🤯 🤕 Too much information, other instructors will put me to sleep, but your videos keep me excited and motivated to learn. I can even watch your videos several times. :)
What I like about your method of explaining is the occasional use of comparisons and reference to past lessons. This helps me connect the entire course together in my head and also to develop a point of view and not only just remember facts. Thanks again!
For those having trouble understanding, just realize that the fields in the header all work together to get a few things done. Firstly, enable QoS via the DSCP field. Secondly, three fields are dedicated to the division of a packet into 'fragments' if it is too large. Fragmentation and reassembly is facilitated by the Identification, Flags and Fragment Offset fields. Lastly, and of course far from least..the Source and Destination fields provide inter-network routing. I left some fields off but the important thing to note is what important functions the fields provide. For rote memorization of field sizes and packet minimums and maximums, the flashcards really do help, so do them! It is free!
Man, this is a lot of information. I really have to attack the flash cards. I get the basic concept but its a lot of material to remember for a header. Thanks for the flashcards and the visuals. It will aid a lot in studying this material. I may have to watch it a few times and study this deck separate from my combined deck until I nail it.
@@cornilpatidar honestly, you probably won't see one question about this stuff on the test to include most of the stuff in the first 10 days worth of videos. If you were going for a lessor cisco exam like the CCST you would see this stuff, but the ccna expects you already know this stuff. It's a great foundation for what's to come. Unfortunately everyone wants to skip over the entry level certs and go to the much harder certs, which is why folks end up here. The same happens with Comptia certs. Everyone skips net+ and A+ and goes straight for Security+.
I recommend watching it again and trying to learn it. This is probably more detail than you need to know for the exam, but at least be familiar with the purpose of each section of the IPv4 header.
I was about to post a comment ''is this video complicated for everyone or just me?'', and I saw your comment first :) so it seems that it is complicated for most of us.
It's great that someone published that kind of material and provides all other sources, it's really better than paid courses on well known platrofms i used to did. Thank you Jeremy
Hello Jeremy I hope you are doing well, Im Glad to find out in youtube a talented/professional person like you helping people to learn and grow up their knowledge, at this point of my life Im studying to become a Juniper Routing engineer, however I have my networking knowledge based with Cisco, im reviewing the networking basics back again and found your material and help me a lot to complete what im studying I hope I can have my certifications and keep studying learning so I can help others like you do, once again thank you for your support and help and God bless you!!!
@@George-mk7lpMy canadian school district has some. We have a CCNA course. But it's probably a little excessive in terms of time 3 hours a day every day for a year is too much of a time commitment for me.
Each router that a packet encounters decrements the value in the packet's TTL field by 1. So at each hop, the IPv4 header changes, and the router must recompute the value of the header checksum field. The Wikipedia article "Internet checksum" notes that there are quick ways to do this when that's the only change. (Presumably there's more overhead when packet fragmentation occurs.) IPv6 gets rid of layer-3 header checksums.
This is a most fantastic course! I have ordered the ENCOR course from your site as well! I have also taken the CCNA gold boot camp course. It is well thought out and structured but I find the presentation that you offer and your style of teaching to be far superior. Merci Jeremy!
This is the best ever video on this topic. No one can explain ccna topics than you have done. You made these difficult topics too easy to understand and memorize. Thanks a lot.. Respect.🙏
Hi Jeremy! I'm currently at Day 10 of your CCNA course, but I've found it much more effective to learn the theoretical and practical material from you than from the paid course. Unfortunately, I need to participate in the private school's course as well to be eligible for the regulatory exam, because I need the certificate to apply to the accredited exam center. But, to say something positive, the two complement each other, and my instructor was surprised that I can apply what I learned from you in their course as well. I'm studying to become a junior system administrator, and we are covering CCNA RS1 and RS2 as part of the curriculum
Sir your videos are very helpful in gaining basic concept and learning. Thanks for your efforts. If you please provide the slides along with the videos, it would be be really helpful to reviewing it and remembering. Thanks ♥️
I must say, I am really enjoying those video classes much better than the online classes I have been attending. Gives me the Edge is grasping information. Many blessings & Thanks to you keep up the good work/videos.
Thank you so much for these amazing videos. You do a great job of making things simple. This was a lot to chew, but you made it easy to understand. This is really helping me.
Compliments of the season J, Travel but now back and ready to roll. Thanks again for yet another bomb for more to come . Always grateful. Time to dive in
You know what, I can't help myself to stop watching your videos specially on weekend because once I started one video I need to continue until I fell sleep or need to eat to pee! :D thank you so much Jeremy for such a wonderful and amazing videos, flashcards, and labs... one of the best channel I should say.
Dang it, today i was sitting like 2h on the flashcards to memorize the information. So far Ethernet Header and IPv4 Header things ware the hardest to remember :D Thanks Jeremy.
Well, so far so good. Your lessons are really right sized. As a software developer and having some knowledge of the domain, I'm progressing a little bit faster, but it's still really informative and I think, speed would not be the case after certain point. Anki cards are really useful piece. Thanks for your effort to share invaluable knowledge and I will certainly thank you after course is passed.
