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New Member


Hi All,

I have several Cisco 3560C setup at multiple stations. The Cisco 3560C are connected in a daisy chain between each other using 100BASE-BX10-D and 100BASE-BX10-U SFP. So, on the first Cisco 3560C (station 1), I have a U-type connecting to the second Cisco 3560C (station 2.). The second Cisco 3560C (station 2) will have a D-type and U-type SFP where the D-type connects to the previous station 1 on its U-type SFP. This setup repeats for station 3 onwards.

It seems that these connections between the stations, I noticed that the Cisco switch registers the link at 100Mb half-duplex and I see incrementing CRCs and collisions. I am not able to hard-code the interface to 100Mb FULL as it seems that the interface configuration does not give me the option to do a 'speed 100' or 'duplex full'.

Is this normal for these kinds of SFP?

Below are some outputs:

Cisco IOS Software, C3560C Software (C3560c405-UNIVERSALK9-M), Version 12.2(55)EX3, RELEASE SOFTWARE (fc2)

Technical Support:

Copyright (c) 1986-2011 by Cisco Systems, Inc.

Compiled Wed 10-Aug-11 07:37 by prod_rel_team

Image text-base: 0x00003000, data-base: 0x02100000

Switch(config)#do sh int status

Port      Name               Status       Vlan       Duplex  Speed Type

Fa0/1                        notconnect   15           auto   auto 10/100BaseTX

Fa0/2                        notconnect   15           auto   auto 10/100BaseTX

Fa0/3                        notconnect   15           auto   auto 10/100BaseTX

Fa0/4                        notconnect   15           auto   auto 10/100BaseTX

Fa0/5                        connected    15         a-full  a-100 10/100BaseTX

Fa0/6                        notconnect   15           auto   auto 10/100BaseTX

Fa0/7                        notconnect   15           auto   auto 10/100BaseTX

Fa0/8                        notconnect   15           auto   auto 10/100BaseTX

Fa0/9                        notconnect   15           auto   auto 10/100BaseTX

Fa0/10                       notconnect   15           auto   auto 10/100BaseTX

Fa0/11                       connected    trunk      a-full  a-100 10/100BaseTX

Fa0/12                       connected    trunk      a-full  a-100 10/100BaseTX

Gi0/1                        connected    trunk      a-half  a-100 100BaseBX-10U SFP

Gi0/2                        connected    trunk      a-half  a-100 100BaseBX-10D SFP

Switch#sh interfaces gigabitEthernet 0/2

GigabitEthernet0/1 is up, line protocol is up (connected)

  Hardware is Gigabit Ethernet, address is c025.5c11.928d (bia c025.5c11.928d)


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

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

  Encapsulation ARPA, loopback not set

  Keepalive not set

  Half-duplex, 100Mb/s, link type is auto, media type is 100BaseBX-10D SFP

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

  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: 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 80000 bits/sec, 22 packets/sec

  5 minute output rate 16000 bits/sec, 16 packets/sec

     74931 packets input, 21611558 bytes, 0 no buffer

     Received 48734 broadcasts (39982 multicasts)

     0 runts, 0 giants, 0 throttles

     667 input errors, 667 CRC, 0 frame, 0 overrun, 0 ignored

     0 watchdog, 39982 multicast, 0 pause input

     0 input packets with dribble condition detected

     23385 packets output, 3857612 bytes, 0 underruns

     0 output errors, 564 collisions, 1 interface resets

     0 babbles, 29 late collision, 0 deferred

     0 lost carrier, 0 no carrier, 0 PAUSE output

     0 output buffer failures, 0 output buffers swapped out

Hall of Fame Super Gold

Re: 100BASE-BX10 SFP

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

Possible fault with your fibre.  The value should be "255/255" and nothing else. 

This will explain your high CRC.

As to your duplex, I have no experience using the BX SFP so I don't know why your link has negotiated to "half duplex". 

Can you change the settings of the interface to full duplex?

New Member


It is not just one fibre. All adjoining stations on the 100BASE-BX10 SFP are showing me 100 half-duplex.

Hall of Fame Super Gold


In my opinion, you have two issues:

1.  You could have a faulty fibre optic link; and

2.  Half-Duplex. 

New Member


Yes scope all connections with a 900 micron 200x scope, and clean anything you can.













If its clean, check the TX/RX power levels with a power meters.  End-to-end; bidirectional test, on both lamdas.

Because of the CWDM going on, I'm not sure I'd trust the internal "show hard" or

"show interfaces interface-id transceiver detail" internaly.

Obviously this is something common/systemic since it happens betwen multiple locations.

Is the fiber the common denominator?


You might try the following commands, to see if you can get the interface to be release the a-half duplex mode.  

media-type gbic

no negotiation auto