Routing Fundamentals and Subnets

dingdongboomNetworking and Communications

Oct 27, 2013 (3 years and 9 months ago)

79 views



Routing Fundamentals and Subnets


Objectives:


Routed Protocols


IP Routing Protocols


The Mechanism of Subnetting




By


Adwoa Afful (Mrs)



IP Address



IP Address Grouping



Routed and Routing Protocols


Consider that a packet needs to be sent from node A to
node F. How would it decide which path to take?



Routing Protocol vs Routed Protocol


A
routed

protocol

1.
defines the end to end addressing and the packet
format of a packet that is forwarded between
nodes on different networks.


Internet Protocol (
IP
) is a
routed protocol



A
routing

protocol

1.
e
xchanges topology information with adjacent
routers to update and maintain their routing tables.


2.
selects the best path through a network


RIP

is a
routing protocol



Routed Protocol


A protocol is a set of rules



A routed protocol is a set of rules that determines how
computers at the source and destination communicate with each
other across networks



packet format



end to end addressing



In order for a protocol to be routable, it must provide the ability
to assign both a network number and a host number for each
individual device.




Internet Protocol IP


IP is a
connectionless, unreliable, best
-
effort delivery protocol



As information flows down the layers of the OSI model, the data is
processed at each layer.


IP accepts whatever data is passed down to it from the upper layers.



IP Packet Header



Network Layer Devices in Data Flow



Network Layer Devices in Data Flow


As a
frame is received at a
router

interface.


The MAC address is checked

to see if the frame is directly
addressed to the router
interface, or a broadcast.


The
frame header and trailer
are removed

and the
packet
is passed up to Layer 3
.


The
destination IP address is
compared to the routing table

to find a match.


The packet (
datagram)
is
placed in a
new frame with
the MAC address of the next
hop interface
.


The frame is then
transmitted.

If a match is found

or
there is a default
route,

the packet will be sent to the
interface specified in the matched routing
table statement otherwise
packet is
discarded



Packets Travel Across Links in a Frame


Packets NEVER travel through the network


they are
carried within frames


A new frame MUST be created to carry the packet over each individual link


Routers provide the IP address of the next hop interface (router or host)


The ARP table provides the MAC address of this IP address for the frame destination



Router Protocol Stripping



Connectionless Network Services



Telephone Calls: Connection
-
oriented



Connectionless vs. Connection
-
Oriented


In a
connection oriented system
is established
between the sender and the recipient before any
data is transferred.



example: Telephone



In a
connectionless system
, the destination is not
contacted before a packet is sent.



example: Postal system



TCP

is connection oriented


IP

is connectionless



Connectionless Network Services


The Internet is a huge network where packets are routed according to their
IP addresses.


IP is unreliable and best
-
effort as IP does not verify that the data reached its
destination and therefore does not resend missing packets.


Reliability and resending of packets is handled by the upper layer protocols.


IP may be used in conjunction with TCP to add a Layer 4, connection
-
oriented service that checks for missing segments and resends them to
provide reliability.



The IPv4 Packet Header

Time
-
to
-
live (TTL)


Count Decreases with every hop
This prevents packets from
looping endlessly.



Routing



The Network Layer



Routing


Routing is an OSI Layer 3 function.



Routers connect networks (or subnetworks)



Routing is the process of finding the most efficient
path from one device to another (router)



Routers must maintain routing tables and make sure
other routers know of changes in the network
topology. This function is performed using a routing
protocol to communicate network information with
other routers




Routing Through a Network


A router is a network layer device that uses one
or more routing metrics to determine the
optimal path through the network



Routing Metrics



Data Encapsulation



Layer 3 Routing and Layer 2 Switching



Routers Reduce the Size of Broadcast Domains


Routers
block LAN broadcasts
, so a broadcast storm
only affects the broadcast domain from which it
originated



Switched
networks
do not block broadcasts



Routing and Switching in a Network



Layer 2 Switching and Layer 3 Routing



The Routing Process



ARP Tables and Routing Tables



Router and Switch Features Comparison



The difference between a routed and routing
protocol


revisited



Routed Protocol



Routing Protocol



Routed Vs Routing protocols


A Routed Protocol:



A
network protocol

suite that provides enough information in its
network layer address

to allow a
router to forward it to the next device

and ultimately to its destination.



