MTU not being set to advertised size by dhcp server

joca · 2026-03-08 17:53:01

I have tried both dhcpcd and dhclient on archlinux and the MTU size being advertised by my dhcp server is not getting set.
If I run tcpdump and watch the wire for the dhcp advertisement i can see coming from the dhcp server:

...
MTU (26), length 2: 9000
...

setting manually with ip command works fine.

if i run dhcpcd with the -d flag, i do not see any log message around setting the mtu.

I know I can fix this with an exit hook, but I would like to know why this isn't working in what I assume is the designed manner.

seth · 2026-03-08 21:05:04

https://man.archlinux.org/man/dhcpcd.conf.5.en#option

joca · 2026-03-08 22:41:28

seth wrote:

https://man.archlinux.org/man/dhcpcd.conf.5.en#option

I have read that and am already setting in dhcpcd.conf:

option interface_mtu

In my original post, I stated i also ran dhcpcd with -d to get debug options, and do not see any message about setting the mtu either.

Last edited by joca (2026-03-08 22:43:59)

seth · 2026-03-08 23:09:58

Ah, hook got ditched - https://github.com/NetworkConfiguration … /issues/67

Last edited by seth (2026-03-09 13:40:27)

Lone_Wolf · 2026-03-09 11:55:44

Seth, that links to the post the link is in . Probably a C/P error ?

seth · 2026-03-09 13:40:46

Seems like, sorry and thanks - the intended link was https://github.com/NetworkConfiguration … /issues/67

Arch Linux

#1 2026-03-08 17:53:01

MTU not being set to advertised size by dhcp server

#2 2026-03-08 21:05:04

Re: MTU not being set to advertised size by dhcp server

#3 2026-03-08 22:41:28

Re: MTU not being set to advertised size by dhcp server

#4 2026-03-08 23:09:58

Re: MTU not being set to advertised size by dhcp server

#5 2026-03-09 11:55:44

Re: MTU not being set to advertised size by dhcp server

#6 2026-03-09 13:40:46

Re: MTU not being set to advertised size by dhcp server

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