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johnm
johnm
New Member
August 12, 2019
Question

DNS being passed when not permitted

  • August 12, 2019
  • 1 reply
  • 2831 views

Why is DNS traffic being passed even though it is not explicitly permitted?  Such things cause me concern.  Is it the DNS helper?

 

Version: FortiGate-500E v6.0.5,build0268,190507 (GA)

 

flow trace:

id=20085 trace_id=2449 func=print_pkt_detail line=5494 msg="vd-root:0 received a packet(proto=17, 202.xx.17.50:53743->104.44.193.243:53) from agg1.930. " id=20085 trace_id=2449 func=init_ip_session_common line=5654 msg="allocate a new session-07c990cc" id=20085 trace_id=2449 func=vf_ip_route_input_common line=2591 msg="find a route: flag=04000000 gw-122.yy.111.60 via agg1.200" id=20085 trace_id=2449 func=fw_forward_handler line=751 msg="Allowed by Policy-4294967295: SNAT" id=20085 trace_id=2449 func=__ip_session_run_tuple line=3322 msg="SNAT 202.xx.17.50->122.yy.111.61:53743" id=20085 trace_id=2449 func=__ip_session_run_tuple line=3373 msg="run helper-dns-udp(dir=original)"

    1 reply

    johnm
    johnmAuthor
    New Member
    August 16, 2019

    a bit more info... so it appears to be the "implicit-allow-dns".  I believe that may be set when choosing NGFW Policy-mode.  The problem is that "implicit" rule does not use the central SNAT policy, and does an interface SNAT regardless.  bug?

     

    https://help.fortinet.com/fos60hlp/60/Content/FortiOS/fortigate-firewall/Concepts%20-%20Firewall/DNS%20traffic%20in%20NGFW%20policy-mode.htm?Highlight=policy%20mode

     

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