Sub Netting and Routing
-
Upload
ewane-bernard -
Category
Documents
-
view
222 -
download
0
Transcript of Sub Netting and Routing
-
8/3/2019 Sub Netting and Routing
1/89
SUBNET & ROUTINGSUBNET & ROUTINGSUBNET & ROUTINGSUBNET & ROUTING
Sritrusta SukaridhotoSritrusta Sukaridhoto
LecturerLecturerPens EEPISPens EEPIS--ITSITS
-
8/3/2019 Sub Netting and Routing
2/89
Netmask / Subnet maskNetmask / Subnet masktutorialtutorial
Netmask / Subnet maskNetmask / Subnet masktutorialtutorial
-
8/3/2019 Sub Netting and Routing
3/89
IP AddressingIP AddressingIP AddressingIP Addressing
-
8/3/2019 Sub Netting and Routing
4/89
Subnet & Routing 4
IP addressing Introduction to IP addressing
Classes of IP addressing
Why Subnet Masks are necessary?
How to create subnet masks
-
8/3/2019 Sub Netting and Routing
5/89
Subnet & Routing 5
Why are IP addresses
written as bits? In order for data to pass along the media, it must
first be changed to electrical impulses.
When a computer receives these electricalimpulses, it recognizes two things: the presenceof voltage on the wire or the absence of voltageon the wire.
-
8/3/2019 Sub Netting and Routing
6/89
Subnet & Routing 6
-
8/3/2019 Sub Netting and Routing
7/89
Subnet & Routing 7
What format do IP
addresses use?
-
8/3/2019 Sub Netting and Routing
8/89
Subnet & Routing 8
How are IP addresses
expressed in dottednotation?
-
8/3/2019 Sub Netting and Routing
9/89
Subnet & Routing 9
Why are IP addresses
necessary? IP addressing makes it possible for data
passing over the network media of the
Internet to find its destination. Because each IP address is a 32-bit value,that means that there are four billiondifferent IP address possibilities.
IP addresses are hierarchical addresseslike phone numbers and zip codes.
-
8/3/2019 Sub Netting and Routing
10/89
Subnet & Routing 10
How do IP addresses make itpossible for data sent via the
Internet to find its destination?
It is because each network connected to theInternet has a unique network number.
To ensure that each network number on theInternet will always be unique and unlike thatof any other number, an organization called
the International Network InformationCenter, or InterNIC
-
8/3/2019 Sub Netting and Routing
11/89
Subnet & Routing 11
How do IP addresses
incorporate network addresses? Every IP address has two parts. These are
known as the network number and the host
number.
-
8/3/2019 Sub Netting and Routing
12/89
Subnet & Routing 12
What are the different
classes of networks? There are three classes of IP
addresses that a company can receive
from the InterNIC. The InterNICreserves class "A" IP addresses forgovernments throughout the world,
class "B" IP addresses for mediumsize companies, and class "C"
-
8/3/2019 Sub Netting and Routing
13/89
Subnet & Routing 13
IP addressing Classes of Networks
N H H HClass A:
N N N HClass C:
N N H HClass B:
Network number assigned by NIC
Host number assigned by Systems Administrator
1 Byte 1 Byte 1 Byte 1 Byte
-
8/3/2019 Sub Netting and Routing
14/89
Subnet & Routing 14
IP addressing IP Address Bit Patterns
0 Network# Host #Class A:
Bit #1 2 - 8 9 32 (24 bits)
Class A address range
1.0.0.0 126.0.0.0 (127.0.0.0 is for loopback)
Private Class A address: 10.0.0.0
Number of hosts: 224 -2 = 16,777,214
8 16 24 32
-
8/3/2019 Sub Netting and Routing
15/89
Subnet & Routing 15
IP addressing IP Address Bit Patterns
Class B:
Bit #1 3 - 16 17 32 (16 bits)
Class B address range
128.0.0.0 191.255.0.0
Private Class B : 172.16.0.0 172.31.0.0
Number of hosts: 216 - 2 = 65,534
1 0 Network # Host #
2
8 16 24 32
-
8/3/2019 Sub Netting and Routing
16/89
Subnet & Routing 16
IP addressing IP Address Bit Patterns
Class C:
Bit #1 4 - 24 25 32 (8 bits)
Class C address range
192.0.0.0 233.255.255.0
Private Class C : 192.168.0.0
Number of hosts: 28 - 2 = 254
2
8 16 24 32
1 1 0 Network # Host #
3
-
8/3/2019 Sub Netting and Routing
17/89
Subnet & Routing 17
-
8/3/2019 Sub Netting and Routing
18/89
Subnet & Routing 18
How many classes of
Networks are there? you have learned about three classes
of networks that can be assigned by
the InterNIC. In fact, there are five classes of
networks. However, only three of
these are used commercially.
