CCNA Notes : cont...
31. Ethernet_II has a type field to identify the upper-layer
protocol. 802.3 has only a length field and can't identify the
upper-layer protocol.
32.To find valid hosts given an IP address (say 156.16.3.52) and a
subnet mask (sat a 12-bit subnet). The valid hosts are determined as
below:
A
12-bit subnet mask gives us 255.255.255.240; 4094 subnets, each with
14 hosts. (Host addresses of all zeros and all 1s can't be
assigned). The 156.16.3.52 is in the 48 subnet range. The valid
range is through 49 - 62. 63 is a broadcast address.
Here is how you get the subnet range:
1.
Find the subnet mask. In this case, default subnet mask for Class B
address is 255.255.0.0. There are additional; 12 bits in the subnet
mask. Now the subnet mask looks like:
11111111.11111111.11111111.11110000. This is equal to
255.255.255.240.0.
2.
Now, deduct the lowest value octet (Which is non zero), from 256.
Here, (256-240)=16.
This is the value that the subnets are incremented. Therefore, you
will have hosts with values from:
156.16.3.1 to 156.16.3.14 (All 0s and all 1s host
addresses can not be used)
156.16.3.17 to 156.16.3.30
156.16.3.33 to 156.16.3.46
156.16.3.49 to 156.16.3.62 and so on.
It
is important to know that subnets are incrementing here by a factor
of 16.
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