QSpiders - Good to Know Network Concepts

Computer Networks - Network Layer 1
The Network Layer

Computer Networks: RoutingComputer Networks: Routing 22
Network Layer issues -Network Layer issues -

Concerned with getting packets from source
to destination.

The network layer must know the topology of
the subnet and choose appropriate paths
through it.

When source and destination are in different
networks, the network layer (IP) must deal
with these differences.
* Key issue: what service does the network
layer provide to the transport layer
(connection-oriented or connectionless).

Network Layer Design GoalsNetwork Layer Design Goals
1. The services provided by the network layer
should be independent of the subnet
topology.
2. The Transport Layer should be shielded
from the number, type and topology of the
subnets present.
3. The network addresses available to the
Transport Layer should use a uniform
numbering plan (even across LANs and
WANs).

Figure 7.2
Physical
layer
Data link
layer
Physical
layer
Data link
layer
End system
α
Network
layer
Physical
layer
Data link
layer
Physical
layer
Data link
layer
Transport
layer
Transport
layer
Messages
Messages
Segments
End system
β
Network
service
Network
service
Copyright ©2000 The McGraw Hill Companies Leon-Garcia & Widjaja: Communication Networks
Network
layer
Network
layer
Network
layer

Application
Transport
Internet
Network
Interface
Application
Transport
InternetInternet
Network 1 Network 2
Machine A Machine B
Router/Gateway
Network
Interface
Network
Interface
Figure 8.3

R
R
R
R
S
SS
s
ss
s
ss
s
ss
s
R
s
R
Backbone
To internet or
wide area
network
Organization
Servers
Gateway
Departmental
Server
Figure 7.6
Copyright ©2000 The McGraw Hill Companies
Leon-Garcia & Widjaja: Communication Networks
Metropolitan Area
Network (MAN)

Interdomain level
Intradomain level
LAN level
Autonomous system
or domain
Border routers
Border routers
Figure 7.7
Internet service
provider
Wide Area Network
(WAN)

RA
RB
RC
Route
server
NAP
National service provider A
National service provider B
National service provider C
LAN
NAP
NAP
(a)
(b)
Figure 7.8
National ISPs
Network Access
Point

Packet 2
Packet 1
Packet 1
Packet 2
Packet 2
Figure 7.15Copyright ©2000 The McGraw Hill Companies Leon-Garcia & Widjaja: Communication Networks

Goals of the Network Layer

The network layer is concerned with getting
packets from the source all the way to the
destination

the network layer must
− know the topology of the communication subnet
− choose route to avoid overloading some of the
communication lines and routers while leaving
others idle
− deal with problems when the source and
destination are in different networks

Services Provided to the Transport
Layer

Connectionless (unreliable) services
− each packet must carry the full destination
address
− no packet ordering and flow control should be
done

Connection-oriented (reliable) services
− a network layer process on the sending site must set up a
connection to its peer on the receiving side
− when a connection is set up, two processes can enter a
negotiation about service parameters
− packets are delivered in sequence
− flow control is provided automatically

International Organization of the
Network Layer

virtual circuit
− a route from the source to the destination is
chosen as part of the connection setup
− primarily for connection-oriented service

datagrams
− each packet sent is routed independently of its
predecessors
− for connection-oriented and connectionless
services

Datagram Vs. Virtual Circuit
Issue Datagram Virtual Circuit (VC)
Circuit Setup Not needed Required
Addressing Each packet contains the full
source and destination address
Each packet contains a short
VC number
State
information
Subnet does not hold state
information
Each VC requires subnet table
space
Routing Each packet is routed
independently
Route chosen when a VC is set
up; all packets follow this route
Effect of router
failures
None, except for packets lost
during the crash
All VCs that passed through the
failed router are terminated
Congestion
control
Difficult Easy if enough buffers can be
allocated in advance for each
VC

Routing

Packets are often routed from the source to
the destination hop by hop.

Two networks are connected by at least a
router. The network is defined from the
point of view of the network layer.

Types of Routing

Static Routing (Nonadaptive Routing)
− Routes to destinations are predetermined and are
not dependent on the current state (traffic,
topology etc.) of the network.

Dynamic Routing (Adaptive Routing)
− Routes being learned via exchange of routing
information to reflect changes in the topology and
traffic.

