Business Data Communication Exam 3
Use ipconfig/all... What is the lease duration of the IP address
5 days, 8 hours
Say you have a /15 network address. You are asked to create subnets with at least 1,000 hosts/subnet. What is the maximum number of such subnets you can create
?
What is the subnet mask you will use for the previous question
?
How many hosts can a /18 network support?
A /18 network has 14 bits in the host ID part. This network can support 2^14 - 2 = 16,382 hosts
What is a subnet mask?
A subnet mask is a number that tells the host which bits in an IP address constitute the network ID and subnet ID of the network. The subnet mask is a 32-bit number comprising a sequence of 1's followed by a sequence of 0's. The 1's are bit positions of the network and subnet ID and the 0's are bit positions of the host ID
Describe how subnetting is similar to the three-part organization of telephone numbers.
A telephone number has three parts as well. The area code denotes the metro area, the second part identifies the exchange and the last four numbers identify the phone receiver. In the IP address, the network ID identifies the organization, the subnet ID identifies the department and the host ID identifies the host within the department.
What is ARP? What is it used for?
Address Resolution Protocol, a protocol that dynamically determines the network-layer IP address associated with a data-link-layer physical hardware address. ARP is used to find Ethernet addresses at the data-link layer for destinations with a known IP address and to discover the MAC address of the device at the next hop when its IP address is known
How do you determine the number of subnets needed in an organization?
An analysis of the business determines the most suitable number of subnets for the organization. Each functionally independent unit of the organization is a candidate for a subnet
IP addresses are used for routing. Why are non-routable IP addresses useful?
Any person or organization may use these addresses internally without any co-ordination with any Internet registry. Routers do not advertise routes with non-routable addresses to other organizations.
What are the three types of address allocation schemes in DHCP? Under what conditions is each of these categories of address allocation preferred?
Automatic, manual and dynamic allocation. Automatic allocation is used to connect an IP address to a host permanently, like for a networked printer. The client PCs would only have to be set up once to use the specified IP address. Manual allocation is also permanent; however, the network administrator will manually specify the IP addresses to be allocated to individual devices on the network. Dynamic allocations are only available for a limited time. The IP addresses are leased out for short durations by the DHCP server for short durations. The lease has to be extended or the IP address will become available for another client.
Briefly describe the operation of ARP.
Before the first packet in a stream is transmitted, the sender creates a special packet called an ARP request and broadcasts it on the LAN. The computer/ router with the address replies with its MAC address.
Using an example, describe the three-part interpretation of IP addresses when subnetting is used.
Consider the IP address 131.247.99.108. Since we know that this IP address is part of the 131.247.0.0/ 16 network, we know that the first two octets identify the network to which the address belongs. Assuming 8-bit subnet IDs, the 99 in the third octet identifies the subnet and the 108 in the fourth octet identifies the host within the subnet.
What is DHCP? Why is it useful?
DHCP, or dynamic host configuration protocol, is a technology that enables automatic assignment and collection of IP addresses. DHCP is useful because it greatly simplifies the allocation of IP addresses. DHCP also improves the efficiency of allocating IP addresses.
What is DNS? What is it used for?
Domain name system, the set of databases that performs the correspondence between the domain name and its IP address. The domain name system was developed to make it easier for humans to identify computers. It simplifies the use of computer networks on a day-to-day basis.
What is a zone in the context of DNS?
Domains are called zones in the context of the domain name service. Each name server is responsible for its zone and only for its zone. Zones may have sub-zones and each sub-zone is responsible for its own zone.
Describe how subnetting is similar to the multi-part organization of zip codes.
Each zip code identifies a national region and the additional 4 digits that determine a more specific location. Subnetting does the same; starts out with a bigger area and condenses to get a more specific location.
Describe the process used by a name server to resolve the IP address of a URL typed by a user.
Every computer on the Internet knows the IP address of a name server it can use. When a user types a URL, the resolver in the computer first asks its name server for the IP address corresponding to this URL.
What are non-routable IP addresses?
IP addresses within three pools of IP addresses that may be used by anybody within any network without permission from the internet registries. These IP addresses can be reused as often as necessary.
Describe the NAPT operation, i.e., describe how the IP addresses in a packet change as a request packet travels from a source with an RFC 1918 address to a destination and the reply comes back to the source.
If an incoming packet does not match an existing entry in the NAT forwarding table, the NAT translator will not know which computer in the internal network to send the packet to. The ports of the routers are assigned IP addresses and are used to route the packets to the customers' homes. When packets leave the home they have a source address. When replies are received at the home, the router uses NAPT to translate the source address to the internal RFC 1918 UP address used inside the home.
Briefly describe the sequence of operations that allow a freshly booted DHCP client to obtain an IP address from a DHCP server on the network.
In a typical DHCP client-server interaction 1. Client sends a DHCP DISCOVER 2. Server responds with DHCP OFFER 3. DHCP REQUEST broadcasts client selection 4. Selected server sends DHCP ACK
What is network address translation? Why is it useful?
It is the Third component of 3-part solution to IP address shortage. Method by which IP addresses are mapped from one address block to another, providing transparent routing to end hosts. The single external IP address can support many clients in the internal network. The NAT router translates between internal IP addresses and its own external address. It is designed to support outbound connections from the internal network
What is NAPT? How can it improve the efficiency of utilizing IP addresses, compared to NAT, without port translation?