-
8/3/2019 Sub Netting and Routing
19/89
Subnet & Routing 19
reserved for multicast
purposes and experimental
purposes? The highest number listed was 223.
You may have wondered why the
highest value was only 223 and not255, since there are 255 possiblevalues for an octet.
in IP addresses the values 224through 255 are not used in the firstoctet for networking purposes.
-
8/3/2019 Sub Netting and Routing
20/89
Subnet & Routing 20
What IP addresses are
reserved for the Networks? By convention, in IP addressing schemes,
any IP address that ends in all binary
zeroes is reserved for the networkaddress.
Thus, in a class "A" network, 113.0.0.0would be the IP address of that network.
Routers use a network's IP address whenforwarding data on the Internet.
-
8/3/2019 Sub Netting and Routing
21/89
Subnet & Routing 21
-
8/3/2019 Sub Netting and Routing
22/89
Subnet & Routing 22
What IP addresses are
reserved for broadcasts? for the network that is 176.10.0.0, the broadcast
address that would be sent out to all devices onthat network would be 176.10.255.255.
-
8/3/2019 Sub Netting and Routing
23/89
Subnet & Routing 23
Who assigns subnet
addresses? As with the host number portion of
class "A," class "B," and class "C
addresses, subnet addresses areassigned locally.
Usually this is done by the network
administrator.
-
8/3/2019 Sub Netting and Routing
24/89
Subnet & Routing 24
-
8/3/2019 Sub Netting and Routing
25/89
Subnet & Routing 25
IP addressing Subnet
mask Subnet Masking - Why?
131 181 115 252IP address
255 255 0 0Netmask
131 181 0 0
10000011 10110101 01110011 11111100
11111111 1111111100000000
00000000
0000000 0000000=
Network
Address
&
-
8/3/2019 Sub Netting and Routing
26/89
Subnet & Routing 26
IP addressing -
Subnetting Subnetting
Is the act of borrowing bits from the host
portion to create smaller networks (calledsubnetworks)
Minimum bits that can be borrowed is 2 -why?
Subnetting is used to reduce the number ofbroadcast domains
Communication between these subnetworks isachieved through a router
-
8/3/2019 Sub Netting and Routing
27/89
Subnet & Routing 27
-
8/3/2019 Sub Netting and Routing
28/89
Subnet & Routing 28
How are subnet addressesconcealed from outside
networks? Subnets are hidden from outside
networks by using a mask.
These are referred to as subnetmasks.
The function of a subnet mask is to
tell devices which part of an addressis the network number including thesubnet, and which part is the host.
-
8/3/2019 Sub Netting and Routing
29/89
Subnet & Routing 29
What format do subnet
masks use? Subnet masks use the same format
as IP addressing.
In other words, they are thirty twobits long and divided into four octets.
Subnet masks have all 1s in the
network and subnetwork portion, andall 0s in the host portion.
-
8/3/2019 Sub Netting and Routing
30/89
Subnet & Routing 30
-
8/3/2019 Sub Netting and Routing
31/89
Subnet & Routing 31
-
8/3/2019 Sub Netting and Routing
32/89
Subnet & Routing 32
How many bits can be borrowed fromthe host number in class "B" and class
"C" networks to create subnets?
Because there are only two octets in thehost field of a class "B network, up to
fourteen bits can be borrowed to createsubnetworks.