Default Routing:
− Traffic to destinations that are unknown to the
router is sent to a default “outlet”.

The Optimality Principle

If router J is on the optimal path from router I
to router K, then the optimal path from J to K
also falls along the same route.
 the set of optimal routes from all sources to a
destination form a tree, called a sink tree, rooted
at the destination.

The goal of all routing algorithms is to
discover and use the sink trees for all
routers.
I
J
Kr1
r2

Sink Tree

Routing Algorithms

Static Routing Algorithms
− Shortest Path Routing
− Flooding
− Flow-Based Routing

Dynamic Routing Algorithms
− Distance Vector Routing
− Link State Routing

Hierarchical Routing

Routing for Mobile Hosts

Broadcast Routing

Multicast Routing

Shortest Path Routing

Find the shortest path between a given pair
of routers.

Cost of a link may be a function of the
distance, bandwidth, average traffic,
communication cost, mean queue length,
delay, etc.

The Dijkstra’s algorithm is used.

Flooding

Every incoming packet is sent out on every
outgoing line except the one it arrived on.

Vast numbers of duplicate packets are
generated.

Application:
− Concurrent updates of all distributed databases

Always choose the shortest path
I
J
K
L
M

Flow-Based Routing

For a given line, if the capacity and average
flow are known in advance, it is possible to
compute the mean packet delay on that line
from queuing theory.

The routing problem then reduces to finding
a routing algorithm that produces the
minimum average delay for the subnet.

Distance Vector Routing

RIP, the distributed Bellman-Ford routing
algorithm, the Ford-Fulkerson algorithm

Each router maintains a routing table giving
the best known distance to each destination
and which line to use to get there.

These tables are updated by exchanging
information with the neighbors.

Distance Vector

Each node maintains a set of triples
− (Destination, Cost, NextHop)

Exchange updates directly connected neighbors
− periodically (on the order of several seconds)
− whenever table changes (called triggered update)

Each update is a list of pairs:
− (Destination, Cost)

Update local table if receive a “better” route
− smaller cost
− came from next-hop

Refresh existing routes; delete if they time out

Distance Vector Routing

Metric used to measure the “distance”
− number of hops
− time delay
− queue length

Drawback
− Count-to-infinity problem
− it reacts rapidly to good news, but leisurely to
bad news.

Traffic may oscillate between the
two links

Hierarchical Routing

When hierarchical routing is used, the
routers are divided into regions
− each router knows all the details about how to
route packets to destinations within its own
region
− each router knows nothing about the internal
structure of other regions.

Broadcast Routing

To simply send a distinct packet to each
destination

Flooding

Multidestination Routing

Spanning Tree Routing

Reverse Path Forwarding

Multidestination Routing

Each packet contains a list of desired
destinations.

When a packet arrives, the router checks all
the destinations to determine the set of
output lines for forwarding the packet. An
output line is selected if it is the best route to
at least one of the destinations.

The router generates a new copy of the
packet for selected output line, with a set of
destinations that are to use the line.

Spanning Tree Routing

Assume each router has knowledge of a
spanning tree (e.q. a sink tree) in the
network.

Each router copies an incoming broadcast
packet onto all the spanning tree lines
except the one it arrives on.

Use minimum number of packets.

Reverse Path Forwarding

Without knowing any spanning tree
if a packet arrives at the line that is normally
used for sending packets to the source of
the broadcast
the router forwards copies of it onto all lines
except the one it arrived on.
otherwise
the packet is discarded

Multicasting

Send a message to all the other members of
the group

group management
− create and destroy groups
− for processes to join and leave groups

routers knows which of their hosts belong to
which group

routers tell their neighbors, so the information
propagates through the subnet

Multicast Routing

Each router computes a spanning tree
covering all other routers in the subnet.

When a multicast packet for a group arrives,
the first router examines its spanning tree
and prunes it, removing all lines that do not
lead to hosts in the group.

Multicast packets are forwarded only along
the pruned tree.

mn trees is needed with n groups, each with
an average of m members.

Core-based Tree for Multicast
Routing

A single spanning tree,called core-based
tree, for a group is computed, with the root
(core) near the middle of the group.

A host first sends a multicasting message to
the core, which then does the multicasting
along the spanning tree.

The tree is not optimal. However only n trees
need to be stored.

