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Overlapping IP ranges and routing

2URGSE2URGSE Member Posts: 220 ■■■□□□□□□□
in CCNA & CCENT
ICND 2 tells me that if 2 routes match a destination IP of 172.16.4.3, the route with the longest prefix will be used to send the packet.

SHOW IP ROUTE RIP

172.16.0.0/16 is variably subnetted, 5 subnets, 4 masks

172.16.1.1/32

172.16.1.0/24

172.16.0.0/22

172.16.0.0/16

0.0.0.0/0


SHOW IP ROUTE 172.16.4.3

Routing entry for 172.16.0.0/16

The book then says the route to be taken is 172.16.0.0/16.

Could this be a mis-print?

I would think the chosen route would be 172.16.0.0/22 since it has a higher prefix.


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    2URGSE2URGSE Member Posts: 220 ■■■□□□□□□□
    Nevermind, I figured it out.

    Longest prefix is 16 (255.255.0.0) vs. 255.255.252.0


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    wbosherwbosher Member Posts: 422
    A prefix of 22 would include the range of 172.16.0.0 - 172.16.3.255.

    A prefix of 16 would be 172.16.0.0 - 172.16.255.255

    The book is correct.
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    AlanJamesAlanJames Member Posts: 230
    most specific route wins :D
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    HeaVenSHeaVenS Registered Users Posts: 3 ■□□□□□□□□□
    Book may be referring to RIP v1 or IP Classful routing. 22 is the preferred more specific route.
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    mattrgeemattrgee Member Posts: 201
    HeaVenS wrote: »
    Book may be referring to RIP v1 or IP Classful routing. 22 is the preferred more specific route.

    The .22 route doesn't include the IP 172.16.4.3.
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    PhildoBagginsPhildoBaggins Member Posts: 276
    I always think about it in binary. The more specific it in in binary is the correct route to take.
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    chmorinchmorin Member Posts: 1,446 ■■■■■□□□□□
    wbosher wrote: »
    A prefix of 22 would include the range of 172.16.0.0 - 172.16.3.255.

    A prefix of 16 would be 172.16.0.0 - 172.16.255.255

    The book is correct.

    Yup. The most specific route... that works! That last bit got me a few times too =p
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    notun1notun1 Member Posts: 51 ■■□□□□□□□□
    2URGSE wrote: »
    ICND 2 tells me that if 2 routes match a destination IP of 172.16.4.3, the route with the longest prefix will be used to send the packet.

    SHOW IP ROUTE RIP

    172.16.0.0/16 is variably subnetted, 5 subnets, 4 masks

    172.16.1.1/32

    172.16.1.0/24

    172.16.0.0/22

    172.16.0.0/16

    0.0.0.0/0


    SHOW IP ROUTE 172.16.4.3

    Routing entry for 172.16.0.0/16

    The book then says the route to be taken is 172.16.0.0/16.

    Could this be a mis-print?

    I would think the chosen route would be 172.16.0.0/22 since it has a higher prefix.


    icon_confused.gif:

    Only matching found in 172.16.0.0/16 for 172.16.4.3 address. the address range for 172.16.0.0/22 is 172.16.0.0 - 172.16.3.255.

    If you have a address like 172.16.1.3 then 172.16.0.0/22 and 172.16.0.0/16 need to consider. in this case highest prefix /22 win(More specific).
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