Thanks Jeremy for your amazing videos! I started taking some Udemy courses on CCNA and your way of presenting the information is so much easier to follow. I find it helpful that you provided anky flashcards and lab sections.
Up till now I didn't have to watch them again. I even started quiting half way through an come back.. them little numbers are tough.. wireshark does help.
Internet Header Length (IHL) The IPv4 header is variable in size due to the optional 14th field (options). The IHL field contains the size of the IPv4 header; it has 4 bits that specify the number of 32-bit words in the header. The minimum value for this field is 5, which indicates a length of 5 × 32 bits = 160 bits = 20 bytes. As a 4-bit field, the maximum value is 15; this means that the maximum size of the IPv4 header is 15 × 32 bits = 480 bits = 60 bytes
Hey Jeremy. Your videos are really helpful, I love to watch them at 2x speed on my commute :D. 1) When do you think this course will end? 2) Do you think that your vids along with the practical and Anki and Odom's OCG should be enough for 200-301?
It is getting more difficult than the other videos before, and I need to replay most of the it all the time. I need to keep saying to myself to: "keep on going and finish what you've started".
Hi Jeremy, thank you so much for the video! I just have a question: There is a FCS field in L2 Trailer. What is the difference between this FCS and the UDP/TCP checksum field? I guess the difference is that the FCS detects the in-transit error of a frame, whereas the UDP/TCP checksum field checks the errors in the data, and attempt to recover it? I just got confused... Thank you again Jeremy!
They just check for errors at different points. The Ethernet FCS is checked and recalculated at each hop in the network on the route to the destination, the IP header checksum is used to check for errors in the IP header itself, and the TCP/UDP checksum is used by the receiving end to check for errors in the entire TCP/UDP segment (including encapsulated data). I'll talk more about TCP/UDP in a future video, including their checksums.
Hey Jeremy! Thank you very much for these videos, I am slowly making my way through them. I have a question if that's ok. I am a bit confused about some terminology. So, if my understanding is correct, all the below information/terminology is correct. Would you be able to confirm that, please? We have: The Application layer (L7) The Presentation layer (L6) The Session layer (L5) The Transport layer (L4): Receives 'Data' from the upper 3 layers and adds a 'Layer 4 header' to it, making it a 'Segment'. The Network layer (L3): This is where Routers operate and IP addresses exist. This layer receives a 'Segment' from layer 4 and adds a 'Layer 3 header' (aka an 'IPv4 header') to it, making it a 'Packet'. The combination (Data+L4Header+L3Header) can be called an 'IPv4 packet'. The Data Link layer (L2): This is where Switches operate and MAC addresses exist. This layer receives a 'Packet' from layer 3 and adds both a 'Layer 2 header' (aka an 'ethernet header') and 'Layer 2 trailer' (aka an 'ethernet trailer') to it, making it a 'Frame'. The combination (L2Trailer+Data+L4Header+L3Header+L2Header) can be called an 'ethernet frame. The Physical layer (L1)
Here are some examples to help you easily understand each field of the IPv4 header: - Source address: Imagine you're sending a letter to your friend. Your address would be the source address, indicating where the letter is coming from. - Destination address: The destination address would be your friend's address, indicating where the letter should be delivered. - Packet length: The packet length would be like the total size of the letter, indicating how many pages it contains. - Type of service: The type of service would be like a note you put on the letter to indicate if it's urgent, confidential, etc. - Identification: The identification would be like a unique number you assign to each letter to be able to properly assemble them if they are divided into pieces. - Flags: The flags would be like indicators on the letter to indicate if it can be divided into pieces or if it's the last piece of a set. - Fragment offset: The fragment offset would be like an indication of the position of each piece of the letter in the set. - Time to live: The time to live would be like a countdown on the letter, indicating how long it can remain in circulation before being discarded. - Protocol: The protocol would be like the type of content of the letter, indicating if it's a regular letter, a postcard, an invitation, etc. - Checksum: The checksum would be like a verification of the letter's integrity, to ensure it hasn't been damaged during transport. - Source and destination addresses: These addresses would be like the addresses of the different post offices the letter passes through along the way. - Options: The options would be like extras you can add to the letter, such as stickers, photos, etc.
You mentioned at 14:04 that the protocol field indicates the protocol of the encapsulated layer 4 PDU. I understand that TCP and UDP are layer 4 protocols. But aren't ICMP and OSPF layer 3 protocols?
The 8-bit Protocol field specifies the next upper-layer header within the data payload of the packet. These upper-layer protocols are identified using IP Protocol Numbers. The following is a list of common IP Protocol Numbers, as assigned by the IANA: 1 ICMP 2 IGMP 6 TCP 9 IGRP 17 UDP 46 RSVP 47 GRE 50 IPSEC ESP 51 IPSEC AH 88 EIGRP 89 OSPF
is it possibile to work with ccna certification even if i dont'have a graduation in this scope? i have always worked in a completely other context, im 33 years old, i love IT and technology world
hi Jeremy, I'm just curious, I understand we need to know ipv4 header concepts in terms of exam and possibly job interviews, but when do you usually need to use them for practical labs/work?
