Subnetting

IP addresses, subnets

25 flashcards · Computer Science · by lakesare

1. What does CIDR stand for?

   Classless InterDomain Routing

2. Name 2 network addressing architectures.

   Classful network (address class system) Classless InterDomain Routing (CIDR) Network addressing architecture used in the Internet from 1981 until the introduction of CIDR in 1993.

3. Describe a classful network.

   Divides the IP address space for IPv4 into 5 address classes by address range. Classes A, B, C are networks of three different network sizes, i.e. number of unicast addresses for hosts. Class D is for multicast. The class E address range is reserved for future or experimental purposes. The first three bits of the most significant octet of an IP address were defined as the class of the address. Links: wikipedia on classful network

4. Why was classful network superseded by CIDR?

   Many sites needed larger address blocks than a Class C network provided, and therefore they received a Class B block, which was in most cases much larger than required. In the rapid growth of the Internet, the pool of unassigned Class B addresses (214, or about 16,000) was rapidly being depleted.

5. What's a subnetwork (subnet)?

   Computers that belong to a subnet are addressed with a common, identical, most-significant bit-group in their IP address. Same most significant bits are exactly what's called a subnet.

6. What IP addresses are private?

   The Internet Assigned Numbers Authority (IANA) reserves the following IP address blocks for use as private IP addresses: 10.0.0.0 to 10.255.255.255 172.16.0.0 to 172.31.255.255 192.168.0.0 to 192.168.255.255

7. What is the purpose of having private IP address ranges?

   Instead of having devices inside a home or business network each using a public IP address, of which there's a limited supply, private IP addresses provide an entirely separate set of addresses that still allow access on a network but without taking up a public IP address space. For example, let's consider a standard router on a home network. Most routers in homes and businesses across the globe, probably yours and your next door neighbor's, all have the IP address of 192.168.1.1, and assign 19…

8. Name 1 reserved IP address.

   The most famous reserved IP is 127.0.0.1. This address is called the loopback address and is used to test the network adapter or integrated chip. No traffic addressed to 127.0.0.1 is sent over the local network or public internet. Technically, the entire range from 127.0.0.0 to 127.255.255.255 is reserved for loopback purposes but you'll almost never see anything but 127.0.0.1 used in the real world. Addresses in the range from 0.0.0.0 to 0.255.255.255 are also reserved but don't do anything at…

9. What does localhost resolve to?

   On modern computer systems, localhost as a hostname translates to an IPv4 address in the 127.0.0.0/8 (loopback) net block, usually 127.0.0.1, or ::1 in IPv6.

10. How an IP address can be subdivided in the classful network?

    To: network address host address , amount of bits depends on an IP class (which's determined by its range)

11. What is a subnet mask?

    It's a 32-bit binary number used to help you find what portion of an IP address is a: network address, and which is a host address. Subnet masks for different IP classes: Class A: 255.0.0.0 Class B: 255.255.0.0 Class C: 255.255.255.0

12. 213.180.193.3/24 What's the subnet mask?

    Subnet mask is 255.255.255.0, meaning that, by ANDing: subnet is 213.180.193.0 host is 0.0.0.3 Keep in mind that subnet mask doesn't have to end in an octet, it can perfectly fine be, e.g., /20.

13. Name 3 parts of subnetted IPv4 address.

    When using subnet addressing, we think of a 32-bit IPv4 address as having an internet portion and a local portion, where: internet portion - identifies a site, possibly with multiple physical networks (prefix) local portion - identifies a physical network and host at that site Conceptually, adding subnets only changes the interpretation of IPv4 addresses slightly. Instead of dividing the 32-bit IPv4 address into a network prefix and a host suffix, subnetting divides the address into an internet…

14. How many physical subnetworks does this setup allow?

    10-bit field allows up to 210 = 1024 networks. Links: wikipedia - subnet and host counts

15. What is fixed-length subnetting?

    When site chooses a division for the local portion of its address and then uses the division throughout the site.

16. What is the drawback of fixed-length subnetting?

    Organization that adopts fixed-length subnetting must choose a compromise. If the organization opts for a large number of physical networks, none of them can contain many hosts.

17. What is variable-length subnetting?

    To allow maximum flexibility in choosing how to partition subnet addresses, the TCP/IP subnet standard permits variable-length subnetting in which a partition can be chosen independently for each physical network. The partition for each subnet and the values chosen for subnet numbers must be assigned carefully to avoid address ambiguity, a situation in which an address is interpreted differently on two physical networks. Thus, network managers are discouraged from using variable-length subnetti…

18. What does network mask cover?

    The mask covers the internet portion of the address as well as the physical network part of the local portion.

19. Express 255.255.255.0 with slash notation.

    For example, instead of writing the dotted decimal value 255.255.255.0, a manager can write /24.

20. Name 2 benefits of subnetting on private networks.

    1. security With logical divisions between subnets, you have greater control over who has access to what. For example, in our departmental example, you could easily restrict those in engineering from accessing file server containing sensitive sales information, and prevent sales from accessing a share that houses classified engineering blueprints. 2. speed Subnetting reduces the amount of broadcast traffic by containing network broadcasts at the subnet level instead of sending all broadcasts to…

21. Which routing protocols send the subnet mask along with their updates?

    Routing protocols can be classful or classless: Classful: DO NOT send the subnet mask along with their updates. Classless: DO send the subnet mask along with their updates. Today, IP addresses are associated with a subnet mask. This was not required in a classful network because the mask was implicitly derived from the IP address itself. Any network device would inspect the first few bits of the IP address to determine the class of the address.

22. Formula for amount of subnets? Formula for amount of (usable) hosts?

    subnets = 2subnet bits hosts = 2host bits - 2 (where all-zero host bits is for a network address, where all-ones host bits is for a broadcast address) Links: wikipedia - subnet and host counts

23. Given: 11000000.10101000.01111011.10000100 - IP address (192.168.123.132) 11111111.11111111.11111111.00000000 - Subnet mask (255.255.255.0) What's subnet address and host address?

    11000000.10101000.01111011.00000000 - Subnet address (192.168.123.0) 00000000.00000000.00000000.10000100 - Host address (000.000.000.132)

24. IP address: 15.32.56.7 = 00001111.32.56.7 What class does this IP belong to?

    IP start with: Class A: 0 Class B: 10 Class C: 110. This one starts with 0, therefore it's A.

25. Given: IP address subnet mask Give formulas for: subnet address host address broadcast address

    subnet address: IP && mask host address: IP && !mask broadcast address: subnet address, but fill in remaining host bits with 1s.