1.2 Frame Forwarding

hello and thank you for watching the second lesson of chapter 1 which is 1.2 frame forwarding in this lesson you will learn about switches cam table content addressable memory table also known as mac address table and what information switches use to build this table and forward the frames in this lesson you will also learn about frame forwarding methods that we have for this lesson i'm going to jump straight to our packet tracer that we were using in the previous lesson and we're going to start learning how does the switch build this cam table but before we do that let's look at the switch's predecessor which was a hub how did that device use to forward the frames right so i'm going to build a network so click on the networking devices select a hub and bring it in our workspace and i'm just going to grab one pc right and do a configuration on this pc and i'll show you a quick method that you can just copy and paste for the next vcs rather than do all these configurations so i'm just going to give an ip address 10.1.1.10 255 255 zero and gateway ten one ten one one one one okay now without me actually bringing another pc and doing the same thing what i can do i can just highlight this pc control c and control v that will create another copy so let's just create four of these yeah right all the configuration will be there so all we need to do is just change the ip the host portion of the address so 20 here that'll be easy dot 30 here so the opening on the other screen dot 30 and the next one dot 40. so this is going to be the 40. okay on the name here i'm just going to change this to 10.1.1.10 that's the name so we know that what's the ip address of the pc this is dot 20 and this is the 30 and this is that 40. now the name doesn't really matter you know you can call it whatever you want right there we go we got four pcs with ip addresses there and we're going to connect these one to a hub with a straight through cable so click and hub you should know that this device works at layer one of the osi model and it doesn't have any cam table or anything what is going to do is as soon as it receives a frame from many of the devices all it will do it will regenerate that frame and it will replicate it so what we're going to do we're going to ping from this device we're going to bring it to this device this from source to destination and as all the frames as they coming in to the switch sorry to the hub hub will replicate them and it will send them it doesn't look anything so it doesn't read any information it will just replicate into every other device apart from the device that came in so it won't send it back this way we will send it to every other device yeah now that's what the hub will do um okay let's just move these so we can see them nicely right there we go okay so if i go to this pc and sorry it's always going down this side and if i just ping for example let me just move here and say ping 10.1.1.40 i think we said the 40 was a the previous one here so let's go here right so we thinking from here we bring in this device here so from pc 10.1.1.10 we bring in 10.1.1.40 which is this one here and i will go to simulation mode and what i want to do is i want to get rid of all these packets the filter and i don't just want to see the pings yeah so i want to see the icmps so icmps and ok so you should say here you see the filter is just icmp and let me go there there we go okay now when i press enter the the data is going to come from this pc it's going to go to the hub and then hub is going to replicate it it's going to send it to every device apart from the device that came in alright so if i press play so now the hub what is going to do if i just go to display you see the hub is just replicated extended everywhere apart from the data when it is the port they came in so now i stopped that and you can see instead of sending it that way it will just replicate it and send it to every port yeah so play you see and these two devices are getting bothered for no reason right so that's what the hub is doing so as soon as packet arrives regenerate each packet and flood it flood it to every port every apart from the port they came in so that's the hub not very popular device in the network in today right okay so the next thing what we're gonna do is actually we i'm gonna go to real time again and again like i showed you before i can just copy control c and control v i got same network as i had earlier but on this network now what i'm going to do is i'm going to delete this hub and i'm going to replace it with the switch so i go to i get a switch and a switch here and connect them so i'll connect this to doesn't matter what port really say port 24 this one here and this one is going to be port say 23 i could connect them to any four doesn't really matter 22 and 21 right now if i go to for example let's just wait for these to go green and the reason why the amber is because the switch is actually making sure there is no loop it's having a loop prevention a check making sure that there's no looping topology then they will go green which will be about 30 seconds here see this one is already going green here right now the switches they won't behave like a hub one once the frame comes in of the switch so as soon as the frame comes in at the switch the switch has something called cam table content addressable memory table and in there we're going to have the mac address the port number vlan id which we are not concerned with it right now next lesson as soon as the frame comes in the switch will look at the source where is the source and the mac address of the source that's the ip address we're going to put the mac address here take the mac address and stick it in the cam table put the mac address here and then put the port number so port number 24 for example and then then look at the destination where is it going where is the destination if the destination is on the table it will forward it directly to the destination if it's not on the table it will flood it same as what hub was doing it will send it to every port fafsa before they came in so they will send it every fourth apart from the port that came in that is known as unknown on unknown unicost address unicost mac address mac address if i if the switch doesn't know the unicast mac address what port is it it's gonna do something called flooding same as what hub was doing flooding a switch was also due for broadcast broadcast and uni uh multicast if there's a multicast frame we'll do and broadcast will do flooding right so the switches for example have this cam table so if i go to switch and to see the cam table in the switch i'll do i go to command line interface right and i'll do show mac address table just to see what switch knows so enable here show mac mac address table and you can see this mac address table on the switches is empty at the moment the switch