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Bug #4397

closed

MTU must be set in same ifconfig command as IP

Added by Chris Buechler over 9 years ago. Updated over 8 years ago.

Status:
Resolved
Priority:
High
Category:
Interfaces
Target version:
Start date:
02/09/2015
Due date:
% Done:

100%

Estimated time:
Plus Target Version:
Release Notes:
Affected Version:
All
Affected Architecture:

Description

Where MTU on an interface is user-defined, the ifconfig command that assigns the IP and IPv6 addresses must include the MTU. For instance, this:

ifconfig vmx1 mtu 9000 
ifconfig vmx1 inet 192.168.1.1 netmask 255.255.255.0

You'll end up with the NIC at MTU 9000, but the link route for 192.168.1.0/24 will be 1500. Doesn't matter if the MTU is set before or after the IP, this is the case.

If you instead run:

ifconfig vmx1 inet 192.168.1.1 netmask 255.255.255.0 mtu 9000

Then both the interface and the link route have the correct MTU. This affects IPv6 the same way, with the same resolution.

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