Defines the format and use of the fields within a packet.



The Internet Protocol (IP) and Novell's Internetwork Packet Exchange (IPX), DECnet,
AppleTalk, Banyan VINES, and Xerox Network Systems (XNS)



A
Routing Protocol:



Provides
processes

for
sharing route information
. Exchange topology info.

To
determining the
best
routing paths

and
transporting packets through an internetwork



Also allows routers to communicate with other routers to

update
and

maintain the
routing tables.



Routing Information Protocol (RIP), Interior Gateway Routing Protocol (IGRP), Open
Shortest Path First (OSPF), Border Gateway Protocol (BGP), and Enhanced IGRP
(EIGRP).



Back to Routing



Path Determination



Path Determination



Routing Tables


Routing tables contain the best routes to all known
networks.



These routes can be either



Static routes, which are entered manually by the system
administrator



Or dynamic routes, which are constructed from information
passed between adjacent routers.



A routing table entry contains
:



Each Destination



The next hop IP address to reach that destination



The metric for the route via that next hop



Outbound router interface for the next hop



Routing Tables



Routing Algorithms and Metrics



Routing Algorithms and Metrics


Routing protocols have one or more of the following design goals:



Optimization


Simplicity and low overhead


Robustness and stability


Flexibility


Rapid convergence




Routing Algorithms and Metrics



Interior and Exterior Gateway Protocols



Interior and Exterior Gateway Protocols


IGPs route data within an autonomous system.


RIP, RIPv2, IGRP, EIGRP, OSPF, IS
-
IS



EGPs route data between autonomous systems


Border Gateway Protocol (BGP)



Interior Gateway Routing Protocols


Link State and Distance Vector Routing Protocols



Examples of distance
-
vector protocols:


Routing Information Protocol (RIP)


Interior Gateway Routing Protocol (IGRP)


Enhanced IGRP (EIGRP)



Examples of link
-
state protocols:


Open Shortest Path First (OSPF)


Intermediate System
-
to
-
Intermediate System (IS
-
IS)



Mechanics of Subnetting



Subnetting


Reasons for subnetting



Provides addressing flexibility for the network administrator.


Each LAN must have its own network or subnetwork address.



Provides broadcast containment and low
-
level security on the LAN.



Provides some security since access to other subnets is only
available through the services of a router.




IP Address Bit Patterns



Introduction to Subnetting


Host bits must are
reassigned (or
“borrowed”) as network
bits.



The starting point is
always the leftmost host
bit.


3 bits borrowed allows 2
3
-
2 or 6 subnets

5 bits borrowed allows 2
5
-
2 or 30 subnets

12 bits borrowed allows 2
12
-
2 or 4094 subnets



Subnetting Chart (Bit Position and Value)



Subnetting Chart (Subnet Mask Identifier)



Subnetting



Subnetting Chart



Subnetting Example


This is an example of subnetting the 192.168.10.0 class C
network into 8 subnets with 32 host addresses per subnet


Note that the first and last subnets are not used (the first can be)


Also the first and last host address in each subnet are not used



Example Host IP Address from Subnet 2

Packet Address

192.168.10.65

11000000.10101000.00001010.010

00001

Subnet Mask

255.255.255.224

11111111.11111111.11111111.111

00000

Subnet Address

192.168.10.64

11000000.10101000.00001010.010

00000


The subnet mask is ANDed with the packet address to
determine the subnet address
-

as shown in the next slides



The Logical ANDing Process



The Logical ANDing Process



Class A and B Hosts



Calculating the Subnet ID



Subnet Mask Defines the Number of Subnets



Find the Subnet Mask



Summary