How to change MTU settings in HPUX 11i

[James Smith_20]

I need to change the MTU setting for the lan0 interface to 1440. If I try to do it in SAM it is greyed out. I tried to edit the /etc/rc.config.d/hpetherconf file and add HP_ETHER_MTU[0]=1440 that did not work either. I then tried ndd -set /dev/tcp tcp_mss_max 1440 and that also did not work.

Am I missing something?

[Joël Techer · Accepted solution]

hi

try lanadmin -x ..
see the man pages for lanadmin beacause i don't remember the syntax

Regards

Jean-Louis

[rick jones]

Out of curiousity, why do you need to chance the MTU to 1440 bytes?

FWIF, while they are related, MSS != MTU - the MSS will only (in theory) change the MSS negotiated by TCP, not the MTU of the link.

It might be possible to set a smaller MTU to specific destinations with the route command.

[James Smith_20]

The workstation I am trying to change is transferring data over an ANX secure connection and the configuration at the other end is setup for an MTU of 1440.

[spex]

Hi,

# lanadmin -M 1440 0

To make the change permanent:
# ls -l /etc/rc.config.d/*lanconf
to get a listing of conf files for your lan interfaces. Then modify the appropriate config for your card.

PCS

[James Smith_20]

Thank you all for the assistance.

The command I used was lanadmin -M 1440 0 which set the MTU and also kept this setting after I rebooted the machine. I did check all the /etc/rc.config.d/*lanconf files and none were modified after I ran the above command. I am not sure where this change is stored at but as long as the settings remain after a restart it doesn't matter.

[James Smith_20]

I was wrong about the settings remaining on reboot. You will need to find the proper lanconf file and edit the setting for MTU for the settings to remain.

[rick jones]

SO this is a pt-pt sort of connection, or is there a router somewhere that should be sending the 11i box ICMP messages about datagrams being too big?

(Sorry if ANX implies the answer, it is to me an unfamiliar TLA)