Chapter 8 - IP Subnetting, Troubleshooting IP, and Intro to NAT Flashcards
When you see a subnet mask or slash notation (CIDR), you should know the following when working with Class C networks.
/25
What do you know about a /25?
128 mask
1 bit on and 7 bits off (10000000)
Block size of 128
2 subnets, each with 126 hosts
/26 And what do you know about a /26? 192 mask 2 bits on and 6 bits off (11000000) Block size of 64 4 subnets, each with 62 hosts
/27 What about a /27? 224 mask 3 bits on and 5 bits off (11100000) Block size of 32 8 subnets, each with 30 hosts
/28 And what about a /28? 240 mask 4 bits on and 4 bits off Block size of 16 16 subnets, each with 14 hosts
/29 What do you know about a /29? 248 mask 5 bits on and 3 bits off Block size of 8 32 subnets, each with 6 hosts
/30 And last, what about a /30? 252 mask 6 bits on and 2 bits off Block size of 4 64 subnets, each with 2 hosts
We know the Class B network address has 16 bits available for host addressing. This means we can use up to 14 bits for subnetting (because we have to leave at least 2 bits for host addressing).
Class - format - default subnet mask
A
network.host.host.host 255.0.0.0
B network.network.host.host255.255.0.0
C
network.network.network.host 255.255.255.0
Question
What is the maximum number of IP addresses that can be assigned to hosts on a local subnet that uses the 255.255.255.224 subnet mask?
1 D. A /27 (255.255.255.224) is 3 bits on and 5 bits off. This provides 8 subnets, each with 30 hosts. Does it matter if this mask is used with a Class A, B, or C network address? Not at all. The number of host bits would never change.
You have a Class A host of 10.0.0.110/25. It needs to communicate to a host with an IP address of 10.0.0.210/25. Which of the following devices do you need to use in order for these hosts to communicate?
A.A Layer 2 switch
B. Router
C. DNS server
D. Hub
- B. Don’t freak because this is a Class A. What is your subnet mask? 255.255.255.128. Regardless of the class of address, this is a block size of 128 in the fourth octet. The subnets are 0 and 128. The 0 subnet host range is 1–126, with a broadcast address of 127. The 128 subnet host range is 129–254, with a broadcast address of 255. You need a router for these two hosts to communicate because they are in different subnets.
What is the subnetwork address for a host with the IP address 200.10.5.68/28?
A. 200.10.5.56
B. 200.10.5.32
C. 200.10.5.64
D. 200.10.5.0
- C. This is a pretty simple question. A /28 is 255.255.255.240, which means that our block size is 16 in the fourth octet (0, 16, 32, 48, 64, 80, and so on). The host is in the 64 subnet.
The network address of 172.16.0.0/19 provides how many subnets and hosts?
A. 7 subnets, 30 hosts each B. 7 subnets, 2,046 hosts each C. 7 subnets, 8,190 hosts each D. 8 subnets, 30 hosts each E. 8 subnets, 2,046 hosts each F. 8 subnets, 8,190 hosts each
- F. A CIDR address of /19 is 255.255.224.0. This is a Class B address, so that is only 3 subnet bits, but it provides 13 host bits, or 8 subnets, each with 8,190 hosts.
You receive a call from a user who is complaining that they cannot get on the Internet. You have them verify their IP address, mask, and default gateway. The IP address is 10.0.37.144, with a subnet mask of 255.255.254.0. The default gateway is 10.0.38.1. What is the problem?
A. Incorrect DNS server address
B. Invalid subnet mask
C. Incorrect gateway IP
D. IP address and mask not compatible
- C. The host ID of 10.0.37.144 with a 255.255.254.0 mask is in the 10.0.36.0 subnet (yes, you need to be able to subnet in this exam!). Do not stress that this is a Class A; what we care about is that the third octet has a block size of 2, so the next subnet is 10.0.38.0, which makes the broadcast address 10.0.37.255. The default gateway address of 10.0.38.1 is not in the same subnet as the host. Even though this is a Class A address, you still should easily be able to subnet this because you look more at the subnet mask and find your interesting octet, which is the third octet in this question. 256 – 254 = 2. Your block size is 2.
If a host on a network has the address 172.16.45.14/30, what is the subnetwork this host belongs to?
A. 172.16.45.0 B. 172.16.45.4 C. 172.16.45.8 D. 172.16.45.12 E. 172.16.45.16
- D. A /30, regardless of the class of address, has a 252 in the fourth octet. This means we have a block size of 4 and our subnets are 0, 4, 8, 12, 16, and so on. Address 14 is obviously in the 12 subnet.
On a network, which mask should you use on point-to-point WAN links in order to reduce the waste of IP addresses?
A. /27 B. /28 C. /29 D. /30 E. /31
- D. A point-to-point link uses only two hosts. A /30, or 255.255.255.252, mask provides two hosts per subnet.
On which of the following devices are you most likely to be able to implement NAT?
A. Hub
B. Ethernet switch
C. Router
D. Bridge
- C. Devices with Layer 3 awareness, such as routers and firewalls, are the only ones that can manipulate the IP header in support of NAT.
You have an interface on a router with the IP address of 192.168.192.10/29. Including the router interface, how many hosts can have IP addresses on the LAN attached to the router interface?
A. 6 B. 8 C. 30 D. 62 E. 126
- A. A /29 (255.255.255.248), regardless of the class of address, has only 3 host bits. Six hosts is the maximum number of hosts on this LAN, including the router interface.
- When configuring the IP settings on a computer on one subnet to ensure that it can communicate with a computer on another subnet, which of the following is desirable?
- C. A computer should be configured with an IP address that is unique throughout the reachable internetwork. It should be configured with a subnet mask that matches those of all other devices on its local subnet, but not necessarily one that matches the mask used on any other subnet. It should also be configured with a default gateway that matches its local router’s interface IP address.
