I have a /24 network that is subnetted into a bunch of small chunks. I have recently gone into each router on the network (mostly Cisco) in order to document how this network had been divided. Now looking at a ping sweep output from:
nmap -sP 192.168.1.*
I see that some but not all reserved "network" and "broadcast" IPs respond to pings. For example, the network 192.168.1.80/29 has the network of 192.168.1.80 and a broadcast of 192.168.1.87. On this particular subnet, both of these IPs give me a ping response from the external interface of the router (192.168.5.20).
Many of the other subnets behave in a similar manor. However others do not. Looking at the router configs, nothing really jumps out at me that looks like it would cause this behavior.
Does anyone know the reason for this behavior? Do I want those addresses to respond or not? Slightly unrelated: should I have reverse DNS entries for the network and broadcast IPs?