The best reason to know them, outside of improving your general knowledge of how networks work, is for when you need to troubleshoot an issue by analyzing packet captures. It helps to be familiar with the contents of the IPv4 header, Ethernet header, etc.
I waited for this one anxiously. Once more, great content. Argh... How I hate having to remember so much information! I like it better when I am calculating. Anyway, it is what it is. It seems like there's still a lot of lessons ahead, Jeremy! I wander just how many more courses till completion of the course? Are you able to advise please?
I agree with you, I don't like memorizing so much information, better to learn through labs and such! But sometimes its necessary. I don't know how many more videos there will be, maybe 50, but I hope to complete the course by the end of this year. I want to make this a complete course, but if you want to get your CCNA soon I recommend using other resources too!
@@JeremysITLab Using other resources? Of course I am. But there's enough to keep me busy as I have begun taking on the lab playlist. And as you stated, yes, there's plenty on the net. I like comparing and contrasting - it helps me learn better. thanks for your great work.
Hey Jeremy. Your videos are really helpful, can you help me to understand ccnp ( routing &switching) how much time taken by you if someone deemands you regarding a ccnp video \
@@JeremysITLab Jeremy, I have my CCNA exam schedule during the 1st week of MAY 2021 and as you said you will post 50 days of videos and I assume there are another 11 days you will post after the 39th video you posted this week, will I be able to finish all your 50 videos before the end of April?? which is 2 months from now.
Hi, Jeremy's IT Lab, great videos I really love the knowledge you are providing to me and others, and please keep up the great work. I still wish I had this when I passed the CCNA back in April 2001. Question about unmanaged switches and when you were speaking in the video about Auto-negotiation between the switch and the device connected and I wanted to know if the same issue of collision occurs if you set manually full duplex & Auto-negotiation can't be detected by the switch. The reason I ask is that I had to displeasure I'm working for a facility that refuses to buy managed switches and wanted to invest unmanaged switches, which prevented us from seeing what was happening on the network.
Thanks for the video, Jeremy. One question: You mentioned the Total length maximum value is - 65535 bytes, while the MTU is only 1500 bytes. Does this mean that one packet can contain maximum of about 40 fragments (1500 bytes MTU + 20+ bytes of IPv4 header for each fragment)?
Hi Andriy! I haven't thought about that, but I think your logic is correct. In the real world, however, I don't think you'll find situations like that often.
No, the number of fragments that can be created from a single IP packet is not directly limited to about 40 fragments based on the IPv4 header size. The number of fragments in an IPv4 packet is determined by the "Fragment Offset" field in the IP header, and the Total Length field, not the size of the IPv4 header alone. Let's break it down with an example: Suppose you have an IPv4 packet with a Total Length of 5000 bytes. Each fragment will have an IPv4 header, which is typically 20 bytes, but the size can vary depending on optional fields and headers (such as options and padding). For simplicity, let's assume a 20-byte IPv4 header. 1. MTU is 1500 bytes: - The first fragment can be 1500 bytes (MTU) in size. - The second fragment can also be 1500 bytes in size. - The third fragment can be 1500 bytes in size. - The fourth fragment can be 500 bytes in size. In this case, you would have 4 fragments, and the Fragment Offset field would be used to indicate the offset of each fragment relative to the original packet. The Fragment Offset is a 13-bit field, so it can represent values from 0 to 8191. In the above example, the first fragment's offset would be 0, the second fragment's offset would be 1500 (bytes), the third fragment's offset would be 3000 (bytes), and the fourth fragment's offset would be 4500 (bytes). These offsets represent where each fragment fits within the original 5000-byte packet. The Fragment Offset is used to reassemble the fragments at the destination in the correct order, and the 13-bit field allows for a wide range of possible offsets within the original packet. So, the number of fragments is not limited to around 40 based on the IPv4 header size. The actual number of fragments depends on the Total Length of the original packet, the MTU of the network, and the Fragment Offset values used to split the packet. The 13-bit Fragment Offset field provides flexibility in determining the offsets for a wide range of fragment sizes and positions within the original packet.
While I'm new at all of this, the flash cards are sometimes confusing to me. Is it just me? The class that I took at a local technical college never made us focus on specific CIDR Numbers. I do appreciate Jeremy's efforts and would even donate money if I could afford to. I'm quite overwhelmed but don't give up very easily. Thanks, Jeremy! Your efforts are much appreciated.
Feel free to add/edit/delete the flashcards as you see fit! Although I highly recommend using flashcards, they don't have to be exactly the ones I made.
Thank you for all of these videos Jeremy! And thank you for the flash cards, they really help to hammer in tons of information like the amount in this video.
That was a lot of information but you make it easier I can not thank you enough man. And by the way is there a way to get the slides of the videos. Thanks man!!
Thank you Elias :) Sorry, I don't provide the slides, I tried converting them to PDF but I use too many animations etc so they need a lot of editing to work for PDF.
I have a question regarding on How errors encapsulated in IPv4 packet is detected: The encapsulated data in the IPv4 header is checked for errors by the encapsulated protocol TCP/UDP, but that is not true for UDP right? If it is UDP the encapsulated data will not be checked for errors, please let me know if my understanding is correct or not. Jeremy sir, thank you so much for this amazing series.
