[c-nsp] 3550<->3750 mtu miss-match, periodic giant errors on cooper

David Freedman david.freedman at uk.clara.net
Mon Mar 15 09:07:19 EDT 2010


Well, the giants are not accompanying drops so usually this means that
they are being accepted.

On an increasing number of IOS based platforms, giants actually refer to
anything over 1500/1518 (even if the interface/system MTU has been
raised above thi) so nothing to worry about.

The "giant" frames are more likely to come from the payload (i.e your IP
network) at a guess

Dave.

Ruzhanskaya Olga wrote:
> Hello List!
> 
> In our network we have some places with common connection design, when two switches are cooper-connected via Gigabit Ethernet ports:
> C3550-48, Gi0/1 <-> Gi1/0/1, C3750G
> 
> 1) 3750G (E)
> IOS version: 12.2(50)SE2
> 3750#sh system mtu 
> System MTU size is 1998 bytes
> System Jumbo MTU size is 9198 bytes
> Routing MTU size is 1500 bytes
> 2) 3550
> IOS version: 12.2(35)SE3
> 3550# sh system mtu 
> System MTU size is 1546 bytes
> 
> On the side of 3550, there are some input errors, exactly - giants. They have periodic manner - 2-3 errors every 40 minutes.
> As I understand, those errors are caused by mtu mismatch. But why are they so periodic? Is it some sort of keepalives (and I shouldn't worry about)?
> Also, there is one location, where Catalysts are connected via fiber (all settings are the same as described ), but there are no such errors=giants. So, can media-type influence errors?  
> 
> Examples:
> -----------------------------------------
> 1) Cooper:
> -----------------------------------------
> 3550(c)#sh int gi0/2                                                                  
> GigabitEthernet0/2 is up, line protocol is up (connected)
>   Hardware is Gigabit Ethernet, address is 0012.4309.4b32 (bia 0012.4309.4b32)
>   Description: ---# Gi trunk to CORE
>   MTU 1546 bytes, BW 1000000 Kbit, DLY 10 usec, 
>      reliability 255/255, txload 14/255, rxload 21/255
>   Encapsulation ARPA, loopback not set
>   Keepalive not set
>   Full-duplex, 1000Mb/s, link type is auto, media type is 1000BaseTX
>   input flow-control is off, output flow-control is off
>   ARP type: ARPA, ARP Timeout 04:00:00
>   1000BaseT module (WS-G5483) in GBIC slot.
>   Last input 00:00:27, output 00:00:24, output hang never
>   Last clearing of "show interface" counters 4d00h
>   Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
>   Queueing strategy: fifo
>   Output queue: 0/40 (size/max)
>   30 second input rate 82605000 bits/sec, 11875 packets/sec
>   30 second output rate 57005000 bits/sec, 6973 packets/sec
>      2113350708 packets input, 1672028074 bytes, 0 no buffer
>      Received 36984218 broadcasts (0 multicasts)
>      0 runts, 478 giants, 0 throttles
>      478 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
>      0 watchdog, 18983558 multicast, 0 pause input
>      0 input packets with dribble condition detected
>      1478563366 packets output, 2493416609 bytes, 10543 underruns
>      0 output errors, 0 collisions, 0 interface resets
>      0 babbles, 0 late collision, 0 deferred
>      0 lost carrier, 0 no carrier, 0 PAUSE output
>      10543 output buffer failures, 0 output buffers swapped out
> -----------------------------------------
> 2) Fiber:
> -----------------------------------------
> 3550(f)#sh int gi0/1            
> GigabitEthernet0/1 is up, line protocol is up (connected)
>   Hardware is Gigabit Ethernet, address is 0011.20a3.8c31 (bia 0011.20a3.8c31)
>   Description: ---# Gi trunk to CORE
>   MTU 1546 bytes, BW 1000000 Kbit, DLY 10 usec, 
>      reliability 255/255, txload 1/255, rxload 1/255
>   Encapsulation ARPA, loopback not set
>   Keepalive not set
>   Full-duplex, 1000Mb/s, link type is auto, media type is 1000BaseLX
>   input flow-control is off, output flow-control is off
>   ARP type: ARPA, ARP Timeout 04:00:00
>   Last input 00:00:05, 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)
>   30 second input rate 602000 bits/sec, 227 packets/sec
>   30 second output rate 455000 bits/sec, 197 packets/sec
>      287412652 packets input, 2003280838 bytes, 0 no buffer
>      Received 1865881462 broadcasts (0 multicasts)
>      0 runts, 0 giants, 0 throttles
>      0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
>      0 watchdog, 1834251298 multicast, 0 pause input
>      0 input packets with dribble condition detected
>      296750587 packets output, 1987939750 bytes, 0 underruns
>      0 output errors, 0 collisions, 1 interface resets
>      0 babbles, 0 late collision, 0 deferred
>      0 lost carrier, 0 no carrier, 0 PAUSE output
>      0 output buffer failures, 0 output buffers swapped out
> 
> Any suggestions are appreciated.
>  
> Best regards,
> Olga 
>   
> 
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