"Understanding TCP Flags: Exploring 3 Additional Flags and Their Processing"
Summary
TLDRThis video from the tech and love channel dives into the intricacies of TCP flags, a crucial component of the TCP header. It explains the purpose of these flags in signaling the state of TCP communication and their use in troubleshooting. The video outlines the six commonly used flags: SYN, ACK, RST, FIN, PSH, and URG, detailing their roles in initiating, acknowledging, resetting, and terminating connections, as well as data transfer. It also clarifies the often-confused URG and PSH flags and introduces three newer flags related to congestion control: ECN-Echo, ECN-Nonce, and CWR. The video is an informative guide for anyone looking to understand the mechanics behind TCP communication.
Takeaways
- đ TCP flags are crucial bits in the TCP header segment, each with a unique purpose and occupying one bit of a nine-bit segment.
- đŠ TCP flags are used to communicate the state of a TCP connection and are essential for network troubleshooting and understanding TCP traffic conditions.
- đ The SYN flag is used to initiate a connection between hosts, marking the beginning of a TCP session.
- đ The ACK flag acknowledges the receipt of a packet, specifically following an initial SYN packet, indicating the readiness to communicate.
- â The RST flag is used to forcefully abort a connection when there is no valid connection or when a host wants to terminate the connection abruptly.
- đ The FIN flag is used for gracefully terminating a connection, signaling the end of data transmission and allowing an orderly shutdown.
- đ The PSH flag is used during data transfer to urge the receiver to process the buffered data immediately instead of waiting for the buffer to fill.
- â° The URG flag indicates that the data is urgent and should be processed with priority, bypassing the usual buffering process.
- đ The ECN-Echo (ECE) flag indicates that a host is capable of Explicit Congestion Notification, helping manage network congestion.
- đĄïž The CWR flag is used by the sender to acknowledge the receipt of an ECE flag, signaling a response to congestion control mechanisms.
- đ The ECN-Nonce flag is used for concealment protection in congestion notification, ensuring that congestion information is accurately communicated.
Q & A
What are TCP flags?
-TCP flags are various types of flag bits present in the TCP header segment, each with its own importance, used to notify a particular state during TCP communication and for troubleshooting purposes.
How many bits are allocated for TCP flags in the TCP header?
-TCP flags are allocated nine bits in the TCP header segment, with each flag occupying one bit.
What is the purpose of using TCP flags?
-TCP flags are used to notify about the state of communication and to let you know about the condition of the TCP traffic.
How many types of TCP flags are commonly used?
-There are six commonly used TCP flags, with three additional flags for special cases.
What are the six commonly used TCP flags?
-The six commonly used TCP flags are SYN (synchronize), ACK (acknowledge), RST (reset), FIN (finish), PSH (push), and URG (urgent).
What is the purpose of the SYN flag?
-The SYN flag is used by each host on the network to initiate a connection.
What does the ACK flag indicate?
-The ACK flag indicates an acknowledgement after the initial SYN packet is sent by the host.
When is the RST flag used?
-The RST flag is generally sent by a host if there is no valid connection or to forcefully terminate a connection.
What does the FIN flag signify?
-The FIN flag is used for gracefully terminating a connection after data transmission is completed.
What is the difference between the URG and PSH flags?
-The URG flag indicates that the incoming packet is urgent and should be sent to the remote host immediately without waiting in the buffer. The PSH flag, however, waits in the queue and requires the data to be stored in the TCP buffer before being sent to the destination.
What are the three additional TCP flags and for what purpose are they used?
-The three additional TCP flags are CWR (Congestion Window Reduced), ECE (Explicit Congestion Echo), and ECN-Nonce (used for concealment protection of ECE). They are used for congestion control and notification in the network.
What does the ECE flag indicate?
-The ECE flag indicates that the host is ECN (Explicit Congestion Notification) capable, meaning it supports ECN during the TCP handshake.
What is the role of the CWR flag in TCP communication?
-The CWR flag is used by the sender to notify the receiver that the sender has received ECE flags and has responded to the congestion control mechanism.
Can you provide an example where the URG flag would be used?
-An example of where the URG flag would be used is in Telnet, where commands input by the user need to be sent to the destination host as soon as possible.
What is an example of a scenario where the PSH flag would be used?
-The PSH flag would be used in FTP, where data transfer, whether large or small, requires confirmation and assurance that the data will reach the destination without loss.
