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Thread: Wildcard again

  1. #1
    Join Date
    Apr 2010
    Posts
    19

    Default Wildcard again

    Guys

    After doing CCNA Virtual Lab Titanium, it graded me wrong because of incorret wildcard configration in the OSPF Practice Scenario.

    It expected the following commands:

    MANUFACTURING#c onfig t
    Enter configuration commands, one per line. End with CNTL/Z
    MANUFACTURING(c onfig)#router ospf 100
    MANUFACTURING(c onfig-router)#network 192.168.10.8 0.0.0.3 area 0

    I understood how to reach number 3 in the last octet (256-Block Size - 1) but I re-read the book and it is not clear for me what it means.What does exactly number 3 tell us?

    Network is 192.168.10.8/30 , host range 192.168.10.9 and 10, broadcast 192.168.10.11. I sincerely did not understand what informatio number 3 matches.

    I read Cisco Press book (Odon) and he does not mention such configuration.

    Thanks in advance.

  2. #2
    Join Date
    Nov 2008
    Location
    Birmingham, UK
    Posts
    1,440

    Default

    It's the number of hosts that can match that address range. It makes more sense in binary, I'll just show the last octet:

    00001000 = .8 for network address
    00000011 = 3 for wildcard

    This means that matches will be made of any bit that matches a 1 in the wildcard position. As they are 'wild' they can match 0 or 1 to be included. So the 3 wildcard matches 192.168.10.8 (00001000), 192.168.10.9 (00001001), 192.168.10.10 (00001010) and 192.168.10.11 (00001011). So now you see the wildcard of 3 actually matches four addresses.
    CCNP R&S, CCNA DC
    Currently studying: CCIE R&S, CCNP Data Centre
    Follow my CCIE progress with study notes on my blog: http://beyondccna.blogspot.co.uk/

  3. #3
    Join Date
    Apr 2010
    Posts
    19

    Default

    Now its clear .
    Thank you very much again!!

  4. #4
    Join Date
    May 2011
    Posts
    39

    Default Not Clear on this

    [QUOTE=Fuzz;1137 2]It's the number of hosts that can match that address range.


    The way i learned how to get the wildcard is by using the formula
    BLOCK SIZE - 1 = wildcard

    In this case /30 .... 256-252 = 4 (block size) -1 = (3 wildcard)

    I see 2 useable host addresses in /30 ...the (.9 & .10), not counting the network .8 and broadcast addresses .11

    FUZZ i don't understand your statement "It's the number of hosts that can match that address range" "

    3 hosts?? are you counting the broadcast address along with 192.168.10.9 (00001001), & 192.168.10.10 (00001010) to get the 3 addresses?

    Thanks,
    PCameron1
    Patrick
    Network+, A+, MCP, CCENT, CCNA

  5. #5
    Join Date
    Dec 2010
    Location
    Left Coast, California
    Posts
    306

    Default

    just a suggestion for all you test takers...dont fuss around with wildcards on the test, you dont have the time to waste. just know it cold.

    x.x.x.252 = 0.0.0.3 (255-252=3)
    x.x.x.248 = 0.0.0.7 (255-248=7)
    x.x.x.240 = 0.0.0.15 (255-240=15)
    etc...

    or just do the block size -1, but you need to just know this cold without thinking. Save the thinking for ciscos other retarded questions, phrased by someone who speaks english as a second language.
    Kevin NET+SEC+A+CCNA
    'All that is not eternal is eternally out of date' ~ C.S. Lewis

  6. #6
    Join Date
    May 2011
    Posts
    39

    Default

    Good advice thank you Ciscodaze. I have one more question.

    If we had this ip as a question ..... 172.21.96.0/20

    Am I correct, the wildcard mask = 0.0.15.255
    Patrick
    Network+, A+, MCP, CCENT, CCNA

  7. #7
    Join Date
    Dec 2010
    Location
    Left Coast, California
    Posts
    306

    Default

    Quote Originally Posted by pcameron1 View Post
    Good advice thank you Ciscodaze. I have one more question.

    If we had this ip as a question ..... 172.21.96.0/20

    Am I correct, the wildcard mask = 0.0.15.255

    that would be the correct conversion for /20...the particular IP given will result is the range of 192.21.96.0 - 192.21.111.255

    But that may not be the correct answer for a question...say they were asking you to indicate a range of subnets that would give you 6 subnets.
    For that all you would need is a /21, or 0.0.7.255 wildcard

    you can practice with a wildcard calculator here
    http://www.subnet-calculator.com/wildcard.php
    Last edited by ciscodaze; 11-27-2011 at 04:09 PM.
    Kevin NET+SEC+A+CCNA
    'All that is not eternal is eternally out of date' ~ C.S. Lewis

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