how to implement uRPF when multiple WAN and LAN interfaces exists

[mohammed hashim]

hi,

in this topology:

R1 knows about 8.8.8.8 through both ISP-1 and ISP-2,

how to configure R1 to match the picture when spoof packets came from WAN, or LAN, these spoof packets should be denied, without affecting the redundancy 

appreciate your help,

[Philip D'Ath]

The effectiveness of RPF on dual homed ISP connections is rather limited.  Assuming both ISPs also advertise a default route, you can probably use something like:

On the ISP interfaces you'll need to use something like:

ip verify unicast source reachable-via any allow-default

I personally wouldn't use RPF in this scenario due to the risk of something going wrong.