Outlines
đŹ Introduction to TCP Flags
This paragraph introduces the concept of TCP flags, which are integral parts of the TCP header. It explains that TCP flags are bits that signify different states during TCP communication. The paragraph also mentions that there are nine types of TCP flags, six of which are commonly used, and three are for special cases. The purpose of these flags is to notify the state of communication and aid in troubleshooting TCP traffic.
đ Common TCP Flags and Their Functions
This section delves into the six commonly used TCP flags: SYN, ACK, RST, FIN, PSH, and URG. SYN is used to initiate a connection, ACK to acknowledge the receipt of packets, and RST to forcefully abort a connection. FIN is used for gracefully terminating a connection after data transmission. PSH and URG flags are related to data transfer, with PSH indicating that the receiver should process the data immediately and URG signaling that the packet is urgent. The paragraph also sets the stage for discussing three additional, less commonly used flags in the subsequent paragraphs.
đ Clarifying Urgent and Push Flags
The third paragraph focuses on the distinction between the URG and PSH flags, which are often sources of confusion. URG indicates that a packet is urgent and should be sent to the host without delay, bypassing the TCP buffer. In contrast, PSH waits in the queue and ensures data integrity, especially important in applications like FTP where data loss is not acceptable. The paragraph also provides examples of when each flag might be used, such as Telnet for URG and FTP for PSH.
đ TCP Buffering and Data Transfer
This paragraph explains the process of data transfer in TCP, emphasizing the role of the TCP buffer. It describes how data from the application layer is held in the TCP buffer before being sent to the receiver. The paragraph also contrasts the immediate transfer of data indicated by the URG flag with the queuing process that occurs with the PSH flag, highlighting the importance of buffer management in TCP communication.
đ§ Advanced TCP Flags for Congestion Control
The fifth paragraph introduces three additional TCP flags related to congestion control: ECE, ECN-Nonce, and CWR. ECE (Explicit Congestion Echo) indicates that a host is capable of using ECN, which is a mechanism for signaling congestion in the network. ECN-Nonce is used for concealment protection when congestion is detected. CWR (Congestion Window Reduced) is sent by the sender to notify the receiver that it has reduced its congestion window in response to an ECN signal. These flags are crucial for managing network traffic and preventing congestion.
Mindmap
Keywords
đĄTCP Flags
đĄTCP Header
đĄSYN Flag
đĄACK Flag
đĄRST Flag
đĄFIN Flag
đĄPSH and URG Flags
đĄCWR Flag
đĄECE Flag
đĄECN Nonce
Highlights
TCP flags are crucial components of the TCP header, indicating the state of a TCP communication.
There are nine types of TCP flags, six commonly used and three for special cases.
TCP flags are used for notifying the state of communication and for troubleshooting purposes.
SYN (Scene) flag is used to initiate a connection between hosts.
ACK (Acknowledgement) flag is used to respond to the initial SYN packet, indicating the start of a connection.
RST (Reset) flag is used for forcefully terminating a connection.
FIN (Finish) flag is used for gracefully terminating a connection after data transfer.
PSH (Push) and URG (Urgent) flags are used for data transfer, with PSH waiting in queue and URG sending immediately.
URG flag indicates an urgent packet that should be sent without waiting in the buffer.
PSH flag ensures data is sent to the application layer without delay, waiting in the TCP buffer queue.
Telnet is an example where the URG flag is used to ensure immediate command delivery.
FTP uses the PSH flag to ensure data integrity and avoid loss during file transfers.
ECE (Explicit Congestion Echo) flag indicates a host's capability for Explicit Congestion Notification (ECN).
CWR (Congestion Window Reduced) flag is used by the sender to respond to congestion control mechanisms.
ECN Nonce flag is used for concealment protection in congestion notification.
The three additional TCP flags (ECE, ECN Nonce, CWR) are relatively new and focus on congestion management.
Understanding the difference between PSH and URG flags is crucial for network communication optimization.
TCP flags play a vital role in managing the flow and congestion of data packets in a network.
