FortiClient IPsec VPN does not connect sometimes

[damianhlozano]

Hello team!!

I hope you are doing well!!

We have 2 Fortigates 100F in HA with many IPsec VPNs for FortiClient users.

Just one user has a problem to connect from his house.  When he use another internet connection in the same computer this works fine but with his own ISP sometime does it fails (Sometimes work also)

When this fails, I can see the following logs on Fortigate:

date=2025-09-11 time=12:38:58 eventtime=1757605138121774900 tz="-0300" logid="0101037134" type="event" subtype="vpn" level="notice" vd="root" logdesc="IPsec phase 1 SA deleted" msg="delete IPsec phase 1 SA" action="delete_phase1_sa" remip=RemoteIP locip=LocalIP remport=18052 locport=4500 outintf="port9" cookies="b77cf798b4edb960/b7f28e5eae0677b7" user="1011" group="N/A" useralt="N/A" xauthuser="N/A" xauthgroup="N/A" assignip=N/A vpntunnel="IPsec-IT-W3" fctuid="N/A" advpnsc=0
date=2025-09-11 time=12:38:38 eventtime=1757605118948074500 tz="-0300" logid="0101037127" type="event" subtype="vpn" level="notice" vd="root" logdesc="Progress IPsec phase 1" msg="progress IPsec phase 1" action="negotiate" remip=RemoteIP locip=LocalIP remport=18102 locport=500 outintf="port9" srccountry="Argentina" cookies="b77cf798b4edb960/b7f28e5eae0677b7" user="1011" group="N/A" useralt="N/A" xauthuser="N/A" xauthgroup="N/A" assignip=N/A vpntunnel="IPsec-IT-W3" status="success" init="remote" mode="aggressive" dir="outbound" stage=1 role="responder" result="OK" fctuid="N/A" advpnsc=0
date=2025-09-11 time=12:38:38 eventtime=1757605118977300400 tz="-0300" logid="0101037127" type="event" subtype="vpn" level="notice" vd="root" logdesc="Progress IPsec phase 1" msg="progress IPsec phase 1" action="negotiate" remip=RemoteIP locip=LocalIP remport=18102 locport=4500 outintf="port9" srccountry="Argentina" cookies="b77cf798b4edb960/b7f28e5eae0677b7" user="1011" group="N/A" useralt="N/A" xauthuser="N/A" xauthgroup="N/A" assignip=N/A vpntunnel="IPsec-IT-W3" status="success" init="remote" mode="aggressive" dir="inbound" stage=2 role="responder" result="DONE" fctuid="N/A" advpnsc=0
date=2025-09-11 time=12:38:38 eventtime=1757605118977889960 tz="-0300" logid="0101037127" type="event" subtype="vpn" level="notice" vd="root" logdesc="Progress IPsec phase 1" msg="progress IPsec phase 1" action="negotiate" remip=RemoteIP locip=LocalIP remport=18052 locport=4500 outintf="port9" srccountry="Argentina" cookies="b77cf798b4edb960/b7f28e5eae0677b7" user="1011" group="N/A" useralt="N/A" xauthuser="N/A" xauthgroup="N/A" assignip=N/A vpntunnel="IPsec-IT-W3" status="success" init="local" mode="xauth" dir="outbound" stage=1 role="initiator" result="OK" fctuid="N/A" advpnsc=0

If I ping the Fortigate IP from the computer, I get answers, so this is not a route issue.

I thought maybe this is another issue with his ISP, but I dont think so, because sometimes does this work.

Do you have any idea?

Thanks in advance.

Regards,

Damián

[AEK]

Hi Damian

According to your description I suspect the ISP, even if the issue is intermittent.

You should contact the ISP to ask if there is any limitation or restriction with IPsec.