Blog Post

In this section, we will discuss the SD-Access control plane. You can also refer SD-WAN blog to learn about the workflow of SD-WAN. The SD-Access uses LISP or Locator Identity Separation Protocol as a control plane mechanism. LISP separates the location of a device from its identity by maintaining a database.

The following topics will be covered in this blog:

• LISP Mapping System
• LISP Approach
• LISP Terminologies.
• LISP Header

LISP Mapping System

The LISP mapping system uses MAP System (MS) & MAP Resolver (MR) as an analogy that we have in DNS.

 
– DNS resolves IP Addresses for queried Name

– LISP resolves Locations for queried Identities

LISP Approach

Lisp namespaces

• EID (Endpoint identifier) is the IP address of a host.
• RLOC (Routing Locator) is the IP address of the LISP router of the host.
• EID-to-RLOC mapping is the distributed architecture that maps EIDs to RLOCs (routing locator)

The below diagram explains how LISP works:

• The End client will be connected to the End Node.
• The end devices will be inside the End Point Identity (EID) Space.
• In between SD-Access Fabric, we have a collapsed Border & Control Node.
• In between the Edge node and Border node, we have an RLOC space that represents the location.
• In the mapping system (Control node), we will have EID to RLOC mapping. The main purpose of this mapping is that if the source user doesn’t know the destination, then you can do the query to the mapping system and this MAP server will send the response to the destination.
• The whole mechanism works as At the moment the End Points will get connected to the Edge device, they will send that entry to MAP Server so that Mapping Server knows that Endpoint to the Location shown in the above diagram.

Terminologies

Let us understand the terminologies used inside the LISP.

1. EID: End-point Identity
2. RLOC: Router Location
3. ITR: Ingress Tunnel Router
4. ETR: Egress Tunnel Router
5. XTR: It represents both Ingress & Egress Tunnel Router.
6. PXTR: Proxy Tunnel Router
7. MS: Map System
8. MR: Map Resolver

Header Format

The LISP contains five different bits:

• N (Nonce present bit)
• L (Locator status bit)
• E (Echo Nonce request bit)
• V (Map version bit)
• I (Instance ID bit)

                                                                                   Fig:  LISP IPv4 Header Format

This article explains how the LISP control plane mechanism does work in SD-Access. We hope that while going through this article, you will be able to understand the basic workflow behind LISP in SDA fabric and how Endpoint Identity (EID) gets mapped to Routing Locator (RLOC).

In continuation of this blog, we will discuss how VXLAN works in the next blog for SD-Access where we will discuss the VXLAN protocol and its terminologies along with VXLAN Header.

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Author
Sani Singh
Consultant – Enterprise Networking