CCIE Topic: 1.1b Layer 2 Protocols

hey everyone welcome back i'm charles judd i had a really good weekend of study this past weekend but man what a monday i woke up as i normally do around 6 a.m because i like to get an early start while the house is quiet i like to do some studying and labbing and this morning i sat down to discover that my main computer that i used for this was just completely unresponsive and so it really derailed my mooring and there's a time when that would have been enough to just make me throw in the towel for the day after spending hours troubleshooting that but i was eventually able to get things back in relatively normal working order so that i could make this video for you and i wanted to share that just out of transparency because we all have those moments when our study plans they get completely derailed we get completely demotivated and so for me it's important that i have a disciplined study routine so that my discipline will carry me through the times that i'm not particularly feeling inspired or maybe i'm feeling discouraged so just wanted to share that as a word of encouragement i also wanted to say thanks for all the encouragement that you sent to me so far the outpouring has been absolutely incredible and unexpected so thank you so much for that thank you for subscribing thank you for sharing it's been absolutely amazing i read through every single comment from here on youtube from my website and my social media channels and it's been great to see so many people following along as they're on their own ccie journey so having said that let's jump into today's content continuing down the ccie enterprise infrastructure blueprint the next subsection under our network infrastructure topic is layer 2 protocols and we're first going to look at cdp and lldp both of those are layer 2 link layer protocols and they help us discover directly connected neighboring devices so first let's compare those protocols and then we'll jump into a lab topology and see how that can be useful during the lab exam so first let's mention that functionally these protocols are pretty similar cdp is the cisco discovery protocol and that's a cisco proprietary technology whereas the link layer discovery protocol or lldp that's a vendor-neutral version of that back in the days of cdp version one cisco used to actually license that out to other vendors so for example you might see cdp version one on an older hp switch i've certainly ran across that before but with vendors outside of cisco these days lldp has pretty much taken over those duties cisco devices do support both protocols so in most cases it's really just a matter of preference with what you're using in your own network if you have a mixed environment if you have both cisco devices and devices from other vendors then you'll obviously want to be more mindful of what you're using also there's an extension to lldp called lldp med or lldp for media endpoint devices that was added to address ip phones in regard to voice over ip needs things like quality of service power over ethernet and so on and that's really the primary reason we would use lldp with cisco so that we can communicate between non-cisco endpoints such as maybe a non-cisco iphone and our cisco based network we can use lldp to assign vlans or poe requirements to iphones using that so the big differences here between those are that by default we have cdp enabled on cisco devices whereas lldp is disabled by default cdp version 2 is the default version that's going to be enabled and that is backward compatible with version 1 in case you have older equipment and of course you can see the difference in the hello and hold timers between the protocols both of those protocols do send in clear text so that can be a security issue you might want to limit these protocols to particular ports or you might want to specifically disable them for some interfaces and again you can see that of course cdp is cisco proprietary lldp is vendor neutral so let's take a practical look at using these protocols here i'm on a device named switch one and i'm pretending that i have no idea about what my lab topology looks like so i'm just going to start by beginning a sketch i'm going to try to sketch out the topology and i'm going to try to discover what that looks like using cdp or lldp so i'm on switch one here so i'll just add that to my diagram and very simple show command show cdp neighbors we can see the device id so for example we have a device named switch 2 the local interface on this switch that it's connected to we can see the hold time and we can see the port id at the very end which is the remote interface that we're connected to so this tells us that switch 2 is connected here on gig zero slash zero into gig zero slash two on switch to itself now we also have a second device switch three connected to gig zero slash one and just as it is with switch 2 the local interface that we're connected to on that switch is gig 0-2 so let's go ahead and add these devices into our topology we know we have three switches currently so we'll add switch to we'll add switch three switch two connected to gigs zero slash zero switch three connected to gig zero slash one now obviously since i'm in a lab environment i already have connections to these other switches but in the real world what if we didn't have those what if we were actually trying to discover neighbors and connect into those well we could say show cdp neighbors detail and that's going to give us obviously more detailed information so if we scroll up here we see switch 2 and we see an ip address for switch 2. so that's going to be very helpful for us we have a management ip address now that would hopefully allow us to connect via ssh or telnet into this other device if we scroll down we'll see the same thing at the bottom of our output for switch 3 as well so very helpful information now let's jump over to switch 2 and this time let's use show lldp neighbors just to show you that we get a similar output here and i'll actually run the cdp version of that command as well so that you can see that the outputs are essentially identical so let's continue to add to our diagram we can see what we already know about our connection to switch one