COMPUTER NETWORKS UNIT 3

INTERNETWORKING
In this section, we discuss internetworking, connecting
networks together to make an internetwork or an
internet.
Need for Network Layer
Internet as a Datagram Network
Internet as a Connectionless Network
Topics discussed in this section:

Network layer in an internetwork

Network layer at the source, router, and destination

Network layer at the source, router, and destination (continued)

IPv4
The Internet Protocol version 4 (IPv4) is the delivery
mechanism used by the TCP/IP protocols.
Datagram
Fragmentation
Checksum
Options

Position of IPv4 in TCP/IP protocol suite

Service type or differentiated services

Encapsulation of a small datagram in an Ethernet frame

Protocol field and encapsulated data

Detailed fragmentation example

Example of checksum calculation in IPv4

IPv6
The network layer protocol in the TCP/IP protocol suite
is currently IPv4. Although IPv4 is well designed, data
communication has evolved since the inception of IPv4
in the 1970s. IPv4 has some deficiencies that make it
unsuitable for the fast-growing Internet.
Advantages
Packet Format
Extension Headers

IPv6 datagram header and payload

Table Next header codes for IPv6

Table Priorities for congestion-controlled traffic

Table Priorities for noncongestion-controlled traffic

Table Comparison between IPv4 and IPv6 packet headers

Table Comparison between IPv4 options and IPv6 extension headers

TRANSITION FROM IPv4 TO IPv6
Because of the huge number of systems on the Internet,
the transition from IPv4 to IPv6 cannot happen
suddenly. It takes a considerable amount of time before
every system in the Internet can move from IPv4 to
IPv6. The transition must be smooth to prevent any
problems between IPv4 and IPv6 systems.
Dual Stack
Tunneling
Header Translation

ROUTING
DELIVERY
The network layer supervises the handling of the
packets by the underlying physical networks. We define
this handling as the delivery of a packet.
Direct Versus Indirect Delivery

FORWARDING
Forwarding means to place the packet in its route to its
destination. Forwarding requires a host or a router to
have a routing table. When a host has a packet to send
or when a router has received a packet to be forwarded,
it looks at this table to find the route to the final
destination.
Forwarding Techniques
Forwarding Process
Routing Table

Route method versus next-hop method

Host-specific versus network-specific method

Simplified forwarding module in classless address

Table Routing table for router R1 in Figure 22.6

Hierarchical routing with ISPs

Common fields in a routing table

Configuration of the server for Example 22.6

UNICAST ROUTING PROTOCOLS
A routing table can be either static or dynamic. A static
table is one with manual entries. A dynamic table is one
that is updated automatically when there is a change
somewhere in the Internet. A routing protocol is a
combination of rules and procedures that lets routers in
the Internet inform each other of changes.
Optimization
Intra- and Interdomain Routing
Distance Vector Routing and RIP
Link State Routing and OSPF
Path Vector Routing and BGP

Distance vector routing tables

Initialization of tables in distance vector routing

Updating in distance vector routing

Example of formation of shortest path tree

Table Routing table for node A

Example of an AS and its graphical representation in OSPF

Initial routing tables in path vector routing

Stabilized tables for three autonomous systems

Internal and external BGP sessions

MULTICAST ROUTING PROTOCOLS
In this section, we discuss multicasting and multicast
routing protocols.
Unicast, Multicast, and Broadcast
Applications
Multicast Routing
Routing Protocols

Multicasting versus multiple unicasting

Shortest path tree in unicast routing

Taxonomy of common multicast protocols

Group-shared tree with rendezvous router

Sending a multicast packet to the rendezvous router

COMPUTER NETWORKS UNIT 3

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COMPUTER NETWORKS UNIT 3