Router and Routing Algorithm

Router

-A router acts as a junction between two or more
networks

-Routers use IP addresses to identify packet
recipients (commonly a layer 3 item)

-Routers communicate with other routers to
build/identify complex data paths

(=> routing)

Router

layers in Router

layers in Router

Routing

-A router acts as a junction between two or more networks
-Routers use IP addresses to identify packet
recipients (commonly a layer 3 item)
-Routers communicate with other routers to
build/identify complex data paths

routing Overview

Types of routing
- static routing
- dynamic routing

Dynamic mechanisms
- distance vector
- link-state algorithm

Routing basics

-Routing takes place on IP level

network layer (3)

-Routing is needed

- when the packages‘ destination is beyond the own network

- to manage traffic between different networks

-Routes are determined by routers

- Therefore routers uses so called routing-tables

Basic Routing algorithms using by Router

Static routing

— Predefined static route between two hosts in

different networks

— Static routes are defined in so called static

routing tables

— Advantages:

- Routes are transparent and comprehensible

- Routes are trusted .

(at least the direct neighbors & default gateway)

- Simple tracing of errors (who to blame)

— Disadvantages:

- High administration effort and very large routing tables

static routing tables

static routing tables

Static Routing in LAN

— In local area networks (LANs)

static routes_are used to

connectthe Internal hosts

to superior networks

 

— Therefore each hosts has an

entry_ In Its routing table, to

specn‘y the router, that has

to be used as default gateway

(at the border of the LAN)

Dynamic routing

— Router is able to select packages' routes dynamically

— This selection is determined by different routing
protocols / Implementations

— Advantages:
- Less care necessarily
- Short reaction time on failures or resources bottlenecks

— Disadvantages:
- Exchange of control information necessarily
- Error tracing is more difficult
- Installation required



— Used where static routing is nearly impossible
- the number of networks / subnets is to large
- high dynamic network structures / metrics

— Used to interconnect a huge number of larger networks

Dynamic Routing

(so called autonomous systems)
- distributed enterprise networks
- distributed educational networks

-> the ”parts”, which build the internet


— Autonomous System (AS)

is an IP network that is administrated
as one single entity

e.g. universities, lSPs, international
companies

— The connection between all public
ASs is called the internet

— AS's external routers use
Exterior Gateway Protocols (EGP)
to exchange the routing information

Autonomous Systems

— The worldwide standard EGP is the Border Gateway Protocol


— Autonomous Systems (AS)
are IP networks that are
administrated as one
single entity

— Within an AS the router uses
Interior Gateway Protocols

— IGPs route between the subnets
of an AS

— At the ed e of the AS the routers
speak EG and IGP

— Both, EGP and IGP are dynamic routing
protocols

The two kinds of dynamic protocols

Main principles of the two kind of dynamic protocols:

- Distance vector protocols:

tell your neighbours, how the world looks for you

e.g. RIP (routing information protocol)
- Link-state protocols:

tell the world, who your neighbours are

e.g. OSPF (open shortest path first)
based on Dijkstra‘s algorithm

- Overview: RIP

— Routing Information Protocol

— Defined in RFC 1058

— Uses UDP protocol to exchange routing information
- via port 520

— Distributed computing of the routes

— Maximum of 15 hops

— No authentication of routers (less secure)

— Distributed computing of the routes

After initialization each router possesses a matrix
that stores the distances to all possible destination
networks (called routing table)

The used metric here is the hop count and gets increased
for each router, the package has to passes hrough

Hop count 16 means destination network is unreachable
Update time is every 30 sec

— if router is not responding for 180 sec, it gets tagged as
unreachable

Overview: RIP

Overview: OSPF

— Open Shortest Path First

— Defined in the RFC 2328

— Uses IP protocol 89

— Decentralized computing of the shortest way

between two routers

(Dijkstra algorithm - shortest path first)

— no hop-count-Iimit

(—> suitable for large networks)

— Authentication via MD-5 checksum

7 After initia/izat/on each router possesses a map of

the whole network topology

* Used metric is mostly the accumulated bandwidth

7 Using “hello protocol” to ensure, that the neighbours

are still available (hello package every 10 - 30 sec)

7 Actualization of the network information via the flooding

protocol (broadcasting to whole network)

r If there is no respond for a certain number of hello

packages all routers get informed / updated by using

flooding packages

OSPF - Algorithms

Sequence in principles of OSPF - Algorithms

Sequence in principles of OSPF - Algorithms

IP Subnetting

Subnetting

With the rapid growth of the Internet & the ever-increasing

demand for new addresses, the standard address class structure

has been expanded by borrowing bits from the Host portion to

allow for more Networks.