we can see that our local interface is gig zero slash two connected into gig zero slash zero on switch one but now we've learned some additional information we have redundant connections now we see those to switch three locally we have gig zero slash zero and zero slash one connecting over there also using gig zero slash zero and zero slash one on the far end so let's go ahead sketch that into our topology and just for completion let's go to switch three we'll say show lldp neighbors and we don't see anything new here we see information it looks like we already know so now it looks like we have a complete view of our simple lab topology one more thing to show you we can run show cdp and that's going to give us information about our timers and it's also going to allow us to verify the version we're using you can see we're using cdp version 2 advertisements same thing for lldp we can say show lldp and that's going to give us more information it's going to list our hello and hold timers let's look at udld now unidirectional link detection this is another layer two protocol and we typically see that used with fiber optic interfaces where we would have two strands of fiber one dedicated for transmitting data and one dedicated to receiving data they would both connect into the same fiber module port but the tx and rx are separated into separate strands of fiber udld is used to detect if a unidirectional condition occurs so if our fiber connection stopped passing traffic in one direction that could cause maybe a spanning tree loop or a variety of other problems really if we have two switches configured for udld they communicate by exchanging hello messages to the well-known mac address seen here each device would send its own device id which is typically its serial number along with a port id and a timeout value if the far end device if the remote device doesn't return that hello message if it doesn't echo back those values to the original switch it's assumed that there is a unidirectional condition in place and depending on what mode we're in depends on what happens on that switch port we have two potential modes of operation we have normal mode and aggressive mode under normal mode if a unidirectional link is detected that port will be marked as having an undetermined state and a syslog message will be created in aggressive mode which is the recommended mode of operation if a unidirectional condition is detected the switch will begin sending a udld message at one second intervals for eight seconds if none of those messages are returned then the port will be placed into an error disable state so we're using the same topology here as we just looked at with cdp and lldp let's jump on our switch here i'm already connected to switch 3 and let's look at how we can configure udld so first let me clear off some space we go under global configuration mode and let's say udld and use contextual help we can use the message keyword option if we want to set the udld hello time if we want to do that and we have enable and we have aggressive so you can probably surmise that if we just say enable that's going to enable udld for normal mode while the aggressive keyword will shut down our interface if there's a udld condition and that is the recommended option so i'm going to use that command now i do want to point out here that if you notice our help output this tells us that this enables udld globally on fiber ports and again that's typically where we would use udld but we can use that for twisted pair ethernet cable as well however that does require a bit of a different configuration the recommendation from cisco is to use udld always with fiber and to enable that globally just as we did here but i'll show you how we can also do that at an interface level in fact if we say do show udld just another verification here you can see that on gig zero zero for instance it tells us that udld is disabled so this has not enabled udld for any of my gigabit ethernet interfaces we can do that by going under interface gig zero zero we can say udld let's look at our contextual help and we have the option of port and we have only one option listed as aggressive now if we just hit enter here that's going to enable normal mode or we can append the aggressive keyword which i want to do and that's going to enable the recommended mode where the port would be shut down now if we back out say do show udld this time you'll notice that now gig 0 0 is listed as enabled and we are in aggressive mode now what happens if our port interface gets shut down let's talk about a couple of ways that we can recover from that we can simply say udld reset which is a global command and you can see we're told no ports are currently disabled by udld but that would reset all of the ports that have been shut down by udld if we needed to do that we can also of course just bounce the interface with a shut followed by a no shut command or we can use some of those automatic error disable recovery options that we looked at in a previous video so we can say air disable recovery cause and if we look at contextual help near the very bottom of that we're gonna see our ud ld condition so this is going to enable a timer to automatically attempt to recover from udld errors where the port has been disabled now we could also say recovery interval as we looked at previously if we wanted to set our timer interval shorter again the default for that is five minutes which is quite a long time so you're probably going to want to set that recovery interval smaller if you're using the automatic recovery option so that's a look at some layer two protocols relevant to the ccie lab exam i hope you found this content useful and i want to thank you for taking the time to watch i'll see you soon with another video about what i'm learning

Channel: Charles Judd

Views: 2,059

Keywords: cisco, ccie, cisco enarsi, ccie enterprise infrastructure, cisco enarsi 300-410, cisco encor 350-401, ccie lab, my ccie journey, ccie training, layer 2 switch, switch administration, 1.1b layer 2 protocols, ccie blueprint, cisco discovery protocol, cdp, link layer discovery protocol, lldp, unidirectional link detection

Id: hrQff3fTViY

Length: 13min 56sec (836 seconds)

Published: Mon Jul 20 2020