Just a note with respect to the DSCP field. There are actually 8 bits available in that field. The first six are split into two sections, the first three bits are for IP precedence backward compatibility, the next three are for DSCP, and the last two bits for the ECN (which is used in WRED for QoS) you can see the eight bits when you show the field in wire shark at 19:56. Probably more information than required for CCNA but still ....
@@JeremysITLab All I was saying is the DSCP field contains 8 bits not 6. I don't argue dscp uses only the first 6 bits.. that being said, its your course, and I wasn't attempting to throw stones at your work. It's actually pretty good.
If it's hard, it means we are progressing! Keep it up fam
Thank you :)
good analogy
Did you get your CCNA brother?
🤯 🤕 Too much information, other instructors will put me to sleep, but your videos keep me excited and motivated to learn. I can even watch your videos several times. :)
Indeed there is a lot of information to remember! Glad my videos are helping you :)
he is professional in this area
@Studio S.S Do not try to remember everything like this, write notes, I use dropbox paper and it really helps!
Facts
Yes that's a lot of information!! The flashcards are really good but there are also too many of them! 56 just for this lesson is too much i think 🤕🥴
What I like about your method of explaining is the occasional use of comparisons and reference to past lessons. This helps me connect the entire course together in my head and also to develop a point of view and not only just remember facts. Thanks again!
Thanks, glad to hear that :)
when I get a job inshallah , I will send you on paypal ..
you are the reason why I love network now
thank u so much for the effort , please dont stop
Thank you so much, I'm glad you love networking!
Hi were you able to get job?
I have never seen content like this relating to CCNA or network fundaments. Seriously I appreciate you sir with all my heart.
For those having trouble understanding, just realize that the fields in the header all work together to get a few things done. Firstly, enable QoS via the DSCP field. Secondly, three fields are dedicated to the division of a packet into 'fragments' if it is too large. Fragmentation and reassembly is facilitated by the Identification, Flags and Fragment Offset fields. Lastly, and of course far from least..the Source and Destination fields provide inter-network routing. I left some fields off but the important thing to note is what important functions the fields provide. For rote memorization of field sizes and packet minimums and maximums, the flashcards really do help, so do them! It is free!
Man... this part rough , thanks all the works you've done for us .
It is simply amazing how you make complicated content so simple. Thanks so much Jeremy.
Thanks Joyce :)
Hello my fello Kenyan🤝🤝
Man, this is a lot of information. I really have to attack the flash cards. I get the basic concept but its a lot of material to remember for a header. Thanks for the flashcards and the visuals. It will aid a lot in studying this material. I may have to watch it a few times and study this deck separate from my combined deck until I nail it.
Did you pass the exam? Is it necessary for the exam?
@@cornilpatidar honestly, you probably won't see one question about this stuff on the test to include most of the stuff in the first 10 days worth of videos. If you were going for a lessor cisco exam like the CCST you would see this stuff, but the ccna expects you already know this stuff. It's a great foundation for what's to come. Unfortunately everyone wants to skip over the entry level certs and go to the much harder certs, which is why folks end up here. The same happens with Comptia certs. Everyone skips net+ and A+ and goes straight for Security+.
@@JB-jn9kb a + and net + is kinda useless for those already in college
Time could not erase the nature of your teaching in sharing us knowledge... You become a part of my IT career... Thanks a lot GOD BLESS...
Thanks for your comment, I'm happy to help :)
Your walk throughs are always so helpful. I had struggled to find any class that as in depth as I need but now i feel confident I can pass my CCNA!
Thank you for this amazing series. This is saving me tons of money and time. Thanks to you I can utilize this quarantine time to me benefit!
Thank you, I'm glad you're using the time well ;)
this is the first video in this course that i didnt understand it well its very complicated for me :( i hope its not very important in the exam
I recommend watching it again and trying to learn it. This is probably more detail than you need to know for the exam, but at least be familiar with the purpose of each section of the IPv4 header.
true i agree too. it's a bit complicated i assume .
but thanks jeremy keep posting. we will understand at one point
@@JeremysITLab Do you think it’s important to memorize cabling distances and ip header byte information?
I was about to post a comment ''is this video complicated for everyone or just me?'', and I saw your comment first :) so it seems that it is complicated for most of us.
Even I couldn’t understand this one , is there any way to understand it better
It's great that someone published that kind of material and provides all other sources, it's really better than paid courses on well known platrofms i used to did. Thank you Jeremy
Thank you, Marcin :)
Truly best explanation ever. I have covered 17 videos and I have promised myself to complete all the videos after watching this one. Thanks sir.
Your clear pronunciation is appreciated. It helps in understanding the context.
Thank you, I'm glad to hear that :)
Hello Jeremy
I hope you are doing well,
Im Glad to find out in youtube a talented/professional person like you helping people to learn and grow up their knowledge, at this point of my life Im studying to become a Juniper Routing engineer, however I have my networking knowledge based with Cisco, im reviewing the networking basics back again and found your material and help me a lot to complete what im studying I hope I can have my certifications and keep studying learning so I can help others like you do, once again thank you for your support and help and God bless you!!!
