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ex3400 setup MTU size on specific interface.

‎11-23-2018 07:31 AM

Hi all, hope you are well !!!

I have an issue with ex3400 ( Junos 15.1X53-D58.3 ) where I want to setup specific MTU on an interface ge-3/0/10 which is a L2 Access port with a specific Vlan assigned to it. 

I go edit interface ge-3/0/10 >> Set mtu 1500.
Then, set disable >> commit

then, delete disable >> commit

This is to make sure interface goes down and then up to be 100% sure that change will apply. 
When I do this, the VLAN where my interfece belongs to has MTU 1500 instead of 1514.

How is it possible 1 physical port 's settings to affect the entire Vlan users and loose connectivity ?

Is there any other step that must be done before this setting is applied to the interface ?
Thanks in advance. 

2 REPLIES 2
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Ethernet Switching

Re: ex3400 setup MTU size on specific interface.

‎04-05-2019 08:05 AM

Good day,

 

Please use this link to understand how MTU calculated.

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Ethernet Switching

Re: ex3400 setup MTU size on specific interface.

‎04-06-2019 06:00 AM

Vendors differ in how the calculate the size of standard ethernet so Juniper & ALU for example include the extra 14/18 bytes while Cisco does not.

 

In short if you are using standard ethernet, just don't change the MTU manually.  Only make this adjustement if you are using jumbo frames of some size.

 

What problem were you seeing on the link that made you suspect a MTU mismatch issue?

 

Steve Puluka BSEET - Juniper Ambassador
IP Architect - DQE Communications Pittsburgh, PA (Metro Ethernet & ISP)
http://puluka.com/home
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