Module 4 part 2.pdf this is computer networs module for cse students for study

21.1
Network Layer:
Address Mapping,
Error Reporting,
and Multicasting
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

21.2
21-1 ADDRESS MAPPING
The delivery of a packet to a host or a router requires
two levels of addressing: logical and physical. We need
to be able to map a logical address to its corresponding
physical address and vice versa. This can be done by
using either static or dynamic mapping.
Mapping Logical to Physical Address
Mapping Physical to Logical Address
Topics discussed in this section:

21.3
Figure 21.1 ARP operation

21.5
Figure 21.3 Encapsulation of ARP packet

21.6
Figure 21.4 Four cases using ARP

21.7
An ARP request is broadcast;
an ARP reply is unicast.
Note

21.8
A host with IP address 130.23.43.20 and physical address
B2:34:55:10:22:10 has a packet to send to another host
with IP address 130.23.43.25 and physical address
A4:6E:F4:59:83:AB. The two hosts are on the same
Ethernet network. Show the ARP request and reply
packets encapsulated in Ethernet frames.
Solution
Figure 21.5 shows the ARP request and reply packets.
Note that the ARP data field in this case is 28 bytes, and
that the individual addresses do not fit in the 4-byte
boundary. That is why we do not show the regular 4-byte
boundaries for these addresses.
Example 21.1

21.9
Figure 21.5 Example 21.1, an ARP request and reply

Mapping Physical to Logical Address:
RARP
BOOTP
DHCP
21.10

21.11
Figure 21.7 BOOTP client and server on the same and different networks

21.12
DHCP provides static and dynamic
address allocation that can be
manual or automatic.
Note

Control Protocol
◼ IP provides unreliable and connectionless datagram
delivery
◼ What problem can arise which can go unattended?
◼ cannot find a router to the final destination
◼ time-to-live expired?
◼ What if the final destination host must discard all
fragments of a data gram?
21.13

21.14
21-2 ICMP
The IP protocol has no error-reporting or error-
correcting mechanism. The IP protocol also lacks a
mechanism for host and management queries. The
Internet Control Message Protocol (ICMP) has been
designed to compensate for the above two deficiencies.
It is a companion to the IP protocol.
Types of Messages
Message Format
Error Reporting and Query
Debugging Tools

Types of Messages
◼ The error-reporting messages report problems that a
router or a host (destination) may encounter when it
processes an IP packet.
◼ The query messages, which occur in pairs, help a host
or a network manager get specific information from a
router or another host
21.15

21.16
Figure 21.8 General format of ICMP messages
8-byte header and a variable-size data section. Although the general
format of the header is different for each message type, the first 4
bytes are common to all.
The data section in error messages carries information for finding
the original packet that had the error. In query messages, the data
section carries extra information based on the type of the query.

21.17
ICMP always reports error messages to
the original source.
Note

21.18
Figure 21.9 Error-reporting messages

21.19
Important points about ICMP error messages:
❏ No ICMP error message will be generated in
response to a datagram carrying an ICMP error
message.
❏ No ICMP error message will be generated for a
fragmented datagram that is not the first fragment.
datagram having a multicast address.
datagram having a special address such as
127.0.0.0 or 0.0.0.0.
Note

Destination unreachable
◼ When a router cannot route a datagram
◼ Host cannot deliver a datagram
◼ Discard and inform
◼ Can be created by either a router or the
destination host
21.20

Source Quench
◼ IP is connectionless
◼ Lack of flow control
◼ Gives rise to congestion
◼ It informs the source that the datagram has been
discarded.
◼ It warns the source that there is congestion somewhere
in the path and that the source should slow down
(quench) the sending process
21.21

Time Exceeded
◼ Two cases:
◼ TTL expired
◼ Not all fragments arrived at host in time
of same massage
21.22

21.23
Figure 21.11 Redirection concept

21.24
Figure 21.12 Query messages

21.25
21-3 IGMP
The IP protocol can be involved in two types of
communication: unicasting and multicasting. The
Internet Group Management Protocol (IGMP) is one
of the necessary, but not sufficient, protocols that is
involved in multicasting. IGMP is a companion to the
IP protocol.
Group Management
IGMP Messages and IGMP Operation
Encapsulation
Netstat Utility

21.26
Figure 21.16 IGMP message types

21.27
Figure 21.17 IGMP message format

21.28
Table 21.1 IGMP type field

21.29
Figure 21.18 IGMP operation

21.30
In IGMP, a membership report is sent
twice, one after the other.
Note

21.31
The general query message does not
define a particular group.
Note

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