MTU mismatch - video problem

[mrnsmn75h]

Hi guys.

I have a lot of brocade MLX connected in MPLS with BGP and I have video traffic traveling. Connected to one MLX I have a 3750 stack and here some DVR and pc that can view the video coming from the various camera, and here with have the following issue: the video quality is good but the flow is jerky, we lose pieces of video. The video use TCP e not UDP.

I have tried to view the video from other site in the network and the flow is perfect; we have just upgraded the bandwidth and now the traffic is 20% of a 10Gb link. The link between Brocade and Cisco is a trunk link and the only thing that I see is the MTU misconfiguration on the two side of the link:

Cisco 3725#sh interfaces tenGigabitEthernet 2/1/2 mtu

Port      Name               MTU
Te2/1/2                      1500

Brocade MLX#sh interfaces ethernet 2/2 | include MTU
  MTU 1548 bytes, encapsulation ethernet

On the Cisco interface I see also the counters of "too Large Frame" increasing, but no collision or error:

KYE0005ARSCTT_BECCARIA#sh interfaces tenGigabitEthernet 2/1/2 controller | include large
            0 Late collisions                      0 Invalid frames, too large
            0 VLAN discard frames          144317107 Valid frames, too large
      6215997 Too large frames

Are "Too large Frames" dropped? Do you think that the MTU misconfiguration can cause a lot of problem? The services traveling on this link are important and i do not know when the customer will confirm me a maintenance window.

Thanks in advance

Simone

[Joseph W. Doherty]

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Posting

My understanding is, too large (or giants) frames will be discarded upon receipt.

Generally 3750s support jumbo frames, but it must be configured (globally).  (It may require a reboot.)

3750s are a bit infamous for dropping packets when traffic is bursty.  How do your egress drops stats appear?

[mrnsmn75h]

I have no drops: Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0

But the problem is in input, the flow is from Brocade with MTU 1548 to Cisco with MTU 1500, folowing the complete output:

KYE0005ARSCTT_BECCARIA#sh interfaces tenGigabitEthernet 2/1/2 controller
TenGigabitEthernet2/1/2 is up, line protocol is up (connected)
  Hardware is Ten Gigabit Ethernet, address is 885a.92ef.ca36 (bia 885a.92ef.ca36)
  MTU 1500 bytes, BW 10000000 Kbit/sec, DLY 10 usec,
     reliability 255/255, txload 5/255, rxload 20/255
  Encapsulation ARPA, loopback not set
  Keepalive not set
  Full-duplex, 10Gb/s, link type is auto, media type is SFP-10GBase-SR
  input flow-control is off, output flow-control is unsupported
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:37, output 00:00:05, output hang never
  Last clearing of "show interface" counters 3d03h
  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 799151000 bits/sec, 102408 packets/sec
  5 minute output rate 222854000 bits/sec, 57633 packets/sec
     26393904101 packets input, 24799491780544 bytes, 0 no buffer
     Received 24644078 broadcasts (16494209 multicasts)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 16494209 multicast, 0 pause input
     0 input packets with dribble condition detected
     14533451940 packets output, 5731290258832 bytes, 0 underruns
     0 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 TenGigabitEthernet2/1/2         Receive
 266649744922 Bytes                     962787095111 Bytes
    548250365 Unicast frames               981571342 Unicast frames
       119116 Multicast frames                580181 Multicast frames
       383424 Broadcast frames                286669 Broadcast frames
            0 Too old frames            958800536163 Unicast bytes
            0 Deferred frames               38469064 Multicast bytes
            0 MTU exceeded frames           18346816 Broadcast bytes
            0 1 collision frames                   0 Alignment errors
            0 2 collision frames                   0 FCS errors
            0 3 collision frames                   0 Oversize frames
            0 4 collision frames                   0 Undersize frames
            0 5 collision frames                   0 Collision fragments
            0 6 collision frames
            0 7 collision frames                1009 Minimum size frames
            0 8 collision frames           275289500 65 to 127 byte frames
            0 9 collision frames             5520231 128 to 255 byte frames
            0 10 collision frames           65232568 256 to 511 byte frames
            0 11 collision frames           54672109 512 to 1023 byte frames
            0 12 collision frames          155956905 1024 to 1518 byte frames
            0 13 collision frames                  0 Overrun frames
            0 14 collision frames                  0 Pause frames
            0 15 collision frames
            0 Excessive collisions                 0 Symbol error frames
            0 Late collisions                      0 Invalid frames, too large
            0 VLAN discard frames          425765871 Valid frames, too large
            0 Excess defer frames                  0 Invalid frames, too small
         5026 64 byte frames                       0 Valid frames, too small
    370524241 127 byte frames
      2287189 255 byte frames                      0 Too old frames
      9275605 511 byte frames                      0 Valid oversize frames
      6086759 1023 byte frames                     0 System FCS error frames
    143092959 1518 byte frames                     0 RxPortFifoFull drop frame
     17481127 Too large frames
            0 Good (1 coll) frames
            0 Good (>1 coll) frames

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

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Posting

For drop stats, I was also asking about all the other (egress) ports.

If Brocade is 1548 and Cisco is 1500, then Brocade might be sending frames larger than the 3750 is configured to accept.

You stats still show a count for "Valid frames, too large", and Cisco says for that:

Valid frames, too large

The number of frames received on an interface that are larger than the maximum allowed frame size.

I would understand that as to imply those frames will be dropped.

[mrnsmn75h]

Hi Joseph.
I have no drops on the others interfaces, consider that the fragmentation happen on ingress and the frame are the correct size when goes to the interfaces. The think I need to know:
- are "Too large frames" dropped?
- are "Valid frames, too large" dropped? In this case i think no...
Can this situation cause video degradation?

Thank

Simone

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

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In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

Again, my reading is, too large frames, whether valid or invalid, are dropped.

Video will be degraded by drops, it also can be degraded by additional latency and/or jitter, especially if real-time video.

[mrnsmn75h]

Thanks Joseph.

This morning I have connected a PC directly to the switch and the video flow is perfect; I have just finished a meeting and now I know that the video's flow transits through DVR...and the analysis goes on.

Concerning large frame I can be agree with you but I'd like to find some official documentation about this, and to be honest I do not understand why have to drop a "Valid frames, too large"

Rgds

Simon

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

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In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

From reading Cisco documentation, a too large valid frame means the frame's FCS was good.  Basically, it appears to be a valid jumbo frame, but the hardware isn't prepared to accept an otherwise valid, but over sized, frame.