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Now previously before cider was used we had class full address masks so we had class a addresses Class
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B addresses and Class C addresses a class a subnet supports about 16 million addresses and uses the
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mosque to far 5.0 dot 0 0 0.
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Class B networks support about 65000 host addresses with a mask of 2 5 5 or 2 4 5 0 0 0 plus C networks
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support 254 host addresses and use a mask of 255 or 2.5 by 5.2 per 5.0.
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The problem with this method is what happens if a company wants to support 3000 hosts for example.
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So if the network had 3000 hosts which of these three address classes.
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Would the company get well they could get a Class B address but that's an awful waste of a lot of addresses.
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About sixty five thousand addresses are available in a class B subnet.
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But in this example the company only needs 3000 host addresses.
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They could get multiple class C networks but that means that they going to be allocated many Class C
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addresses which has a negative effect on Internet routing tables.
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Now rather than doing that we can move the subnet mask insider.
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Notice in Class A B and C addresses the subnet mask is set on the Octet boundary.
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Notice in Class A B and C addresses the subnet mask is set on the Octet boundary plus a first 8 bits.
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Class B first 16 bits.
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Class C first 24 bits.
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But rather than doing that with CIDA the subnet mosque can be somewhere in the middle.
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It doesn't have to be on the test boundary.
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Here's another example.
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In this example we've got a subnet mask of 255 dot 2 2 4 0 0 2 4 5 in binary is 8 binary ones 2 to 4
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is 3 binary ones followed by 5 binary zeros.
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So if we count the number of binary ones that gives us 11 so 255 2 2 4 2 0 0 0 is the same as Slash
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eleven the network portion is on the left hand side the host portion is on the right hand side.
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But notice once again that the divider between network and host is not on the Octet boundary it's somewhere
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within this octet.
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So in this example the most significant three bits of that octet are network and the remaining portion
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of the octet is host.
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Now in the subheading videos I'm going to show you this in a lot more detail.
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We're going to work out various types of sub netting.
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What I need you to understand with regards to cider at this point is that cider allows us to implement
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a variable length subnet masks no longer do we have plus a b and c networks where class A is always
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slash 8.
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Class B is always slash 16 and Class C is always slash 24 when cider is used.
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The mosques can vary and that's what we use today.
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So from 1993 cider is more preferable than classical network mosques.
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Now once again in the subheading videos I'm going to discuss subletting in a lot more detail so please
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refer to those videos if you want to learn more about how to subnet a network or how to work out the
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maximum hosts that can be supported on a subnet or which addresses the first address or lost address
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or what is the broadcast address and so forth for a specific subnet.
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