Computer Network

Instructions:-

Computer Network

R3.) What is the difference between routing and forwarding?

R12.) Do routers have IP addresses? If so, how many?

P16.) Suppose an application generates chunks of 40 bytes of data every 20msec, and each chunk gets encapsulated in a TCP segment and then an IP datagram. What percentage of each datagram will be overhead, and what percentage will be application data?

R9.) How big is the MAC address space? The IPv4 address space? The IPv6 address space?

(R13) What is the 32-­‐bit equivalent of the IP address 214.16.90.14?  Don’t use a calculator, because you won’t be allowed one during the exam.

Convert the IP address 11010011 00101110 00110011 10010000 to dotted decimal. Don’t use a calculator, because you won’t be allowed one during the exam.

(R18) Suppose you purchase a wireless router and connect it to your cable modem. Also suppose that your ISP dynamically assigns your wireless router one IP address. Also suppose that you have five PCs at home that use 802.11 to wirelessly connect to your wireless router. Describe in detail how IP addresses are assigned to the five PCs? Is DHCP used? Is NAT used?

(R23) Is it necessary that every autonomous system use the same intra-­‐AS routing algorithm?

R11.) Why is an ARP query sent within a broadcast frame? Why is an ARP response sent within a frame with a specific destination MAC address?

R14.) Consider Figure 5.15 How many subnetworks are there, in the addressing sense of Section 4.4?

R16.) Suppose that N switches supporting K VLAN groups are to be connected via a trunking protocol. How many ports are needed to connect the switches? Justify your answer.

P14) Consider three LANs interconnected by two routers, as shown in figure 5.33.

A. Assign IP addresses to all of the interfaces. For subnet 1 use address of the form 192.168.1.xxx; for Subnet 2 uses addresses of the form 192.168.2.xxx; and for subnet 3 use addresses of the form 192.168.3.xxx.

B. Assign MAC addresses to all of the adapters.

C. Consider sending an IP datagram from Host E to Host B. Suppose all of the ARP tables are up to date. Enumerate all the steps, as done for the single-router example in section 5.4.1.

D. Repeat (c), now assuming that the ARP table in the sending host is empty (and the other tables are up to date).

Solution

Computer Network

R3.) What is the difference between routing and forwarding?

Forwarding is a local matter that figures out the best output link within a router. Routing is within the whole network to plan the best path from source to destination.

R12. Do routers have IP addresses? If so, how many?

Yes. They have one address for each interface.

R16. Suppose an application generates chunks of 40 bytes of data every 20 msec, and each chunk gets encapsulated in a TCP segment and then an IP datagram. What percentage of each datagram will be overhead, and what percentage will be application data?

40’bytes’in’the’two’headers

overhead’=’40/70’=’57%

data’=’30/70’=’43%

R9.) How big is the MAC address space? The IPv4 address space? The IPv6 address space?

A MAC has 6 tuples of hexadecimal values (12 places for values).

IPv4 uses 32-bit addressing.

IPv6 uses 128-bit addressing.

Therefore: MAC : 16^12 = 281474976710656 addresses

IPv4 : 2^32 = 4294967296 addresses

IPv6 : 2^128 = 3.4028236692093846346337460743177e+38 addresses

(R13) What is the 32-­‐bit equivalent of the IP address 214.16.90.14?  Don’t use a calculator, because you won’t be allowed one during the exam.

11010110.00010000.01011010.00001110

Convert the IP address 11010011 00101110 00110011 10010000 to dotted decimal. Don’t use a calculator, because you won’t be allowed one during the exam.

211.46.51.144

(R18) Suppose you purchase a wireless router and connect it to your cable modem. Also suppose that your ISP dynamically assigns your wireless router one IP address. Also suppose that you have five PCs at home that use 802.11 to wirelessly connect to your wireless router. Describe in detail how IP addresses are assigned to the five PCs? Is DHCP used? Is NAT used?

Each PC will request an address from the router, which is acting as a DHCP server. The router will assign each machine an address from a block of private address, which contains invalid Internet IP addresses. NAT is not used to assign addresses to PCs.

(R23) Is it necessary that every autonomous system use the same intra-­‐AS routing algorithm?

No.  Each AS is allowed to pick any intra-­‐AS routing algorithm.  However, all AS must use the same inter-­‐AS routing algorithm (BGP)

• Consider a subnet with prefix 101.101.101.64/28. How many unique addresses can be assigned to this block?

4 host bits = 2^4 = 16 addresses

• Consider a subnet with prefix 101.101.101.64/28. How many unique addresses can be assigned to this block?

4 host bits = 2^4 = 16 addresses

Answer the following questions using the forwarding table shown below:

Range of IP Addresses	Outgoing Interface
200.95.20.0/24	1
200.0.0.0/8	2
200.95.0.0/16	3
Other	4

1. What outgoing interface would a packet addressed to 198.84.16.22 go to? 4
2. What outgoing interface would a packet addressed to 200.95.14.6? 3
3. What outgoing interface would a packet addressed to 200.12.0.12? 2