hi! i'm using slackware 14 64bit. i receive my official ip-address from isp via dhcp. if i'm using slack's default program 'dhcpcd' - which is started by rc.inet1 script, it works, but mtu's are decreased to 576 - according to this worth traffic is very very slow...
if i send a kill to the dhcpcd-process and i run dhclient, the mtu's are set to the default 1500 and internet works fine. so my question is: why is it so? why does dhcpcd not work as it should? of course, i can use dhclient in future, but this isn't the goal...
thx for your help

michael

You can add a "-C" option to dhcpcd in "/etc/rc.d/rc.inet1.conf". That how to use "-C" to bypass setting the MTU is given as an example in "man dhcpcd".

Refer to this post for how to add dhcp options in "/etc/rc.d/rc.inet1.conf".

1 members found this post helpful.

thx for your quick answer... i'm in office now, but i'll try your hint if i'm home.

Something sounds odd. 576 is the minimum MTU value the DHCP protocol requires to operate, although the standard says you can specify a smaller value in the options. I would expect most clients would ignore such values or default to the minimum 576; as it would make little sense to configure an interface that way because lease renewals would likely fail.

In absence of any MTU option configured I am getting an MTU of 1500 after calling dhcpcd. Is it possible you have some unusual MTU dhcp option on this network? You would need to look at the DHCP server configuration, it may be that dhcpcd is trying to do the right thing and respect an option that other clients are ignoring.

You can probably change

option interface_mtu

to

nooption interface_mtu

in /etc/dhcpcd.conf if you don't have control of the dhcpserver.

your tip was great - it works