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From "Andrija Panic (JIRA)" <>
Subject [jira] [Commented] (CLOUDSTACK-7790) VXLAN interface MTU change from 1450 to 1500 and JUMBRO frames
Date Wed, 26 Nov 2014 09:37:13 GMT


Andrija Panic commented on CLOUDSTACK-7790:

Now I see the way to acually make this works, and that is to really increase MTU in the first
place on the physical device (ethX or bridge).

When vxlan driver creates new vxan interface and corresponding bridge - it will create MTU
that is exactly 50bytes smaller than the MTU on the physical device ethX/bridge.

This was never mentioned in the documentation in the first place. But at least there is a
correct way to setup things. Will try to update docs.

> VXLAN interface MTU change from 1450 to 1500 and JUMBRO frames
> --------------------------------------------------------------
>                 Key: CLOUDSTACK-7790
>                 URL:
>             Project: CloudStack
>          Issue Type: Bug
>      Security Level: Public(Anyone can view this level - this is the default.) 
>          Components: Network Controller
>    Affects Versions: 4.4.1
>         Environment: NOT important - CentOS 6.5, elrepo kernel 3.10 - 
>            Reporter: Andrija Panic
>            Priority: Critical
>              Labels: frames, jumbo, vxlan
> By default, when using vxlan as isolation method for Guest traffic - cloudstack created
vxlan vbidge and interface, and set's MTU for those to 1450 bytes.  Problem is that default
OS MTU for any VM is 1500 and all packets get droped (except maybe DHCP and ping which uses
smaller packets).
> 1) Current proposed solution is to change MTU inside VM/template to 1450 - which is absolutely
NOT user friendly and degrades performance
> 2) Better approach - set MTU on vxlan interface and bridge to a default value of 1500,
and ask ADMIN to increase MTU to 1600 bytes on physical interface ethX or cloudbrX and enable
at least 1600 frames on physical network
> 3) Even better - add GUI component to CloudStack for a MTU value, so the ADMIN can deploy
JUMBRO frames accross whole Guest network - this should be probably enabled per network offering,
or similar.
> Current setup, require MTU change inside VM is not a good solution, and does not enable
user to use JUMBRO frames at all...

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