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Dell SmartFabric OS10 User Guide Release 10.5.4

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Default MTU Configuration

Maximum transmission unit (MTU) defines the largest packet size that an interface can transmit without fragmentation. The MTU of an interface determines whether to accept the packet ingress and egress in the switch. The interface drops any packet with size exceeding the MTU.

If you have not configured the MTU value for an interface, the default value is set automatically. Any packet exceeding this value is dropped. Starting from Release 10.5.4.4, the default MTU value is 9216 bytes. Previously, the default value was 1532 bytes. To build an MTU with higher value, configure the default MTU of the system to the required value.

You can use the following commands for MTU configuration:

  • default mtu <val>—configure a custom MTU value to all the interfaces that do not have a user configured MTU.
  • no default mtu—assign the system default value to interfaces with no custom MTU value.
  • show default mtu—verify the default MTU value at the system level.
  • show interface—view the current MTU set on the interface at the interface level. Configurations that are made at the interface level override the system default for that specific interface.
NOTE: If default MTU is configured globally and if VLAN is configured with non-default MTU, configure non-default MTU on the VLAN members as well.
NOTE: Set the MTU value on all interfaces, including logical and physical interfaces between BGP peers (iBGP and eBGP), to be uniform to avoid L2 and L3 VPN flaps.

The following examples show how to display and modify the default MTU using CLIs:

Display the default MTU 

OS10# show default mtu
Default MTU 9216 bytes
System default with no user configuration 
OS10# show interface ethernet 1/1/1
Ethernet 1/1/1 is up, line protocol is down
Hardware is Eth, address is 90:b1:00:00:00:a0
    Current address is 90:b1:00:00:00:a0
Pluggable media present, QSFP+ type is QSFP+ 40GBASE-LR4
    Wavelength is 1311
    Receive power reading is no power
Interface index is 11
Internet address is not set
Mode of IPv4 Address Assignment: not set
Interface IPv6 oper status: Disabled
MTU 9216 bytes, IP MTU 1500 bytes
LineSpeed 0, Auto-Negotiation off
Flowcontrol rx off tx off
ARP type: ARPA, ARP Timeout: 60
Last clearing of "show interface" counters: 20:45:24
Queuing strategy: fifo
Input statistics:
     0 packets, 0 octets
     0 64-byte pkts, 0 over 64-byte pkts, 0 over 127-byte pkts
     0 over 255-byte pkts, 0 over 511-byte pkts, 0 over 1023-byte pkts
     0 Multicasts, 0 Broadcasts, 0 Unicasts
     0 runts, 0 giants, 0 throttles
     0 CRC, 0 overrun, 0 discarded
Output statistics:
     0 packets, 0 octets
     0 64-byte pkts, 0 over 64-byte pkts, 0 over 127-byte pkts
     0 over 255-byte pkts, 0 over 511-byte pkts, 0 over 1023-byte pkts
     0 Multicasts, 0 Broadcasts, 0 Unicasts
     0 throttles, 0 discarded, 0 Collisions,  wred drops
Rate Info(interval 30 seconds):
     Input 0 Mbits/sec, 0 packets/sec, 0% of line rate
     Output 0 Mbits/sec, 0 packets/sec, 0% of line rate
Time since last interface status change: 20:45:25
 
 
OS10# configure terminal
OS10(config)# default mtu 9000
OS10(config)#

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