I appreciate how you split up the information into multiple videos! Makes it a lot easier.
The flashcards are what i missed in my days in school. I would have been a genius by now :). Thank you Jeremy.
Me too! I would have definitely gotten higher scores on my tests if I used flashcards in school!
you mean high school? you guys get network course in HS?? Which country is it?
@@George-mk7lp Flash cards can be used in any kind of studies. This has nothing to do with Cisco or networking. Flash cards is a studying tool.
@@BijouBakson oh sorry I thought u mean network related flashcards .. I just heard that there are networking classes in some US high schools..
@@George-mk7lpMy canadian school district has some. We have a CCNA course. But it's probably a little excessive in terms of time 3 hours a day every day for a year is too much of a time commitment for me.
your explanation is very clear jeremy. I just could say thank you for all these incredible lesson you've delivered
Each router that a packet encounters decrements the value in the packet's TTL field by 1. So at each hop, the IPv4 header changes, and the router must recompute the value of the header checksum field. The Wikipedia article "Internet checksum" notes that there are quick ways to do this when that's the only change. (Presumably there's more overhead when packet fragmentation occurs.) IPv6 gets rid of layer-3 header checksums.
Whew! That was a lot, but I retained more than I thought I would. Jeremy, I love you, bro.
Yeah there's a lot to remember...watch the video again if you have to.
@@JeremysITLab You should reply. I love myself too 🤣
This is a most fantastic course! I have ordered the ENCOR course from your site as well! I have also taken the CCNA gold boot camp course. It is well thought out and structured but I find the presentation that you offer and your style of teaching to be far superior. Merci Jeremy!
This is the best ever video on this topic. No one can explain ccna topics than you have done. You made these difficult topics too easy to understand and memorize. Thanks a lot.. Respect.🙏
I forgot much of this stuff damn me! A revision always does the trick. Let's revise with the flashcard now! Thank you Jeremy.
Always important to review! With so much information to remember, it's easy to forget some of it.
@@JeremysITLab Yup!
this is fairly the best thing ive ever found on youtube EVER. thank you!!
Glad you like it :)
Came here on Keith Barker's reccomendation ( CBT nuggets) and i am not dissapointed. Some of the best learning on youtube. Thank you
This was an insane video but loved the learning! Onto my flash cards! Thanks Jeremy!
Yeah there's a lot of info in this one!
I'm just Impressed how brilliantly do you explain hard stuffs. Thank you for your work!
Hi Jeremy!
I'm currently at Day 10 of your CCNA course, but I've found it much more effective to learn the theoretical and practical material from you than from the paid course. Unfortunately, I need to participate in the private school's course as well to be eligible for the regulatory exam, because I need the certificate to apply to the accredited exam center.
But, to say something positive, the two complement each other, and my instructor was surprised that I can apply what I learned from you in their course as well.
I'm studying to become a junior system administrator, and we are covering CCNA RS1 and RS2 as part of the curriculum
Sir your videos are very helpful in gaining basic concept and learning. Thanks for your efforts. If you please provide the slides along with the videos, it would be be really helpful to reviewing it and remembering. Thanks ♥️
Thank you, I will make a PDF of the slides and put it in the description. I'll do it this weekend if I can.
@@JeremysITLab Thanks A lot Sir for responding, you are really doing a great Job. Keep it Up Sir.!
I must say, I am really enjoying those video classes much better than the online classes I have been attending. Gives me the Edge is grasping information. Many blessings & Thanks to you keep up the good work/videos.
Thank you! Glad you like the videos
Fantastic video, I loved that you made examples to demonstrate fragmentation and showed how to view it in wireshark.
I love the series so far. I am on day 13 and am looking forward to completing this course. Commenting this on every video for the algorithm.
Thank you so much for these amazing videos. You do a great job of making things simple. This was a lot to chew, but you made it easy to understand. This is really helping me.
Cheers, I'm glad it helped!
I am addicted to your way of teaching. I don't find the videos from other instructors as detailed and brilliant. Kindly make a few videos on Wireshark
Compliments of the season J, Travel but now back and ready to roll. Thanks again for yet another bomb for more to come . Always grateful. Time to dive in
Welcome back Glenn!
You know what, I can't help myself to stop watching your videos specially on weekend because once I started one video I need to continue until I fell sleep or need to eat to pee! :D thank you so much Jeremy for such a wonderful and amazing videos, flashcards, and labs... one of the best channel I should say.
Dang it, today i was sitting like 2h on the flashcards to memorize the information. So far Ethernet Header and IPv4 Header things ware the hardest to remember :D
Thanks Jeremy.
The wire shark part was a good idea. I’m finally able to understand those fields when using it
Thanks! I had to watch all the videos for days 11 and 12 and then come back and rewatch this video before I could understand, but I do understand now.
Thanks for teaching us today's lpv4 header, so understandable
Thank you :)
Well, so far so good. Your lessons are really right sized. As a software developer and having some knowledge of the domain, I'm progressing a little bit faster, but it's still really informative and I think, speed would not be the case after certain point. Anki cards are really useful piece.
Thanks for your effort to share invaluable knowledge and I will certainly thank you after course is passed.
