Investigating Strange Network Issues with Fortigate and Dual ISP
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TechWhiz42
I'm running a Fortigate with dual ISP SD WAN. This morning, users reported that they couldn't access Office 365 webmail, while those with the local Outlook app seemed fine. All O365 websites (like Admin, Outlook, Teams) wouldn't load, but installed apps are working without a hitch. I didn't see any outage notifications, so I started digging into the issue. I switched to my mobile hotspot, and everything loaded perfectly. This led me to suspect we might have a local issue, so I forced my machine to connect to our backup ISP, which made all Office services accessible again. Could this indicate an upstream routing issue with our primary ISP, or am I missing something?
Answers
You might want to run a tracert on both of your ISPs to pinpoint where the primary connection fails. If the issue is before the two lines reconverge, it could definitely indicate an upstream routing problem.
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I managed to restart the system during lunch, and I'm leaning towards a stale route being the culprit here. Luckily, everything seems normal now!
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Does your Fortigate tunnel traffic to one of their data centers, or is it just managing local SDWAN? If it's only local, then it's really just measuring connectivity and keeping that NAT table intact.
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