                 0 SymbolErr frames
     10377917 Excess Defer frames                   0 Collision fragments
            0 Good (1 coll) frames                  0 ValidUnderSize frames
            0 Good (>1 coll) frames                 0 InvalidOverSize frames
            0 Deferred frames                       0 ValidOverSize frames
            0 Gold frames dropped                   0 FcsErr frames
            0 Gold frames truncated
            0 Gold frames successful
            0 1 collision frames
            0 2 collision frames
            0 3 collision frames
            0 4 collision frames
            0 5 collision frames
            0 6 collision frames
            0 7 collision frames
            0 8 collision frames
            0 9 collision frames
            0 10 collision frames
            0 11 collision frames
            0 12 collision frames
            0 13 collision frames
            0 14 collision frames
            0 15 collision frames
            0 Excess collision frames

LAST UPDATE 880 msecs AGO

[Georg Pauwen]

Hello,

try to increase the hold queue on the interface and change the queuing to fair-queue:

interface GigabitEthernet1/0/1

hold-queue 2000 in

fair-queue

[Leo Laohoo]

Carl,
Nothing wrong with the output. Just make sure the numerator and denominator of the "Reliability" should only be 255. If it is other than 255 then there is something wrong.

[carl_townshend]

Hi Leo

I am seeing the reliability drop below 255, sometimes 240/255 etc

Is this because the output drops/errors are incrementing and thus reporting the interface reliability to go down?

How do I see the ports default hold queue size? Is it 40 by default ?

[Seb Rupik]

The reliability, tx and rx load figures are based on a rolling 5 minute (by default) window.

cheers,

Seb.

[Leo Laohoo]

---

@carl_townshend wrote:

 1702202 output errors, 0 collisions, 0 interface resets

---

Carl, 

I take back my previous statement.  

There is a fault with this link.  Because this link is copper, please run a TDR.

[carl_townshend]

Hi

The output errors are incrementing with the output drops, is this really a link issue or congestion issue?

cheers

[carl_townshend]

Hi

See below, the cable to the NTE was replaced this morning

Interface Speed Local pair Pair length        Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi1/0/1   100M  Pair A     0    +/- 1  meters Pair A      Normal
                Pair B     N/A                N/A         Not Completed
                Pair C     3    +/- 1  meters N/A         Short
                Pair D     3    +/- 1  meters N/A         Short

[Leo Laohoo]

Whao. Replace the cable nearest the switch.
Pair C & D are both "short". No wonder the link won't go 1 Gbps.

[carl_townshend]

Hi Leo

It is a 100Mbit link full duplex both ends, so pair C and D won't be used, the cable was replaced this morning, still same issue.

what are your thoughts ?

[paul driver]

Hello

Have you tried not hard coding the interfaces?

[carl_townshend]

Hi, no we haven't done this

I have logged a call to the ISP to check, my feeling is either a bug in the 3850 code, or the output errors are making the interface reliability go down

cheers

[Leo Laohoo]

If the cables have been replaced, re-run the TDR and post the output.