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Test question - mikrotik In MikroTik RouterOS, Layer-3 communication between 2 hosts can be achieved by using an address subnet. Which one of those "/29" "/30" "/31" "/32"? Why?


I understand subnetting such as "x.x.x.x/n"(CIDR not. ..) but i don't understand what is it asking me for.. i mean you can connect 2 hosts even with /24, but on the internet you have to change it because of the bigger network, so, bigger networkID and that kind of stuff (at least this is what i've understood)... still can't get the difference between using /29,30,32 ... when should i use those, and why. I'd really appreciate an "in-dept" explanation.

  • We could use more context, but I can gues that they are taling about a point to point connection. And a /32 will do for that. (no need for broadcast or net address in a 2 host link). – Hennes Jan 18 '17 at 15:10
  • actually the right answers are : /29,/30, /32, because of multibox selection, so yeah, /32 is right but why /29, /30 then? D: – Rafael SoWhat Jan 18 '17 at 15:17
  • Well, with /31 you could use 2 IPs and Network ID and broadcast. And anything bigger will also work but waste more IPs. Depending on the exam question that is either a waste and thus wrong (even though it will work), or it is preparing for the future but allocating slightly more than needed. – Hennes Jan 18 '17 at 15:20
  • with this "thinking", i can presume that /31 should work, yes it would waste IPs, but the question asks which one is correct between "/29,30,31,32"... but if you answer /31 it logs the answer as error. Can't figure out why >:( – Rafael SoWhat Jan 18 '17 at 15:26
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/31 is a special case and only should be used for Point to Point and has its own RFC 3021. It is a little unclear but it might because the test did not specify that this is Point to Point but rather just a network with only two hosts.

A /30 will give you two usable hosts with one broadcast and one network ID. I am unaware of when you would not need a broadcast and network ID. however you usually also have a gateway which takes away from one of the usable hosts but it is still considered two usable hosts

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I actually tested the /32 option and it does not work:

[admin@OB1] > ip addr pr
Flags: X - disabled, I - invalid, D - dynamic 
 #   ADDRESS            NETWORK         INTERFACE                                
 0   102.168.88.11/32   102.168.88.11   ether4  

[admin@OB2] > ip addr pr
Flags: X - disabled, I - invalid, D - dynamic 
 #   ADDRESS            NETWORK         INTERFACE                                
 0   192.168.88.10/32   192.168.88.10   ether4

[admin@OB2] > ping 192.168.88.11
  SEQ HOST                            SIZE TTL TIME  STATUS             
    0                                                no route to host   
    1                                                no route to host   
    2                                                no route to host   
    sent=3 received=0 packet-loss=100% 

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