Title: Chapter 13 Internetworking Technologies
1Chapter 13Internetworking Technologies
- Part III Wide Area Networks and Internetworking
Technologies
2Topics Addressed in Chapter 13
- Internetworking technologies and the OSI model
- Business rationale for internetworking
technologies - Using repeaters to connect LAN segments
- Using bridges to connect two LANs
- Routers and network layer connections
- Using gateways to connect networks above the
network layer - Internetworking via switches
- Remote access technologies
- Wireless access to corporate networks
- Intranets and extranets Web-based internetworking
3Internetworking and the OSI Model
- Internetworking technologies are used to
interconnect networks - The OSI reference model provides an appropriate
context for understanding internetworking
technologies (see Figure 13-3) - Although some internetworking technologies span
two or more layers of the OSI model, most can be
classified as physical layer, data link layer,
network layer, or higher layer technologies
4Figure 13-3
5Physical Layer Technologies
- One of the main responsibilities of physical
layer interconnection technologies is to overcome
signal attenuation (see Figure 13-1) - Repeaters are used in digital communication
systems - Amplifiers do this in analog systems
- Repeaters are also used to overcome distance
limitations in this role they function as signal
relay stations (see Figure 13-2) - Repeaters can be standalone devices and be used
for media conversion. - Repeating capabilities are typically included in
LAN shared media hubs, patch panels, and
punchdown blocks - Optical repeaters are available for fiber optic
networks
6Figure 13-1
7Data Link Layer Connections
- Three key functions of data link layer protocols
are data delineation, error detection, and
address formatting - Bridges are used to interconnect two LANs at the
data link layer (see Figure 13-4) - Bridges have more intelligence than physical
layer technologies they have to examine (filter)
data link layer frames transmitted in one network
to determine if they should be forwarded to the
other network (see Figure 13-5) - Layer 2 switches are also used to connect two
networks at the data link layer
8Figure 13-5
9Network Layer Connections
- The network layer of the OSI reference model is
responsible for packet routing in networks with
multiple alternative paths from sender to
receiver (see Figure 13-6) - Routers are widely used network layer
internetworking technologies - After determining the destination address of the
recipient, a router chooses the best route for a
packet based on routing tables and routing
algorithms - Layer 3 switches have routing capabilities
10Figure 13-6
11Higher Layer Connections
- Network connections that operate above the
network layer are generically called gateways - Gateways often support protocol conversion
because the networks they interconnect use
different network layer protocols (see Figure
13-7)
12Figure 13-7
13Business Rationale for Internetworking
Technologies
- Internetworking technologies enable LANs to be
interconnected. LANs can also be connected to
LANs. In addition, WANs can be interconnected.
Hence, internetworking technologies are used by
businesses to create enterprise-wide networks - Internetworking technologies can also be used to
form interorganizational systems that connect an
organization and one or more business partners - The ability to forge larger networks from smaller
ones facilitates resource sharing and
communication enterprise-wide
14Repeaters Connecting LAN Segments
- Repeaters are used in LANs to overcome signal
attenuation and distance limitations - They are also used to connect LAN segments (see
Figures 13-8 and 13-9) - Some LAN standards specify the maximum number of
LAN segments that can be created - Repeater capabilities are specified in Table
13-1. - Repeater limitations include insensitivity to
data errors and the recreation of collisions that
originate in one segment to all other segments
15Figure 13-8
16Figure 13-9
Table 13-1
17Bridges Connecting Two LANs
- Bridges are used to connect two LANs at the data
link layer of the OSI model (see Figure 13-11) - Bridges possess more intelligence than repeaters
and are typically more costly - Unlike repeaters, bridges handle complete frames
- This means that they can isolate problems to a
LAN and reduce the likelihood of transferring
noise or collisions from one network to the other - Bridges listen to traffic on each network they
are often called promiscuous listening
technologies - Bridges are typically implemented as standalone
devices
18Figure 13-11
19Bridge Functionality
