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Maximum Transmission Unit Design

Latest reply: Dec 22, 2018 09:44:28 1533 5 10 0 0

Generally, the IP layer controls the maximum length of frames that are sent each time. Any time the IP layer receives an IP packet to be sent, it checks to which local interface the packet is to be sent and queries the MTU of the interface. Then, the IP layer compares the MTU with the packet length to be sent. If the packet length is greater than the MTU, the IP layer fragments the packet to ensure that the length of each fragment is smaller or equal to the MTU.

If forcible unfragmentation is configured, certain packets are lost during data transmission at the IP layer. To ensure jumbo packets are not dropped during transmission, you need to configure forcible fragmentation. In this case, you can run the mtu command to set the size of a fragment.

In the MAN network, the customer will deploy many VPN service, such as the L3VPN, L2VPN. The data packet of these VPN service is bigger than the comman IP data packet, if the MTU is small, there will have a lot of fragmented packet.

In this case we can set the MTU of the interface.

In Huawei device the default value of MTU is 1500, we can change it as below:

NE20/NE40/NE9000 configuration template is as below:

Table 1-1 MTU Configuration in NE05/NE20/NE40/NE9000

#

interface interface-type   interface-number

mtu 9192

#

commit

#

For the S5720, we can configure the MTU on the VLANIF interface directly, if we configure it on the physic interface, we should change the port on Layer 3.

The S5720 MTU configuration template is as below:

Table 1-2 MTU Configuration in S5720

#

interface interface-type   interface-number

undo portswitch

mtu 9192

#

interface vlanif vlan-id

mtu 9192

#

This is what I want to talk about/share with you today, thank you!


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YOO
Created Dec 22, 2018 08:40:32

It is very helpful for the learner in the first stage.can you add more picture?
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JoneSnow
Created Dec 22, 2018 08:42:57

What's the effect of different MTU values?
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DZKM
Created Dec 22, 2018 08:55:44

Why you can add pictures???
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Yolanda_617
Created Dec 22, 2018 09:40:23

Hope to add more pic
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user_2915719
Created Dec 22, 2018 09:44:28

Wrong MTU settings easily cause wired problems, this post is quite useful.
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