chapter6-1in the networksthavdbjdjdj.ppt

Chapter 6 Dr. Ali Al-Hamdi 1
Chapter 6
Network Layer Protocols
Part III: Network Layer

 Chapter topics include:
 Discussion of IPv4 protocol,
 Discussion of ICMPv4,
 Mobile IP discussion.
Lead-in

 6.1.1 Overview
 IGMP services
 ICMP services
 ARP services
 IPv4 services
 IPv4 problems (best-effort delivery)
 Solutions
6.1 Internet Protocols

 6.1.2 Datagram Format: IPv4

 6.1.2 Datagram Format
 Protocol field

 6.1.3 Fragmentation
 Motivations
 Example
 Maximum Transfer Unit Format

 Related fields
 16-bit identification field
 3-bit flages field
 13- bit fragmentation offset field
 Example

 Detailed example

 Fragmentation reassembling strategy
The final destination host can reassemble the original datagram from the
fragments received (if none of them is lost) using the
following strategy:
a. The first fragment has an offset field value of zero.
b. Divide the length of the first fragment by 8. The second fragment has an
offset value equal to that result.
c. Divide the total length of the first and second fragment by 8. The third
fragment has an offset value equal to that result.
d. Continue the process. The last fragment has its M bit set to 0.
e. Continue the process. The last fragment has a more bit value of 0.

 6.1.4 Options
 Header Parts?
 Options are used for
 Network testing and debugging
 Option processing is required of the IPv4 software
 Options categories
 Single-byte options
 Multi-Byte Option

 6.1.4 Options
 Single-Byte Option
 No operation: 1-byte option used as a filler between options.
 End of operation: 1-byte option used for padding at the end of the
option field.
 Record Route: used to record the Internet routers (up to 9 addresses)
that handle the datagram, and debugging and management purposes.
 Strict Source Route: used by the source to predetermine a route for the
datagram as it travels through the Internet with a specific criteria such as?

 6.1.4 Options
 Loose Source Route: similar to the strict source route, but it is less
rigid. Each router in the list must be visited, but the datagram can visit
other routers as well.
 Timestamp: used to record the time of datagram processing by a router
expressed in milliseconds from midnight, Universal time or GMT. So, it
can help users and managers track the behavior of the routers in the
Internet.

 6.1.5 Security of IPv4 Datagram
 Packet Sniffing
 Packet Modification
 IP spoofing
 IP Sec
 IP Sec services
 Defining algorithms and keys
 Packet encryption
 Data integrity
 Origin authentication

 IPv4 deficienies
 Possible situations of errors occurrence?
 Lack of mechanisms such as host management and
queries
 Solution?
 Facts about ICPM
 Operating layer
 ICMP messages are first encapsulated inside IP
datagrams before going to the lower layer.
6.2 ICMPv4

6.2 ICMPv4
 6.2.1 Messages
 Message types
 Error reporting messages: report problems that a router or a host
(destination) may encounter when it processes an IP packet. ICMP does
not correct errors, it simply reports them. Error correction is left to the
higher-level protocols.
 Query message: help a host or a network manager to get specific
information from a router or another host to probe or test the liveliness of
hosts or routers in the Internet, find the one-way or the round-trip time for
an IP datagram between 2 devices, or even find out whether the clocks in
two devices are synchronized.

6.2 ICMPv4
 6.2.1 Messages
 Message Format

 6.2.1 Messages
 Error Reporting Messages
 Rules ICMP follows
6.2 ICMPv4

6.2 ICMPv4
 6.2.1 Messages
 Destination Unreachable: uses different codes (0 to 15) to define the
type of error message and the reason why a datagram has not reached its
final destination (code 0 is used for this purpose). For example, when we
use the HTTP protocol to access a web page, but the server is down.
 Source Quench: informs the sender that the network has encountered
congestion and the datagram has been dropped; the source needs to slow
down sending more datagrams. In other words, ICMP adds a kind of
congestion control mechanism to the IP protocol by using this type of
message.

6.2 ICMPv4
 6.2.1 Messages
 Redirection Message: used when the source uses a wrong router to
send out its message. The router redirects the message to the appropriate
router, but informs the source that it needs to change its default router in
the future. The IP address of the default router is sent in the message.
 Time exceeded: When the TTL value becomes 0, the datagram is
dropped by the visiting router and a time exceeded message (type 11)
with code 0 is sent to the source to inform it about the situation. The time-
exceeded message (with code 1) can also be sent when not all fragments
of a datagram arrive within a predefined period of time.

