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Created attachment 1613928 [details]
Reproducer

Description of problem:

Considering scenario eth0 and two VLANs on top eth0.10 and eth.20 all of them with MTU 2000. When we change the MTU of eth0 and eth0.20 and apply this config the MTU of eth0.10 is reverted to default value (1500), but in the NM has still 2000 in the config. 


Version-Release number of selected component (if applicable):

NetworkManager-1.20.0-3.el8.x86_64

How reproducible:

100%

Steps to Reproduce:

Full reproducer is in attachment. 

Actual results:

76: dummy_abc: <BROADCAST,NOARP,UP,LOWER_UP> mtu 2200 
77: dummy_abc.10@dummy_abc: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 
79: dummy_abc.20@dummy_abc: <BROADCAST,NOARP,UP,LOWER_UP> mtu 2200 


Expected results:

76: dummy_abc: <BROADCAST,NOARP,UP,LOWER_UP> mtu 2200 
77: dummy_abc.10@dummy_abc: <BROADCAST,NOARP,UP,LOWER_UP> mtu 2000 
79: dummy_abc.20@dummy_abc: <BROADCAST,NOARP,UP,LOWER_UP> mtu 2200

https://gitlab.freedesktop.org/NetworkManager/NetworkManager/merge_requests/273

Can you please target this for RHEL 8.1.1?

(In reply to Beniamino Galvani from comment #4)
> (In reply to Beniamino Galvani from comment #3)
> 

Editing the MTU/s on a server, especially on a hypervisor is a common practice and supported by layered products like RHV.
This problem seems like a regression (seems to have worked before) and it is too basic not to handle as soon as possible.

Setting flags for inclusion in 8.1.z.

Anita, can you please approve this Z stream request by setting zstream+ ?

Thanks!
Sushil

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2020:1847