Ethernet Switches & Routers

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New Contributor
Posts: 3
Registered: ‎04-21-2010

"Class 3 transmit frames discarded due to timeout"

In the clips from one of my switches that has only one ISL, I am seeing a number of Class 3 trasmit frames discarded due to timeout.sw

These error reports are occurring on the ISL.

So my question is, how does the switch signal the target that a number of frames were discarded in the transmission between the switches.   Is one of the EOF flags used? Are more than one used to signal this condition, and if so, which ones? And what is the timeout value at which time the frames are discarded?

Thanks in advance,

- Steve

BTW, I strongly believe the ISL to be overloaded, and I am sometimes getting errors reported at the host, and sometimes not.  The not reported cases are the ones; I am worried about, since it provides an opportunity for data inconsistencies.

   

SW5120054:admin> porterrshow
          frames      enc    crc    crc    too    too    bad    enc   disc   link   loss   loss   frjt   fbsy
       tx     rx      in    err    g_eof  shrt   long   eof     out   c3    fail    sync   sig
     =========================================================================================================
  0:   60.4m 266.4m   0      0      0      0      0      0      0     24      0      0      0      0      0
  1:    0      0      0      0      0      0      0      0      0      0      0      0      0      0      0
  2:    0      0      0      0      0      0      0      0      0      0      0      0      0      0      0
  3:    0      0      0      0      0      0      0      0      0      0      0      0      0      0      0
  4:    0      0      0      0      0      0      0      0      0      0      0      0      0      0      0
  5:    0      0      0      0      0      0      0      0      0      0      0      0      0      0      0
  6:    0      0      0      0      0      0      0      0      0      0      0      0      0      0      0
  7:    0      0      0      0      0      0      0      0      0      0      0      0      0      0      0
  8:   40.5m  27.7m   0      0      0      0      0      0    110      1      0      2      2      0      0
  9:  685.1m 476.3m   0      0      0      0      0      0    108      0      0      2      2      0      0
10:  466.4m 336.0m   0      0      0      0      0      0     54      0      0      1      1      0      0
11:  504.9m 353.8m   0      0      0      0      0      0     54      0      0      1      1      0      0
12:    6.4k   3.2k   0      0      0      0      0      0    326      0      0      6      6      0      0
13:  397.2m 746.2m   0      0      0      0      0      0      0     15      0      0      0      0      0
14:  336.1m 466.4m   0      0      0      0      0      0      0      1      0      0      0      0      0
15:  353.8m 504.9m   0      0      0      0      0      0      0      1      0      0      0      0      0
16:  308.7m 238.8m   0      0      0      0      0      0     54      0      0      1      1      0      0
17:    0      0      0      0      0      0      0      0      0      0      0      0      0      0      0
18:  225.8m  32.6m   0      0      0      0      0      0    187.0k  23      0      2      3      0      0
19:    4.1g   2.5g   0      0      0      0      0      0    324      0      0      6      6      0      0
20:  238.8m 308.7m   0      0      0      0      0      0      0      1      0      0      0      0      0
21:   61.4k  61.4k   0      0      0      0      0      0      0      0      0      0      0      0      0
22:  670.4m 461.8m   0      0      0      0      0      0     55      0      0      1      1      0      0
23:    2.5g   4.1g   0      0      0      0      0      0      0      6      0      0      0      0      0
24:   10.8m  35.6m   0      0      0      0      0      0      0      1      0      0      0      0      0
25:    6.4k   3.2k   0      0      0      0      0      0    324      0      0      6      6      0      0
26:    3.3k   1.7k   0      0      0      0      0      0    326      0      0      6      6      0      0
27:    3.3k   1.7k   0      0      0      0      0      0    389      0      0      6      6      0      0
28:   35.6m  10.8m   0      0      0      0      0      0     56      0      0      1      1      0      0
29:  540.9m 609.3m   0      0      0      0      0      0      0     15      0      0      0      0      0
30:    1.6k   3.1k   0      0      0      0      0      0      0      6      0      0      0      0      0
31:    1.6k   3.1k   0      0      0      0      0      0      0      6      0      0      0      0      0
32:    4.2k   2.6k   0      0      0      0      0      0    325      0      0      6      6      0      0
33:  803    468      0      0      0      0      0      0    330      0      0      6      6      0      0
34:  384    708      0      0      0      0      0      0      0      6      0      0      0      0      0
35:    0      0      0      0      0      0      0      0      0      0      0      0      0      0      0
36:   63.9k  65.5k   0      0      0      0      0      0      0      6      0      0      0      0      0
37:    0      0      0      0      0      0      0      0      0      0      0      0      0      0      0
38:  864    492      0      0      0      0      0      0    329      0      0      6      6      0      0
39:    0      0      0      0      0      0      0      0      0      0      0      0      0      0      0
SW5120054:admin> portstatsshow 0
stat_wtx                1289999955  4-byte words transmitted
stat_wrx                3954830401  4-byte words received
stat_ftx                60467468    Frames transmitted
stat_frx                266451918   Frames received
stat_c2_frx             0           Class 2 frames received
stat_c3_frx             266431084   Class 3 frames received
stat_lc_rx              9327        Link control frames received
stat_mc_rx              0           Multicast frames received
stat_mc_to              0           Multicast timeouts
stat_mc_tx              0           Multicast frames transmitted
tim_rdy_pri             1           Time R_RDY high priority
tim_txcrd_z             4742733     Time TX Credit Zero (2.5Us ticks)
tim_txcrd_z_vc  0- 3:  0           0           4742733     0
tim_txcrd_z_vc  4- 7:  0           0           0           0
tim_txcrd_z_vc  8-11:  0           0           0           0
tim_txcrd_z_vc 12-15:  0           0           0           0
er_enc_in               0           Encoding errors inside of frames
er_crc                  0           Frames with CRC errors
er_trunc                0           Frames shorter than minimum

