IPv6 SLAAC and DNS Overview | Cisco CCNA 200-301

[Music] and welcome everybody it's great to have you my name is Keith Barker I'm a CC CI and this channel is 100% focused on the techniques and topics and technologies around CCNA and currently that flavor is 200 - 300 and it's great to have you I had a request to do a packet tracer lab on slack not the nut like commute not the teamwork app on the internet and that people use on their computers or other the stateless address auto-configuration facility that is involved with ipv6 so I thought well before I do a lab and a packet tracer lab that gives you a chance to practice it I probably ought to spend just a few minutes here in this video sharing with you how it works and what our options are and then give you an opportunity to see how its configured and then we'll follow it up with a packet tracer lab so without further ado let's talk about why we'd use automatic address assignment of any type imagine we have two or three hundred clients PCs devices mobile devices laptops desktops servers nails if we need to sign all those addresses manually that takes a lot of work so in the world of ipv4 we use a feature called the DHCP the dynamic host configuration protocol we know it we love it and it's very effective and giving lots of people the correct IP addresses along with options like their default gateway and the correct DNS server to use and so forth well in ipv6 we also have the option of using DHCP for version 6 but we have a couple different options beyond just DHCP one of those is SLA AC let me show you share with you a topology and then let's talk about some of our options and I'll walk you through how to configure it and verify it as well so let's use this white board right here and let me go and bring a pin up I'm not sure what it is but I i dial everything in for the presentation I then I at the last minute like oh I'm gonna need a pen there's a pen alright so with ipv6 the option of stateless address auto-configuration also known as slack here's how it works you go to your device whether it's Linux or Windows or Mac OS what-have-you and there's gonna be an option for ipv6 one of those options is Auto config and if you select Auto config what its gonna do it's automatically gonna get an IP address on the network and you might ask well how in the world is on what network it's on and here's how it works we take this router this router interface right here and it has an IP address and we enable the router for ipv6 unicast routing so if the cisco router that's literally the command you do so we have an address here and all automatically that router if it's ipv6 unicast routing and it has an ipv6 address it's gonna issue what's called a RA a router advertisement periodically and basically that in that router advertisement it says hey this is the network and you know what in fact I've got one let me let me hide that pin for a moment and let me show it to you I just captured it about I don't know about ten minutes ago and it is it is somewhere close let me bring it up and there it is okay so let me bring this in and just check the screen to make sure we can all see it great all right yeah me minimized as well all right thanks for your patience there so this right here is a router advertisement from a Cisco router that has ipv6 unicast routing enabled so right here it says it's a router advertisement and router advertisements in ipv6 leverage the protocol of ICMP so down in this router advertisement it's advertising a lot of information including the network or networks it's connected to so what this says right here is that this piece right here of the router advertisement indicates hey this is the 2001 DB 8 6 78357 network with a 64 bit mask that's what's in this router advertisement and so when the PC connects to this network and says I want to do Auto config it can go ahead and do our solicitations color router solicitation it's asking hey anybody write any routers out there so that goes out to FF 0 2 colon colon 2 that's the ipv6 multicast address for all routers so a client says hey what network is this I'm asking for basically a router solicitation which would trigger a router to issue this router advertisement so we don't have to wait 200 seconds the interval might be we can just go ahead and do a request we get this advertisement from the router and then the PC looks at this address this networking says oh this is the street that's the 64-bit network that I want and then it will go through the process of automagically configuring a host address for that subnet and it also goes through a process called duplicate address detection just to make sure he's not gonna he or she is not going to use the same exact host addresses mails on that network so the default router information and how to get off the network all that information can be learned via the router advertisements all right so if we are using SLA a/c that's the mechanism behind it that's the stateless other automatic address assignment are out and I could dress configuration this to see there and that's how the PC works gets an IP address just by doing a router solicitation finding out what the network is and then creating its own host portion on that networking it's on the road alright so that is also called stateless from a DHCP per state is stateless because no one's tracking that client like hey what address did you get and I'm keeping track of that if we were using DHCP for version 6 we have an option I'll put v6 there we also have an option for stateful hey I get right out here I'm keeping it all keeping all that little box we can also use with DHCP we've used state full and was stateful basically it works like ipv4 is DHCP where the client looks for a DHCP server and then gets an IP address assigned by a DHCP server and then uses that ipv6 address so stateless is when it does it on its own stateful is when a DHCP server hands out the IP address now there is a really big problem with a lot of this and let me share with you what that is the problem is if this client is stateless using slack stateless address auto-configuration in fact the acronym slack is s and L and a and a and C so stateless address auto-configuration if it's