Thanks Jeremy for your amazing videos! I started taking some Udemy courses on CCNA and your way of presenting the information is so much easier to follow. I find it helpful that you provided anky flashcards and lab sections.
Again, this video is so clear, so understable. Thank you so much :)
Thank you for all your comments :)
Thank you very much. I know that I will rewatch this video however your explanation of things really simplify complexities of this networking world.
Thank you :)
That's a lot of information in one video...🤯
I had to watch it 3 times to understand..!
this video marks the end of my CCNA journey
lol why
Folks, I'd like to welcome you to Jeremy's IT Lab.
Up till now I didn't have to watch them again. I even started quiting half way through an come back.. them little numbers are tough.. wireshark does help.
This was the hard one topic, but if you repeate it again and again + ankflash cards it becomes very easy....!
Thanks fella..
@Jeremy You are the best Networking teacher!
Great job Jeremy, keep up the good work.
Internet Header Length (IHL)
The IPv4 header is variable in size due to the optional 14th field (options). The IHL field contains the size of the IPv4 header; it has 4 bits that specify the number of 32-bit words in the header. The minimum value for this field is 5, which indicates a length of 5 × 32 bits = 160 bits = 20 bytes. As a 4-bit field, the maximum value is 15; this means that the maximum size of the IPv4 header is 15 × 32 bits = 480 bits = 60 bytes
I promise to me if i pass the exam i going to convert in a new sponsor of your work. Congratulations, your work is excellent
Thank you! Good luck!
Had to watch this two times, complete the anki flashcards and watch this video again. A lot of great information :D
Hey Jeremy. Your videos are really helpful, I love to watch them at 2x speed on my commute :D.
1) When do you think this course will end?
2) Do you think that your vids along with the practical and Anki and Odom's OCG should be enough for 200-301?
Thank you! I think I will finish the course by the end of this year. Yes, these videos along with Odom's OCG should be enough.
@@JeremysITLab What about just this series itself ? This series will provide everything for the exam right?
@@saravanakumar-tnj nope
@@JeremysITLab do you mean that it would end by the end of 2020?
Hi jeremy, excellent content. Every quiz question will appear in the CCNA exam?
Comforting to see that others found this to be a truck load of data.
Incredible Information.
Thank you so much Jeremy!
You're the GOAT!! 🐐
Do we need all these information for real world works? Or we just need to understand the fundamentals which will help hands on?
Buenos videos, Jeremy! Adquirí mucho conocimiento con estos videos. Gracias! Saludos.
Muchas gracias!
It is getting more difficult than the other videos before, and I need to replay most of the it all the time. I need to keep saying to myself to: "keep on going and finish what you've started".
I almost quit after this video, but we have to continue what we started
Hi Jeremy, thank you so much for the video! I just have a question: There is a FCS field in L2 Trailer. What is the difference between this FCS and the UDP/TCP checksum field? I guess the difference is that the FCS detects the in-transit error of a frame, whereas the UDP/TCP checksum field checks the errors in the data, and attempt to recover it? I just got confused... Thank you again Jeremy!
They just check for errors at different points. The Ethernet FCS is checked and recalculated at each hop in the network on the route to the destination, the IP header checksum is used to check for errors in the IP header itself, and the TCP/UDP checksum is used by the receiving end to check for errors in the entire TCP/UDP segment (including encapsulated data). I'll talk more about TCP/UDP in a future video, including their checksums.
Hey Jeremy! Thank you very much for these videos, I am slowly making my way through them. I have a question if that's ok. I am a bit confused about some terminology. So, if my understanding is correct, all the below information/terminology is correct. Would you be able to confirm that, please? We have:
The Application layer (L7)
The Presentation layer (L6)
The Session layer (L5)
The Transport layer (L4): Receives 'Data' from the upper 3 layers and adds a 'Layer 4 header' to it, making it a 'Segment'.
The Network layer (L3): This is where Routers operate and IP addresses exist. This layer receives a 'Segment' from layer 4 and adds a 'Layer 3 header' (aka an 'IPv4 header') to it, making it a 'Packet'. The combination (Data+L4Header+L3Header) can be called an 'IPv4 packet'.
The Data Link layer (L2): This is where Switches operate and MAC addresses exist. This layer receives a 'Packet' from layer 3 and adds both a 'Layer 2 header' (aka an 'ethernet header') and 'Layer 2 trailer' (aka an 'ethernet trailer') to it, making it a 'Frame'. The combination (L2Trailer+Data+L4Header+L3Header+L2Header) can be called an 'ethernet frame.
The Physical layer (L1)
Good summary!
To be honest, this is world No.1 lecture!🤗
Jeremy you have made the content so easy to understand. hats off for your incredible work. many many thanks
hi i am glad to learn from you actully i having question
what will be the whole bytes of IPv4header ?
In quiz question 2, perhaps (c) is correct as well. If the minimum is 5, zero indicates some kind of issue.
Hey Jeremy thanks for the videos. I have one question . Will you cover vlan and intervlan concepts in this course
Yes I will cover those topics!
Here are some examples to help you easily understand each field of the IPv4 header:
- Source address: Imagine you're sending a letter to your friend. Your address would be the source address, indicating where the letter is coming from.
