I'm confused how CIDR broadcasts work when using the all 1's address (255.255.255.255
).
From my early (Classful networking days), I recall that ping 255.255.255.255
from a machine on a Classful network causes every device on that subnet to respond. I also know that we can have directed broadcasts (e.g. 192.168.1.255
).
Now, with CIDR, device addresses need not fall into the /24 (or /16, /8) buckets, and instead may be placed into smaller or larger buckets. This means that a directed broadcast address can be different. However, what happens when a device on a CIDR subnet pings 255.255.255.255
?
For example:
Hostname Device IP CIDR? Directed Broadcast
------------------------------------------------------
Host A 192.168.1.17 Class C 192.168.1.255
Host B 192.168.2.12 /27 192.168.2.31
Host C 192.168.2.35 /27 192.168.2.63
Host D 192.168.2.72 /27 192.168.2.95
I know, for each of the above Directed Broadcast addresses, each Host (and any peers) will receive a ping
from its respective broadcast address. That is, Host A runs ping 192.168.2.63
it is seen by Host C and not by Hosts B or D.
If Host A pings 255.255.255.255
, every device on 192.168.1.0/24
receives that ping.
What happens if Host C runs ping 255.255.255.255
? Will only subnet 192.168.32/27
see the ping? Will the all 1's address hit Hosts B and D, too?