using that and it gets its own IP address let's say the client is using us put in it's going to have some wacky long the dress but list for grins say gets an address now the question is is this PC ever gonna want to use DNS and the answer is yes clients and computers we use DNS that's where we can type in a name like a URL like Bubba comm or CBT Nuggets comm or something else and behind the scenes it resolves that name to an IP address that's DNS well if we're using stateless Auto config which we're doing right here how do we learn DNS information now this this is a challenge that's being addressed pretty aggressively and there's some new standards on saying hey this router is doing router advertisements why not just be able to tuck in or include that information the DNS server information in the router advertisements okay great when that's standardized and every is doing it it'll be great however on a lot of gear it's not standardized so but we still need this PC to use the DNS server and we don't want to have to manually configure that so one other solution is this we could tell the PC yeah go ahead and do Auto config but we could also tell the PC for your address use Auto configuration but also go ahead and use DHCP for the other options when I say other options I mean things like a DNS server or a domain name or other details that that client may need to use so it's like a it's like a split the clients doing looking at the address the network and doing Auto config for its IP address for ipv6 and then it can reach out and go to a DHCP server and say hey I don't need an IP address what I need is other information such as the DNS server to use another way we control that this is interesting when we control that is we have the router in its router advertisements play with two flags specifically for this now these flags are labeled M and O not zero but oh and the M means managed and here's how it works in fact let me show you one and I'll show you how it works I've got a capture of that also I did it about 45 minutes ago just got out my packet analyzer and okay so in this graphic right here in these flags currently everything's set to zero for the flags and so if the flags are set to zero for managed this means if it's zero the client when it sees that router advertisement and it sees this managed flag to zero it's not set that tells the client hey you're on your own regarding getting an IP address if the managed flag is set to a one and on that means to the client hey you need to get your IP address from a DHCP server along with any other options of that DHCP server me hand out to you for ipv6 the other option here is the this guy right here which is the oh so that's the oh flag for the other configuration so if the managed is set to zero which means you're on your own get your own IP address figure it out from the router advertisement but we have the other bit the other configuration bit set to one that's what tells the client okay I'm getting my IP address on my own but I am going to go ahead and talk to the DHCP server and ask them about the other options such as hey what DNS server should I use that's it that's how the EM and obits work inside the router advertisements so let me clear that off and I'll so let me show you what a couple these look like so this so this is a router advertisement with the O and the M bits off I think I have another graphic here here we go here's another one where I have the M bit set 201 which means get you a client you see this router advertisement I know the network's here but what I want you to do is I want you to go ahead and get your IP address assignment from a DHCP server which would be stateful DHCP for ipv6 and then have one more and that has the the öbut or the M bit is not set which tells the client get your own IP address figure it out and from the network prefix I'm giving you and this RA and the one in the the bit set for other says go ahead and contact DHCP server and we'd have to supply what that DHCP server is to go ahead and back off that just was again so the other I'm getting too far ahead of myself so the other bit if it's set to on means configure on ipv6 address and then go ahead and use DHCP services to learn other information like so the question is how do we control a router to force it to set the M bit 201 or set the obut to a one and the answer is we do it in a router configuration if it's a Cisco router so I'd like to I'm in fact I can just put those in fact let's do this if you've got packet tracer version 7.3 or can I know it supported in 7.3 maybe even older versions let me show you how you can configure the interface and verify that it's actually working as indicated and they'll give you a nice walk through if you want to practice this on your own so we'll practice sitting up the router will set up the ipv6 interface will enable ipv6 routing will enable no bit set for the M or o that will enable the M bit and then will enable the o bit and that way you'll have a full range of motion on how to configure it all right so let's bring up packet tracer and survey says there it is so blank screen blank Cavan's green field so you can start just like I'm right here if you want to practice this and let's go ahead and grab I'll click on routers and then grab a 29:11 boom right there and let's go ahead and click on so we could put a switch in there or we could just take a switch yeah the switch isn't gonna buy us much so I'm just going to go ahead and take a PC and use a crossover cable to go ahead and connect it directly to the router and that's the kind of cable we would need because they're both expecting talk to us which but we're time to talk to each other so we use a crossover cable and let's go to the router and let me slide this over here and for our plan let's use this let's use this address right here 2001 DB 8 6 7 8 3 20 : : and we'll use 1 for the router and then we'll use Auto config for the PC all right back to packet tracer here we go alright so at the router let's make that window a little bit bigger they check my feedback monitor here alright look you know what that's too big all right let's make it a little bit bigger great we'll click on the CLI and we'll say no we