- When a bridge receives a data link layer frame
from one network (or segment), it verifies that
it is correctly formatted and if necessary,
forwards it to the other network.Two LANs
connected by a bridge behave like a single LAN - Frame filtering is one of the most important
functions performed by a bridge this is the
process of reading the destination address in the
frames header and determining if it should be
forwarded to the other networkFiltering rates
are measured in frames or packets per second - Forwarding is the process used by a bridge to
send a frame from one network to the other - Format conversion is necessary if the bridge
connects LANs with dissimilar data link protocols - Bridges that connect dissimilar LANs are called
translating bridges (see Figure 13-12) - Forwarding rates are measured in frames per
second - Additional bridge functions are summarized in
Table 13-2
20Figure 13-12
21Table 13-2
22Types of Bridges
- Various kinds of bridges exist including
- Transparent connect two similar LANs
- Translating connect two different LANs
- Learning (adaptive) builds routing tables from
network traffic - The spanning tree algorithm enables bridges to
exchange routing information with each other - Source routing bridges used in token ring
networks - Remote bridges used to interconnect LANs via WAN
services (see Figure 13-14 and Table 13-4) - Wireless can be used to bridge remote LANs
located within a few miles of each other
23Figure 13-14
24Routers Network Layer Connections
- Key network layer functions include
- Routing forwarding data to its destination along
its best route - Network control exchanging node status
information among routing nodes to facilitate the
best routing for messages - Congestion control attempting to reduce
transmission delays by sharing information about
network traffic and message queue length among
routers or network switches
25Message Routing Processes
- Message routing processes can be centralized or
distributed - In networks that centrally determine packet
routing, one router is designated as the network
routing manager to which all other routers
periodically forward network status information - Distributed routing determination requires each
router to periodically send network status
updates to the other routers in the network - Routing can be categorized as static, weighted or
dynamic - In static routing, the same path between two
nodes is always used - In weighted routing, each alternative path is
given a weight based on perceived use random
numbers are generated for incoming packets to the
same destination to determine which path to use
(see Figure 13-16) - Dynamic (adaptive) routing attempts to select the
best current route based on network conditions
it considers path failures and congestion (see
Figure 13-17)
26Figure 13-16
Figure 13-17
27IP Routing
- When an Internet node sends a message to another
Internet node, it must know the destination
nodes IP address - This may be resolved from a URL using the
Internets domain name system - The IP routing process is summarized in Figure
13-20 - IP routing may also be used in networks that are
not attached to the Internet (see Figure 13-21)
28Figure 13-20
29Types of Routers
- Three types of routers can be identified for
organizations whose networks are attached to the
Internet - Internal used to route packets between the
subnets or the networks included in a particular
subnet - Border used to route messages between an
organizations network and the Internet - External route messages between border routers
across the Internet backbone (these are also
called Internet backbone routers) - These are illustrated in Figure 13-19
- Dial-up routers enable geographically dispersed
LANs to be connected over dial-up digital WAN
services such as ISDN (see Figure 13-22) - High-speed routers, such as edge routers, enable
network traffic to be routed over high-speed ATM
networks or SONET services - Terabit routers are capable of forwarding
hundreds of millions of packets per second and
have throughput rates of more than one trillion
bits per second
30Figure 13-19
31Figure 13-22
32Router Functionality
- Like bridges, filtering and forwarding rates are
often used as router performance measures - Unlike bridges, routers only process packets that
are addressed to them - Also unlike bridges, forwarding decisions are
based on destination addresses in network layer
packet headers - Routers can also be used to limit access to a
network many have firewall capabilities - Multiprotocol routers are capable of forwarding
messages using more than one network layer
protocols - Encapsulation may be used to enable non-routable
