Environment

• Red Hat Enterprise Linux (All versions).

Issue

• How to test a particular MTU value is support ?
• How I can check if this MTU size is supported by each Network Card ?
• Is there any checklist to verify our environment is prepared for enable MTU change ?
• How to test the custom Jumbo Frames are supported ?

Resolution

• Testing the MTU is supported in the network.

Raw

# ping -M do -s 8972 [destination IP]

Note: there is an overhead of 28 bytes for the packet size. 8 bytes for ICMP headers and 20 bytes for Ethernet header, so the MTU is 28 bytes larger than the figure you establish through the method above. So to test for MTU of 9000, you actually need to set your ping packet size to 9000-28 = 8972.

• By adjusting the MTU value its possible to find the supported MTU value in the network.

• If the MTU value is not enables in the client side the ping output will be :

  Raw

  PING xxx.xxx.xxx.xxx (xxx.xxx.xxx.xxx): 8184 data bytes
  ping: sendto: Message too long
  

• If the MTU value is enabled in client but not in destination (or switch in between) the ping output will be :

  Raw

  PING xxx.xxx.xxx.xxx (xxx.xxx.xxx.xxx): 8184 data bytes
  Request timeout for icmp_seq 0
  

• If the MTU is supported and enabled in client and destination the ping output will be :

  Raw

  PING xxx.xxx.xxx.xxx (xxx.xxx.xxx.xxx): 8184 data bytes
  8192 bytes from xxx.xxx.xxx.xxx: icmp_seq=0 ttl=128 time=0.714 ms