Congestion

When too many packets are present in (a
part of) a subnet, performance degrades.
This situation is called congestion.
Packetdelivered
Packet sent
Maximun carrying
capacity of subnet
Perfect
Desirable
Congested

Congestion Control

goal
− make sure the subnet is able to carry the
offered traffic

Congestion causes
− bursty data
− insufficient memory
− slow processor
− low-bandwidth line

Flow Control vs. Congestion Control

Congestion control
− Make sure the subnet is able to carry the
offered traffic
− It is a global issue, involving the behavior of all
the hosts, all the routers, and etc.

Flow Control
− Relate to the point-to-point traffic between a
given sender and a given receiver.

Flow Control vs. Congestion Control
1 Gbps
1000 Gbps
PC
Super
Computer
100 Kbps
1 Mbps 1000
1000
Flow
Control
Congestion
Control

General Principles

Open Loop
− make sure congestion does not occur in the first
place
− Deciding when to accept new traffic, deciding
when to discard packets and which ones, …

Make decision without regard to the current state of the
network

Closed Loop
− monitor the system to detect congestion (where
and when)
− pass this information to places where action can
be taken
− adjust system operation to correct the problem

Congestion Control Algorithm
Taxonomy (closed loop)

explicit feedback
− Packets are sent back from the point of
congestion to warn the source.

implicit feedback
− The source deduces the existence of
congestion by making local observations, such
as the acknowledgement time.

Load Shedding

when routers are being inundated by
packets that they can not handle, they just
throw them away.

Packet discarding policy
− Wine: Old is better than new.
− Milk: New is better than old.
− Priority Control

Jitter Control

The jitter is the amount of variation in the
end-to-end packet transit time.

The jitter can be bounded by computing the
expected transit time for each hop along the
path.
− When a packet arrives at a router, the router
checks to see how much the packet is behind or
ahead of its schedule. This information is stored
in the packet and updated at each hop. If the
packet is ahead of schedule, it may be held just
enough to get it back on schedule. If it is behind
schedule, the router tries to get it out the door
quickly.

Congestion Control for Multicasting

Multicast flows from multiple sources to
multiple destinations (cable television)

if it is the sender that reserves bandwidth
− each sender should track membership changes
− regenerate the spanning tree at each change

RSVP (Resource reSerVation Protocol)
− it is the receiver that reserves bandwidth

Bandwidth Reservation
Senders
Receivers
1 2
3 4 5
Senders
Receivers
1 2
3 4 5
Senders
1 2
3 4 5
Bandwidth
reserved
for source 1
Bandwidth
reserved
for source 1
Bandwidth
reserved
for source 2

X.25
Internetworking
B
802.4 LAN802.3 LAN
802.5 LAN
R
DECnet
R
SNA
R
R

Internetworking
Application
Presentation
Session
Transport
Network
Data Link
Physical
Application
Presentation
Session
Transport
Network
Data Link
Physical
7
6
5
4
3
2
1
Layer
APDU
PPDU
SPDU
TPDU
Packet
Frame
Bit
Application Protocol
Presentation Protocol
Session Protocol
Transport Protocol
Host A Host B
Network
Data Link
Physical
Network
Data Link
Physical
Router Router
Internal Subnet Protocol

How Networks Differ

Service offered
− Connection-oriented versus Connectionless

Protocol
− IP, IPX, CLNP, AppleTalk, DECnet, etc.

Addressing
− Flat (802) versus hierarchical (IP, PDN, PSTN,
ISDN, etc.)

Multicasting/Broadcasting
− Present or absent

How Networks Differ (Cont.)

Packet size
− Every network has its own maximum

Quality of service
− Present or absent

Error handling
− Reliable, ordered, and unordered delivery

Flow control
− Sliding window, rate control, others, or none

How Networks Differ (Cont.)

Congestion control
− Leaky bucket, choke packets, etc.

Security
− Privacy rules, encryption, etc.

Parameters
− Different timeouts, flow specifications, etc.

Accounting
− By connection time, by packet, by byte, or not at
all

Tunneling
EthernetEthernet
RR
WAN
IP
Ethernet header
Ethernet frame
IP
WAN packet header
WAN packet
IP
Ethernet header
Ethernet frame
Using encapsulation of IP packets
The same type
of network

Firewalls

Packet filter router is a router equipped with
some extra functionality that allows every
incoming or outgoing packet to be inspected.

