# PROBLEM DESCRIPTION

During installation, if automatic netowrk configuration is selected, the
MTU size provided by the DHCP server is not set.

This is crucial if d-i runs in a virtual machine (Proxmox, qemu) which MTU
is set to a lower value than 1500 and thus results in an unaccessible
network connection when d-i tries to contact the repository server. Then,
wget hangs for a really, really long time and returns with an error and no
mirror is used.

Circumventing this issue by manually setting desired MTU after configuring
the network (ip link dev <dev> set mtu <size>) works flawlessly.

Also, there is no possibility to set the MTU size during manual network
configuration.



# STEPS TO REPRODUCE

Run d-i inside a vm (Proxmox, qemu) with a host's MTU size less than 1500.


# EXPECTED BEHAVIOR

The MTU size provided by the DHCP server should be recognized and used to
configure the network.

Hi Michael,

Michael <reportbug@hemathor.de> (2026-05-12):

Did you try writing to /sys/class/net/<interface>/mtu?

It seems busybox's udhcpc only supports a limited set of DHCP options,
and MTU isn't on the list, from a quick look at common.h (commented out
#defined) and common.c, which implement option parsing.


Cheers,