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13 Cards in this Set
- Front
- Back
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There are three possibilities with subnet design: |
No mask meets the requirements One mask meets the requirements Multiple masks meet the requirements |
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To maximize the number of hosts/subnet: |
To make this choice, use the shortest prefix mask (that is, the mask with the smallest /P value), because this mask has the largest host part. |
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To maximize the number of subnets: |
To make this choice, use the longest prefix mask (that is, the mask with the largest /P value), because this mask has the largest subnet part. |
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To increase both the numbers of supported subnets and hosts: |
To make this choice, choose a mask in the middle of the range, which gives you both more subnet bits and more host bits. |
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______ simply means that the subnet design uses more than one mask in the same classful network. |
Variable Length Subnet Masks (VLSM) |
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VLSM can be helpful for both public and private IP addresses, but the benefits are moredramatic with public networks. Why? |
With public networks, the address savings help engineers avoid having to obtain another registered IP network number from regional IP address assignment authorities. |
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To support VLSM, the routing protocol must _______. |
advertise the mask along with each subnet. Without mask information, the router receiving the update would be unable to determine network address from host address. |
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classless routing protocols _____. |
advertise the mask with each advertised route |
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classful routing protocols _____. |
do not advertise the mask with each advertised route |
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Five steps to using VLSM |
1. pick subnet mask 2. Calculate all possiible subnet numbers of network using mask 3. Make list of existing subnets by comparing the list 4. Rule out overlapping subnets 5. Choose new subnet ID from remaining subnets |
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Route summarization tools enable engineers to _____. |
advertise one route that replaces several smaller routes, with the new route matching the same range of addresses. Doing so alleviates some of the waste: wasted effort, bandwidth, RAM, and CPU. |
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Benefits of route summarization: |
reduces size of routing tables but a router can still route packets to all the destination network shorter tables mean routing performance can be improved and memory saved in the router improves convergence time for routing protocols because their is less to do |
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Steps for setting up a summary route: |
1. list all to-be-summarized subnet numbers in decimal, in order lowest to highest 2. Note the low and high end of the range of addresses for all combined subnetsby noting the numerically lowest subnet ID and numerically highest subnetbroadcast address. 3. pick a starting prefix length 4. Calculate new potential summary subnet/mask |
