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Disable bad bugfix in 9.405-5 "Fix [NUTM-2840]: [AWS] UTM ignores MTU sent by DHCP server"

Vegard77Norway

Do not do this if you don't feel comfortable messing up your UTM. 

I'm pretty shure this voids the warranty.  But my UTM is pretty useless using a MTU of 576 from my ISP.

The 9.405-5 upgrade introduces a mandatory, non disable, usage of the MTU provided with DHCP, if one is provided.

A lot of us have ISP's that provide bad MTU values. Like my own ISP giving a MTU of 576 (Confirmed with wireshark).

This is what you need to do to disable the usage of MTU from DHCP. Beware, you will be touching the system, and also.. it will not update MTU based on any DHCP.

(I'm not telling you how to get into the UTM, if you don't know... you have no business being there... better wait for the fix.)

In the 

/var/chroot-dhcpc/etc

There is a file named: default.conf

cat default.conf

interface "[<INTERFACE>]" {
timeout 20;
retry 60;
script "/usr/sbin/dhcp_updown.plx";
request subnet-mask, broadcast-address, time-offset,
routers, domain-name, domain-name-servers, host-name,
domain-search, nis-domain, nis-servers,
ntp-servers, interface-mtu;
[<HOSTNAME>]
}

"interface-mtu" : If you remove that (not the following ;!!!), and take your interface down/up, your MTU is possible to edit by hand again in the GUI.

AND ... it will use the number you give it, not the dumb MTU value one of your ISP's let be in their equipment because they did not bother to change it.

Finally I have a UTM back up and working, and I can get back to business.



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  • Hi,

    Interesting post and to update all, this is under development NUTM-4992.

    Thank you for patience.

    Sachin Gurung
    Team Lead | Sophos Technical Support
    Knowledge Base  |  @SophosSupport  |  Video tutorials
    Remember to like a post.  If a post (on a question thread) solves your question use the 'This helped me' link.

  • in reply to sachingurung

    sachingurung said:

    Hi,

    Interesting post and to update all, this is under development NUTM-4992.

    Thank you for patience.

    Thanks for the feedback!

    Next time you try to support [feature](Jumboframes at AWS) through modifcation of [featuresett](DHCP client) I hope you consider that there might be bad configs floating around. 

    AWS is like a vacation resort compared to the rest of the ISP's out there. Making modifications based on a tiny part of the ecosystem is dangerous.

    But, I guess you have re learnt that experience.

    By the way. I tried to share this with you moments after the update hit. As a homeuse license user I was not able to file a ticket.

    I don't have a problem with that. Just don't expect us to help, if we can not file tickets, and Sophos don't bother to read the forum.

    [6]

Reply
  • in reply to sachingurung

    sachingurung said:

    Hi,

    Interesting post and to update all, this is under development NUTM-4992.

    Thank you for patience.

    Thanks for the feedback!

    Next time you try to support [feature](Jumboframes at AWS) through modifcation of [featuresett](DHCP client) I hope you consider that there might be bad configs floating around. 

    AWS is like a vacation resort compared to the rest of the ISP's out there. Making modifications based on a tiny part of the ecosystem is dangerous.

    But, I guess you have re learnt that experience.

    By the way. I tried to share this with you moments after the update hit. As a homeuse license user I was not able to file a ticket.

    I don't have a problem with that. Just don't expect us to help, if we can not file tickets, and Sophos don't bother to read the forum.

    [6]

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