Fortinet NSE4 Training - Reverse Path Failure (RPF)

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Reverse Path filter or Reverse Path Failure (aka RPF) can be a tricky concept to grasp. In this video I provide some examples with short, concise explanations that will help you understand what RPF is and why we use it.

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[TomWhi]

I'm glad you went with a diagram because I think it lands so much better than I can imagine a demo would. I got a question on the NSE4 on RPF and yours was the first video that made sense.

[RedEyeCoding]

man... do you have any idea how i've been looking for a clear explanation. So many folks on here (youTube) make it difficult to understand....geez. thank you so much.

[darkcnotion]

Excellent, also I learned feasible ignores the distance metric but checks priority.

[robertchism]

Wow. This was good, Chris! Very simple explanation. Thank you.

[eduardodacunha]

Thank you for sharing the content, it was very easy to understand after your explanation.

[networkengineerblogs]

A few people have asked how it works with a default route. In feasible/loose mode it will be no different for a default route. The default route counts as a valid route. Source: NSE4 study guide.

[GGoblin]

The most easy explanation on RPF ever, thank you very much sir!
This helps with refreshing nse4 knowlegde for NSE7 cert :)

[ravichande]

Chris, i guess there is some misconception as RPF checking is all about checking source IP address in routing table and not Destinaion IP address. Here is the study guide RPF notes.. "The reason behind the RPF check is that if FortiGate receives a packet on an interface, and FortiGate doesn’t have a route to the packet source address through the incoming interface, then the source address of the packet could have been forged, or the packet was routed incorrectly. In either case, you want to drop that unexpected packet, so it doesn’t enter your network."

[kmcgaughmohr]

Thanks for the easy and clear explanation!

[anthonywainman]

Fantastic Vid! A clear and concise explanation... this really helped me understand RPF. Thanks Chris.

[saifemran]

Another great video. Thank you, Chris!

[dermyan]

Great explanation. Just what I was hunting around for. I wonder though, what impact does a default route have route matching?

[deepakkhadka]

Very easy to understand .. Great explanation.

[ajeesh]

Hi Chris, my doubt is when a default route to internet like Destination=0.0.0.0/0 and exit interface wan .How the RPF will work here, for example the fortigate have a default route to internet like this

set status enable
set dst 0.0.0.0 0.0.0.0
set gateway 218.208.110.1
set distance 10
set weight 0
set priority 0
set device "wan2"

[shomrshabbos]

good video. pls make more for the lab setup used in previous video's. also are there books you used to pass the exam?

[arthurfaizal]

so in this case, those 3 address at the top act as source or destination?

[skitheworld]

But always there is a default route, so feasible will never stop no spoof, ???

[ale]

Can you recommend a good book for the ns4?

[anonymoususer]

Not clear or helpful and wastes too much time at the beginning .