Ping a network address

[unfraget1]

Hi here!

i was confused about pinging address of network

i've the next scheme:

i sending ping from R1 to the address 172.16.0.0, and R2 reply to me from the linknet of address 10.1.2.2, as result, i can see replay on R1.

R1#ping 172.16.0.255
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.0.255, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/10/16 ms

what happened is? and why i can ping address 172.16.0.0

[Dennis Mink]

you are pinging a broadcast address. what happens if you ping 

172.16.0.2???

[unfraget1]

ping doesn't pass. because, on R3 don't have a default gateway. 

[Dennis Mink]

R2 responds to the directed broadcast from R1.

check this url to get an insight into the mechanmnism:

https://learningnetwork.cisco.com/thread/25864

[unfraget1]

but, "The no ip directed broadcast has been the default on routed interfaces for a number of years now."
https://learningnetwork.cisco.com/thread/41894

in this case the R2 shouldn't responce to me

[unfraget1]

in addition, the direct broadcast for network the 172.16.0.0/24 this is 172.16.0.255, but we do send ping to address 172.16.0.0

[unfraget1]

guys, have a any ideas? :)