College of Computer Engineering and Sciences
ITAP 2431 – Network Management
Assignment # 3
Name: Noof Al-sowidan
ID:200800579
Q1. How does TCP ensure reliable delivery of packets?
(2 Marks)
To ensure reliability, TCP is able to recover from data that is damaged, lost, duplicated, or delivered out of
sequence. In order to do this, TCP assigns a sequence number to each byte transmitted. The receiving host's
TCP must return an ACK for bytes received within a specified period. If this is not done, the data is
retransmitted. Damaged data is handled by adding a checksum to each segment. If a segment is detected as
damaged by the receiving host's TCP, it will discard the segment. The sender will resend the segment since
the ACK was never sent.
Q2. What are the main differences between IPv4 and IPv6?
IPv4 : uses 32 bit addresses
IPv6: uses128 bit addresses
Q3. Why does TCP need to perform “Reassembly” of packets?
(2 Mark)
(2 Marks)
TCP reassembly causes the sensor to reassemble a TCP session's packets before they are compared against the
signatures. This helps keep resources from being tied up. There are three TCP session reassembly options you
can choose from: No Reassembly, Loose Reassembly, and Strict Reassembly.
Q4. Explain how Reassembly of packets is being done in TCP.
(2 Marks)
A dissector gets a tvbuff_t pointer which holds the payload of a TCP packet. This payload contains the header
and data of your application layer protocol.
When dissecting an application layer protocol you cannot assume that each TCP packet contains exactly one
application layer message. One application layer message can be split into several TCP packets.
You also cannot assume that a TCP packet contains only one application layer message and that the message
header is at the start of your TCP payload. More than one messages can be transmitted in one TCP packet, so
that a message can start at an arbitrary position.
This sounds complicated, but there is a simple solution. tcp_dissect_pdus() does all this tcp packet
reassembling for you. This function is implemented in epan/dissectors/packet-tcp.h.
Q5. Explain the main 2 functions of the routing layer.
•
•
Centralized routing
– Decisions made by one central computer
– Used on small, mainframe-based networks
Decentralized routing
– Decisions made by each node independently of one another
– Information need to be exchanged to prepare routing tables
– Used by Internet
Q6. What is the difference between static and dynamic routing?
•
•
(2 Marks)
(2 Marks)
Static routing:
– Uses fixed routing tables developed by network managers
• Each node has its own routing table
• Changes when computers added or removed
– Used on relatively simple networks with few routing options that rarely change
Dynamic routing or Adaptive routing:
– Uses routing tables at each node that are updated dynamically
– Based on routing condition information exchanged between routing devices