Subnetting reduces the size of the routing tables stored

in routers.

Subnetting extends the existing IP address base &

restructures the IP address.

As a result, routers must have a way to extract from a IP

address both the Network address & the Host address.

Subnetting Networks ID

A 3-step example of how the default Class A subnet

mask is applied to a Class A address:

subnetting networks ID

Subnetting, Subnet & Subnet Mask

-Subnetting, a subnet & a subnet mask are all

different.

-In fact, the 1 st creates the 2 nd & is identified by the 3 rd .

-Subnetting is the process of dividing a network & its

IP addresses into segments, each of which is called a

subnetwork or subnet.

Subnetting

-A network has its own unique address, such as a

Class B network with the address 172.20.0.0 which

has all zeroes in the host portion of the address.

-From the basic definitions of a Class B network &

the default Class B subnet mask, you know that this

network can be created as a single network that

contains 65,534 individual hosts.

Benefits of Subnetting

-Fewer IP addresses are needed to provide

addressing to a network & subnetting.

-Subnetting usually results in smaller routing tables

in routers

Example of Subnetting

-when the network administrator divides the

172.20.0.0 network into 5 smaller networks: –

172.20.1.0, 172.20.2.0, 172.20.3.0, 172.20.4.0 &

172.20.5.0 –

-the outside world still knows the network as

172.20.0.0, but the internal routers now break the

network addressing into the 5 smaller subnetworks.

Subnetting Example 

Subnetmask Function

-The function of a subnet mask is to determine whether an IP address

exists on the local network or whether it must be routed outside the

local network.

-It is applied to a message’s destination address to extract the network

address.

-If the extracted network address matches the local network ID, the

destination is located on the local network.

-However, if they don’t match, the message must be routed outside the

local network.

Subnetting Concept

-The key concept in subnetting is borrowing bits from

the host portion of the network to create a subnetwork.

-Rules govern this borrowing, ensuring that some bits

are left for a Host ID.

-The rules require that two bits remain available to use

for the Host ID & that all of the subnet bits cannot be

all 1s or 0s at the same time ( -2 ).

Fixed Subnet (Classful)

Fixed Subnet (Classful)

CIDR: Classless InterDomain Routing

- Subnet portion of address of arbitrary length

- Address format: a.b.c.d/x, where x is # bits in subnet portion

of address subnet part host part:

Example:

11001000 00010111 00010000 00000000

200.23.16.0/23

Knowing How to Calculate Subnets

To determine the number of subnets & hosts per

subnet available for any of the available subnet

masks, 2 simple formulas to calculate these numbers:

Knowing How to Calculate Subnets

Class A Subnetting Options

Class A Subnetting Options

Class B Subnetting Options

Class B Subnetting Options

Class C Subnetting Options

SubnetMask                      SubnetMask                   # Hosts

255.255.255.0/24                                                    256 (254)

255.255.255.128 /25                                              128 (126)

255.255.255.192 /26                                                  64 (62)

255.255.255.224 /27                                                  32 (30)

255.255.255.240 /28                                                  16 (14)

255.255.255.248 /29                                                      8 (6)

255.255.255.252 /30                                                      4 (2)

Subnetting

Example:

In network 192.168.10.0

255.255.255.0

We have here ONE Class C network, with 253 usable IPs

for Client-PCs.

The usable IP range of this network is

192.168.10.1 - 192.168.10.254

The very last IP of each Subnet is called:

Broadcast-Address

In this example 192.168.10.255 and it is NOT! usable for host

PCs

If we want to divide this network in two parts,we must use

subnetting

With subnetmask 255.255.255.128 we divide the network in two

Parts :

    192.168.10.1 – 192.168.10.127

    192.168.10.128 – 192.168.10.255

So in this example BEFORE, we had one big network but

With the change of the subnetmask we divided it in two smaller

networks

First with Subnetmask 255.255.255.0 we had this network:

192.168.10.0

The range:

192.168.10.1, 192.168.10.2

...

