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New Member

3640 with CRC errors on FastEthernet

I'm a novice at this so please bear with me. I'm getting excessive CRC

errors (1000/hour) on my FastEthernet interface:

Cisco#show inter fa0/0

FastEthernet0/0 is up, line protocol is up

Hardware is AmdFE, address is [masked]

Description: HPH LAN segment

Internet address is [masked]

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

reliability 254/255, txload 1/255, rxload 1/255

Encapsulation ARPA, loopback not set

Keepalive set (10 sec)

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

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

Last input 00:00:00, output 00:00:00, output hang never

Last clearing of "show interface" counters never

Input queue: 1/200/0/0 (size/max/drops/flushes); Total output drops: 0

Queueing strategy: fifo

Output queue: 0/40 (size/max)

5 minute input rate 135000 bits/sec, 62 packets/sec

5 minute output rate 119000 bits/sec, 39 packets/sec

919684 packets input, 227671290 bytes

Received 586948 broadcasts, 0 runts, 0 giants, 0 throttles

3002 input errors, 3002 CRC, 0 frame, 0 overrun, 0 ignored

0 watchdog

0 input packets with dribble condition detected

993314 packets output, 252568077 bytes, 0 underruns

0 output errors, 0 collisions, 2 interface resets

0 babbles, 0 late collision, 0 deferred

0 lost carrier, 0 no carrier

0 output buffer failures, 0 output buffers swapped out

The switch was rebooted around 3 hours ago.

The router has a ds3/atm module (nm-1a-t3) -- the WAN and the

FastEthernet module -- the LAN.

The 3640 is hooked up to a Linksys Gigabit Ethernet Switch using

cat5e cable. Most of the other systems on this switch are at 1000Mb/s vs.

the 3640 router at 100Mb/s. The switch shows no errors on any of

the ports. I've swapped both the cable to the router and the

FastEthernet module itself (had a spare), with no noticible change.

As for diagnosing this issue, I'm confused by "3002 input errors".

In my mind "input" could mean input from the router (via the WAN) or

input from the LAN. Is it possible the ATM module is spitting out

bad packets internally to the router? What else should I look at?

Thanks much. -- Bud

1 ACCEPTED SOLUTION

Accepted Solutions
Hall of Fame Super Bronze

Re: 3640 with CRC errors on FastEthernet

It seems you are forcing the speed/duplex setting at the 3640, go with auto/auto.

4 REPLIES
Hall of Fame Super Bronze

Re: 3640 with CRC errors on FastEthernet

It seems you are forcing the speed/duplex setting at the 3640, go with auto/auto.

New Member

Re: 3640 with CRC errors on FastEthernet

That seems to have fixed it! I assumed that fixing it at 100/full would be best. What was the error in my thinking and what did you see that tipped you off?

-- Bud

Hall of Fame Super Bronze

Re: 3640 with CRC errors on FastEthernet

You mentioned you were connecting to a LinkSys switch (which most likely is non-managed) so the switch is running auto/auto by default. Setting the speed/duplex in the router to 100/FD would produce a speed/duplex mismatch.

See Cisco table here:

http://www.cisco.com/en/US/products/hw/switches/ps700/products_tech_note09186a00800a7af0.shtml

The show interface output stated you were hardcoding the speed/duplex.

New Member

Re: 3640 with CRC errors on FastEthernet

Thanks again!

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