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Maniphest T9464

WWAN interface mtu not updating
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Description

I have noticed a bug where the MTU size from the configuration does not actually update the wireless interface MTU. So it is set in the cli, gets validated and the interface restarts but the change is not applied.

So I run

set interfaces wwan wwan0 mtu 1000
commit

It takes a few seconds to process and restart.

I then run

show interfaces wwan

and get

wwan wwan0 {
  address dhcp
  apn REDACTED
  authentication {
    password PASSWORD
    username USERNAME
  }
  description "SIM card"
  mtu 1000
}

But when I run

run show interfaces

I still get

Codes: S - State, L - Link, u - Up, D - Down, A - Admin Down
Interface    IP Address         MAC                VRF        MTU  S/L    Description
-----------  -----------------  -----------------  -------  -----  -----  ----------------
wwan0        REDACTED           n/a                default   1500  u/u    SIM card

Details

Version
-
Is it a breaking change?
Behavior change
Issue type
Bug (incorrect behavior)

Related Objects

Event Timeline

MSonger created this task.Wed, Oct 14, 2:18 PM
Viacheslav subscribed.Wed, Oct 14, 2:48 PM

Which version?

Viacheslav triaged this task as Normal priority.Wed, Oct 14, 2:48 PM
MSonger added a comment.Wed, Oct 14, 3:54 PM

This behaviour was observed on our current production version from January 2026.
I have tried it on the rolling version from the 7th October but i cannot get this version to work because it is affected by the interface renaming bug (T9291), so the WWAN interface will not come up at all.
I guess we have to wait until the bug is fixed before we can test if the bug we discovered is still applicable.

pasik subscribed.Wed, Oct 14, 4:43 PM