HP 5920 Series Configuration Manual page 365

Figure 121 uRPF work flow
Yes
Source IP address
matches an ARP entry?
No
1. uRPF checks source address validity:
Discards packets with a broadcast source address.
Discards packets with an all-zero source address but a non-broadcast destination address. (A
packet with source address 0.0.0.0 and destination address 255.255.255.255 might be a
DHCP or BOOTP packet and cannot be discarded.)
Proceeds to step 2 for other packets.
Checks the received packet
Broadcast source
address?
No
All-zero source address?
No
Matching FIB entry
found?
Yes
Yes
Loose uRPF?
No
Yes
Matching route is a direct
route?
No
Receiving
interface matches the
output interface of the
matching FIB entry？
No
354
Yes
Yes
Yes
Broadcast destination
address?
No
Default route found?
Yes
Yes
Loose uRPF?
No
Receiving
Yes
interface matches the output
interface of the default
route？
Yes
Allows the packet to pass
No
Discards the packet
No
No