[c-nsp] C3750E routing jumbo frames

[David DeSimone]

Artyom Viklenko <artem at aws-net.org.ua> wrote:
>
> Can you show output of 'sh int gi1/0/9'?
> What MTU you see in it?

MTU looks correct:

GigabitEthernet1/0/9 is up, line protocol is up (connected)
  Hardware is Gigabit Ethernet, address is xxxx.xxxx.xxxx (bia xxxx.xxxx.xxxx)
  MTU 9000 bytes, BW 1000000 Kbit, DLY 10 usec, 
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Full-duplex, 1000Mb/s, media type is 10/100/1000BaseTX
  input flow-control is off, output flow-control is unsupported 
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input never, output 00:00:01, 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 184000 bits/sec, 12 packets/sec
  5 minute output rate 6000 bits/sec, 9 packets/sec
     43906882 packets input, 51922635816 bytes, 0 no buffer
     Received 78 broadcasts (0 multicasts)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 0 multicast, 0 pause input
     0 input packets with dribble condition detected
     35639936 packets output, 10247979705 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

> IMHO, you need mtu command in interface config.

For our 6500's this is true, "mtu 9000" is needed in the interface
config.  However, Our 3500's and 3700's do not accept this command. 
They appear to derive the MTU from the VLAN membership.

I will be deploying a new router next week, so I will get yet another
chance to confront this issue.  Confirmed that the new router does show
the 'system mtu routing 9000' in its preconfigured state, so I'll see
what happens after we connect the first servers to it.

-- 
David DeSimone == Network Admin == fox at verio.net
  "I don't like spinach, and I'm glad I don't, because if I
   liked it I'd eat it, and I just hate it." -- Clarence Darrow


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