OSPF Multi Area Explained

hey what's up guys welcome to sir pros in this video we're going to be looking at multi area OSPF okay so multi area OSPF this is the expansion to the single area OSPF video if you haven't watched that video and you're not familiar with OSPF then you're in the wrong place go check that video out give it a like leave a little comment and come back when you're done okay so if you have watched that video then our little five Reuter Network should look familiar you will also know that OSPF floods link state information to all neighboring routers using LSAs each Rooter then takes those LSAs and builds a linked state database they then run the SPF algorithm finally the rooters choose their best routes based on the route cost and that's fine in our teeny-tiny Network a less think beer imagine you have a hundred or 500 or even a thousand rooters now first of all is highly unlikely your network will look like this but let's just take a second to admire the beautiful symmetry of this network okay so now we've taken that in what do you think will happen when using single area OSPF in this massive network well we're going to run into a few problems problem number one the link state database will be huge every router will have a copy of the same LSD be filled with information about every router and every link within the entire network probably information that it doesn't even really care about all of this information can even start to fill up the disk space problem number two not only was the database be huge so will the routing table with a route to each subnet this means every time a packet comes in your Reuters may need to search through hundreds or even thousands of routes before it finds the right one this will also impact the disk space and even the processing power of the route itself issue number three updates everywhere anytime a link or Rooter is changed disabled or enabled cables are pulled out cables are plugged in updates are flooded throughout the entire network not only that but each Rooter will have to rerun the SPF algorithm every time an update is sent introducing OSPF multi areas the solution to all of our OSPF problems using multi area OSPF will reduce the size of our link state database summarize our routing tables and it will contain update messages to a single area the price we pay for all this o SPF goodness complexity and a little extra time let's take a closer look at how this actually works but first let's mix it up a little and use a brand new network diagram so we're going to split these rooters into areas an area is simply a group of Reuters now it goes about saying this is a very simple five Reuter Network so no need for multi areas however for the sake of simplicity imagine each area containing multiple Reuters generally speaking is recommended to have less than 50 Reuters in an area but there's no real harp limit it already depends on the processing power of your Reuters when it comes to designing your OSPF areas there's some planning that needs to be done first of all you need to start with area zero this is known as the backbone area every other area must join to the backbone area secondly to benefit from OSPF areas you need to plan your subnetting as you can see here everyone has all of the ten dot something networks an area too has all of their 172 16 some think networks this really is the key to successful OSPF areas let's take a look at how we can summarize our roots root 2/2 and root of 3 are known as area order rooters or ABR's these are special reuters that have interfaces in two or more areas this gives them the power to summarize roots from each area for example root 2 2 and take all of the 10 dot something networks and say hey any package to the 10.0.0.0 network send them my way root 2 3 also says any traffic for the 172.16.0.0 leave it to me and they both sent a single route to area 0 Ruta - Andrew - free will also summarize area zero subnet - area one and two this route summarization instantly wipes out all of our OSPF problems the routing table is drastically reduced because huge subnet chunks are summarized into a single route as a result of this there are far less LSAs flying around reducing the size of the LS DPS the updates are usually contained within their own areas as well for example Rooter 1 doesn't care if the 172 or 16.5 dot 0 link goes down all it knows is root 2 3 has all of the 172 or 16 subnets so it just sends it over and let's route a free deal with it this stops the need to run SPF every time a change occurs unless that change happens within the rooters own area the exception to this would be if the ABR interface went down itself it would then need to tell the other areas has something terrible has gone wrong so after some careful planning and a little extra time we now have a scalable OSPF network using multiple areas before finishing we've already looked at ABR's but there are some others backbone Reuters these are all Reuters that are in or partially in the backbone area so in this case root of one root of 2 and root of 3 our backbone Reuters area board of riches we've already looked at these and their ridges that connect to more than one area ruta to Andrew to free our ABR rooters internal rooters these are all rooters within a single area but not the backbone area ruta for Andrew to five are known as internal rooters lastly autonomous system boundary ruta ASPR these are Reuters that connect to other non OSPF routing protocols such as BGP or TIG RP for example this may be your edge router connection to the public internet or another autonomous system network that's it for multi area OSPF with a bit of planning and some extra time you really can scale up her SPF far and wide if you liked this video remember to Like comment and subscribe it really does keep these videos coming thank you for watching

Channel: CertBros

Views: 97,437

Rating: 4.984127 out of 5

Keywords: open shortest path first (protocol), multiarea ospf, routing and switching, cisco, cisco training, ospf, eigrp, open shortest path first, link-state protocol, link state protocol, link state advertisement, cisco routing, ospf explained, ospf routing protocol tutorial, open shortest path first protocol, how ospf works, ospf routing protocol, routing & switching, ccna (field of study)

Id: PIMnj2oqYIo

Length: 8min 6sec (486 seconds)

Published: Mon Dec 10 2018