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T1 Serial Overruns causing CRCs?

I work for a service provider and I have a customer that is complaining of drops and CRC errors on his T1, but only when he's pushing traffic across it.  The T1 has been stress tested repeatedly and is clean.  When the customer tries to FTP a file from one location to the site in question, he sees CRC errors on his interface as well as overruns.  My thought is with the overruns, he's over utilizing the T1, but will the overruns also show up as CRCs on his interface.  See his snapshot below:


nterface Serial0/0/0
description Connection--To--
ip address x
no ip unreachables
no ip proxy-arp
encapsulation ppp
load-interval 30
service-module t1 cablelength short 110ft
service-module t1 timeslots 1-24
no cdp enable
Serial0/0/0 is up, line protocol is up
  Hardware is GT96K with integrated T1 CSU/DSU
  Internet address is x
  MTU 1500 bytes, BW 1536 Kbit/sec, DLY 20000 usec,
     reliability 255/255, txload 16/255, rxload 4/255
  Encapsulation PPP, LCP Open
  Open: IPCP, loopback not set
  Keepalive set (10 sec)
  Last input 00:00:00, output 00:00:00, output hang never
  Last clearing of "show interface" counters 01:54:36
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 2367
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  30 second input rate 27000 bits/sec, 18 packets/sec
  30 second output rate 99000 bits/sec, 18 packets/sec
     281023 packets input, 50926429 bytes, 0 no buffer
     Received 0 broadcasts (0 IP multicasts)
     16 runts, 1 giants, 0 throttles
     250 input errors, 215 CRC, 0 frame, 18 overrun, 0 ignored, 1 abort
     328138 packets output, 248533623 bytes, 0 underruns
     0 output errors, 0 collisions, 1 interface resets
     0 unknown protocol drops
     0 output buffer failures, 0 output buffers swapped out
     2 carrier transitions
     DCD=up  DSR=up  DTR=up  RTS=up  CTS=up

Hi Tater, CRC is kind of a

Hi Tater, CRC is kind of a catchall for Cisco. I have seen in some cases links become so saturated that it does cause CRC errors. But if that customer is sending only 99000 bits a second that's like .09 megabit while a T1 is 1.544 megabit. Overrun and Output drop is usually indicative of over utilization but given the amount of traffic on the T1 I may be guessing but you do you have a policy map?


Another good indication of an actual physical issue is going to be the reliability scale 255/255.  Repeatedly run a command like


show inter ser0/0/0 | inc (CRC)|(reliability)|input)


Do this many times over for about 5-10 minutes and see if there is a fluctuation in the reliability. I guess the real question is, is there an actual service impact? If it, then I don't think it matters. I know on my network, almost every ATM connection we have be it T1, DS3 or sonet, they all have CRC errors and a lot of time slowly incrementing but it's not any real issue.


-Tom Please mark answered for helpful posts
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