PROBLEMS AND EXERCISES

Transcription

1 Departamento de Tecnología Electrónica Computer Networking Ch4: Network layer PROBLEMS AND EXERCISES Network Layer 4 72

2 Pr1: Fragmentation Consider a router that has received a IP_PDU with 2400 bytes from one of its interfaces and has to forward it through a 700 bytes MTU. How many IP_PDUs will router forward to this output interface? Indicate values for fragment identifier, flag, fragment off fields and length of each IP_PDU. Network Layer 3 73

3 Pr2: Classful addressing Next figure shows one router interconnecting two networks. Answer the questions reasonably assuming classful addressing is used: a) What is the available address range for each network, the broadcast address for each network and the routing table of the router and the routing table of a the end system in each network? Give an example about a possible configuration of router interfaces and of the end systems A and B. b) Suppose network klayer in an end system in network k sends a IP_PDU PDU whose destination address is Which network layer in the destination network will receive this IP_PDU? c) Suppose network layer of an end system in network sends a IP_PDU PDUwhose destination is Which network layer in the destination network will receive this IP_PDU? Network Layer 3 74

4 Pr3: Classless addressing Suppose a company is assigned the CIDR block CIDR / /24 a) How many subnets could you create inside this company? b) Which network prefix, broadcast address and available IP address range would each subnet have if the amount of end systems to connect in each subnet is 20? c) Would you change your answer if it was 30 end systems? Network Layer 3 75

5 Pr4: Classless addressing Consider a router that interconnects three subnets: subnet 1, subnet 2, and subnet 3. Suppose all of the interfaces in each of these subnets are required to have the prefix / /24. Also suppose that Subnet 1 is required to support up to 63 end systems, Subnet 2 up to 95 end systems and Subnet 3 up to 16 end systems. Determine reasonably if it is possible to address these three subnets. Network Layer 3 76

6 Pr5: NAT, interface configuration Next figure shows a public institution network that accesses to the Internet via router R2. Determine reasonably: a) How many end systems as maximum is possible to connect to each subnet of this institution? b) Is it necessary that router R2 implements NAT? c) Suppose R2 doens t implement NAT. Which network prefix would appear in the routing table in a router in the Internet, e.g. RI, to identify that institution? d) Could this institution address a new subnet? How many end systems could it connect as maximum? e) Suppose that the interface E0 of R2 has the next configuration: IP address= , netmask= , and all end systems have to be able to access to the Internet and communicate to other end systems inside the institution. Indicate the configuration for interfaces of routers R1 and R2, the minimum content of their routing tables and of the one end system in each subnet. Network Layer 3 77

7 Pr6: Addressing Next figure shows a public institution network that accesses to the Internet via router R2. Determine reasonably: a) If classful addressing was used, how many networks would be neccessary? Which class should be used for a minimum address waste? b) Would it be possible to address all subnets of the institution with a CIDR block /25? In that case, assign the right network address for each institution subnet. c) Would it be possible to connect a new subnet with 13 PCs through a free interface of R1? In that case, indicate the content of the routing table of R2 that makes the amount entries be minimum. (Note: interface E0 of R2 has the following configuration: IP addr= , netmask= All PCs of this institution are able to access to the Internet). d) Would you change your answer for question c) if the subnet connects to a free interface of R2 instead to R1? Network Layer 3 78

8 Pr7: NAT Figure shows two companies, X and Y, that access to the Internet through a router that implements NAT. A and B are web servers that are in the Internet. All devices are configured rigthly and classless addressing is used. Answer reasonably to this questions: a) Is it possible that a PC of the Company X, e.g. that has IP address , opens a web page from server A in its browser? In that case, indicate source and destination IP address that IP_PDUs received by the server would have and the IP_PDUs received by the client. Otherwise, explain what the problem is. b) Is it possible that a PC of the Company Y, e.g. that has IP address , opens a web page from server A in its browser? In that case, indicate source and destination IP address that IP_PDUs received by the server would have and the IP_PDUs received by the client. Otherwise, explain what the problem is. c) Is it possible that a PC of the Company X, e.g. that has IP address , opens a web page from server B in its browser? In that case, indicate source and destination IP address that IP_PDUs received by the server would have and the IP_PDUs received by the client. Otherwise, explain what the problem is. Network Layer 3 79

9 Pr8: Addressing Figure shows the network topology ofa company where hosts accessto the Internet through a router (1) that supports NAT. Router 1 is connected to the networks /24 and /24 through two different interfaces. Router RTX is in the Internet and it is not part of the company network. Classless addressing (CIDR) is used. a) How many broadcast domain are there in the company network? b) Provide an address assignment for this network taking into account that you have to leave as maximum address vacant as possible for future extensions. Subnet A is required to have 125 PCs and subnet B is required to have 61 PCs. i. Indicate, reasonably, IPaddress and netmask for all interfaces in routers 1,2 and 3. ii. Which address range would remain available for future extensions? Using all address space obtained, indicate reasonably network prefixes that allow the more number of hosts. c) Indicate, reasonably, the minimum content of the routing tables for all three routers (1, 2 y 3), for all PCs in the company may interchange ec gedatagramsag a among them and damong the Internet e and the less traffic cas possible is generated. d) Regarding router RTX, is it necessary to include any entry in the routing table to address the company? Indicate why and, if it is the case, a possible IP address for next hop. Network Layer 3 80

10 Pr9: IP configuration Consider the network showed in the figure that has access to the Internet, uses classless addressing and has all routers interfaces configured as it is shown in the table (note: all are not shown). Router (Interface) Prefix notation configuration R0 (E0) /23 R0 (E1) /30 R1 (E0) /23 R1(E1) /30 R2(E0) /30 Rext (E1) /30 a) Indicate, reasonably, IP address and netmask for interfaces E1 and E2 of router R2. b) Indicate, reasonably, if the following IP addresses are rigth in the described context: i. IP addr = and netmask = to a PC in network Alpha. ii. IP addr = and netmask = to a PC in network Alpha. iii. IP addr = and netmask = to a PC in network Bravo. iv. IP addr = and netmask = to a PC in network Bravo. c) Indicate, reasonably, the minimum content of the routing tables of router R2 and of a exterior router (Rext) connected to interface E0 of R2. d) If routers R0, R1 and R2 are replaced by a switch that interconnect networks Alpha and Bravo directlyto to the exterior router (Rext), being in the same broadcast domain. Which changes are necessary to do in the configuration of nodes in both networks and in the configuration of the exterior router in order to keep the connectivity (among PCs and to the Internet). NOTE: Parameter IP address in nodes of Alpha and Bravo cannot be modified. Network Layer 3 81

11 Pr10: Fragmentation Consider a router connecting two broadcast domain, 1 and 2. In each domain there is only one logic network. Broadcast domain 1 has MTU=1500 bytes and broadcast domain 2 has MTU = 760 bytes. In broadcast domain 1 there is a PC, PcA, that is running a process in port that implements the client side of an aplication layer protocol called X. In the same domain there is other PC, PcB, that is running a process in the port implementing the server side of the X protocol. If UDP in PcA receives a send request from port of an A_PDU of 1472 bytes to the port in PcB, determine reasonably: a) How many UDP_PDU and IP_PDU will UDP and IP receive, respectively, in PcB? And which size in bytes will they be? b) Would you change your answer if PcB was in broadcast domain 2? Why? (Note: In this case, PcB has been configured rightly in the corresponding logic network in that broadcast domain) Nivel de Red 3 82