Application gateway (e.g.a mail gateway)
may examine headers and/or contents of
messages.
Application
Gateway
Packet
Filtering
Router
Packet
Filtering
Router
Inside
Outside

Internet Network Layer Protocol

The IP (Internal Protocol) Protocol

IP Addressing

Subnets

Internet Control Protocols
− The Internet Control Message Protocol (ICMP)
− The Address Resolution Protocol (ARP)
− The Reverse Address Resolution Protocol
(RARP)

Internet Network Layer Protocol

The Interior Gateway Routing Protocol:
Open Shortest Path First (OSPF)

The Exterior Gateway Routing Protocol:
Border Gateway Protocol (BGP)

Internet Multicasting

Mobile IP

Classless InterDomain Routing (CIDR)

IPv4

IPv6

54
IPv4 Header Format
• Version – The IP version number, 4.
• Header length – The length of the datagram
header in 32-bit words.
• Type of service – Contains five subfields that
specify the precedence, delay, throughput,
reliability, and cost desired for a packet. (The
Internet does not guarantee this request.) This
field is not widely used on the Internet.
• Total length – The length of the datagram in
bytes including the header, options, and the
appended transport protocol segment or packet.
The maximum length is 65535 bytes.

55
IPv4 header format
• MF – More Fragments. All fragments except the
last one have this bit set.
• Fragment offset – The relative position of this
fragment measured from the beginning of the
original datagram in units of 8 bytes.
• Time to live – How many routers a datagram
can pass through. Each router decrements this
value by 1 until it reaches 0 when the datagram
is discarded. This keeps misrouted datagrams
from remaining on the Internet forever.
• Protocol – The high-level protocol type.

56
IPv4 header format
• Header checksum – A number that is
computed to ensure the integrity of the header
values.
• Source address – The 32-bit IPv4 address of
the sending host.
• Destination address – The 32-bit IPv4 address
of the receiving host.
• Options – A list of optional specifications for
security restrictions, route recording, and source
routing. Not every datagram specifies an
options field.
• Padding – Null bytes which are added to make

57
The IP Protocol
The IPv4 (Internet Protocol) header.

58
The IP Protocol
Some of the IP options.
5-54
• http://www.iana.org/assignments/ip-parameters

59
IP Addresses
• An IP address really refers to a network
interface, so if a hosts are on two network, it
must have two IP addresses.
• Traditionally, IP addresses were divided into the
five categories: A, B, C, D, E.
• Network numbers are managed by a nonprofit
corporation called ICANN (Internet Corporation
for Assigned Names and Numbers) to avoid
conflicts.
• Network address, which are 32-bit numbers, are
usually written in dotted decimal notation. In
this format, each of the 4 bytes is written in

60
IP Addresses
IP address formats.

61
IP Addresses
• The value 0 means this network or this host. The
value of -1 (all 1s) is used as a broadcast address
to mean all hosts on the indicated network.
• 0.0.0.0 is used by hosts when booted.
• IP addresses with 0 as network number refer to
the current network. 156.26.10.0.
• 255.255.255.255 broadcast on local network
• The addresses with a network number and all 1s
in the host field allow machines to broadcast to
remote LANs.
• 127.0.0.1, loopback

62
IP Addresses
Special IP addresses.

63
IP Addresses
• dig - DNS lookup utility
cs742@kirk:~$ dig www
; <<>> DiG 9.2.1 <<>> www
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 28011
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0
;; QUESTION SECTION:
;www. IN A
;; AUTHORITY SECTION:
. 10800 IN SOA A.ROOT-SERVERS.NET. NSTLD.VERISIGN-
GRS.COM. 2003110201 1800 900 604800 86400
;; Query time: 139 msec
;; SERVER: 156.26.10.130#53(156.26.10.130)
;; WHEN: Sun Nov 2 21:32:40 2003
;; MSG SIZE rcvd: 96

