Exercise 6.1.
With reference to Figure 6.4, consider host B with IP address which sends a datagram with 2000 bytes of payload and identification = 27,901 to host A with IP address Assuming routing at minimum distance (number of hops), default MTU except for network N2 in which this parameter assumes value 1500 bytes, show graphically the format of the IP datagrams, for all the known fields, exchanged between hosts and routers.

Figure 6.4 Network configuration according to Example 6.1 (Exercise 6.1).

Exercise 6.6.
Partition the class A network with address in subnets /17 (i.e. with netmask having the first 17 bits set at 1), determining the number of subnets that are obtained and the decimal format of the subnet number 163. This last “network” is in turn divided into subnets /n that allow addressing at least 1023 hosts each. Determine the subnet prefix /n, the resulting number of subnets and the broadcast address of subnet number 10.

Exercise 6.10.
An operator manages the following physical networks: (i) network N_1 that connects 40 hosts, (ii) network N_2 that connects 100 hosts, (iii) network N_3 that connects 14 hosts, (iv) network N_4 that connects 8 hosts, and obtains from the Internet authority multiple blocks of addresses starting at address Assuming classful addressing without variable length netmask adoption, assign blocks of IP addresses to individual networks starting from the smallest available address, specifying for each of them also the corresponding netmask, in order to minimize the total number of addresses that can no longer be used outside these four networks.

Exercise 6.12.
An operator manages the following physical networks: (i) network N_1 that connects 40 hosts, (ii) network N_2 that connects 100 hosts, (iii) network N_3 that connects 14 hosts, (iv) network N_4 that connects 8 hosts, and obtains an Internet address block from the Internet authority starting from address Assuming classful addressing, suppose that the administrator is going to associate a subnet with the following rules to each of the physical networks from N_1 to N_4: (i) all routers support variable length subnet mask (VLSM), which allows assigning variable length netmasks to different subnets; (ii) the subnet associated with each physical network must be such that the number of addresses not used by the hosts is as small as possible; (iii) the four physical networks are associated with blocks of contiguous addresses starting from the network address with smallest net-id and host-id.

Exercise 6.20.
With reference to the address translation functionality implemented in a router R, identify the “mapping” table of a NAPT having only one public address, which interfaces three hosts, H_1, H_2, H_3, of a private network whose addresses are the last three private addresses of the block in class B; these hosts access an FTP server S_1, a mail server POP3 S_2 and a WWW server S_3 with the first public address, respectively, in class A, in class B and in class C. It is assumed that the NAPT device selects the largest possible values for identifying the NAPT port number starting from host H1 and that each host selects the smallest value as the private port identifier.

Exercise 6.23.
Wiven the routing table below of an IP router for increasing netmasks (the netmask and the next hop router are shown for each network address). build a table that specifies the next hop that the router assigns according to the longest prefix match algorithm to datagrams whose destination IP address is:,,,, 88.32. 7.4,,,,,

Exercise 6.26.
Repeat Example 6.15 identifying the routing table of router R_5 ordered by netmasks of increasing value and also aggregating addresses, if possible, in order to reduce the entries of the routing table.

Figure 6.15 Network configuration according to Example 6.15 (Exercise 6.26).

Exercise 6.31.
A network is given having 6 nodes, A, B, C, D, E, F, and 10 edges, A-B of cost 1, B-C of cost 2, C-D of cost 3, D-E of cost 2, E-F of cost 6, F-A of cost 4, A-E of cost 11, B-F of cost 3, C-E of cost 7, CF of cost 3. Determine the evolution of the routing table of node E on the basis of the distance vectors received from the adjacent nodes in the first four updating steps of the routing tables, assuming that the vectors are transmitted between nodes at the same times and that the updating in each node occurs only once per step considering all the vectors received.

Exercise 6.33.
Consider a six-node network of which node D just connected to the network receives the following sequence of LSU messages, indicating the cost of traversing the links between adjacent nodes shown in the following table. Assuming that the cost is the same for both directions of each link, show how receiving these LSU messages allows the construction of the complete network topology seen by node D.

Exercise 6.34.
For the network topology found in Exercise 6.33, find the minimum spanning tree (MST) for node D, which therefore is the tree root, applying the Dijkstra’s algorithm.