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We all know that the first address of any sub-net is network identifier and it can't be assigned to any hosts. For example in network 10.1.1.4/30, the address 10.1.1.4 is network identifier.

If suppose I ping this address from one of the hosts in the sub-net, who are all will reply me?

  1. Is there any specification in RFCs on this behavior?
  2. Could you please show me the code reference in Linux kernel handling ICMP_REQUEST with all-zero host-bit address.

Thanks in advance.

  • Just because you said it very definitively, ip subnet-zero/the network identifier can sometimes be assigned by manually allowing it, and after cisco 12.0 the ability to assign it is the default [Cisco] (cisco.com/c/en/us/support/docs/ip/…) In that case, you're likely to get a response from the assigned host. – flerb Jul 19 '17 at 14:03
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If you check RFC 1812 you will read this:

4.2.3.1 IP Broadcast Addresses
(2) SHOULD silently discard on receipt (i.e., do not even deliver to applications in the router) any packet addressed to 0.0.0.0 or { <Network-prefix>, 0 }. If these packets are not silently discarded, they MUST be treated as IP broadcasts (see Section [5.3.5]). There MAY be a configuration option to allow receipt of these packets. This option SHOULD default to discarding them.

which IMHO explain why you receive answers from all the hosts in target network

And 20 years ago there was such DoS attack with spoofed source address and ping to network IP. But will be better to discus this subject here

  • 3
    It is worth pointing out that most systems follow the RFC these days, and will not respond to broadcast pings (either through the subnet broadcast, or the unspecified address, or any of the 'all hosts' multicast addresses). – Austin Hemmelgarn Jul 19 '17 at 14:40
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    I don't see any reason, except 'historical' ones, why the all-zeros host address couldn't be used as a valid address. The usual argument goes that it is reserved to be used as the network identifier, but whether to interpret the address as a network id or host address can be determined from the context. In fact, RFC 4632 (CIDR Address Strategy) implies that the all-zeros host address can be used, but practice shows otherwise. – Johan Myréen Jul 19 '17 at 15:14

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