IP address that is the equivalent of /dev/null

Question

Is there an IP address that would result in any packet sent to be ignored (blackholed)?

I know I can always set up a router with an IP address and then just have it ignore all packets sent to it, but does such a thing exist to save me the trouble?

Solution 1

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.)

Solution 2

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).

Solution 3

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.

Solution 4

There's no "standard blackhole address" as such, nor is there really any requirement for it. You don't say what you're actually trying to achieve, so I can't help you do so, but here are some wrong solutions for your problem that would answer your question as you asked it:

• You can use an RFC1918 address that's not in use on your network and rely on your ISP to drop it for you. For example, if you're only using some parts of 192.168, 10.255.255.1 would be null-routed by your ISP (which would get it thanks to your default gateway).
• You can use an IP address that's reserved for future use (and will probably never be used); that's the old "Class E" range. It'll do the same as above, but will work even if you use all of the private address ranges already (by having much broader netmasks than necessary, I doubt that you'll have millions of attached devices). For example, 254.0.0.1 will never (legally) refer to a real device.
• On the machine where you need this, you can add a drop-only target; using an unused address such as the above, for example, iptables -I OUTPUT -d 254.0.0.0/8 -j DROP will ensure anything sent to that "network" will be silently dropped instead of bothering any gateways, or even causing traffic on the actual network interface.

Again, you probably don't actually want any of this, even if you think it's convenient - it's not, it's confusing and non-obvious and not a good solution to whatever your problem really is.

Solution 5

Test Ranges

I would probably suggest one of the "TEST-NET" address ranges, "for use in documentation and examples. It should not be used publicly".

192.0.2.0/24
198.51.100.0/24
203.0.113.0/24

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"Bogon" (Bogus/Fake) Ranges

I'm not sure where to say here, this appears to be more of a practice that an Internet gateway would provide, rather than a specific way to implement a packet that is routed somewhere it shoudln't be

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Local Ranges

There is also loopback address range, 127.0.0.0/8, eg 127.0.0.255. Though its still possible for things to exist there, specifically any services on the local machine, at least you won't interfere with any machines on the network (unless your have network services that are backed by other network services I guess).

127.0.0.0/8

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Illegal Destination Ranges

Perhaps the illegal address 0.0.0.0 can be used as well, though 0.0.0.0/8 is reserved for "Used for broadcast messages to the current ("this")" so there is risk of broatcasting on that.

0.0.0.0/8

The Wikipedia Page for Null Route states:

Null routes are typically configured with a special route flag, but can also be implemented by forwarding packets to an illegal IP address such as 0.0.0.0, or the loopback address.

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Refs: https://en.wikipedia.org/wiki/Reserved_IP_addresses

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Comments

[Adriano P]

There are some devices (like routers and switches from that San Francisco co.) that use a Null interface that could be used as a black hole to malicious traffic. One should point a route to that Null interface so all traffic to that route be discarded.

[Nowak Grzegorz]

I am curious, why is the question tagged "spam-prevention"?

[VL-80]

@WChargin, I hope that was a joke - devnull-as-a-service.com does not seem to have anything to do with networking and even it does look like a crap. What is this: When we say "government" we mean NSA, CIA, FBI, TSA, Communist Party of China (CPC), Nestle, The Coca-Cola Company, the KGB, some of your coworkers and our friends (especially if there is something funny).?

[wchargin]

@Nikolay yes, it was a joke, as is the website. See their Github README: "It's mostly about the enterprise, cloud, *-as-a-Service and criticism on it." (emphasis mine)

[VL-80]

@WChargin, I see this point! Nice joke (: !

[Tyler Durden]

@MikePennington The idea is to route spam SYN packets to the black hole. If you just refuse them, they move on to the next target. If you blackhole them, their socket blocks until it times out. This can slow down a spam server by 1000x or more. Imagine if we had 1000x less spam.

[LawrenceC]

If you want something that will receive TCP traffic, but do nothing with it, something quick can be setup with nc (or netcat). As @Nikolay says though, there's not a "blackhole" IP that does this automatically.

[Bandrami]

At least not in IP4

[Tyler Durden]

254.0.0.1 does not black hole packets, I get a "transmit failure" error.

[RBerteig]

+1 for "you probably don't actually want any of this..."

[user2357112]

@Bandrami: What about IPv6, then?

[VL-80]

@user2357112, just look at his answer. It is just below mine.

[corsiKa]

Sending data to something reserved for future use is only a good idea until that future use is realized.

[mirabilos]

They can also be REJECTed instead of DROPped, so…

[Bandrami]

Very good point, though I highly doubt that IP4 will be expanded much again.

[WGH]

But is the router guaranteed to drop the packets? Because if it returns ICMP "destination unreachable", it would be not what the OP asked for.

[Tyler Durden]

192.0.2.0 seems to work on my first try, not returning any packets so far. I will do some more testing.

[ThorSummoner]

I overall opted to use localhost on the highest port 65535 though, Because I wanted to ensure no traffic would leave the host.

[Drakes]

If you specify the port, then you have to specify each protocol as well: TCP, UDP, etc. and in doing so, some traffic may escape your rules (e.g. ICMP).

[zeroimpl]

These techniques are quite useful for quickly testing how an application/website behaves when encountering unexpected network glitches...

[Tyler Durden]

I can confirm that 240.0.0.0 works. When I try to ping that address the computer hangs, which is what we want.