er_toolong              0           Frames longer than maximum
er_bad_eof              0           Frames with bad end-of-frame
er_enc_out              0           Encoding error outside of frames
er_bad_os               0           Invalid ordered set
er_rx_c3_timeout        0           Class 3 receive frames discarded due to timeout
er_tx_c3_timeout        24          Class 3 transmit frames discarded due to timeout
er_c3_dest_unreach      0           Class 3 frames discarded due to destination unreachable
er_other_discard        0           Other discards
er_type1_miss           0           frames with FTB type 1 miss
er_type2_miss           0           frames with FTB type 2 miss
er_type6_miss           0           frames with FTB type 6 miss
er_zone_miss            0           frames with hard zoning miss
er_lun_zone_miss        0           frames with LUN zoning miss
er_crc_good_eof         0           Crc error with good eof
er_inv_arb              0           Invalid ARB
open                    0           loop_open
transfer                0           loop_transfer
opened                  0           FL_Port opened
starve_stop             0           tenancies stopped due to starvation
fl_tenancy              0           number of times FL has the tenancy
nl_tenancy              0           number of times NL has the tenancy
zero_tenancy            0           zero tenancy

Valued Contributor
Posts: 931
Registered: ‎12-30-2009

Re: "Class 3 transmit frames discarded due to timeout"

So my question is, how does the switch signal the target that a number of frames were discarded in the transmission between the switches.   Is one of the EOF flags used? Are more than one used to signal this condition, and if so, which ones? And what is the timeout value at which time the frames are discarded?

Class 3 traffic is connectionless so no acknowlegdements are sent. A higher level protocol needs to check is all frames are received and if not reqeust an resend of the sequence. Errors can arise due to high traffic volumes or perhaps zoning errors.

But if you think your ISL are oversubscribed, try adding another and or look at portperfshow to see how much traffic it handels

Super Contributor
Posts: 635
Registered: ‎04-12-2010

Re: "Class 3 transmit frames discarded due to timeout"

I don't beleave that you will see with perfshow an overloaded ISL.

Dicards are very often IO driven and not through put driven errors. Portperfshow will not show you IO related problems.  It displays through put.

The discards are due to timeout which basicly mean the frame is hold for a while in the ASIC. The switch didn't get a receive ready back from the other side of the ISL. And this means a device on the other end of the ISL is not processing the data as quick as they are delivered.

You can provide an additional ISL but if this will increase the speed of the slow device which cause the problem.

If you add an additional ISL the discards will decrease but this doesn't fix the real problem. You just increase to "parking area" for  frames on the way to the destination.

Keep in mid that the server which are reporting these IO error are maybe only a sufferer,

Check bottleneckmon feature to find the bad guy on your SAN.

Watch for ports with a high buffer credit zero value.

The error counter shows many ENC out. Are these values static or did they increase?

If they increasing I would check the cables and SFPs before working on the discard issue,

I hope this helps,

Andreas

New Contributor
Posts: 3
Registered: ‎04-21-2010

Re: "Class 3 transmit frames discarded due to timeout"

Thank you for your advice on how to correct the problem, however that is not what I was looking for exactly

If the switch knows it dropped a Class 3 frame that was part of a exchange going between initiator and target, how does the switch signal the target the fames have been lost?   Or is the responsibily of the receiver of the exchange to figure out it did not get all the frames in the exchange?

Super Contributor
Posts: 635
Registered: ‎04-12-2010

Re: "Class 3 transmit frames discarded due to timeout"

The receiver will run into an timeout and notice an incomplete exchange.

The switch can drop command frames or data frames. If I rember this correctly in case of a dropped command frame the recovery tooks longer compared to data frames. But not sure at the moment.

I hope this helps,

Andreas

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