don't want to do the initial configuration dialog and I'm not going to do too much more than just the basics of what's needed here so config T interface gig 0 cero which party should bring it up and that was shut down good start and let's do a set up the IP draw song gig 0-0 ipv6 address 2001 DB 8 6 7 8 3 let me check the IP address 20 ok so we'll put in 20 here : : 1 with a slash 64-bit mast boom we've got an ipv6 address now let's do a do show ipv6 interface gig 0/0 and check this out this says here's my global address that we just configured fantastic here is its link local address that it automatically configured non-routable just good for the local link it's on and it joins some multicast groups including FF 0 2 : : 1 that's everybody who speak in ipv6 is a member of that multicast group oh and what he hasn't joined yet is he hasn't joined the all routers multicast group and that's because we didn't enable ipv6 routing let's do that next so if we do a I'm gonna go back to global config ipv6 unicast routing and then now let's do a do show doing the do just because I'm in configuration mode do show ipv6 interface 4 gig 0 not Jeff gigs slash 0 and now check this out it's now joined the all routers multicast group which is great so now if somebody does a router solicitation they're gonna send it to that multicast group for all routers then the router can hear it and send the router advertisement including the network information also laugh right check it out all these down here and below it's all showing that we're now doing router advertisements because we're doing ipv6 unicast routing fantastic let's go finish our config um where were we interface gig 0/0 well they do show run just so I can look at the config alright so there it is ipv6 address and oh ok so right now we're doing router advertisements but what we're not doing is we're in the router advertisements the M and the obits they're all set to zeros meaning we're telling the client the the client gets an IP address they're just gonna do slack on their own and our AC these are a messages little slack on their own and they won't have DNS information and we it won't have a DHCP server assign ipv6 address the client will do it on its own and we can verify the to just go to client and here on the client we'll go to config and we'll go to fastethernet zero and we'll say right here under ipv6 Auto config and it's done if you go to settings I'll look at this it also has an ipv6 default gateway which is our one or not our one its router zero we didn't renamed in Marwan so this PC is good to go if we go to the desktop and go to a command prompt and just to an ipv6 config that's a little thing in the emulator here in packet tracer ipv6 config slash all there is this link local address there's this ipv6 address there's this default gateway which is the link local address of the router and it doesn't have a DNS server at the moment so this is this is an example of stateless Auto config and not using DHCP services in any way now if we wanted to what we could do is we could configure a DHCP server and then we could tell the client with the router advertisements hey the obut the other configuration information is set to a one go ahead and get dns information from the dns or get the dns get the DNS server information via DCP now to do that they walk you through it well simply well first of all if we're gonna use DHCP to provide options to a client we need to have a DHCP server and so I only have one router right here so I'm going to create a pool for an ipv6 DHCP server where we can include the DNS server information so we can have the client get it from us so let's say ipv6 DHCP pool and we'll call us our pool not my pool not your pool our pool so we're going to call our pool and we have some options here oh well DNS server is all I want to add here let's say the DNS server is 2001 ABC - 3 : : 5 I'd make sure don't we see it we'll say yeah but that's the DNS server we're heading out so now we have this pool this ipv6 pool we're not we're not specifying a network at Wrestle I wanted to hand out the IP address are the DNS information from the DHCP pool now to go back and actually make this work we're gonna go to interface gig 0/0 and say ipv6 DHCP server question mark now on live gear there's also an option called automatic which means it would automatically find a pool but this case we're just gonna refer to the DHCP pool we just created which was called our pool all right and let's do a quick show do do show run and I run I run so far away okay so there's our pool with the DNS server in it and there's our gig 0 0 and it has an ipv6 address it has ipv6 DHCP server our pool if we go back to the client and I'm just gonna bounce the client physical is there there should be a power button here somewhere oh there there click off click on and as it powers out let's go back to config and fastethernet and let's put it back to auto config and let's go back to desktop and we'll do a we'll do an IP config ipv6 config /all alright so it's still getting its own IP address with slack but check it out no DNS server it's not learning a DNS server why why is that did you catch it the answer is on the router interface I did not specify whether or not to set the öbut to on and as a default they're all off if we go back and look at this packet capture I did a few moments ago right here so we need this other convey bit set in the router advertisements but currently without any what we have is this we have the the managed address flag which is saying hey get your IP address directly from a DHCP server and all the other options it's off and the other the OU flag is off which means hey you're on your own for IP address but we need to go ahead and have you use DHCP to get the other options like a DNS server and by default all these bits right here that m and the obits are off so here is the secret sauce in training the router to set the bits for M or o2 and on so if we do M we're set for manual for configuration of an IP address and all the options if we set o the clients on its own for IP addresses and the client will then go to the DHCP server for the other options including DNS so let's go back to the router and here's how