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We have a problem out on the internet, and it's a situation that exists on all

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of our

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networks, but it especially affects the internet thanks to the routing table

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size.

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The routing table on the internet, as of the time of this video, is rapidly

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approaching

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1 million routes.

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Technically we're at about 980,000 by the time you're watching this, we might

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have surpassed

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a million, and it's just going to keep going up and up and up.

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And so think about the size of a router that needs to look through the entirety
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And so think about the size of a router that needs to look through the entirety

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of the internet

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routing table in order to forward traffic.

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Because any network we have, let's say we've got router 1 here, we've got a

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bunch of hosts

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out here, and I want to send a packet to subnet A.

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Well how does router 1 know where A lives?

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Well maybe we have a default route that points us to the internet.

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Let's say we have router 10 up here, that is in the internet officially.
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Let's say we have router 10 up here, that is in the internet officially.

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Well router 10 doesn't get to have a default route at this point, because

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router 10 has

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multiple paths through the internet, through routers 22 and 37, let's say.

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And so it can't have a default route.

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Instead, maybe it can have some summarized routes in there, which would

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essentially be a partial

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internet route routing table.

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But for the most part we're going to end up having the full routing table size.

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So we've got all of the subnets in the entire internet, and I've got to make
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So we've got all of the subnets in the entire internet, and I've got to make

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sure that

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I look through here and find where subnet A is, and then forward the traffic on

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.

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So maybe eventually we land on a router down here, router 5, and it has subnet

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A attached.

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Meanwhile maybe I've got another link up here and a link over here.

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We've got router 7, and it has subnet B.

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So now if I send a packet to subnet B, same situation, I'm going to follow my
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So now if I send a packet to subnet B, same situation, I'm going to follow my

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default route,

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send it to router 10, it's going to have to look through and find B, and it's

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going to

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forward it to router 22, and router 22 is going to have to do the same thing

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and look through

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the full internet routing table until it finds B and send it on.

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And so the problems that exist is we start to identify them over here.

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First and foremost, we need very high performance routers.

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And those routers must have very high memory for the sake of storing the table.
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And those routers must have very high memory for the sake of storing the table.

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Well this amounts to a very expensive router, which is no good for anybody

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trying to manage

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routers, but it also just makes it very difficult for service providers to be

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able to affordably

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manage their internet routers.

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Furthermore as we might imagine, this is also going to add some amount of

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latency because

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I have to look through this entire routing table with every single hop.
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I have to look through this entire routing table with every single hop.

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I have to look through it on router 10, and then I look through it on router 22

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, and in

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our case subnet B was only a few hops away.

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But imagine if it's a dozen hops through the internet or more.

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Well, we're going to do a lot of internet routing table lookups, and chances

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are that's going

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to introduce quite a bit of latency.

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Now we were using a method on the internet for a long time.

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We still use it in the form of route summarization.

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The problem is route summarization did not stop us from approaching 1 million
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The problem is route summarization did not stop us from approaching 1 million

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routes.

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And there's a few reasons for that.

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First of all, it's very difficult to do summarization when you don't have a

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hierarchical network.

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Now we do have some amount of hierarchy in the internet because different

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service providers

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own different IP address blocks.

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But the hierarchical nature of the internet has also gotten more difficult over

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time just

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as it has organically grown.

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The other big issue that we have out here is the concept of traffic engineering
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The other big issue that we have out here is the concept of traffic engineering

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, which

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essentially allows us to attempt to force traffic one way or the other through

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the internet.

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And how do we do that?

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Well, the way we do that is by dis aggregating our routes, which is the

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opposite of summarization.

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In other words, maybe subnet A down here is a slash 24 subnet.

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And so it's a slash 24 everywhere in our different internet routing tables,
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And so it's a slash 24 everywhere in our different internet routing tables,

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plus 24.

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There we go.

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But there is a particular host out here, a particular web server.

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It's very important where a lot of application and users are trying to connect

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to.

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And so we also send a slash 32 for this device out into the internet.

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This way I can control.

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I can say, "Hey, I want you to see this slash 32 as a better metric than I want

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you to see

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it.
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it.

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Everybody to come down this path in order to get to that specific host."

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And so that is going to create a lot more routes out in the world.

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Because now we're again doing the opposite of summarization, we are actually

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dis aggregating

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our routes.

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So Cisco decided to come up with a solution that they believe is going to help

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resolve

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these specific problems.

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And that solution is the locator ID separation protocol or Lisp, which again,
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And that solution is the locator ID separation protocol or Lisp, which again,

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this is a Cisco

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solution.

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The idea here is to try to eliminate the need to store the full routing table

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on all of

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these interim routers.

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Now again, we said at the very start of this, that every network requires us to

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have a route.

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We benefit on the organizational side because we have a default route as a
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We benefit on the organizational side because we have a default route as a

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catch all.

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But all these other routers, I mean, if I get a packet destined for subna A and

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I don't

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have subna A in my routing table, I'm going to have to drop that.

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And it doesn't have to be an exact match.

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It could be a summarized route, but I have to have a route that represents A.

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So how in

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the world can I say, "Well, let's just install a few routes on router 10.

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Let's draw it up here."

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Now with Lisp, maybe we've got just a few routes on router 10 and still know

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how to get
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how to get

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out to these other subnets.

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So all of our internet routers now just have a partial table.

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Well, the reason that we can get away with this is that we give access to the

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routes via

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a database.

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So we are still going to have a store of the full routing table on some level,

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or maybe

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I should at least say that we've got a significant number of routes located out
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I should at least say that we've got a significant number of routes located out

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here in this database.

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And again, we all have access to this.

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So what's going to happen now is thanks to Lisp, router 10 can receive this

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packet destined

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for router A.

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And it's going to essentially request, "Hey, where is, I said router, but there

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's subnet

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A. Where is subnet A?"

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Well subnet A is attached to router 5.
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Well subnet A is attached to router 5.

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And so I'm going to inform router 10, "Hey, it's where router 5 lives."

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I did not tell it where the identity is.

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I did not say, "Hey, this is where the subnet, or here's what the subnet is

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that you're

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looking for."

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That would be providing the identity.

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Instead, I provided the location.

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This, as we call it the routing locator, or the location for this specific

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route, it's

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attached to router 5, which means all I have to do is know where router 5 is
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attached to router 5, which means all I have to do is know where router 5 is

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here.

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Though I send the packet to router 5 via a tunnel, because the destination has

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to be to router

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5.

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The only way I could change the destination of the packet is to encapsulate the

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original

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destination packet into another one.

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So I'm going to use a tunnel, board it to router 5, and allow router 5 to go

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out to subnet

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A.

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Now did router 10 have to install subnet A into its routing table?

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No.

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It just had to know where it lived, which is via router 5.
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It just had to know where it lived, which is via router 5.

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And so the only routes I need to know are the other routers.

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So now I can accomplish this goal.

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I don't need to have the full routing table on these routers.

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I have access to the routes via a database, but in the end, all I'm given is

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the location

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of where that subnet is, and I forward it to that router.

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So we are going to drill into the details of all of this, but from a high level
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So we are going to drill into the details of all of this, but from a high level

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, again,

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the goal here is to keep this in mind.

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We want to make it so we can have much cheaper routers that can go through

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routing tables

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much faster, reduce the latency, and still get our packets to arrive at the

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destination.