Transcripts
[Music]
hello everyone welcome back to the tech
love channel in today's video we are
going to discuss about tcp flags so tcp
flags is one of the
important segment in the tcp header so
in this video we will learn what are the
tcp flags what is the use of tcp flags
and the most important types of tcp
flags let's first see what is the tcp
flags tcp flags are some various type of
flags bits present in the tcp header
segment
each flag has its own importance
also
flag segment is for nine bits and each
flags is one bit means the flag segment
is for
nine bit
total
and each flag is for
one bit they consider for one bit as
size
now let's see
what is the use of tcp flags so tcp
flags are used to notify a particular
state
during a tcp communication it can also
be used for the troubleshooting purpose
so this is basically let you know about
the condition of the tcp traffic
if anyone asks to you what is the use of
tcp flags you can simply say that this
flag is used to notify about the
condition of the tcp traffic
the use of tcp flags is
to let you
know
about
the state of
communication
okay
now let's see
the types of tcp flags
so the types of tcp there are nine types
of tcp flags
nine
types of
tcp
flags
6 flags we commonly use
and 3 are three flags
for
special case
let's first see these six flags these
are the only flags we commonly know and
we commonly use
in our daily network life
so the first in the sixth flag is
scene
flag second
act acknowledgement flag
third
rst reset
fourth
fin
finish
fifth
puss
and sixth
is
urgent
urg urgent flag
so
if we
see the basic
of these flags so seen and act flag is
used
to initiate
a connection
these are the only flag which we use to
initiate connection
and then reset and fin flag so these
flags are used for
aborting a connection
you can simply say
reset and fin flag used for abort
connection and push and urgent flag is
used for
data transfer
these are the high level definition for
these flags
other three additional flags
which are let's call it
number seven
that is cwr
number eight
e
c e
and number nine
ns
so about this three flag we will discuss
later in the detail
now let's start and discuss each flag
one by one
so our first flag that is
the scene flag
so sim flag is the first flag that every
host every host on the network
use to initiate a connection
this flag is used by each host on the
net to initiate the connections
so this will be like this
there is a one pc
and the second pc so whenever they start
communicating to each other
they will first
to start the communication so syn flag
is basically used
to initiate
connection
by
each host
the next one is
acknowledgement
ack is the short form
acknowledgement flag
so
acknowledgement fact this flag indicates
that the acknowledgement after the
initial
syn packet sent by the host
let's say
here is a pc
one and pc2
so pc1 send a
syn packet
to pc
2
so the pc2 will reply
or you can say the acknowledgement will
be performed on behalf of
the scene initiative
so this is this flag
sent
after
initial
syn packet
initial scene
packet
send by host
next one is
reset
r is
t
reset flags
so reset flags generally host
send this flag if there is
none
segment connection
so this flag has a special case if there
is a non-segment connection then this
reset flag will be sent by the host
also in case of no libel connection to
answer at the remote host
means
if this pc
one is requesting to some other pc a
remote pc we can say
and if this remote pc does not having
the liable answer of the connection in
that case this
remote pc will
this remote pc will reply with
reset flag
or you can also say if they want to
terminate the connection forcefully if
the pc1 and pc2 want to terminate the
connection
because of anything
so they can use
reset flag
reset flag
to terminate the connection forcefully
forcefully
the next one is
fin
finish flag
finish flag is also similar to reset
but
reset works for forcefully connection
termination and fin works for gracefully
termination of connection
what will happen here
pc1 will
send something so they will start scene
then they will
will be
snack
let's say then
pack
dc connection
created then they've done some
data transfer
and at the end
each of them
will
see each other
for fin
fin
to finish the connection gracefully and
finish acknowledge
so this is how they
completely
gracefully terminate the connection
after data transmission once the data is
com transmission is completed they
gracefully terminate the connection so
this is for use of fin flag
we can say simply
gracefully
terminate
the
connection
after this four flag
this two flag is very confusing so in
many interviews
or in many ways we have seen the
difference between
urgent
and
push flag
they are
same as per their behavior but
a very basic and very main difference
that make them different from each other
let's
learn about them as well let's discuss
about them as well
let me remove this
um
okay
let me write
like this urgent flag is here
and
whose flag is here
okay
so what happened for both of them
so this flag urgent flag
urgent flag indicate that incoming
packet as urgent
and this need to be sent to the remote
host without waiting
in the buffering
and process
immediately what happened
let me create
so let's call it
this one is the
header
so what happened
there is a
segment called
urgent pointer
in the tcp header inside the tcp header
whenever a packet sent from
a
to
host b
and if they want the packet to be
immediately transferred to the
host b
so they can use
urgent flag
telnet is an example we can say