- Destination address: The destination address would be your friend's address, indicating where the letter should be delivered.
- Packet length: The packet length would be like the total size of the letter, indicating how many pages it contains.
- Type of service: The type of service would be like a note you put on the letter to indicate if it's urgent, confidential, etc.
- Identification: The identification would be like a unique number you assign to each letter to be able to properly assemble them if they are divided into pieces.
- Flags: The flags would be like indicators on the letter to indicate if it can be divided into pieces or if it's the last piece of a set.
- Fragment offset: The fragment offset would be like an indication of the position of each piece of the letter in the set.
- Time to live: The time to live would be like a countdown on the letter, indicating how long it can remain in circulation before being discarded.
- Protocol: The protocol would be like the type of content of the letter, indicating if it's a regular letter, a postcard, an invitation, etc.
- Checksum: The checksum would be like a verification of the letter's integrity, to ensure it hasn't been damaged during transport.
- Source and destination addresses: These addresses would be like the addresses of the different post offices the letter passes through along the way.
- Options: The options would be like extras you can add to the letter, such as stickers, photos, etc.
You mentioned at 14:04 that the protocol field indicates the protocol of the encapsulated layer 4 PDU. I understand that TCP and UDP are layer 4 protocols. But aren't ICMP and OSPF layer 3 protocols?
The 8-bit Protocol field specifies the next upper-layer header within the data
payload of the packet. These upper-layer protocols are identified using IP
Protocol Numbers.
The following is a list of common IP Protocol Numbers, as assigned by the
IANA:
1 ICMP
2 IGMP
6 TCP
9 IGRP
17 UDP
46 RSVP
47 GRE
50 IPSEC ESP
51 IPSEC AH
88 EIGRP
89 OSPF
is it possibile to work with ccna certification even if i dont'have a graduation in this scope? i have always worked in a completely other context, im 33 years old, i love IT and technology world
Hey Jeremy. You just made it very easy. Thank you.
Actually, I just need to know what is the total number of videos that will cover the exam?
Thank you! I think there will be at least 50 videos.
Jeremy's IT Lab, Thank you!
13:16 A simple Google search shows Operating Systems use different TTL default values:
MS-Windows 128
Mac 60, 64
Linux 64, 255
Yep, being able to google is an essential skill for network engineers
hi Jeremy, I'm just curious, I understand we need to know ipv4 header concepts in terms of exam and possibly job interviews, but when do you usually need to use them for practical labs/work?
The best reason to know them, outside of improving your general knowledge of how networks work, is for when you need to troubleshoot an issue by analyzing packet captures. It helps to be familiar with the contents of the IPv4 header, Ethernet header, etc.
I waited for this one anxiously. Once more, great content. Argh... How I hate having to remember so much information! I like it better when I am calculating. Anyway, it is what it is. It seems like there's still a lot of lessons ahead, Jeremy! I wander just how many more courses till completion of the course? Are you able to advise please?
I agree with you, I don't like memorizing so much information, better to learn through labs and such! But sometimes its necessary.
I don't know how many more videos there will be, maybe 50, but I hope to complete the course by the end of this year. I want to make this a complete course, but if you want to get your CCNA soon I recommend using other resources too!
@@JeremysITLab Using other resources? Of course I am. But there's enough to keep me busy as I have begun taking on the lab playlist. And as you stated, yes, there's plenty on the net. I like comparing and contrasting - it helps me learn better. thanks for your great work.
6:15 I reckon it the maximum length of the field options should be 60 bytes in stead of 40
Nope, 40 bytes is correct
I was also confused at first, but since option is IHL>5, 15-5=10, 10×4 bytes, 40 bytes
Need to go through again because am a fresher but great thanks for the time and energy.
Thank you :)
Hey Jeremy. Your videos are really helpful, can you help me to understand ccnp ( routing &switching) how much time taken by you if someone deemands you regarding a ccnp video
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THANKS !
I just wanna ask a question
How long does this course last for ?
I think the course will be about 50 days, but I'm not sure.
@@JeremysITLab Jeremy, I have my CCNA exam schedule during the 1st week of MAY 2021 and as you said you will post 50 days of videos and I assume there are another 11 days you will post after the 39th video you posted this week, will I be able to finish all your 50 videos before the end of April?? which is 2 months from now.
I was so overwhelmed watching this video for the fourth time!
Thank you so much for your efforts and amazing explanation. I'm so grateful 🙂
Well im sure I will watch this tutorial 10 Times to be fit in the subjects............THANK YOU.
Hi, Jeremy's IT Lab, great videos I really love the knowledge you are providing to me and others, and please keep up the great work. I still wish I had this when I passed the CCNA back in April 2001. Question about unmanaged switches and when you were speaking in the video about Auto-negotiation between the switch and the device connected and I wanted to know if the same issue of collision occurs if you set manually full duplex & Auto-negotiation can't be detected by the switch. The reason I ask is that I had to displeasure I'm working for a facility that refuses to buy managed switches and wanted to invest unmanaged switches, which prevented us from seeing what was happening on the network.
Thanks for the video, Jeremy.
