What exactly does the "show interfaces" RELIABILITY indicator tell me?

Unanswered Question
Aug 31st, 2007

In the "show interfaces" IOS command, when reliability falls below 255/255, does that indicate physical errors on the interface or does it indicate frame errors in the packets (or both)?

I have a customer who's ISP-facing interface is showing around a 240 to 250 out of 255 reliability (see "show int" cut-and-paste below).

Can I narrow this down to a physical problem or is it more likely something simple like duplex mismatch or similar?

Ethernet0 is up, line protocol is up

Hardware is PQUICC Ethernet, address is 0009.xxxx.xxxx (bia 0009.xxxx.xxxx)

Description: connected to Internet

Internet address is xx.xx.xxx.xxx/29

MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec,

reliability 248/255, txload 8/255, rxload 9/255

Encapsulation ARPA, loopback not set

Keepalive set (10 sec)

Full-duplex, 10BaseT

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 00:19:52

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

Queueing strategy: fifo

Output queue: 0/40 (size/max)

5 minute input rate 389000 bits/sec, 80 packets/sec

5 minute output rate 342000 bits/sec, 70 packets/sec

83216 packets input, 49013057 bytes, 0 no buffer

Received 9868 broadcasts, 0 runts, 1 giants, 0 throttles

3448 input errors, 1917 CRC, 1530 frame, 0 overrun, 0 ignored

0 input packets with dribble condition detected

75054 packets output, 55232531 bytes, 0 underruns

0 output errors, 0 collisions, 0 interface resets

0 babbles, 0 late collision, 0 deferred

0 lost carrier, 0 no carrier

0 output buffer failures, 0 output buffers swapped out

I have this problem too.
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Edison Ortiz Fri, 08/31/2007 - 14:06

>In the "show interfaces" IOS command, when reliability falls below 255/255,

> does that indicate physical errors on the interface or does it indicate frame errors in the packets (or both)?

You won't have frame errors without having input errors so the reliability measures the input and output errors counter.

>Can I narrow this down to a physical problem or is it more likely something simple like duplex mismatch or similar?

Start with the duplex mismatch, fairly easy solution. If that doesn't work, examine the physical connectivity between devices.

purohit_810 Fri, 08/31/2007 - 16:45

Hi,

output seems to be CRC error also. {Read below with care and Mainly concetrate on CAT-5 Cable... are you using CAT-5 cable????? because u are using 10baseT port}

Mosst probably when Relibility Low and CRC error shows,

CRC:

CRC = cyclic redundancy check. A CRC error occurs when the CRC generated by the originating station or far-end device does not match the checksum calculated from the data received. On a LAN, this usually indicates noise or transmission problems on the LAN interface or the LAN bus. A high number of CRCs is usually the result of collisions or a station transmitting bad data.

To resolve the issue:

Excessive noise

Step 1

Use the show interface ethernet exec command to determine the status of the device's Ethernet interfaces. The presence of many CRC errors but not many collisions is an indication of excessive noise.

Step 2

Inspect the cables for damage.

Step 3

Look for badly spaced taps1, which could cause reflections.

Step 4

If you are using 100Base-TX, make sure you are using Category 5 cabling.2

URL: http://www.cisco.com/univercd/cc/td/doc/product/voice/ics/ics25/icstg25/tsether2.htm

Regards,

Dharmesh Purohit

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