A class "C" network has only one octet inthe host field. Therefore, only up to six
bits can be borrowed in class "C networksto create subnetworks.
-
8/3/2019 Sub Netting and Routing
33/89
Subnet & Routing 33
What happens to the subnet maskaddress if only some of the bits in an
octet are borrowed? Imagine that you have a class "B network. This
time however, instead of borrowing all eight bitsof the third octet, only seven bits are borrowed
to create subnetworks. Using binary representation, in this example, the
subnet mask would be11111111.11111111.11111110.00000000.
Therefore, 255.255.255.0 can no longer be usedas the subnet mask.
-
8/3/2019 Sub Netting and Routing
34/89
Subnet & Routing 34
If only seven bits are borrowed in a class"B" network, what would the subnet mask
be in dotted decimal notation? HINT: To convert any eight bit binary number
into a decimal number, total the powers of 2 that
occur in the number.
-
8/3/2019 Sub Netting and Routing
35/89
Subnet & Routing 35
What determines how many subnetworkscan be created by borrowing bits from
the host field?
Can you figure out all of the possiblecombinations of 0s and 1s if four bits are
borrowed from the host field to createsubnetworks?
16 from 0000 to 1111. However, you knowthat 1111 is reserved for broadcast and
0000 means this network.
-
8/3/2019 Sub Netting and Routing
36/89
Subnet & Routing 36
How many subnetworks can becreated by borrowing five bits
from the host field? Answer: Thirty-two
subnetworks or 25 =32
subnetworks can be created byborrowing five bits from thehost field.
-
8/3/2019 Sub Netting and Routing
37/89
Subnet & Routing 37
Which numbers in a subnetwork
are reserved for broadcasts? In previous section, we used an example of
a class "C" network in which three bits are
borrowed from the host field. You learnedthat when three bits are borrowed fromthe host octet, up to eight subnetworkscan be created each having up to thirty-
two hosts. You also learned that IP addresses endingin all binary 1s are reserved forbroadcasts. The same is true for
subnetworks.
-
8/3/2019 Sub Netting and Routing
38/89
Subnet & Routing 38
For IP address 197.15.22.160 on the sameclass "C network. How would this be
expressed in a binary numbering scheme? Answer: If 197.15.22.160 is converted to
binary format, it becomes
110001010.00001111.00010110. 10100000. The first three bits in the last octet, 101,indicate that this is the sixth subnetwork.As before the remaining bits are all binary
0s. This means that the IPaddress197.15.22.160 must be one that isreserved for a subnetwork address.
-
8/3/2019 Sub Netting and Routing
39/89
Subnet & Routing 39
Subnet mask How do we determine how many bits to
borrow for a subnet?
Determine the number of sub networksrequired
Work from the MOST significant (LHS)bits of the first octet after the network
number and calculate the number of bitsneeded to create the required number ofsubnetworks
-
8/3/2019 Sub Netting and Routing
40/89
Subnet & Routing 40
Subnet mask Example: You are given a class B address and you are
required to create 1000 subnetworks.
By working from the LHS of the (first octetafter the network number) 3rd octet,calculate the number of bits to equal or slightlyexceed 1000. (ie 2x = > 1000)
This would equate to 210 or 1024-2 networks
Hence you will need to borrow 10 bits from thehost portion to create 1000 subnetworks
-
8/3/2019 Sub Netting and Routing
41/89
Subnet & Routing 41
Subnet mask Example:
The subnetmask in this instance would
be255.255.255.192
How many host per network can youobtain from this addressing scheme?
11111111 11111111 11111111 11 000000
10 Bits Borrowed
(subnetmask)Natural Class B netmask6 bits left
for hosts
-
8/3/2019 Sub Netting and Routing
42/89
Subnet & Routing 42
Subnet mask How do we determine how many bits to
borrow for a subnet given the number ofhosts required?