6.2 ICMPv4
 6.2.1 Messages
 Parameter problem: A parameter problem message (type 12) can be
sent when either there is a problem in the header of a datagram (code 0)
or some options are missing or cannot be interpreted (code 1).

 6.2.1 Messages
 Query Messages
 Echo request and echo replay: are used by a host or a router to test
the liveliness of another host or router. A host or router sends an echo
request message to another host or router; if the latter is alive, it responds
with an echo reply message using 2 debugging tools: ping and traceroute.
 Timestamp request and timestamp replay: are used to find the
round-trip time between 2 devices or to check whether the clocks in 2
devices are synchronized. The timestamp request message sends a 32-bit
number, which defines the time the message is sent. The timestamp reply
resends that number, but also includes 2 new 32-bit numbers representing
the time the request was received and the time the response was sent.
6.2 ICMPv4

 6.2.1 Messages
 Debugging Tools
 Tools used: ICMP uses ping and traceroute
 Function: determining the viability of a host or router (ping) and
tracing the route of a packet (traceroute) respectively.
 Ping
 Operation: The source host sends ICMP echo-request messages; the
destination, if alive, responds with ICMP echo-reply messages. The ping
program sets the identifier field in the echo-request and echo-reply
message and starts the sequence number from 0; this number is
incremented by 1 each time a new message is sent.
6.2 ICMPv4

 6.2.1 Messages
 Debugging Tools
 Ping Example:
6.2 ICMPv4

 6.2.1 Messages
 Debugging Tools
 Traceroute or Tracert
 Used by: UNIX and Windows respectively
 Tasks: find the packet path from a source to the destination + RTT cal.
 Type of messages used: time-exceeded and destination-unreachable.
 Traceroute Operation: If there are n routers in the path, the traceroute
sends (n + 1) messages. The first n messages are discarded by the n
routers, one by each router; the last message is discarded by the
destination host. The traceroute client program uses the (n + 1) ICMP
error-reporting messages received to find the path between the routers.
6.2 ICMPv4

 6.2.1 Messages
 Debugging Tools
 Example
6.2 ICMPv4

 6.2.1 Messages
 Debugging Tools
 Traceroute Operation (estimating RTT): Most traceroute
programs send three messages to each device, with the same TTL value,
to be able to find a better estimate for the round-trip time.
6.2 ICMPv4

 6.2.1 Messages
 Debugging Tools
 Example (estimating RTT): Traceroute program uses three probes
for each device and gets three RTTs.
6.2 ICMPv4

 6.2.1 Messages
 Debugging Tools
 Traceroute orTracert
 Tracert Operation: The tracert program in windows behaves
differently. The tracert messages are encapsulated directly in IP
datagrams. The tracert, like traceroute, sends echo-request messages.
However, when the last echo request reaches the destination host, an echo
replay message is issued.
6.2 ICMPv4

 6.2.3 ICMP Checksum
6.2 ICMPv4

 6.3.1 Addressing
 Main problem in mobile communication? Why?
 Stationary Hosts
 Mobile Hosts: solutions
 Changing the address
 How?
 Drawbacks
6.3 MOBILE IP

 6.3.1 Addressing
 Mobile Hosts
 Two Addresses
6.3 MOBILE IP

 6.3.2 Agents
 Home Agent
6.3 MOBILE IP

 6.3.2 Agents
 Forgien Agent
 Collocated care-of address
 Advantage of collocated care-of address
 Disadvantage of colloctaed care-of address
6.3 MOBILE IP

 6.3.3 Three Phases
6.3 MOBILE IP

 Agent Discovery
 Agent Advertisement
6.3 MOBILE IP

 Agent Discovery
 Agent Solicitation
6.3 MOBILE IP

 Registration
 Steps for registration
 Registration Request
6.3 MOBILE IP

 Registration
 Registration Reply
6.3 MOBILE IP

 Data Transfer: Operation

6.3 MOBILE IP

 6.3.4 Inefficiency in Mobile IP
 Double Crossing
6.3 MOBILE IP

 6.3.4 Inefficiency in Mobile IP
 Triangle Routing
 Solution?
6.3 MOBILE IP

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