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FCL DNS issues after SSLVPN had been connected

FortiEMS internal DNS Servers are configured on the all Ethernet adapters if SSLVPN is online.

  • jfi. FortiGate distributes the DNS Servers configured in the SSLVPN Settings, or the Portal.

You may change this behavior, if you select the VPN Profile click  Advanced and then disabl prefer SSL VPN DNS

Below you may find further informations.

Maybe you’re also expieriencing DNS cache issues, then you may also check the DNS Cache Service Control.


Screenshot is from FortiEMS Server 6.4.8 but applies also to version 7.0.x and maybe above

Windows Client DNS cache troubleshooting tips

check your current DNS Servers for your adapters with ipconfig /all

Check the Windows Client DNS cache with ipconfig /displaydns

You may verify the currently resolved ip address  for a domain with a ping.

ping

PS C:\Users> ping www.c3it.net

Ping wird ausgeführt für www.c3it.net [81.19.159.38] mit 32 Bytes Daten:

Antwort von 81.19.159.38: Bytes=32 Zeit=29ms TTL=53

check DNS cache

PS C:\Users> Get-DnsClientCache -Name www.c3it.net

Entry                     RecordName                Record Status    Section TimeTo Data   Data

                                                    Type                     Live   Length

—–                     ———-                —— ——    ——- —— —— —-

www.c3it.net              www.c3it.net              A      Success   Answer    2269      4 81.19.159.38

nslookup to your DNS server (! this might not be the same result as if you do a simple ping)

PS C:\Users> nslookup www.c3it.net

Server:  UnKnown

Address:  fda1:3fb1:0:10f::1

Nicht autorisierende Antwort:

Name:    www.c3it.net

Address:  81.19.159.38

wireshark (usally it would be a overkill to troubleshoot a simple DNS request)