data link protocols, such as SDLC, to be routed
over TCP/IP networks
33Routing Protocols
- Routing protocols enable routers to adapt to
changes in network conditions and topologies
they enable routers to exchange network status
updates in order to keep the information in
routing tables current - There are three major categories of routing
protocols - Distance vector protocols base routing decisions
on the distance (number of hops) to every other
router in the network - Examples include RIP (Routing Information
Protocol) and EIGRP (Enhanced Interior Gateway
Routing Protocol) - Link state protocols compute best routes by
consulting a complete copy of the network
topology and traffic conditions - Examples include OSPF (Open Shortest Path First),
NLSP (NetWare Link Services Protocol) , and IS-IS
(Intermediate System-to-Intermediate System) - Path vector protocols maintain comprehensive
lists of known routes and networks between
senders and receivers. - BGP (Border Gateway Protocol) is an example
34Gateways Connecting Networks Above the Network
Layer
- Gateways connect dissimilar networks networks
that do not share a common physical, data link,
or network layer protocol - A gateway can connect two or more networks above
the network layer of the OSI model - A gateway reconciles differences between the
networks it connects and serves as a protocol
converter - In some instances, a complete network or WAN
service may serve as a gateway between two
networks (see Figure 13-23) this is possible if
gateways exist to connect each of the two
networks to the WAN service
35Figure 13-23
36Switches
- Switches are widely used to interconnect
networks. Like other internetworking
technologies, these correspond to OSI model
layers (see Figure 13-24) - These include
- Layer 2 switches function like bridges by
sending frames to destinations based on MAC
addresses (see Figure 13-25) - Layer 3 switches are capable of layer 2
switching and layer three routing both layer 2
and layer 3 switches may be used to create
virtual LANs (VLANs) - Layer 4 switches can route TCP/IP messages based
on well known port addresses in TCP headers in
addition to layer 2 or layer 3 addresses - Backbone attached LAN switches enable switched
connections between devices attached to the same
LAN as well as switched access to a high-speed
backbone network or router (see Figure 13-26) - Backbone switches enable switched
interconnections among various types of LANs as
well as switched access between LANs and a
backbone network or WAN services (see Figure
13-27)
37Figure 13-24
38Figure 13-25
39Figure 13-26
40Figure 13-27
41Remote Access Technologies
- Remote access technologies provide network access
to teleworkers - Two major types of remote access exist
- Remote client (node) computing occurs when client
applications on remote nodes communicate with
server applications via dial-up or other WAN
links (see Figure 13-28a) - Remote control applications are run on the server
rather than the client remote nodes function as
terminals or thin clients (see Figure 13-28b) - Three major approaches exist for remote users to
access LAN resources (see Figure 13-29) - Dial-in connection to a LAN-attached
microcomputer - Dial-in connection to a LAN modem
- A LAN modem is essentially a modem with a NIC
- Dial-in connection to a communication server (see
Figure 13-30) - A communication server provides dial-in and
dial-out services for LAN users these are also
called remote access servers, remote node
servers, and telecommuting servers
42Figure 13-29
43Figure 13-30
44Wireless Access to Corporate Networks
- Explosive growth in wireless communication
technologies is fueling interest in wireless
internetworking technologies - Two important wireless internetworking
technologies are wireless bridges and mobile IP - Wireless bridges enable organizations to link
LANs that are located within a few miles of each
other - These enable organizations to avoid carrier
service charges - Mobile IP enables users to roam among wireless
LANs - Mobile IP clients must be installed on each
mobile wireless device to enable it to
communicate with mobile IP servers or routers in
corporate network offices
45Interconnections via Web Technologies
- Organizations are increasingly leveraging TCP/IP
applications to create intranets and extranets - Firewalls enable remote users to access corporate
intranets from virtually anywhere via Web
browsers - Clientless network operating systems, such as
NetWare 6, also enable remote users to access
corporate network resources via Web browsers
46Chapter 13Internetworking Technologies
- Part III Wide Area Networks and Internetworking
Technologies