64
IP Addresses
• nslookup – query Internet name servers
interactively
cs742@kirk:~$ nslookup www.wichita.edu
Note: nslookup is deprecated and may be removed from future releases.
Consider using the `dig' or `host' programs instead. Run nslookup with
the `-sil[ent]' option to prevent this message from appearing.
Server: 156.26.10.130
Address: 156.26.10.130#53
www.wichita.edu canonical name = BLANCA.wichita.edu.
Name: BLANCA.wichita.edu
Address: 156.26.1.160
• Find out the address in Windows: ipconfig/all

65
What is IPv6?
• IPv6 stands for "Internet Protocol Version 6“ and
is also referred to as IPng (IP next generation).
• IPv6 is the protocol designed by the IETF (The
Internet Engineering Task Force) to replace the
current version Internet Protocol, IP Version 4
(IPv4).
• The core set of IPv6 protocols were made an
IETF Draft Standard on August 10, 1998.
• For more information about IPv6, refer to
http://www.ipv6.org/.

66
Why is IPv6? More Addresses!
• IP address allocation history:
1981 ~ IPv4 protocol published
1985 ~ 1/16 total space
• More addresses are needed despite increasingly
intense conservation efforts
– CIDR (classless inter-domain routing)
– PPP address sharing
– NAT (network address translation)
• Theoretical limit of 32-bit space: ~4 billion
devices
Practical limit of 32-bit space: ~250 million
devices

67
IPv6
• IPv6 major goals were:
– Support billions of hosts, even with inefficient address
space allocation.
– Reduce the size of the routing tables.
– Simplify the protocol, to allow routers to process packets
faster.
– Provide better security (authentication and privacy) than
current IP.
– Pay more attention to type of service, particularly for
real-time data.
– Aid multicasting by allowing scopes to be specified.
– Make it possible for a host to roam without changing its
address.
– Allow the protocol to evolve in the future.
– Permit the old and new protocols to coexist for years.

68
IPv6
• SIPP (Simple Internet Protocol Plus) was
selected and given the designation IPv6.
• The main features of IPv6:
– IPv6 has longer addresses than IPv4.
– Improved header processing with better support for
options and enhanced routing functionality
– Auto-configuration
– Better security support
– Better support for Quality of Service (QoS)

69
What’s new in IPv6
• Bigger Address Space
– 128 bits: solving the address shortage issue: 232
(4.2
billion) to 2128
(340 undecillion or 3.4 x 1038
)
– There are enough IPv6 address to assign
• 1 million networks per human
• A separate IPv6 address on every square inch of every
planet in the solar system
• Improved Header Processing and Enhanced
routing functionality
– Redefinition of IP options in header (7 versus 13 in IPv4)
• Format is improved for quicker processing
• Some fields are classified such that they may be ignored
by intermediate nodes
– Inclusion of flow label
– Elimination of checksum (let higher layer to compute
their own checksum)
– Enhanced routing functionality such as roaming a host

70
• Auto-configuration
– Reduced Administrative Overhead
• Much of the administrative load for IPv4 nodes involves
allocating and managing their IPv4 addresses
• IPv6 nodes are able to configure their addresses
automatically (Plug and play)
– Support renumbering
• Experience has shown that Internet nodes don’t keep the
same IP address for their life time
• A network (e.g., an enterprise intranet) will need renumber
based on topology change (wholesale reconnection to
another ISP)
• An IPv6 node discovers the need for configuring a new
IPv6 address for itself.

71
• Better security support
– Reduced Administrative Overhead
• Much of the administrative load for IPv4 nodes involves
allocating and managing their IPv4 addresses
• IPv6 nodes are able to configure their addresses
automatically (Plug and play)
• Support renumbering
– Experience has shown that Internet nodes don’t keep
the same IP address for their life time
– A network (e.g., an enterprise intranet) will need
renumber based on topology change (wholesale
reconnection to another ISP)
– An IPv6 node discovers the need for configuring a new
IPv6 address for itself.

72
Why isn't IPv6 here now?
• Why isn't IPv6 here now?
– The situation of lack of address spaces are different
in different countries.
– Some transition solutions such as NAT (Network
Address Translation) are there.
– There are still not so many applications available for
IPv6.
– But mobile phones have pushed fast deployment of
IPv6.

