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Bug #11291

closed

WireGuard MTU Can Flap between 1420 and 1500

Added by Christian McDonald about 3 years ago. Updated about 3 years ago.

Status:
Resolved
Priority:
Normal
Assignee:
Category:
WireGuard
Target version:
Start date:
01/22/2021
Due date:
% Done:

100%

Estimated time:
Plus Target Version:
Release Notes:
Affected Version:
2.5.x
Affected Architecture:

Description

The default WireGuard MTU is typically 1420. However , I’ve observed cases where the wg interfaces will flap between 1500 and 1420. Explicitly configuring an MTU on the interface configuration fixes it

Actions #1

Updated by Christian McDonald about 3 years ago

I've nailed down clear reproduction steps...assuming that you have a WG tunnel and it's corresponding wg interface assigned.

  1. Go to the WG interface configuration and click save and apply.
  2. Check Status > Interfaces and the WG interface will have an MTU of 1500
  3. Go to the VPN > Wireguard > Tunnel configuration and click save
  4. Check Status > Interfaces again and the WG interface will now have an MTU of 1420

This is obviously problematic and was discovered by OSPF adjacency issues because the remote end had a fixed MTU of 1420, which is the WG default. I've disable MTU mismatch detection on both ends for the time being.

Actions #2

Updated by Jim Pingle about 3 years ago

  • Status changed from New to In Progress
  • Assignee set to Jim Pingle
Actions #3

Updated by Jim Pingle about 3 years ago

  • Status changed from In Progress to Feedback
  • % Done changed from 0 to 100
Actions #4

Updated by Christian McDonald about 3 years ago

Looks good, thanks for the quick update

Actions #5

Updated by Jim Pingle about 3 years ago

  • Status changed from Feedback to Resolved

MTU is stable on current snapshots. It's 1420 even after save/apply on an assigned interface.

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