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Understanding uRPF Loose Mode /Strict Mode,

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Last Modified: 2018-09-16
Understanding uRPF Loose Mode /Strict Mode,

Let's say we have R1 connected on both of its 2 interfaces to R2 and R3
R1 interface IP address(192.168.12.1/24) connecting to R2
R1 interface IP address(192.168.13.1/24) connecting to R3

R2 interface IP address(192.168.12.2/24) connecting to R1
R3 interface IP address(192.168.13.3/24) connecting to R1

R2 has a loopback 0 with ip address 2.2.2.2/32

R1 has static route : Ip route 2.2.2.2 255.255.255.255 192.168.12.2

For test purpose I have created lopback 0 on R3 with the same IP address 2.2.2.2/32 as the loopback 0 on R2

With Strict Mode or Loose Mode configured, I can ping from R2 (source Loopback 0:2.2.2.2) to R1 (192.168.12.1)
I can see the ping replies. but I cannot ping from R3 (Source Loopback 0: 2.2.2.2) to R1 (192.16.13.1).
However when reading online, it states that with Loose Mode, R1 will accept packets from R3 and with Strict Mode it does not.
from my side, I still cannot see the difference between Strict/Loose Mode as both will cause Ping fails from R3 source loopback 0 to R1

Any clarification on this ?

Thank you
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Author

Commented:
Ping Reply still times out, when Ping Request comes from a different Source Interface than the one when send the static route to.
and this is either for Strict or Loose mode..

So this makes me unable to see the difference between both modes.

Author

Commented:
I will revisit this topic later