1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

subnet question

Discussion in 'General Cisco Certifications' started by fran1942, Sep 25, 2010.

  1. fran1942

    fran1942 New Member

    2
    0
    1
    can someone please confirm the answer to this:

    For the following class B address, what is the network address of the fourth usable subnet ?
    162.21.122.152 /25

    Thanks kindly.
     
  2. TheITCrowd

    TheITCrowd Kilobyte Poster

    250
    3
    37
    Its a bit early but I believe if Im reading it right you would have to break it down to a /27 to get 4 subnets:

    4 network address woul be:

    162.21.122.128/27
    162.21.122.160/27
    162.21.122.192/27
    162.21.122.224/27

    so the 4th would be 162.21.122.224/27 gateway .225 broadcast .255
     
    Certifications: Network + |CCNA |MCTS-70-680,MCTS-70-401, MCTS-70-656, MCTS-70-351 |HP AIS ProCurve Networking -2011 | HP2-896 |VCD-CP27|JNCIA |Hewlett Packard ASE - Network Infrastructure (2011)
    WIP: 642-813
  3. gosh1976

    gosh1976 Kilobyte Poster

    337
    18
    35
    This is a bit confusing to me. At first I was thinking about it the same way as the 1st answer by theITCrowd but if you are given a class B address then the normal subnet mask is /16 so 9 bits have already been borrowed. 2^9 is 512 so there are 512 subnets without taking any further bits. :confused3 ???
     
    Certifications: A+, Net+, MCDST, CCENT, MCTS: Win 7 Configuring, CCNA
  4. soundian

    soundian Gigabyte Poster

    1,460
    71
    107
    The question doesn't make any sense to me either, but for different reasons.
     
    Certifications: A+, N+,MCDST,MCTS(680), MCP(270, 271, 272), ITILv3F, CCENT
    WIP: Knuckling down at my new job
  5. CONF T

    CONF T New Member

    9
    0
    23
    HELLO

    may answer is if u want 2 se the rang of the subnet u should look at the last bis on subnet mask

    /25= 255.255.255.128 the rang is

    162.21.122.0 ---162.21.122.128
    162.21.122.129---162.21.123.0
    162.21.123.1----162.21.123.128
    162.21.123.129---162.21.124.0

    i think 95% is the correct answer
     
    Certifications: CCNA CCNP
    WIP: CCIE
  6. ibar

    ibar New Member

    2
    0
    11
    Hello Fran1942

    Just started ICND1 and been doing some subnetting practice at home and thought I give this a try.

    162.21.122.152/25 since 162 lies between 128 - 191 => a class B address

    Interesting octet in this case is 152 => 1001 1001

    Applying subnet mask to 1001 1000 gives 1000 0000 (i.e. 128 ) => network increment = 256 - 128 = 128

    So the subnets are as follows:

    162.21.122.128
    162.21.123.0
    162.21.123.128
    162.21.124.0
    162.21.124.128
    etc..
    etc..

    Not entirely sure what you mean by usable subnets since if I am not mistaken they are all usable are they not :confused3

    Can someone double check my calculations because I really want to know the answer to this question.
     
    Certifications: Network+, Server+, Security+
    WIP: ICND1
  7. CONF T

    CONF T New Member

    9
    0
    23
    the zero and 128 ipes r not usable
     
    Certifications: CCNA CCNP
    WIP: CCIE
  8. GSteer

    GSteer Megabyte Poster

    627
    31
    109
    162.21.122.152 /25

    a /25 does give a mask of 255.255.255.128

    or in binary 11111111.11111111.11111111.10000000

    Technical you are in the class B range, the first octect of 162 shows this as per ibar's explanation but we're dealing with a CIDR address style as defined by the /25 which actually indicates that we're using hosts in the 4th octect only.

    The remainder of the host bits 2^7 gives you 128(-2) hosts (the -2 is for the network address and the broadcast address) and the ranges of:

    162.21.122.0/25
    162.21.122.128/25

    Something isn't right with the question as you do not have a 4th useable subnet, you only have two subnets available.

    So, where'd the question come from?

    A good deeper explanation is here: http://www.akadia.com/services/ip_routing_on_subnets.html
     
    Certifications: BSc. (Comp. Sci.), MBCS, MCP [70-290], Specialist [74-324], Security+, Network+, A+, Tea Lord: Beverage Brewmaster | Courses: LFS101x Introduction to Linux (edX)
    WIP: CCNA Routing & Switching
  9. billyr

    billyr Kilobyte Poster

    262
    20
    35

    Agreed - there is no 4th subnet, there is something wrong with the question.
     
    Certifications: CCNP, CCSI, MCSE W2k/W2k3, MCITP_SA
    WIP: Taking it easy for a while.

Share This Page

Loading...