192.168.10.253, 192.168.10.254, 192.168.10.255

Now with Subnetmask 255.255.255.128 we have these two networks:

1st Subnet:

{ 192.168.10.0 (!NOT usable for Host PCs)

192.168.10.1, 192.168.10.2,192.168.10.3,

...

192.168.10.125, 192.168.10.126, 192.168.10.127 }

2nd Subnet:

192.168.10.128

192.168.10.129, 192.168.10.130,192.168.10.131,

...

192.168.10.253, 192.168.10.254,192.168.10.255 (is NOT! usable for Host PCs)

Used Bits for Network

Examples:

/16 = 255.255.0.0 =

11111111.11111111.00000000.00000000

/20 = 255.255.240.0 =

11111111.11111111.11110000.00000000

Calculation of a subnetmask for a specified number of hosts

Example:

You get the following order:

"Create a subnet with minimum 10 host Ips".

1st : 

Calculate a power of two, that is minimum 10:

2^3 = 8 Is it enough?

2^4 = 16

It is higher than 10 AND WORKS!

2nd :

Now put the LAST 4 Bits of your subnetmask to 0:

11111111.11111111.11111111.11110000

That is in decimal 255.255.255.240

With this subnetmask, you have at least 10 Host IPs in the

subnet, without wasting to much IP Addresses !

Assignment

A: You get this order as system administrator:

A. The company has a network with 150 computers. Create a Subnet from

“ 172.31.0.0 ” so that it is smallest possible subnet to provide

enough IPs.

B. Convert the second IP of your solution to Hexadecimal.

Calculating the the Broadcast IP of a Subnet

Example:

There is a subnet 172.16.64.0/20

Question:

What is the BROADCAST of that subnet?

1st , /20 means 255.255.240.0

2nd , Analyze the subnet octet to find out the "network-jump"

240 means in binary 11110000

The last of the 1's is equal to decimal 16

That is our "network-jump"

(128/64/32/16/8/4/2/1)

The last network started at 172.16.64.0

16 is the "network-jump". That means our next

network starts from 172.16.80.0 – 172.16.95.255

and the next one?

+16    172.16.96.0 - 172.16.111.255

+16    172.16.112.0 – 172.16.127.255

...

Because the next subnet in the example starts from

172.16.80.0, the broadcast must be 172.16.79.255

Because that IP before the next subnet starts is the

Broadcast Address !

OSI and TCP/IP Models

OSI and TCP/IP Models

The OSI Reference Model

- Planned to be a protocol stack for use

- Reference & communication model

- Used for troubleshooting

- It divides a complex process into small and

realizable units

The OSI Reference Model

Data Encapsulation:

The basic action of OSI

– Each layer responds services from superior layer

and issue services to the subordinate

– data moves into this seven layers to get the control

information

- Control informations are added in header & footer

- Headers and footer are fields that contain control

information

- Like post message

Each layer has its own PDU (Protocol Data Unit) which

contains different information

The PDU contains of a header and data field

Horizontal Connection

Horizontal Connection

Encapsulation Words

Packet

– Naming data unit in each step

- The data traveling through the media

Frame

- In data link layer

Datagram

– In network layer

Segment

– In transport layer

– Sequence

- Collection of segments

Message

– In Application layer

Encapsulation

Encapsulation

The difference between OSI and TCP/IP Models

OSI and TCP/IP Models

TCP Packet Structure

TCP Source Port - Port of sending host

Destination Port – Port of End Point Destination

Sequence # – Sequence of Bytes transmitted

in a segment, required to verify that all bytes are

received

Acknowledgment Number – The sequence number

of the byte the local host expects to receive next

Data Length – Length of the TCP Segment

Flags – Specified what content is in the segment

Window – How much space is currently available in

the TCP window

Checksum – Verify that the Header is not corrupted

TCP Port

A TCP port provides a specific location for delivery of

TCP Segments. Port Numbers below 1024 are well-

known, and are assigned by:

Internet Assigned Numbers Authority (IANA)

TCP Port

In Ubuntu to see list of ports: less /etc/services

Well-Known ports

– For network applications

– Range

1-1023

Registered ports

– Range

1024 – 49151

– Can be either source or destination

– Used by organizations to register specific applications

such as IM application

Private ports

– Range

49152 through 65535

– Used as source ports, these ports can be used by any applications