doesn't know any device doesn't know any mac address does not how he learns it port nothing it's empty the mac address table okay so what we're going to do is we're going to go to this pc and we're going to look at what mac address table that what mac address does he have so command line and to find the mac address was ipconfig forward slash all to see what mac address table we have okay not table what mac address so physical address of that pc is this so let me copy that right and i'm just going to put it here that's the physical address of this pc so the switch what it's going to do is going to take this mac address as soon as the frame hits the switch it's going to take that mac address at the moment just want to verify we don't have anything yet okay excellent so now what we're going to do is i have an icmp here that i can see it but i want to also see the arp messages address resolution protocol messages so those messages so we see now arp and icmp now if i go to this machine and i'll do ping i'm going to ping the pc up 10.1.1 if you want to see what this pc what information has resolved you do r minus a and this species already knows the mac address of the other pc will not send our message to clear this r minus d that will clear it and now the pc doesn't know so if i do r minus a it doesn't know any interest so when you ping this machine it's going to send an op message first and then it's going to forward the the icmp message okay let's let's start again so i go to this machine and i'll do ping 190 sorry 10.1.1.40 and press enter now you should see two packets one packet first packet is arp this one is going to be arp address resolution protocol and this is a broadcast broadcast wrote cost and that's going to be like it's going to ask everybody because it's broadcast when it hits the switch we said that for the switch is going to flood that broadcast to every port that came in but the switch first is going to look at the source mac address it's going to put it on his cam table and it's going to flood it and then the device with the correct ip address will reply and switch will look at the source mac address and put in his cam table right and then send it directly to the pc one here or 10.10 in the end okay let's have a look um if i just clear this and just go to this pc and press go forward that's the up message going to the switch now the switch has learned the mac address state mac address of pc1 of dot 10 yes so show mac address you can see that mac address here it's just been added so this mac address has just been added here because the package the frame is coming into the switch switch says okay i'll just take that mac address put it in my table and i'll put this for five minutes and then look at the destination destination is the broadcast because it's r so because it's up destination is gonna forward to every port right apart from it's not gonna send it back this way but it's going to send it to every other port connected on the switch but it's there in the mac address of the source so you learn it from the source okay so if i press play you can see now now it's just going to send it to everyone now if we go to this pc and we're just going to take the mac address of this pc right so if i bring this pc here go to desktop and look at the mac address save mac address so ip config forward slash all and you can see the mac address or the physical address let's just take the mac address here ctrl c oh i can here i can say copy i think and i'll paste it here right now this is the mac address of this pc this vc will create a reply and it will send it back but the reply the op reply is going to be unicost right so the switch if you look at the switching still right if you look at the switch show mac address table you see the switch only knows of that pc mac address so when i when i reply so send send it back now the switch will say okay i got a mac address source mac address is this right let me put that on my mac table and destination mac address is this i know exactly where the destination is so i'm just going to forward it here right so if i if we look at the table of the switch so if i repeat the command show mac address table now the switch says okay well i just got a frame with this mac address came to this port so 9580 this mac address came on port 23 and the destination is this mac address so since i know where the destination is i'm just going to send it directly there i'm not going to flood it so if he knows where the destination is is going to send it directly if it doesn't know where the destination is it's just going to flood it yeah okay so let's let's continue there c sends it directly and then the next is just going to be the normal one-to-one communication he's not gonna flood it now because he knows the destination he knows the source so as soon as this guy gets a frame back to the switch so he's getting a frame for from 40 it adds another five minutes sends it to pc.10 when it gets a when he gets a frame from pc.10 it's going to add another five minutes so it resets the counter so the mac address table is always going to be the counter it's going to be five minutes here all the information but it doesn't know about these two ip for example the frame like the the mac address of the dot 13.20 here okay let's go let's clear this so if i go if i ping so dot 10 then again the first it's going to okay let's it's an icmp so let's have a look okay let's let's clear this i'll go to real time and i want to ping the dot um i should pick 20 20 right so i'm going to ping everything yeah 30 and 40. okay the other one i was pinging myself here so okay this pc if when this pc pings all of the pc so ping 10 1 10 ping 30 and ping 40 40. okay and this pc let's bring from this pc so now all the pcs they know they know the they have done the arp yes so that's what i'm doing so ping 10.1.1.10 20 and 40. okay now all the pcs so if i go to this pc and i'll do r minus a you can see it knows the mac address of dot 20 pc it knows the mac address of the 30 and he models mac addresses.40 it knows all of them as well as the switch has learned all of them now so if i do show mac address now knows all four pcs the 21 mac address that's that one there 22 mac address that's that one there 23 mac address that one on the top and 24 mac address the one underneath here right so what we can do here we can do clear mac address table like if it was brand new switch now switch doesn't know anything the pc's knows the arp table but the switch doesn't right so when i send a unicast from this pc i'm going to forward a unicost i see input packet not the broadcast unicos from here this pc is going to send it from this source to this destination for example but the switch doesn't know where the destination is so since the switch doesn't know where the destination is it's going to take this it's going to flood it it's going to send it this