One question: You mentioned the Total length maximum value is - 65535 bytes, while the MTU is only 1500 bytes.
Does this mean that one packet can contain maximum of about 40 fragments (1500 bytes MTU + 20+ bytes of IPv4 header for each fragment)?
Hi Andriy! I haven't thought about that, but I think your logic is correct. In the real world, however, I don't think you'll find situations like that often.
No, the number of fragments that can be created from a single IP packet is not directly limited to about 40 fragments based on the IPv4 header size. The number of fragments in an IPv4 packet is determined by the "Fragment Offset" field in the IP header, and the Total Length field, not the size of the IPv4 header alone.
Let's break it down with an example:
Suppose you have an IPv4 packet with a Total Length of 5000 bytes. Each fragment will have an IPv4 header, which is typically 20 bytes, but the size can vary depending on optional fields and headers (such as options and padding). For simplicity, let's assume a 20-byte IPv4 header.
1. MTU is 1500 bytes:
- The first fragment can be 1500 bytes (MTU) in size.
- The second fragment can also be 1500 bytes in size.
- The third fragment can be 1500 bytes in size.
- The fourth fragment can be 500 bytes in size.
In this case, you would have 4 fragments, and the Fragment Offset field would be used to indicate the offset of each fragment relative to the original packet. The Fragment Offset is a 13-bit field, so it can represent values from 0 to 8191.
In the above example, the first fragment's offset would be 0, the second fragment's offset would be 1500 (bytes), the third fragment's offset would be 3000 (bytes), and the fourth fragment's offset would be 4500 (bytes). These offsets represent where each fragment fits within the original 5000-byte packet.
The Fragment Offset is used to reassemble the fragments at the destination in the correct order, and the 13-bit field allows for a wide range of possible offsets within the original packet.
So, the number of fragments is not limited to around 40 based on the IPv4 header size. The actual number of fragments depends on the Total Length of the original packet, the MTU of the network, and the Fragment Offset values used to split the packet. The 13-bit Fragment Offset field provides flexibility in determining the offsets for a wide range of fragment sizes and positions within the original packet.
Hi jeremy thanks again for the wonderful video , i have a question - do i need to memorize the bit sizes for every field ?
Probably not! But only Cisco knows exactly what questions are on the exam.
Thanks you so much for the valuable contains..... love from INDIA Mumbai
thank you for this amazing course and for wonderful explanation
While I'm new at all of this, the flash cards are sometimes confusing to me. Is it just me? The class that I took at a local
technical college never made us focus on specific CIDR Numbers. I do appreciate Jeremy's efforts and would even donate money if I could afford to. I'm quite overwhelmed but don't give up very easily. Thanks, Jeremy! Your efforts are much appreciated.
Feel free to add/edit/delete the flashcards as you see fit! Although I highly recommend using flashcards, they don't have to be exactly the ones I made.
hey Jeremy I hope you reply >> quick question in which episode you mentioned the maximum size of an Ethernet payload which is 1500 bytes?
Thank you for all of these videos Jeremy! And thank you for the flash cards, they really help to hammer in tons of information like the amount in this video.
carry on big man god bless you. 👍👍👍
Thank you sir!
That was a lot of information but you make it easier I can not thank you enough man. And by the way is there a way to get the slides of the videos. Thanks man!!
Thank you Elias :) Sorry, I don't provide the slides, I tried converting them to PDF but I use too many animations etc so they need a lot of editing to work for PDF.
Okay I will keep a note then. Again Thank you for the videos.
I have a question regarding on How errors encapsulated in IPv4 packet is detected: The encapsulated data in the IPv4 header is checked for errors by the encapsulated protocol TCP/UDP, but that is not true for UDP right? If it is UDP the encapsulated data will not be checked for errors, please let me know if my understanding is correct or not.
Jeremy sir, thank you so much for this amazing series.
UDP also checks for errors! It has a checksum field.
@@JeremysITLab thank you!!
Just a note with respect to the DSCP field. There are actually 8 bits available in that field. The first six are split into two sections, the first three bits are for IP precedence backward compatibility, the next three are for DSCP, and the last two bits for the ECN (which is used in WRED for QoS) you can see the eight bits when you show the field in wire shark at 19:56. Probably more information than required for CCNA but still ....
You can call that whole byte the ‘ToS byte’, but I wouldn’t say the whole byte is the DHCP field, since only the first 6 bits are used for DHCP.
@@JeremysITLab All I was saying is the DSCP field contains 8 bits not 6. I don't argue dscp uses only the first 6 bits.. that being said, its your course, and I wasn't attempting to throw stones at your work. It's actually pretty good.
@@jimwelch707 'DSCP' is the name of those first 6 bits, not the whole byte. I'm going by the RFC definitions.
If you want a name for the whole byte it's 'DS', although I usually hear it still called 'TOS'.
@@JeremysITLab We're good - I've heard it called TOS as well
صلوا على الحبيب المصطفى صلى الله عليه وسلم
Crazy desgin and engineering.
this course is GOLD!!
Great content and explanation! Are the Anki Flash Cards still available? I can't seem to find the link. Thank you!
Yep, the link is in the top line of the description!