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New Member

Fast ethernet problem on 3845

Hello everyone,

I am facing a strange problem We have Cisco 3845 router and ISP has provided a MPLS link. When we terminate it on laptop our next hop starts pinging. but when we connect it on router it donot ping to next hop. We changed the slot of WIC card and also replaced the card. After replacing the card and changing the slot we were properly recieving the ping replies but it stops after some time. Interface remains up and up . No log is there is logging.

Please suggest if there any way to get the exact problem or how to resolve the problem




Re: Fast ethernet problem on 3845

please post a sh interface fa x/x !

check output hangs ? errors ?

New Member

Re: Fast ethernet problem on 3845

MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec,

   reliability 255/255, txload 1/255, rxload 1/255

Encapsulation ARPA, loopback not set

Keepalive set (10 sec)

Half-duplex, 100Mb/s, 100BaseTX/FX

ARP type: ARPA, ARP Timeout 04:00:00

Last input 02:08:01, output 00:00:02, output hang never

Last clearing of "show interface" counters never

Input queue: 0/75/22994/0 (size/max/drops/flushes); Total output drops: 0

Queueing strategy: fifo

Output queue: 0/40 (size/max)

5 minute input rate 0 bits/sec, 0 packets/sec

5 minute output rate 0 bits/sec, 0 packets/sec

   18312085 packets input, 3573047684 bytes

   Received 22148 broadcasts, 0 runts, 0 giants, 0 throttles

   1 input errors, 0 CRC, 1 frame, 0 overrun, 0 ignored

   0 watchdog

   0 input packets with dribble condition detected

   29238839 packets output, 3470205501 bytes, 0 underruns

   291840 output errors, 315890 collisions, 4 interface resets

   0 unknown protocol drops

   0 babbles, 138884 late collision, 38754 deferred

   9 lost carrier, 0 no carrier

   0 output buffer failures, 0 output buffers swapped


Re: Fast ethernet problem on 3845

could you please change the duplex to full and do the ping test ?

New Member

Re: Fast ethernet problem on 3845

it is negotiated by it. we have configured  that interfa

ce to duplex auto and speed auto


Re: Fast ethernet problem on 3845


if one side is hard coded to full duplex (sp side) and the other side to auto (your side),

the side configured for auto should fall back to half duplex ..

configuring a full duplex should do the job !

again would be interested to know link speed/duplex mode of your Laptop NIC card too which you were telling worked without any issues.

New Member

Re: Fast ethernet problem on 3845

laptop is working on auto auto also when I change router port to full duplex . it's line protocol goes down. 

Re: Fast ethernet problem on 3845

Why do you have the interface set to half-duplex?

Change it to full-duplex so that you should not see collision errors and not so many output errors.

You can clear the interface counters and try the connection again to see if the errors persist.

I assume that when you connect the laptop or the router, you're using the same IP configuration on both?

Are you hardcoding the IP information or getting it dynamically?