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Large MTU on 1.3.1-S1
Open, Requires assessmentPublicBUG


I've recently compiled the 1.3.1-S1, built from source. Upon loading this image onto my device, the configured MTU values are no longer respected.
My configuration specifies an MTU of 9000 for each of my ethernet interfaces.

Upon booting into the image built on Wed 30 Mar 2022 19:20 UTC, no errors are observed, but all interfaces show MTU 1500.
Upon booting into the image built on Wed 23 Mar 2022 13:16 UTC, no errors are observed, and all interfaces show MTU 9000.

Setting the MTU on the broken image via "ifconfig eth0 mtu 9000" sets the MTU on the interface to 9000.

When booted into the broken image, upon loading config.boot, which specifies MTU 9000 on all interfaces, the terminal reports no configuration deltas detected. No changes applied since commit isn't available since nothing has changed.
When deleting the MTU on an interface, setting it, and committing the change, no errors are reported, and all interfaces continue to show MTU 1500.

All of this yields broken connectivity in my network given the drop of support for setting jumbo frames on interfaces via the configuration utility.


Difficulty level
Unknown (require assessment)
Why the issue appeared?
Will be filled on close
Is it a breaking change?
Behavior change
Issue type
Bug (incorrect behavior)

Event Timeline

I can't reproduce it in VyOS 1.3.1-S1 and VyOS 1.3-stable-202206240423

[email protected]:~$ show conf com | match eth1
set interfaces ethernet eth1 address 'dhcp'
set interfaces ethernet eth1 mtu '9000'

[email protected]:~$ show interfaces ethernet eth1
eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9000 qdisc pfifo_fast state UP group default qlen 1000

@Fretela which nics are you using?

sudo ethtool -i eth0