73
The Main IPv6 Header
The IPv6 fixed header (required).

74
• Version. 4 bits. - IPv6 version number.
• Traffic Class. 8 bits. - Internet traffic priority
delivery value.
• Flow Label. 20 bits. - Used for specifying special
router handling from source to destination(s) for a
sequence of packets.
• Payload Length. 16 bits, unsigned. - Specifies
the length of the data in the packet. When set to
zero, the option is a hop-by-hop Jumbo payload.
• Next Header. 8 bits. - Specifies the next
encapsulated protocol. The values are compatible
with those specified for the IPv4 protocol field.

75
• Hop Limit. 8 bits, unsigned. -For each router that
forwards the packet, the hop limit is decremented
by 1. When the hop limit field reaches zero, the
packet is discarded. This replaces the TTL field in
the IPv4 header that was originally intended to be
used as a time based hop limit.
• Source address. 16 bytes. - The IPv6 address of
the sending node.
• Destination address. 16 bytes. -The IPv6
address of the destination node.

76
How Was IPv6 Address Size Chosen?
• Some wanted fixed-length, 64-bit addresses
– easily good for 1012
sites, 1015
nodes, at .0001
allocation efficiency
– minimizes growth of per-packet header overhead
– efficient for software processing
• Some wanted variable-length, up to 160 bits
– compatible with OSI NSAP addressing plans
– big enough for auto-configuration using IEEE 802
addresses
– could start with addresses shorter than 64 bits & grow
later
• Settled on fixed-length, 128-bit addresses
(340,282,366,920,938,463,463,374,607,431,768,211,45
6 in all!)

77
IPv6 Addresses
• Classless addressing/routing (similar to CIDR)
• Notation: x:x:x:x:x:x:x:x (x = 16-bit hex number)
– Contiguous 0s are compressed: 47CD::A456:0124 =
47CD:0000:0000:0000:0000:0000:A456:0124
– IPv6 compatible IPv4 address: ::128.42.1.87
• Address assignment
– provider-based (can’t change provider easily)
– Geographic
• IPv6 has many different kinds of addresses
– unicast, anycast, multicast, loopback, IPv4-embedded,
care-of, manually-assigned, DHCP-assigned, self-
assigned, solicited-node, and more.
– One simplification: no broadcast addresses in IPv6! –
uses multicast to achieve same effects

78
Prefix
0000 0000
0000 0001
0000 001
0000 010
0000 011
0000 1
0001
001
010
011
100
101
110
1110
1111 0
1111 10
1111 110
1111 1110 0
1111 1110 10
1111 1110 11
1111 1111
Use
Reserved
Unassigned
Reserved for NSAP Allocation
Reserved for IPX Allocation
Unassigned
Unassigned
Unassigned
Unassigned
Provider-Based Unicast Address IPV4-like
Unassigned
Reserved for Geographic-Based Unicast Addresses
Unassigned
Unassigned
Unassigned
Unassigned
Unassigned
Unassigned
Unassigned
Link Local Use Addresses no global uniqueness
Site Local Use Addresses no global uniqueness

79
IPv6 – Multicast and Anycast
• IPv6 describes rules for three types of
addressing: unicast (one host to one other
host), anycast (one host to at least one of
multiple hosts), and multicast (one host to
multiple hosts).
• The introduction of an "anycast" address
provides the possibility of sending a message
to the nearest of several possible gateway
hosts with the idea that any one of them can
manage the forwarding of the packet to
others.
• Anycast messages can be used to update

80
IP version 6 – Future Evolution
• The next header field provides for future
evolution.
• If non-zero, it specifies an extension header type
in the packet.
• The extension header types include the services
for router information, route definition, fragment
handling, authentication, encryption information,
and destination information.
• Each extension header type has a specific size
and format and is transmitted after the basic
header and before the payload.

81
Extension Headers
IPv6 extension headers.
5-69

82
Extension Headers
The hop-by-hop extension header for large datagrams
(jumbograms).
The extension header for routing.

83
IPv6 Security and Evolution
• The advantage of implementing security at the IP
level is that it can be applied without the need for
security-aware implementations of application
programs.
• Security in IPv6 is implemented through the
authentication and encrypted security payload
extension header types , for ensuring data
integrity, and for ensuring privacy.
• Instead, isolated “island” of IPv6 will converted,
initially communicating via tunnels. As the IPv6
islands grow, they will merge into bigger islands.
Eventually, all the islands will merge, and the
Internet will be fully converted.

QSpiders - Good to Know Network Concepts

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