Editing Smurf attack (section)

==Method==
A '''Smurf amplifier''' is a computer network that lends itself to being used in a Smurf attack. Smurf amplifiers act to worsen the severity of a Smurf attack because they are configured in such a way that they generate a large number of [[Internet Control Message Protocol|ICMP]] replies to the victim at the spoofed source IP address.

In DDoS, ''[[Denial-of-service attack|amplification]]'' is the degree of bandwidth enhancement that an original attack traffic undergoes (with the help of Smurf amplifiers) during its transmission towards the victim computer. An amplification factor of 100, for example, means that an attacker could manage to create 100&nbsp;Mb/s of traffic using just 1&nbsp;Mb/s of its own bandwidth.<ref>S. Kumar (5 July 2007). {{cite book|chapter-url=https://ieeexplore.ieee.org/document/4271771|chapter=Smurf-based Distributed Denial of Service (DDoS) Attack Amplification in Internet|website=IEEE Xplore|year=2007|doi=10.1109/ICIMP.2007.42|s2cid=14876546|language=en|access-date=2020-12-30|last1=Kumar|first1=Sanjeev|title=Second International Conference on Internet Monitoring and Protection (ICIMP 2007) |page=25|isbn=978-0-7695-2911-0}}</ref>

Under the assumption no countermeasures are taken to dampen the effect of a Smurf attack, this is what happens in the target network with ''n'' active hosts (that will respond to ICMP echo requests).
The ICMP echo request packets have a spoofed source address (the Smurfs' target) and a destination address (the patsy; the apparent source of the attack). Both addresses can take two forms: [[unicast]] and [[Broadcasting (networking)|broadcast]].

The dual unicast form is comparable with a regular ping: an ICMP echo request is sent to the patsy (a single host), which sends a single ICMP echo reply (a Smurf) back to the target (the single host in the source address). This type of attack has an amplification factor of 1, which means: just a single Smurf per ping.

When the target is a unicast address and the destination is the broadcast address of the target's network, then all hosts in the network will receive an echo request. In return they will each reply to the target, so the target is swamped with ''n'' Smurfs. Amplification factor = ''n''. If ''n'' is small, a host may be hindered but not crippled. If ''n'' is large, a host may come to a halt.

If the target is the broadcast address and the patsy a unicast address, each host in the network will receive a single Smurf per ping, so an amplification factor of 1 per host, but a factor of ''n'' for the network. Generally, a network would be able to cope with this form of the attack, if ''n'' is not too great.

When both the source and destination address in the original packet are set to the broadcast address of the target network, things start to get out of hand quickly. All hosts receive an echo request, but all replies to that are broadcast again to all hosts. Each host will receive an initial ping, broadcast the reply and get a reply from all ''n-1'' hosts. An amplification factor of ''n'' for a single host, but an amplification factor of ''n<sup>2</sup>'' for the network.

ICMP echo requests are typically sent once a second. The reply should contain the contents of the request; a few bytes, normally. A single (double broadcast) ping to a network with 100 hosts causes the network to process {{gaps|10|000}} packets. If the payload of the ping is increased to {{gaps|15|000}} bytes (or 10 full packets in [[Ethernet]]) then that ping will cause the network to have to process {{gaps|100|000}} large packets per second. Send more packets per second, and any network would collapse under the load. This will render any host in the network unreachable for as long as the attack lasts.