way it's going to send it this way and it's going to send it this way until the destination replies when the destination replies then it will send it directly it will just forward it here so it will it won't flood it only whether it doesn't know the destination it will slot it right so if i go back to the switch let's have a look still nothing that's good that's good that's what you want so if i go to simulation and go to this pc and ping do r minus a i still have that information and i'm paying the 40. you see what's going to happen now this is a unicost so if i press play the switch will learn this mac addresses right this source mac address so if i do show mac address now he's learned 9a but it doesn't know where the destination is so since it doesn't know where the destination is it floods it sends it to everywhere now when the 40 replies the switch will learn that on his table it will say okay well i got that the mac address of that one and it will forward it directly to there right now i wanna i want you to pay attention if i if i ping for example if i ping from here to here the switch doesn't know it knows this mac address is on this sport but do you think it's gonna send it they say as well or not we said when the switch doesn't know the destination mac address it's gonna flood it yeah so i'm gonna ping the 30 let's say 30 now right and we'll see now the switch knows this mac address that's 423 they knows there's something in there yeah so look 423 he knows the import he knows the import 23 there's this mac address but here is ping in this vc's mac address so when the when the frame comes in the switch will add another five minutes from 9a but it doesn't know where this mac address is so it's going to flood it flooding means everywhere even the ports that's got some information into them right so if i click play look the switch is going to flood it right now when the pc replies he's going to learn the 30s mac address here so if i look here see the 22 port that's the mac address of dot 30. okay it's going to forward it directly there now if i ping this pc this pc the switch doesn't know what is connected on port 21 so it doesn't know for 21. so why not ping the 421 from here so ping which is 20. what do you think is going to happen switch doesn't know where this is so when it goes to the switch switch adds another five minutes for this as a source but it doesn't know where this is so again it will flood it so it will flood every time there's a unknown unicost broadcast and multicast and now i will learn it the mac address as soon as as soon as there's a frame it will learn the mac address of the destination there you go okay so that's how the switch is learning right so we need to know the switch is actually learning the mac address we have ingress and destination address as soon as there's a for example say that this is a source and this is a destination so once the frame hits the port on the switch the switch will learn the mac address we'll put it on this table with fa01 what vlan is for five minutes because the switch doesn't know the destination mac address it doesn't have it on the table it's just going to flood it it's going to send it this way and it's going to send it this way now this pc is going to ignore it it's going to say it's not for me but this pc will become now the source with this mac address and this will be the destination so now when the frame comes in on the switch the switch will say okay well you came on port 13 this is the source mac address let me put that on the table five minutes and the destination is this i know where the destination is so i'm just going to send it directly to the destination and then later on they will learn about this pc as well so the switches they build the mac address table through learning while examining the source mac address they learn it if it's not on the table they will add it on the table if it's already in the table they will put another five minutes and levels forward if the destination is in the table they will for the forwarded directly if the destination is not on the table they will forward it to all the ports part up or apart from the port they came in they will not they they will slot them it's called flooding as well as for broadcast and multicast now there's two types of switches we have a store and forward switch and cut through switches store and forward they will take all the frame and they will store it in memory right before they forward them so they will store them there making sure the crc once you compute the crc which is a frame check sequence is correct if that's valid then they will forward storing forward switches they will not forward any corrupted frames while cut through as soon as they read the destination mac address they will forward the frames okay so story and forward switches store and forward they'll do the error checking making sure they will calculate this frame check sequence before they forward it so they will not forward any frames has been corrupted they will can store up to 9200 bytes for jumbo frames before they forward them and because of automatic buffering provide the flexibility to support any mixed of ethernet speeds while cut through switches as soon as they read the destination mac address they will forward well we have two cut through switches we have rapid frame forwarding that is as soon as we read the destination mac address will forward let's send them but we're not checking the frame check sequence which means that we could be forwarding corrupt data another type of cut through is frame fragment free check the first 64 bytes making sure that there is not been fragmented the frame hasn't been fragmented if the frame hasn't been fragmented then we can forward it again we're not checking the frame check sequence because we just want speed so both switches this switch the the cut through switches that could be forwarded in corrupted frames while storing forward doesn't corrupt sorry it doesn't forward corrupt frames now both they have the advantages and disadvantages for example store and forward switch with the disadvantage there will be it's just gonna forward something it's going to create that delays while they store in the frames while cut through is fast forward in the frames but cut through could be forwarded in corrupted frames thank you for watching lesson 1.2 frame forwarding this is of chapter one basic device configuration please have a look at my other videos in youtube channel and don't forget to subscribe there this has been astrid krasnichi bye

Channel: Astrit Krasniqi

Views: 295

Keywords: boot system flash, Power over Ethernet (PoE), duplex, speed, auto-mdix, show flash, show history, show ip ssh, ip ssh version 2, Loopback Interface, interface loopback x, include, exclude, section, terminal history size

Id: uotHzHL_gl4

Length: 25min 55sec (1555 seconds)

Published: Fri Apr 02 2021