NAPT can vastly expand the availability of IP addresses by enabling each IP address to serve up to 65,536 separate connections to each remote host.
How many subnets can you have on the network in the question above?
Of the 22 bits in the network ID and subnet ID, we know that the network ID takes up 14 bits. Therefore, the subnet ID has 22 - 14 = 8 bits. This gives us 28 - 2 = 254 subnets
What is a recursive query in DNS? When does it become necessary?
Recursive query becomes necessary when your domain name server does not have a cached entry for a TLD for a domain it is asked to search. The name server starts the search from the naming universe. When a DNS query is made, the DNS server can start with one of the root name servers and search down the domain name hierarchy till it finds the authoritative name server for the domain being searched
Why can't a computer with an RFC 1918 IP address be used as a public-facing web server?
Routers and packets at the edge of the enterprise limit the packets using RFC 1918 addresses to the LANs in which they originate. Routers also do not advertise routes that include RFC 1918 addresses to other routers outside the enterprise.
Use nslookup www.google.com, Which server (google or local name) forms name resolution?
Server: UnKnown Non-authoritative answer: Name: www.google.com
What are some of the reasons for the inefficiencies in allocating the available IP addresses?
Since the IP addresses are 32 bits long, there can be 4 billion addresses. These addresses are not assigned very efficiently because they are allocated in blocks by the registries
The broadcast address on a subnet is obtained by replacing the bits in the host part with 1s instead of 0s. What is the broadcast address of the subnet 192.168.1.192/28
Since this address is part of a /28 network, only the last 4 bits are the host ID. Therefore, the broadcast address will only be different in the last octet. 192 = 11000000. Replacing the 4 bits of the host ID part with 1 gives us the octet 11001111. 110011112 = 207. Therefore, the broadcast address on this subnet is 192.168.1.207
What is subnetting?
Subnetting is the division of large blocks of IP addresses allocated to an organization into smaller address blocks called subnets. Each department within the organization can be assigned one or more of these smaller address blocks. Each department's network administrator can use these smaller address blocks to manage their networks
What do the 1s and 0s in a subnet mask represent?
The 1's indicate bits in the IP address that form the network ID and subnet ID. For example, if a subnet mask has 20 1's, the first 20 bits of any IP address in the organization identifies the network ID and subnet ID. The 0's represent the host ID bits in any IP address in the organization
Can 255.255.253.0 be a subnet mask? Why or why not?
The binary representation of 255.255.253 is 11111111.11111111.11111101.00000000 Since the sequence of 1's is interrupted with a 0, this number cannot be a subnet mask
What are the three IP addresses on any network that are not available for allocation to hosts?
The broadcast address (all 1's in the host part) and the network address (all 0's in the host part, default gateway for router
What is address leasing in DHCP?
The duration for which an IP address is provided. The client can request the DHCP server for an extension of the lease before the lease expires
Why is it useful to organize domain names such as www.usf.edu hierarchically as they are done in DNS?
The hierarchical structure of the Internet enables delegation of naming services.
Describe the hierarchical organization of domains on the Internet.
The name at each hierarchical level is a domain a. Domains are sub-domains of their parent domains b. The domain's name includes all names to its right c. Each domain maintains jurisdiction over its immediate sub-domains, and only these sub-domains d. Each domain is responsible to translating these sub-domain names to IP addresses
What is the organizational motivation for subnetting?
The organizational motivation for subnetting is that it facilitates autonomy for the IT groups within organizational units. Each department within the organization can be assigned one or more smaller address blocks and each department's network administrator can use these smaller address blocks to manage their network
In large organizations, what are some disadvantages with allocating IP addresses on a first-come, first-served basis?
The primary disadvantage of allocating IP addresses on a first-come first-served basis is that the network administrator will not have any idea where a host with a given IP address is located on campus. Therefore, if a user with a network connectivity problem calls the network administrator for help, the network administrator would have a very difficult time trying to troubleshoot the problem. Also, first-come first-serve allocation prevents organization of IP addresses.
What are the different network services provided by the typical home wireless router provided by ISPs?
The router typically acts as your DHCP server, your DNS server and your NAPT router.
How do DHCP, non-routable addresses, and NAT help improve the efficiency of utilizing IP addresses and reduce the shortage of IP addresses?
They allow IP addresses to be permanently used, leased, reused and enables them to serve more connections per host.
Say you have a /14 network address. You are asked to create subnets with at least 1,000 hosts/ subnet. What subnet mask should you use?
To obtain 1,000 hosts per subnet, we need 10 bits in the host ID part because 210 = 1,024. The remaining 22 bits in the subnet mask will be 1's. This gives us the subnet mask: 11111111.11111111.11111100.00000000, which in dotted decimal notation is 255.255.252.0
Why are subnet masks needed?
Unlike address classes where the boundary separating the network part from the host part is known from the first octet of the IP address, with CIDR addresses and subnet masks, the sizes of the various parts of the IP address are now completely flexible. For routing purposes, it is necessary to isolate the network ID + subnet ID. Subnet masks are needed to do this
What are the different kinds of top-level domains?
a. Open domains i. Anybody can register 1. .com, .biz, .org, .net, .info b. Limited domains i. Conditions must be satisfied for membership 1. .edu, .int, .gov, .mil, .pro (licensed doctors, attorneys and accountants) c. Industry-specific domains d. Country domains