Determine the number of hosts required Work from the LEAST significant (RHS)
bits of the last octet and calculate thenumber of bits needed to create the
required number of subnetworks
-
8/3/2019 Sub Netting and Routing
43/89
Subnet & Routing 43
Subnet mask Example: You are given a class B address and you require
1000 nodes per subnet
By working from the RHS (last octet) of the4th octet, calculate the number of bits toequal or slightly exceed 1000. (ie 2x = > 1000)
This would equate to 210 or 1024-2 networks Hence you will need to borrow 6 bits from the
host portion to create subnetworks with 1000hosts each
-
8/3/2019 Sub Netting and Routing
44/89
Subnet & Routing 44
Subnet mask Example:
The subnetmask in this instance wouldbe255.255.252.0
How many subnetworks per network canyou obtain from this addressingscheme?
Note: Do you recognise this address asthe student supernet address?
11111111 11111111 111111 00 00000000
6 Bits Borrowed
(subnetmask)Natural Class B netmask10 bits required
for hosts
-
8/3/2019 Sub Netting and Routing
45/89
Subnet & Routing 45
What about a Supernet? A supernet borrows bits from the networkportion to create contiguous nodes to form asuper network
For example Company A has about 1000 nodes to address. A class Baddress would be too big (or may not be available).Solution Supernetting using 4 contiguous class Caddresses
203.10.112.0203.10.113.0203.10.114.0203.10.115.0
(All netmasked to 255.255.255.0)
-
8/3/2019 Sub Netting and Routing
46/89
Subnet & Routing 46
What about a Supernet? By allowing the first 2 bits of the third octet
to be borrowed, a virtual class B address canbe created.
A supernet address of 203.10.112.0
203.10.115.255 is formed with a subnet maskof 255.255.252.0. The Host portion will be expanded from 8 10
bits
Route summarisation can occur to203.10.112.0/22
-
8/3/2019 Sub Netting and Routing
47/89
Subnet & Routing 47
What about a Supernet?
1100101
1
00001010011100
00
0000000
011001011
0000101001110001
00000000
11001011
0000101001110010
00000000
11001011
0000101001110011
11111111
11111111
1111111111111100
00000000
Host portionNetwork Portion
203.10.112.0
203.10.115.255
203.10.113.0
203.10.114.0
255.255.252.0
We have expanded the host portion by 2 bits to 10 bits
-
8/3/2019 Sub Netting and Routing
48/89
Subnet & Routing 48
What is a Broadcast
Address A broadcast address is used to by a
node to communicate with ALL nodes
in a broadcast domain Like the netmask, the broadcastaddress is AND with the networkaddress.
However, the host portion of thenetwork is identified in a broadcastaddress
-
8/3/2019 Sub Netting and Routing
49/89
Subnet & Routing 49
What is a Broadcast
Address A broadcast address does this by inserting all1s in the host portion.
Eg A natural class B broadcast address would look
something like this N.N.255.255 If it is not a classful subnetmask, you can
determine the broadcast address within eachsubnet by locating the host portion and setting
them to all 1s.
