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Undersized frames



I got a Cisco 1841 router with HWIC-4ESW module that's connected to a Catalyst 2960 switch through a trunk link. Both connected interfaces have equal settings (duplex full and speed 100, MTU set as default).

On the switch: "sh interfaces fastEthernet 0/1 counters errors" showing increase in the numbers of undersized frames received by switch:

Port Align-Err FCS-Err Xmit-Err Rcv-Err UnderSize

Fa0/1 0 0 0 0 520

On the switch :"sh interfaces fastEthernet 0/1 controller"

FastEthernet0/1 is up, line protocol is up (connected)

Hardware is Fast Ethernet, address is 0017.0ef8.9c83 (bia 0017.0ef8.9c83)

Description: trunk to 1841 Fa0/0

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

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

Encapsulation ARPA, loopback not set

Keepalive set (10 sec)

Full-duplex, 100Mb/s, media type is 10/100BaseTX

input flow-control is off, output flow-control is unsupported


Transmit FastEthernet0/1 Receive

47325749 Bytes 118224174 Bytes

192797 Unicast frames 115621 Unicast frames

2025 Multicast frames 58934 Multicast frames

2045 Broadcast frames 3309 Broadcast frames

0 Too old frames 111149330 Unicast bytes

0 Deferred frames 4081197 Multicast bytes

0 MTU exceeded frames 211776 Broadcast bytes

0 1 collision frames 0 Alignment errors

0 2 collision frames 0 FCS errors

0 3 collision frames 0 Oversize frames

0 4 collision frames 33710 Undersize frames

0 5 collision frames 0 Collision fragments

0 6 collision frames

0 7 collision frames 12566 Minimum size frames

0 8 collision frames 60372 65 to 127 byte frames

0 9 collision frames 27747 128 to 255 byte frames

0 10 collision frames 6032 256 to 511 byte frames

0 11 collision frames 4243 512 to 1023 byte frames

0 12 collision frames 66904 1024 to 1518 byte frames

0 13 collision frames 0 Overrun frames

0 14 collision frames 0 Pause frames

0 15 collision frames

0 Excessive collisions 0 Symbol error frames

0 Late collisions 0 Invalid frames, too large

0 VLAN discard frames 0 Valid frames, too large

0 Excess defer frames 0 Invalid frames, too small

62571 64 byte frames 33710 Valid frames, too small

100777 127 byte frames

On the router some commands run without any errors.

I test both interfaces on half-duplex (and _ or ) 10Mbps but unsuccessful. I try to connect switch to other interface on HWIC but undersized frames counter still increase in the number. And, of course, I try to use other UTP path. All unsuccessful.

Any idea about the problem ?

Best regards.

Andrey Babkin

New Member

Re: Undersized frames


Check this one:

Looks quite similar to your case.

Best regards,

Mikhail Galiulin

New Member

Re: Undersized frames

Mikhail, thank you for your answer.

I am to draw attention to LED on my C2960, but LED on C2960 newer blinking amber. And IOS version on my device (12.2(25)FX) top-of-the IOS version specified in your link.

I think it's a problem of HWIC-4ESW installed on 1841, but i do not have one more HWIC for check up. And what strange occurrence, that is all other interfaces on HWIC newer have errors while work with hosts directly connected to interface.

Best regards,

Andrey Babkin

New Member

Re: Undersized frames


Check whether it is possible to upgrade IOS on 1841. It can help. According to the document in my previous answer only short dot1q encapsulated frames are counted as undersized, which explains why you never got this error with hosts directly connected to the interface.

Best regards,

Mikhail Galiulin

New Member

Re: Undersized frames

Thans Mikhail.

I shall try to upgrade IOS on 1841. I hope too, it may help.

Best regards,

Andrey Babkin

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