Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. And see here for current known issues.

New Member

Cisco 2620 router slows down and then doesn't respond for awhile

I'm getting complaints from customers that my router slows down, then doesn't respond for awhile -- then it comes back on.  I've checked and it has not power cycled.  I've also noticed that trying to login that sometimes it's hung and cannot access it.   Any ideas what this could be?  I'm using a T1 for my bandwidth.   It's a heavily used network -- heavy internet load.

Should I be getting interface resets?   I've noticed that there are a number of them (see below) and the rouer was last rebooted 17 hours ago.



5 minute output rate 413000 bits/sec, 157 packets/sec
     4753435 packets input, 3416899557 bytes, 0 no buffer
     Received 5625 broadcasts, 0 runts, 622 giants, 0 throttles
     2662409 input errors, 543016 CRC, 1730657 frame, 0 overrun, 0 ignored, 388711 abort
     3886871 packets output, 853661919 bytes, 0 underruns
     0 output errors, 0 collisions, 169 interface resets

5 minute output rate 1403000 bits/sec, 195 packets/sec
     3883591 packets input, 903321446 bytes
     Received 8488 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog
     0 input packets with dribble condition detected
     4681091 packets output, 3458905320 bytes, 0 underruns
     0 output errors, 0 collisions, 1 interface resets
     0 babbles, 0 late collision, 0 deferred
     0 lost carrier, 0 no carrier
     0 output buffer failures, 0 output buffers swapped out


Re: Cisco 2620 router slows down and then doesn't respond for aw

Hi Greg

I could see lots of CRC errors interface flaps(resets) and other link related errors on the interface.

I would suggest to clear the counters once and monitor the link for brief period of time, if you still face similar kinda problem better to check with your telco/sp and get your physical link checked.

Also you have not posted the current reliability of the link which will be available in the first few lines of show interface serial x/x command.

Check your logs using show logs for what exactly happening in your router when it freezes, also check out for faulty dsu/csu device connected to this router.


New Member

Re: Cisco 2620 router slows down and then doesn't respond for aw

Thanks for the reply.  I reset the interface ... the telco claims they were having problems, however the link still does not look clean.  Here are the stats ... what are your thoughts?  It looks like a lot of errors in 6 minutes since being cleared.  Thoughts?

Can you explain the "Reliability" line?


Serial0/0 is up, line protocol is up
  Hardware is PQUICC with Fractional T1 CSU/DSU
  Description: PTP T1 to Qwest DS1IT-11711
   MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
     reliability 236/255, txload 23/255, rxload 77/255
  Encapsulation HDLC, 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 00:06:09
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: weighted fair
  Output queue: 1/1000/64/0 (size/max total/threshold/drops)
     Conversations  1/6/256 (active/max active/max total)
     Reserved Conversations 0/0 (allocated/max allocated)
     Available Bandwidth 1158 kilobits/sec
  5 minute input rate 467000 bits/sec, 110 packets/sec
  5 minute output rate 140000 bits/sec, 98 packets/sec
     41187 packets input, 22887066 bytes, 0 no buffer
     Received 36 broadcasts, 0 runts, 0 giants, 0 throttles
     7380 input errors, 2979 CRC, 2724 frame, 0 overrun, 0 ignored, 1677 abort
     36387 packets output, 5266090 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 output buffer failures, 0 output buffers swapped out
     0 carrier transitions
     DCD=up  DSR=up  DTR=up  RTS=up  CTS=up

New Member

Re: Cisco 2620 router slows down and then doesn't respond for aw

You have several input errors.

I would suggest you to engage the service provider again.

The actual layer 1 issues and its statistics are retrieved from the controllers so issue sh controllers for the serial 0/0. I guess this is a T1 line so "sh controllers T1 0/0"

It will probably show you statistics on intervals for each 15 minutes until the past 24 hours. Then, the last one is the sum of all statistics in the last 24 hrs.

Since you are seeing errors, engage the provider and ask them to make some tests.

Actually, remotely, the provider can not guarantee that there is no problem with its part. This is because the telco is not able to loop the smart jack interface using the customer side interface (Tx and Rx from smart jack that connects the CE).To do so, the only way to prove it, is to loop physically the smart jack using the loopback plug.

Remote tests don't prove the smartjack customer's interface (side). I may say it  does not pass thru the entire smartjack if there is no loopback loop on it.

If the provider tells you that they are good until the smartjack (demark point) but not good to CSU, If they did not prove the smart jack physically it still might be a provider issue.

They must prove the smart jack to state that there are no issues.

Sometimes I have to keep pushing some technicians until they discover a problem related to the WAN circuit. depending on the provider, almost all tests are automated and nobody touch it.

Keep pusinhg the provider, of course, based on technical  arguments.

sometimes, the providers have an external modem. They should check it also.

Then, if provider find nothing wrong after they prove the smartjack and chcking the modem, but you still see errors, check your equipment (its interface/WIC) and the cable.

Basically there are 3 kind of errors:

LOF - Loss of frame

LOS - Loss of signal

OOF - Out of frame

Anyway, there are several counters based on those 3 types and also based on the direction of the problems.


Re: Cisco 2620 router slows down and then doesn't respond for aw

Hi Gregg

Reliability specifies the quality of the physical link connected onto the interface, in normal conditions it should be 255/255 which indicates the link is quite clean and good.

In your case its 236/255 which means still your link is not error-free,also the kinda errors accumulated within 6 mins of clear counter is alarming and definitely requires a through check.

i would suggest the above links for more info.


New Member

Re: Cisco 2620 router slows down and then doesn't respond for aw

Thanks guys ... big help!