-
8/3/2019 Sub Netting and Routing
50/89
Subnet & Routing 50
What is a Broadcast
Address An example of a Broadcast address
131 181HostID
HostID
131 181 255 255
131 181HostID
HostID
&
=
-
8/3/2019 Sub Netting and Routing
51/89
Subnet & Routing 51
What is a Broadcast Address
An example of a cross boundary subnetbroadcast address with a mask of255.255.252.0
131 181 11[2,3,4,5] x
131 181 115 255
131 181 SN + HHostID
&
=
10000011
1011010101110000
00000000
10000011
10110101011100xx
xxxxxxxx
1000001 011100 1111111
Host portionNetwork Portion SNNetworkAddress
Broadcast
Address
Host
-
8/3/2019 Sub Netting and Routing
52/89
Subnet & Routing 52
What is a Broadcast Address
An example of a cross boundary subnetbroadcast address with a mask of255.255.252.0
In this example, IP addresses 131.181.112.0 131.181.115.255 belongto the same subnetwork
10000011
1011010101110000
00000000
10000011 10110101
01110001
00000000
10000011
1011010101110010
00000000
1000001
110110101
011100
11
1111111
1
Host portionNetwork Portion SN131.181.112.0
(Network)
131.181.115.255
(Broadacast)
131.181.113.0
131.181.114.0
k dd
-
8/3/2019 Sub Netting and Routing
53/89
Subnet & Routing 53
Network AddressVS
Broadcast address Remember
A Network address has all the hostbits set to 0
A Broadcast address has all the hostbits set to 1
Therefore 131.181.112.0 is the network address
131.181.115.255 is the broadcast address
-
8/3/2019 Sub Netting and Routing
54/89
Subnet & Routing 54
Network AddressVS
Broadcast address This is important when you are doing
ifconfig and routing commands
For example, if a host has an address131.181.114.10/22
The ifconfig & route commands would be ifconfig eth inet 131.181.114.10 netmask
255.255.252.0 broadcast 131.181.115.255
route add net 131.181.112.0 netmask255.255.252.0 dev eth
H d d t i
-
8/3/2019 Sub Netting and Routing
55/89
Subnet & Routing 55
How do you determineNetwork and Broadcast
address quickly? There are different subnetting exercises
Given an IP address & mask,
What is the network/subnetwork address
What is the network/subnetwork broadcastaddress
What are the assignable address in thatnetwork/subnetwork
What are all the valid subnet addresses How many nodes per subnet
-
8/3/2019 Sub Netting and Routing
56/89
Subnet & Routing 56
Algorithm for deriving
Subnet information Given an IP address, you will usually begiven a net/subnetmask
If you are given the mask Subtract the mask from 256 This is known as the multiplier The first number in each multiplier value
is the network number The broadcast address is the nextmultiplier value subtract 1
-
8/3/2019 Sub Netting and Routing
57/89
Subnet & Routing 57
Algorithm for deriving
Subnet information Eg given the IP address 192.168.0.100
with the subnet mask of255.255.255.240Or 192.168.0.100/28 What is the network number
What is the broadcast address What are the valid IP hosts for the
subnet
-
8/3/2019 Sub Netting and Routing
58/89
Subnet & Routing 58
Subtract 256 from the netmask 256 - 240 = 16 This is the multiplier ie the networks are in steps of 16
(16,32,48,64,96,112 etc)
The IP address 192.168.0.100 is in the range of |100 / 16|which is the 6 th subnetwork
The network address is16* 6 = 96 (01100000b)
The Broadcast address is 96 + 16 - 1
=> 192.168.0.111 (01101111b) ie (next multiplier 1)
Algorithm for deriving
Subnet information
Host portion
Subnetwork portion
-
8/3/2019 Sub Netting and Routing
59/89
Subnet & Routing 59
Algorithm for deriving
Subnet information11000000
1010100000000000
01100100
11111111
11111111 11111111
11110000
11000000
1010100000000000
01100000
11000000 10101000
00000000
01101111
Host portionNetwork Portion SN
IP address
192.168.0.100
Netmask255.255.255.240
Network Address
192.168.0.96
Broadcast Address
192.168.0.111
-
8/3/2019 Sub Netting and Routing
60/89
Subnet & Routing 60
Algorithm for deriving
Subnet information Valid ranges are
192.168.0.97 to 192.168.0.110
Number of allowable hosts 97 to 110 (incl) = 14 or [24]16 - 2 = 14 Remember you cannot use the first address (network address) and the
last address (broadcast address) in the range The number of allowable networks
[24]16 - 2 = 14 ( ie 4 bits used. If a class B address with the last bit subnet,then add another 8 bits to give you 212 2 allowable subnet)
-
8/3/2019 Sub Netting and Routing
61/89
Subnet & Routing 61
Algorithm for deriving
Subnet information What if the IP range goes over 2 octets