for the urgent flag
so what happened
for every connection for every traffic
there is a buffer memory in the tcp
so the
data we sent from source to the
destination the data is stored in the
buffer memory of the tcp and once the
buffer is completed then after the
packet is sent to the destination but in
our case in the urgent flag
the buffer memory will not wait to fill
the memory pull the buffer memory it
will as soon as receive the urgent flag
data and it will as soon as transfer the
data to the destination
okay
now the push flag so argent flag does
not wait let me right
urgent flag does not
does not
wait in
queue
immediately
send
to destination
without
delay
in
buffer
of tcp
it does not hold in the buffer of the
tcp it just immediately sent to the
destination does not hold the cube does
not wait in the queue
opposite of this urgent flag push flag
do the same thing
but
let me create a diagram
uh
layers
layer wise
seven
six
five
four
three
two
one
as we know as per the osi layer seventh
layer is
application layer
then presentation
then session
and then transport so here we have the
tcp on the transport layer
so
inside the tcp header
the buffer will be there
tcp buffer we can say
so our data just comes came from
application layer
our data came from application layer
holding the buffer of the tcp
once the buffer is completed
then the packet is sent to the
this one is
sender
this one is
receiver
this one is also application
layer of receiver
layer 7 layer 6
5
4
3
2 and one
so what happened
once the sender send
the data from application layer the data
sent to the
layer 4 and inside the tcp buffer the
data is
getting buffered and then after
transferred to the
receiver end
at the receiver end it will again store
the data
in the buffer
of tcp header
once the buffer is completed
then after
the data is sent
to the application layer of the receiver
so this is how the pus works
so push
need to
push
need to
wait in the
queue
if there is already ongoing process of
data so puss will wait in the queue
push weight in the queue then also
require the
data
store
in
tcp buffer
so the major difference between push and
urgent is
push does not wait in the queue
and sorry argent does not wait in the
queue and push weight in the queue
push anyhow push have to wait in the
queue
for the example of urgent we have seen
tc telnet
because whenever we put a command on the
tailor that command should be sent to
the destination host as soon as possible
and ftp we can say the example of
push flag so
for the ftp in ftp we send a huge data
we send a big data small data any kind
of data so the data in security should
be confirmed the data should be ensured
to be reached to the destination
for that reason every time we need to
use push flag
means for that this kind of connection
this kind of communication
tcp use push flag because there's no
need to data loss
so this is the difference between pus
and urgent flag
now
let's discuss about the three more
additional flags
these three flags are not so old so they
just came before five six year ago
before that we were using only six flag
till the
argentine post
let me remove this one
i hope you are able to understand the
difference between push and urgent flag
okay
the
seventh flag
according to the new version the seventh
flag
is e c e
e c e
if we
generally discuss about this these three
flags seven eight and nine so these all
flags are only made for congestion
purpose
if there is a condition in the network
then these flags comes under the picture
of the traffic
so the first one is
ece flag ece flags called
explicit
congestion echo
explicit
congestion
echo
this flag indicate that host is ecn
capable ecn means
whenever this flag is on
so this indicate
indicate
host is
ecn enabled
enabled or you can say capable
once means the hotel host is
supportable for ecn ece
capable
so
ecn called as
explicit congestion notification let me
note it
face it
congestion
notification
so these flags indicate that host is ecn
capable during tcp handshake and this
knows it notified by the ecn
field in the ip header set to 11 means
the
ecn header
bit will be set as 11 whenever this is
set as 11
in that case only it understand that it
is a acn field and it is a ecn cap cable
the next one is
ecn
nonce
ecn
so this flag is used for concealment
protection of ece
means if there is a congestion in the
network and that need to be notified
to the user or need to notify to the
sender so this
ecn non flag is used to notify that
there is a ece congestion ec congestion
notification in the network
so this flag is used for
concealment protection
the next one is
number nine cwr
cwr flag and this is called
congestion window reduced
congestion window
reduced
again the another congestion flag
so this flag used by the sender
the cwr flag used by the sender to
notify the receiver that sender has
received ece flags means let's say
here we have a this one is sender
and this one is
receiver so
this cwr flags
cwr flag
notify
the sender the receiver that sender has
received ece flag and responded for the
congestion control mechanism
receiver will get the cwr flag
and
get to know that
this sender has
responded on ecn flag responded on a
congestion flag
on behalf of the sender is
seen
the cwr flag
so these are the all about flag this is
all about the tcp flags if you have any
question any query please let us know in
the comment
thank you for watching please do like
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everyone thank you
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