we're gonna do it just to make sure on the right interface I was a good thing and we're gonna do this ipv6 a question mark and it is ndnd stands for neighbor discovery space and here is how you set those flags if you want the M flag set to on which tells the client to get an IP address from a DHCP server that be stateful DHCP we're gonna use the manage - config - flag that turns the M bit on if we want just the obut on we'd use this option other - config - flag and that's we're gonna do here so let's do a up arrow key other and we're done let's do a show run so we have our pool but it doesn't have any all it has is DNS information the DHCP pool and then a weigh-in gig 0 0 we're specifying that that's the pool we want to use our be available to us and then what here we also have the other bit or the other the obit set with this command here so what should happen is the client should be on its own for an IP address but it should also go out to a DHCP server for the other information including the DNS server let's test it all right here on PC 0 all right so see how here it still says no DNS server let's do an ipv6 I haven't tried this yet uh let's do uh slash renew oh it didn't bark so let's go ahead hit the ipv6 config space slash all yeah still doesn't have a DNS server I hear something to do I'm gonna bounce that bubby that big that bad boy I'm gonna powerbomb turn back on also we could do is just go to the Glo config fastethernet and force it between static and Auto config and that should break at least as well alright so Auto config is set if we go up to global settings and Auto config I don't see the DNS server right here hmm well less troubleshoot as to make sure I've got my detail set up on the router okay so show run so I've got my pool the DNS server that's all I want in there and it's called our pool and it is a DHCP version six server in high pv4 and on gig 0 0 I have ipv6 it oh oh did I do it on the wrong interface I don't see the the other config sitting there maybe I was in CI I don't see it let me go ahead and put it in config T to show history not Hilary history so that's my configuration history buffer right there I said it I set that command so I'm gonna right click copy it interface gig 0/0 and paste and then to show run alright it's definitely there now I'm not sure what happened it was I'll say I'll take the hit for that one but it wasn't working and the config wasn't there and that reinforces it so now that that's done let's go back to our client and we'll go to static for a moment next I'll go to fast ethernet got a static and then Auto config and then just take a peek under global settings and there look at that right there our DNS server shows up now and if you get a desktop and we do a high peak ipv6 ipv6 config I power it off and on that since then and we'll do a ipv6 config slash all and check it out right there there's our DNS server all right well that was fun and a little extra troubleshooting was not intended so it does a little extra bonus all right so quick summary of this discussion slack is the automatic address assignment for a PC or a computer on an ipv6 network it's going to look at the Escondido router solicitation gets a router advertisement looks at the advertised prefix the network and then says great I'll go ahead and create my own host ID on this network sets it up make sure it's not already news with dad duplicate address detection and then it starts to use it the challenge is it doesn't have the other options including things like what DNS server do I use I configured my IP address on my own so we can do is we can have that information in a DNS server or in a DHCP server the datas information in a DHCP server and then use the other bit set on the router interface so that when the client sees it it says oh I'm gonna do Auto config for my own IP address but I'm going to reach out to a DHCP server and ask for the other information including what the DNS server is alright so there's an opportunity to understand what that is and how it works and also a little practice in packet tracer if you want to dimpling also coming up I have another lab that's going to focus on slack and DNS information being learned via DHCP so if you want a full lab to practice with stay tuned for that one as well also I want to point out that as you study for your CCNA I realize as a double CCIE I realized that the CCNA is not the end-all be-all to everything you'll ever need to study but I can guarantee this having if you want to work in networking having the knowledge from the foundation of CCNA is a great idea so if you don't have it yet you to pursue it get it as a stepping stone on the way to your full career and journey and then after CCNA is done then take a look at the next logical step and the next logical step just keep on learning so CCNA is a a component in your journey in the world of Cisco in the world of networking and I love this channel to be an additional resource for you and support in that aspect of your CCNA and then as you master that and keep on going just don't stop learning alright it's been super fun chatting with you and talking with you about the slack and the Auto config and the M and the O flags in ipv6 router advertisements and I'll see you my friend in a very next in a ver now Keith you're doing so good I'll see y'all also by the way if you enjoyed this video or learn something from it give it a like and if you haven't subscribed please subscribe to be alerted when we have new videos that come out and I'll see you in the next live event here on the Keith Barker channel thanks everybody have a great great rest of your day [Music]

Channel: Keith Barker - The OG of IT

Views: 32,503

Keywords: ccna, cisco, 200-301, Cisco CCNA, Cisco Certification, ogit, Keith Barker, ipv6 addressing, ipv6 slaac, ipv6 slaac configuration, ipv6 slaac explained, ipv6 slaac packet tracer, ipv6 slaac vs dhcp, ipv6 slaac cisco, ipv6 slaac wireshark, ipv6 slaac configuration cisco, slaac, ipv6, stateless address autoconfiguration, dhcpv6, packet tracer, cisco ccna 200-301, cisco ccna certification, 200-301 ccna, ccna 200-301, network engineer

Id: eq_eUqPWJwI

Length: 27min 33sec (1653 seconds)

Published: Wed Apr 15 2020