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

[David Freedman]

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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