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DHCP issues on External Interface with ISP

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I have been using UTM for many years now... 6+?  When I first started, there were issues with certain Intel nics when used with DHCP and Cable Modems.

Lately, I have been having problems again.  I have had MANY calls with my ISP, I even went ahead and bought new hardware for my UTM.  Same problem.  I rarely get an IP address from my ISP and when I do, the external interface will only stay "up" for a brief period - and then drop again.

I plugged my "Gateway desktop" directly into my Cable Modem and it ran without an issue for 3 days.  Then I added an ASUS RT-N66 in as a "router".  That ran fine for a week - with A LOT of traffic going through it. 

I add the UTM and BAM!  I am back down again.

My question is - WHERE do I begin to troubleshoot this?  confd logs?  TCPDUMP?  My UTM seems happy to get a DCHP address from my ASUS if I test it that way...  I don't want to bail on Sophos, but I don't know what else to do.  Many years ago, I put an old router between my Cable Modem and my Sophos machine.  I really don't want to do that again.

UTM 9.355-1       

External NIC is an Intel Gigabit PCIe   EXPI9301CT

Quad core i3 with 4GB RAM, 160 GB HDD

Thoughts?  Advice, Similar issues?



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  • 0

    Seems to be the same issue I'm facing with a Netgear LTE modem LB1110 in bridge mode, I have to manually renew the DHCP lease or reset the interface.  After the first lease period expires the interface fails.

    The purpose of this configuration is for DynDNS to work for VPN connections, which works great apart from the issue of DHCP renewal failing.

    I'm back in router mode on the modem and now DHCP renewal works but I can't get DynDNS to work (obviously), it picks up the NAT'd address not ISP assigned.  Modem also doesn't support DynDNS so I can't configure at the modem.

    I see some suggestions for extending the DHCP response timeout, so will give that a try.

     

    Any other suggestions to get this config to work?

Reply
  • 0

    Seems to be the same issue I'm facing with a Netgear LTE modem LB1110 in bridge mode, I have to manually renew the DHCP lease or reset the interface.  After the first lease period expires the interface fails.

    The purpose of this configuration is for DynDNS to work for VPN connections, which works great apart from the issue of DHCP renewal failing.

    I'm back in router mode on the modem and now DHCP renewal works but I can't get DynDNS to work (obviously), it picks up the NAT'd address not ISP assigned.  Modem also doesn't support DynDNS so I can't configure at the modem.

    I see some suggestions for extending the DHCP response timeout, so will give that a try.

     

    Any other suggestions to get this config to work?

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  • 0 in reply to Aoffield

    A coupla things...

    If you can determine that the renewal should occur at about the same time every day, you can create a cron job to do that.  Assuming that the External interface is on eth1 and you want it renewed at 4AM every day add the following line to /etc/crontab-static:

    0 4 * * * root /usr/local/bin/confd-client.plx interface_dhcp_renew_lease eth1

    After you've done that, do something to force WebAdmin to reconstitute /etc/crontab, e.g., change the 'Firmware Download Interval', [Apply], change it back and [Apply].

    If you don't mind the double NAT, you can change your DynDNS 'IP strategy' to "Web service (IPv4)."

    Cheers - Bob

     
    Sophos UTM Community Moderator
    Sophos Certified Architect - UTM
    Sophos Certified Engineer - XG
    Gold Solution Partner since 2005
    MediaSoft, Inc. USA
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