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+2 votes
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is 255.255.255.52 a valid subnet mask? if yes then what is the no. of subnets?
asked in Computer Networks by (37 points) | 94 views

2 Answers

0 votes
It is unconventional but valid subnet,3 bits will be set so now 2^3 =8 subnets and (2^5 )-2 =30 hosts per sunetswill be absolutely correct
answered by Active (1.2k points)
0
I agree with the validity part. But I think to know number of subnets and hosts we need to know the class of the IP the subnet mask belongs to. For classless, it won't be a valid netmask because classless requires contiguous block allotment.
0

@Akhilesh Singla

i agree with your answer. but even if i consider this as Class C.

then also how can i treat this as a valid subnet mask even. as per rules, it says there should continues 1's from Left Most side from Host Bit.   

​​​​​​​11111111.11111111.11111111.00110100  

If This is at all a valid subnet mask can you explain this how ?

+1
It is not a hardcore rule to pick LSBs of host bits. In practical, we take it from LSBs but in theory we can take it from anywhere from the host bits. So theoretically, it is correct. Although, host IPs in one subnet won't be contiguous(like we are used to see) in this case.
0
Promsing pramod :- there is no such rule, its easily understandle to human mind so we make it as a convention but its not rule
0 votes

RFC 950 defines the use of a subnet mask (also referred to as an address mask) as a 32-bit value that is used to distinguish the network ID from the host ID in an arbitrary IP address. The bits of the subnet mask are defined as follows:

  • All bits that correspond to the network ID are set to 1.

  • All bits that correspond to the host ID are set to 0.

Each host on a TCP/IP network requires a subnet mask even on a single segment network. Either a default subnet mask, which is used when using class-based network IDs, or a custom subnet mask, which is used when subnetting or supernetting, is configured on each TCP/IP node.

Now come to question we have totally 8+8+8+3 ( 110100 ). i.e 27 1's we have. 

now no. of zero =32-27=5 

so total no. of ip address possible in this subnet = 25 

total no. of host = 32-2=30

=>>>>> read this

https://tools.ietf.org/html/rfc950#page-15

but for ipv6 this is not used and rfc made it as  a rule

https://superuser.com/questions/979915/are-subnets-always-contiguous-1s

answered by Active (3k points)
edited by


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