This article we're going to take a look at a topic from the on core exam blueprint. That's exam number 350-401, Specifically we're going to consider lisp, Lisp and, Depending on what literature you read, You might see that that stands for the locator id separation protocol or the location id separation protocol either one we're talking about the same thing. What lisp is going to do is take the identity of a device like a pc or a server and break it into two parts.

The first part is the location. Where is it located and then its identity, Which could be its ip address? That's what it typically is and that ip address of the device it can stay the same as we move from one location to another location, All the way around the world. We can keep our ip address now. If you enjoyed this article, Please do me a favor click, The like button down below and subscribe.

So you don't miss any of our weekly content. Now join me in our discussion of lisp, When I started working with bgp connections going out to multiple internet service providers and having my router hold the entire internet routing table. This is back in the late 1990s. It contained about 60 000 entries, But now the internet routing table has grown tremendously.

In fact, Let's go out and take a look at the size of the internet routing table at the time of this recording. Here we see how things used to be when I started working with bgp and doing multi-homing, And we had about 60 000 routes at that point now we're approaching or we've exceeded 800 000 round entries, And it's probably going to be more than that when you read This article and we can do some route aggregation, But sometimes like. If we're doing traffic engineering, We might require that a specific route be injected into bgp. If we're doing multi-homing that configuration might require that we have the full internet routing table. The bottom line is, We have a problem with scalability with the internet routing table, But there's a protocol that can help us out with that.

The protocol is called lisp lisp and that stands for the location, Id separation protocol and by the way, Lisp is useful. In other environments, Too, Like mobility, Environments or internet of things, Applications, But it was originally designed to address the internet, Routing table's, Scalability issue. Now, As the name suggests, Lisp separates a single ip address into two parts: an endpoint identifier or an eid, And a routing locator or an r-lock. This would allow, For example, A device to move from one location on the internet to another location and keep its endpoint identifier or its eid, While updating its routing locator its r-lock, And when we're trying to locate a specific endpoint identifier. What we can do is ask a map resolver and a map.

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Resolver is going to give us information about the current routing locator for that eid. In this case, Let's say that client, A wants to talk to client b client b is currently at lisp site. Two and client a is at lisp site one and that server lists site two. It's got an ip address of 198511001.

Well, That's going to be the address of the routing locator, That's where we need to point traffic to get to client b and the way the map. Resolver knows that client b lives at that address is that the router at lisp site 2 registered that information with a map server and commonly we'll have the map resolver and the map server on the same device like a router and our locks routers representing different lisp Sites t register their information with the map server and then somebody that wants to get to one of those devices t can request information from the map resolver and the map. Resolver is getting information from the map server. We see that commonly written as ms. Mr, For example, Let's say that that router at lisp site 2 wants to register with its map server. What it's going to do is it's going to have information stored locally.

It knows that the network of 19216810624 is available at the arloc router of 198511001. Well, It's going to send that information up to the map server and that map server is going to make an entry in its table. So anybody wanting to go to any ip address in that network, We're going to say, Go to this rlok router and that map server is going to send a confirmation by the way to that registration message. That's going to go back to our rlok router and once we know the r lock that we're sending to the packet that we want to send to another site, We're going to add on a lisp header and we're going to add on a udp header. And that's going to be encapsulated inside of an ip packet with the r-locks, Acting as the source and destination ip addresses notice that the source in that outer header is 20301131.

That's the address of the r-lock that router at lisp site, 1 and the destination is the rlock at lisp site, 2, 198511001, And by the way in that lisp header. It can contain information such as a vrf identifier or a vpn identifier. This is going to give us segmentation and isolation and in the udp header, You might want to make a note that the udp port number that's used by lisp to send data is udp port, 4341 and again. Our goal here is for client a to send traffic to client b. Well, The router at lisp site, One that's going to do the encapsulation of that traffic.

It's called the ingress tunnel router or the itr. It's going to do the encapsulation. It adds the lisp header. It encapsulates everything in that new ip packet and when the packet reaches the destination, The router that does the decapsulation that unwraps everything is going to be that router in our case at lispsite2, That's going to be the etr, The egress tunnel router. So in this example, Client a wants to communicate with client b, So the lisp router at lisp site 1 is going to query the map resolver to say, .

I want to go to this ip address of 19216811 and our map resolver says: oh . I'Ve got an entry for that network that contains that ip address. You should go to an rlock at an ip address of 198511001. So that's what happens. Client a goes up to its itr at lisp site one, And it's going to send traffic over to the r lock that it was told to go to by the map.

In this example, We only had one network at lisp site 2, But we could have had hundreds at that site, All of which were available using that single route locator. This gives us an idea of how lisp can help address that routing scalability issue. We didn't have to contain all those networks that might have been list beside two. We just needed to know how to get to the routing locator and we had another table.

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