Chapter 5 - VLSMs, Summarization, and Troubleshooting TCP/IP Flashcards
Describe the benefits of variable length subnet masks (VLSMs).
VLSMs enable the creation of subnets of specific sizes and allow the division of a classless network into smaller networks that do not need to be equal in size. This makes use of the address space more efficient because many times IP addresses are wasted with classful subnetting.
Understand the relationship between the subnet mask value and the resulting block size and the allowable IP addresses in each resulting subnet.
The relationship between the classful network being subdivided and the subnet mask used determines the number of possible hosts or the block size. It also determines where each subnet begins and ends and which IP addresses cannot be assigned to a host within each subnet.
Describe the process of summarization or route aggregation and its relationship to subnetting.
Summarization is the combining of subnets derived from a classful network for the purpose of advertising a single route to neighboring routers instead of multiple routes, reducing the size of routing tables and speeding the route process.
Calculate the summary mask that will advertise a single network representing all subnets.
The network address used to advertise the summary address is always the first network address in the block of subnets. The mask is the subnet mask value that yields the same block size.
What are the four diagnostic steps Cisco recommends?.
The four simple steps that Cisco recommends for troubleshooting are ping the loopback address, ping the NIC, ping the default gateway, and ping the remote device.
Identify and mitigate an IP addressing problem.
Once you go through the four troubleshooting steps that Cisco recommends, you must be able to determine the IP addressing problem by drawing out the network and finding the valid and invalid hosts addressed in your network.
Understand the troubleshooting tools that you can use from your host and a Cisco router.
The ping 127.0.0.1 command tests your local IP stack, and tracert is a Windows command to track the path a packet takes through an internetwork to a destination. Cisco routers use the command traceroute, or just trace for short. Don’t confuse the Windows and Cisco commands. Although they produce the same output, they don’t work from the same prompts. The command ipconfig /all will display your PC network configuration from a DOS prompt, and arp -a (again from a DOS prompt) will display IP-to-MAC-address mapping on a Windows PC.
What is the summary address and the mask to be used that will summarize the subnet: 192.168.1.0/24 through 192.168.12.0/24
192.168.0.0/20
What is the summary address and the mask to be used that will summarize the subnet: 172.144.0.0 through 172.159.0.0
172.144.0.0 255.240.0.0
What is the summary address and the mask to be used that will summarize the subnet: 192.168.32.0 through 192.168.63.0
192.168.32.0 255.255.224.0
What is the summary address and the mask to be used that will summarize the subnet: 192.168.96.0 through 192.168.111.0
192.168.96.0 255.255.240.0
What is the summary address and the mask to be used that will summarize the subnet: 66.66.0.0 through 66.66.15.0
66.66.0.0 255.255.240.0
What is the summary address and the mask to be used that will summarize the subnet: 192.168.1.0 through 192.168.120.0
192.168.0.0/17
What is the summary address and the mask to be used that will summarize the subnet: 172.16.1.0 through 172.16.7.0
172.16.1.0 255.255.248.0
What is the summary address and the mask to be used that will summarize the subnet: 192.168.128.0 through 192.168.190.0
192.168.128.0 255.255.192.0