Use the same principal
Remember octets with all 0s are consideredboring and will be assigned the mask of 0
You will then have to locate the position in theaddress with both 1s and 0s (interesting byte)and use the same algorithm
Similarly all 1s are also considered boring and willbe given the mask of 255 (eg subnetting the lastbyte of a class B address)
-
8/3/2019 Sub Netting and Routing
62/89
Subnet & Routing 62
Algorithm for deriving
Subnet information Example
QUT students supernet address 131.181.112.0/22
Netmask expanded : 255.255.252.0 Last byte is not interesting hence we set it to 0 for networkand 1 for broadcast
The third byte is interesting256 252 = 4 (multiplier)
Networks are in increments of 4 steps
112/4 = 28 (the 28th subnetwork). Since there is no remainder,it is the beginning of the network address
-
8/3/2019 Sub Netting and Routing
63/89
Subnet & Routing 63
Algorithm for deriving
Subnet information
Network address :
131.181.112.0 Netmask :
255.255.252.0 Broadcast :
112 + 4 1 = 115=>131.181.115.255
Number of valid hosts :210 2 = 1024 2 = 1022 hosts
Number of subnetworks available for this network26 2 = 64 2 =62 subnetworks
Assignable addresses in this subnetwork131.181.112.1 131.181.115.254
Remember, the 1st and last addressescannot be used (Network and
broadcast)
-
8/3/2019 Sub Netting and Routing
64/89
Subnet & Routing 64
handle IP addresses and
subnet masks? Let's assume that a device on another networkwith an IP address of 197.15.22.44 wants to senddata to another device attached to Cisco's
network with an IP address of 131.108.2.2. The data is sent out over the Internet until it
reaches the router that is attached to Cisco'snetwork.
The router's job is to determine which one ofCisco's subnetworks the data should be routed to.
-
8/3/2019 Sub Netting and Routing
65/89
Subnet & Routing 65
h n th t p f ms this
-
8/3/2019 Sub Netting and Routing
66/89
Subnet & Routing 66
when the router performs thisANDing" operation, the host
portion falls through.
The router looks at what is left which
-
8/3/2019 Sub Netting and Routing
67/89
Subnet & Routing 67
The router looks at what is left whichis the network number including the
subnetwork.
h h l k bl
-
8/3/2019 Sub Netting and Routing
68/89
Subnet & Routing 68
The router then looks in its routing tableand tries to match the network number
including the subnet with an interface.
-
8/3/2019 Sub Netting and Routing
69/89
Subnet & Routing 69
How does the "Anding operation
change with different subnet masks? Imagine that you have a class "B network with
the network number 172.16.0.0.
After assessing the needs of his network, the
network administrator has decided to borroweight bits in order to create subnetworks.
When eight bits are borrowed to create subnets,the subnet mask is 255.255.255.0.
Someone outside the network sends data to theIP address 172.16.2.120.
-
8/3/2019 Sub Netting and Routing
70/89
Subnet & Routing 70
-
8/3/2019 Sub Netting and Routing
71/89
Subnet & Routing 71
-
8/3/2019 Sub Netting and Routing
72/89
Subnet & Routing 72
Exercise
Exercise You are given an IP address for a host
172.168.35.10/20
What is/are the
1. Subnet address? 2. Broadcast address? 3. The number of useable hosts available
for this subnet?
4. The number of useable subnets availablefor this network? 5. The assignable address range for this
subnet?Answers
-
8/3/2019 Sub Netting and Routing
73/89
Subnet & Routing 73
Exercise
Exercise Your organisation has been assigned a class B
IP address of 130.10.0.0 You require about 2000 subnetworks
Work out the 1. Subnet mask required for this subnet 2. The network and broadcast addresses for
the first 5 useable subnets
3. The number of hosts for each subnet 4. The assignable address range of the first5 useable subnets
Answers
-
8/3/2019 Sub Netting and Routing
74/89
ROUTINGROUTINGROUTINGROUTING
-
8/3/2019 Sub Netting and Routing
75/89
Subnet & Routing 75
Routing Routing describes a process wherepackets are forwarded from one
network to another. Routing can be performed by devices
such as :
dedicated routers servers with more than one networkinterface: multihomed hosts
switches incorporating a route function.
-
8/3/2019 Sub Netting and Routing
76/89
Subnet & Routing 76
Routers Routing devices typically have morethan one network interface, each
called a port. Routers process datagrams
individually, making routing aprocessing-intensive operation.
