How to change MTU with ip link

Changing the MTU with ip link set is useful when a tunnel, VPN, VLAN, or restrictive WAN path cannot carry the default Ethernet frame size cleanly. Setting the correct MTU helps prevent oversized packets from fragmenting or disappearing when the path overhead is larger than expected.

The MTU is a per-interface link property shown in ip link show output. Running ip link set dev DEVICE mtu MTU updates the live kernel setting immediately, so new traffic on that interface starts using the new frame size as soon as the command succeeds.

An incorrect MTU can create intermittent stalls, retransmissions, or black-holed traffic that is harder to diagnose than a complete outage. Confirm the interface name first, use a value that matches the network design or path-MTU findings, and update the host's persistent network configuration separately if the change must survive a reboot or interface restart.

Steps to change MTU with ip link:

Check the target interface name and its current MTU before making the change.

$ ip link show dev eth0
2: eth0: &lt;BROADCAST,MULTICAST,UP,LOWER_UP&gt; mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
    link/ether 52:54:00:ab:cd:ef brd ff:ff:ff:ff:ff:ff

Replace eth0 with the interface carrying the affected traffic.

Set the new MTU value on the interface.
```
$ sudo ip link set dev eth0 mtu 1400
```
Replace 1400 with the MTU required by the path, tunnel, or overlay. No output usually means the change was accepted.

Verify that the running interface now reports the new MTU.

$ ip link show dev eth0
2: eth0: &lt;BROADCAST,MULTICAST,UP,LOWER_UP&gt; mtu 1400 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
    link/ether 52:54:00:ab:cd:ef brd ff:ff:ff:ff:ff:ff

Test the affected application or path if the MTU change was made for a tunnel, VPN, or constrained network segment.

Success is not only the new value in ip link show. The traffic that required the change should also stop fragmenting or stalling.
Update the persistent network configuration too if the new MTU must survive interface recreation or reboot.

ip link set mtu changes runtime state only, so the value usually reverts when the interface is recreated by the host's normal network configuration tool or after a reboot.