Tutorial 4

Question 1

We noted that network layer functionality can be broadly divided into data plane functionality
and control plane functionality. What are the main functions of the data plane? Of the control
plane?

Answer 1

Data plane:
- packet fowarding, foward datagrams from input links to output links. Lookup function

Control plane:
- routing, determine paths a packet tackets from its source to destination. Control plane is responsible for executing routing protocols, responsding to attached links that go up or down, communicating with remote controllers and performing management functions

Question 2

We made a distinction between the forwarding function and the routing function performed in
the network layer. What are the key differences between routing and forwarding?

Answer 2

Fowarding is a routers local action of transferring packets from its input interfaces to its outut interfaces and fowarding takes place at very short time scales and is implemented in hardware

Routing is network wide process that determines end to end paths that packets take from sources to destinations. Much longer timescales and so implemented in software.

Question 3

We said that a network layer’s service model “defines the characteristics of end-to-end
transport of packets between sending and receiving hosts.” What is the service model of the
Internet’s network layer? What guarantees are made by the Internet’s service model regarding
the host-to-host delivery of datagrams?

Answer 3

service model of network layer is best-effort service. With this service model theres no guarantee that packets will be received in the order in which they were sent and no guarantee of eventual delivery no guarantee on end to end delay and no minimal bandwidth guarantee.

Question 4

Three types of switching fabrics are discussed in Section 4.2. List and briefly describe each
type. Which, if any, can send multiple packets across the fabric in parallel?

Answer 4

Switching via memory

Switching via bus

Switching via interconnection network

an interconnected network can foward packets in parallel as long as packets are being forward to different output ports.

Question 5

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

Answer 5

Yes, they have one address for each interface.

Question 6

What is the difference between a forwarding table that we encountered in destination-based
forwarding in Section 4.1 and OpenFlow’s flow table that we encountered in Section 4.4?

Answer 6

In destination based forwarding, each entry in the forwarding table only contains an IP header field value and the outgoing link interface to which a packet is to be forwarded.

In an OpenFLow table, there is also a set of header field values to to which an incoming packet will be matched, a set of counters that are updated as packets are matched to flow table entries and a set of actions to be taken when a packet matches a flow table entry.