IP address that is the equivalent of /dev/null

There's specifically a blackhole prefix in IPV6, as described in RFC 6666, it's 100::/64. IP4 does not have an explicit black hole like that, but a non-existent host on one of the reserved blocks would have that effect. (e.g., 240.0.0.0/4 is "reserved for future use" and will not be routed by anything.)

There is such a thing as network Black hole.

If there are no devices in the network with IP address 192.168.0.10, then this IP address is kind of black hole and it will "discard" all the traffic to it, simply because it does not exist.

Protocols which keep track of connection state (TCP) can detect a missing destination host. It will not happen with UDP and packets will just die while the sending host will not be informed about that.

You can setup black hole with firewall by setting it up to silently drop packets (not reject) from particular (or many) addresses.

As far as I know there is no such network standard address which will do black hole for you in TCP/IP version 4 (Thanks to Bandrami).

So you have two options:

1. An IP address which was not assigned to any host;
2. Host with firewall which silently drops packets or variations of it, for example using netcat: (as suggested by ultrasawblade).

nc -vv -l 25 > /dev/null will listen for inbound connections on TCP port 25 and pipe the results to /dev/null. More examples here.

The entire subnet also can be a black hole (Null route).

While it isn't a black-hole, you might also want to consider the IPs set aside for test/example purposes (by RFC 5737), especially if your goal is a "safely non-working default" value.

• 192.0.2.0/24 (TEST-NET-1),
• 198.51.100.0/24 (TEST-NET-2)
• 203.0.113.0/24 (TEST-NET-3)

Network operators SHOULD add these address blocks to the list of non-routeable address spaces, and if packet filters are deployed, then this address block SHOULD be added to packet filters.

There's no guarantee that packets to those addresses will be blocked (that depends on your ISP, etc.) but certainly nobody should be already using them.