Description
1. (2pt) Three types of switching fabric are discussed in
Section 4.2. List and briefly describe each type. Which, if
any, can send multiple packets across the fabric in
parallel?
2. (2pt) What is HOL blocking? Does it occur in input ports or
output ports?
3. (1pt) What fields in the IP header can be used to ensure
that a packet is forwarded through no more than N
routers?
4. (1pt) When a large datagram is fragmented into multiple
smaller datagrams, where are these smaller datagrams
reassembled into a single larger datagram?
5. (2pt) Consider the network below
a. Show the forwarding table in router A, such that all
traffic destined to host H3 is forwarded through
interface 3.
b. Can you write down a forwarding table in router A,
such that all traffic from H1 destined to host H3 is
forwarded through interface 3, while all traffic from
H2 destined to host H3 is forwarded through
interface 4?
6. (8pt) Consider a datagram network using 32-bit host
addresses. Suppose a router has four links, numbered 0
through 3, and packets are to be forwarded to the link
interfaces as follows:
Destination Address Range Link Interface
11100000 00000000 00000000 00000000
through 0
11100000 00111111 11111111 11111111
11100000 01000000 00000000 00000000
through 1
11100000 01000000 11111111 11111111
11100000 01000001 00000000 00000000
through 2
11100001 01111111 11111111 11111111
otherwise 3
a. Provide a forwarding table that has five entries, uses
longest prefix matching, and forwards packets to the
correct link interfaces.
b. Describe how your forwarding table determines the
appropriate link interface for datagrams with
destination addresses:
11001000 10010001 01010001 01010101
11100001 01000000 11000011 00111100
11100001 10000000 00010001 01110111
7. (3pt) Consider a router that interconnects three subnets:
Subnet 1, Subnet 2, and Subnet 3. Suppose all of the
interfaces in each of these three subnets are required to
have the prefix 223.1.17/24. Also suppose that Subnet 1 is
required to support at least 60 interfaces, Subnet 2 is
required to support at least 90 interfaces, and Subnet 3 is
to support at least 12 interfaces. Provide three network
addresses (of the form a.b.c.d/x) that satisfy these
constraints.
8. (2pt) Consider sending a 2100-byte datagram into a link
that has an MTU of 700 bytes. Suppose the original
datagram is stamped with the identification number 422.
How many fragments are generated? What are the values
in the various fields in the IP datagram(s) generated
related to fragmentation?
9. (3pt) Consider the network setup below. Suppose that the
ISP instead assigns the router the address 24.34.112.236
and that the network address of the home network is
192.168.1/24.
a. Assign addresses to all interfaces in the home
network
b. Suppose each host has two ongoing TCP connections,
all to port 80 at host 128.119.41.85. Provide the six
corresponding entries in the NAT translation table.
10. (1pt) What is the difference between a forward table in
the destination-based forwarding routers and OpenFlow’s
flow table that we discussed in Section 4.4?
