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XGS - internal DNS issue

Petr Kriz

Good day, I am facing a strange issue with domain name resolution. Some domains are not resolved by XGS internal DNS. Below are nslookups from XGS Advanced shell. It used to work but suddenly stoped few days ago.
Thank you for advice.

DNS Configuration

     Current IPv4 DNS Configuration : Static

          DNS 1 : 8.8.8.8
          DNS 2 : 1.1.1.1
          DNS 3 : N.A.

     Current IPv6 DNS Configuration : Static

          DNS 1 : N.A.
          DNS 2 : N.A.
          DNS 3 : N.A.

SFVH_SO01_SFOS 19.5.3 MR-3-Build652# nslookup -debug www.facebook.com 127.0.0.1
;; connection timed out; no servers could be reached

SFVH_SO01_SFOS 19.5.3 MR-3-Build652# nslookup -debug facebook.com 127.0.0.1
Domain Name Server#  127.0.0.1
Domain Name       #  facebook.com
Resolved Address 1#  157.240.30.35
Total query time  #  8.02 msec
Domain Name       #  facebook.com
Resolved Address 1#  2a03:2880:f13d:83:face:b00c:0:25de
Total query time  #  12.99 msec

SFVH_SO01_SFOS 19.5.3 MR-3-Build652# nslookup -debug www.facebook.com 8.8.8.8
Domain Name Server#  8.8.8.8
Domain Name       #  www.facebook.com
Resolved Address 1#  star-mini.c10r.facebook.com.
Resolved Address 1#  157.240.30.35
Total query time  #  4.87 msec
Domain Name       #  www.facebook.com
Resolved Address 1#  2a03:2880:f13d:83:face:b00c:0:25de
Total query time  #  6.02 msec

Thank you for any hint how to investigate this.

Best regards Petr.



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  • 0

    Hi Petr,

    Thank you for reaching out to Sophos Community.

    Have you tried to use any how-to videos, documentation, Sophos Assistant, or KBA to try to check the issue?

    To verify, your Sophos Firewall DNS is set to Google public DNS 8.8.8.8

    Kindly try to restart the DNS services, test with other DNS servers, and also check the log viewer for any DNS related errors

    Erick Jan
    Community Support Engineer | Sophos Technical Support
    Sophos Support Videos | Product Documentation  |  @SophosSupport  | Sign up for SMS Alerts
    If a post solves your question use the 'Verify Answer' link.

  • 0 in reply to Erick Jan

    Hi, Erik, in the meanwhile it started to work again. But it took 4 days to somehow refresh the internal DNS cache or whatever.
    I had also tried to restart the whole box but with no luck. As you can see if I used internal resolver with nslookup (XGS had DNS set to 8.8.8.8) it returned ;; connection timed out; no servers could be reached. If I used nslookup with explicitly defining the same DNS as has XGS configured - 8.8.8.8, it worked.
    So the question is if it's possible to "flush" the internal DNS cache. Restarting the service or the whole box hadn't helped before it started to work again.
    Perhaps it cached the response of temporary failure of DNS response because of ISP connectivity problems.

    Best regards
    Petr

  • 0 in reply to Petr Kriz

    Hi Petr,

    You can flush the DNS cache by stopping and starting the DNS service on the GUI. You can do this from System Services > Services.

    Or you may try the following.

     How to clear DNS cache ? 

    Also, I would recommend reaching out to Sophos Support if you re-encounter the said issue, create a case, and share it here. 

    Erick Jan
    Community Support Engineer | Sophos Technical Support
    Sophos Support Videos | Product Documentation  |  @SophosSupport  | Sign up for SMS Alerts
    If a post solves your question use the 'Verify Answer' link.

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