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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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Parents

  • Thank you very much VegardOestengen!  We have spent the last 24 hours trying to figure out why after the 9.405-5 update, users were unable to access their network shares on their NAS (QNAP). (They connect via an IPSEC site-to-site VPN). We tried quite a few troubleshooting methods until I found your post here.

    Once we made the changes on the config file in the Sophos, users were able to see the shares on the QNAP again.  Hopefully Sophos fixes this bug in the next UP2DATE patch.

    Thanks again!

  • in reply to ChrisShill

    ChrisShill said:

    Thank you very much VegardOestengen!  We have spent the last 24 hours trying to figure out why after the 9.405-5 update, users were unable to access their network shares on their NAS (QNAP). (They connect via an IPSEC site-to-site VPN). We tried quite a few troubleshooting methods until I found your post here.

    Once we made the changes on the config file in the Sophos, users were able to see the shares on the QNAP again.  Hopefully Sophos fixes this bug in the next UP2DATE patch.

    Thanks again!

    Thanks for the feedback! Its a easy fix once you figure out who / what the culprit is, and have a blueprint to follow.

    Based on the feedback I might actually consider sharing more fix'es in the future. [:$]

    Again. Very good to know someone puts this to good use.

Reply
  • in reply to ChrisShill

    ChrisShill said:

    Thank you very much VegardOestengen!  We have spent the last 24 hours trying to figure out why after the 9.405-5 update, users were unable to access their network shares on their NAS (QNAP). (They connect via an IPSEC site-to-site VPN). We tried quite a few troubleshooting methods until I found your post here.

    Once we made the changes on the config file in the Sophos, users were able to see the shares on the QNAP again.  Hopefully Sophos fixes this bug in the next UP2DATE patch.

    Thanks again!

    Thanks for the feedback! Its a easy fix once you figure out who / what the culprit is, and have a blueprint to follow.

    Based on the feedback I might actually consider sharing more fix'es in the future. [:$]

    Again. Very good to know someone puts this to good use.

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