Dedicated routers offer betterperformance characteristicscompared with multi-homed hosts.
-
8/3/2019 Sub Netting and Routing
77/89
Subnet & Routing 77
Routing Tables To determining the properdestination network for datagrams,
routers consult an internal table. The table consists of records, oneper line, each representing a knownnetwork.
Each record includes a set ofassociated characteristics such asnetmask
-
8/3/2019 Sub Netting and Routing
78/89
Subnet & Routing 78
Building Route Tables. Routing table entries can be built bytwo methods: Static: entries are entered manually by
a network administrator Dynamic: entries are entered
dynamically by routing protocols.Routers learn destination networkaddresses by the periodic exchange ofroute tables between routing devices.Routing protocols use IP to deliver thisinformation.
-
8/3/2019 Sub Netting and Routing
79/89
Subnet & Routing 79
Configuring Routers Before IP routers can perform the routefunction and use routing protocols toexchange route tables, each interface(port) must be correctly numbered with avalid host IP address and netmask.
The IP address must be selected from
within the range for the particularnetwork address. Typically local gatewaysare located the first address in the validhost range.
-
8/3/2019 Sub Netting and Routing
80/89
Subnet & Routing 80
Routing Protocols Routing protocols are used by routers to: learn the location of destination networks.
determine the best route to reach networks.
Examples of routing protocols include: RIP, Routing Information Protocol
OSPF, Open Shortest Path First
BGP, Border Gateway Protocol
-
8/3/2019 Sub Netting and Routing
81/89
Subnet & Routing 81
Routing Protocols - 2 Routing protocols differ in: the way in which they exchange route
tables determine the route to the destination
the information that is communicated
-
8/3/2019 Sub Netting and Routing
82/89
Subnet & Routing 82
Distance Vector Distance Vector routing protocolsbroadcast the entire route table on a
regular basis. RIP2 typically defaultsat once every 30 seconds.Thiscreates considerable network traffic.
They determine the best route pathon the basis of the least numbernumber of hops to reach adestination network.
-
8/3/2019 Sub Netting and Routing
83/89
Subnet & Routing 83
Link State Link state protocols only broadcastchanges to route information after
an initial entire table has been sent. When determining the best path,other factors such as policies (e.g.preferred path) and cost ( timetaken, available bandwidth) caninfluence the choice when multiplepaths are available.
-
8/3/2019 Sub Netting and Routing
84/89
Subnet & Routing 84
IP Routing Before a routing device can forwardan IP datagram it must: examine the Destination Address in the
datagram use the netmask to identify the network
portion of the packets destinationaddress
find a corresponding network address inthe route table and forward the packetto the gateway or interface specified
-
8/3/2019 Sub Netting and Routing
85/89
Subnet & Routing 85
Route Table Fields To forward IP datagrams, the routeruses the following fields of the the
route table: Destination Network Mask
Gateway
-
8/3/2019 Sub Netting and Routing
86/89
Subnet & Routing 86
Destination This field lists the networks which areknown to the router. Addresses may havebeen entered by an administrator, ordynamically learned from thetransmissions of other routers.
Address entries concerned with routing
between network addresses will be of theformat{, 0}
-
8/3/2019 Sub Netting and Routing
87/89
Subnet & Routing 87
Netmask The netmask field provides therouter with the ability to determine
the network address of packetsbeing examined.
A logical AND is performed using thenetmask and the destination address.This logically removes the hostportion allowing the router toidentify the destination
-
8/3/2019 Sub Netting and Routing
88/89
Subnet & Routing 88
Gateway The Gateway field lists the IP addressesof the interface where the datagramshould be sent (forwarded) to reach the
specified Destination. This field may contain :
An IP interface address corresponding to anadjacent router
0.0.0.0
The address of a interface
-
8/3/2019 Sub Netting and Routing
89/89
Destination Hop=0.0.0.0 A Destination of 0.0.0.0 indicates adirectly connected network. Hosts
located on this network can bereached using the local networkmethod. If the network is Ethernet,the ARP protocol is used to find the
physical address of the node.