LISP (Locator/ID Separation Protocol) is a network architecture and protocol designed to address challenges in routing scalability and mobility in modern networks. It achieves this by decoupling the two primary roles of IP addresses:
- Identifying a device or endpoint (ID function)
- Specifying its location in the network (Locator function)
This separation allows networks to be more scalable, efficient, and flexible.
Core Concepts of LISP
- Address Separation
- Endpoint Identifier (EID): A unique identifier assigned to a device (like an IP address) used to identify who is communicating.
- Routing Locator (RLOC): Represents where the device is in the network and is used for routing packets.
- Encapsulation and Decapsulation
- LISP uses encapsulation to route packets from one RLOC to another.
- Encapsulating devices (Ingress Tunnel Routers, or ITRs) wrap packets in an additional header containing the RLOC.
- Decapsulating devices (Egress Tunnel Routers, or ETRs) remove this header to reveal the original packet.
How LISP Works
1. Basic Packet Flow
- When a host sends a packet, the ITR near the sender encapsulates the packet using the EID and RLOC of the destination.
- The packet is routed through the network using the RLOCs.
- The ETR near the receiver decapsulates the packet and delivers it to the final destination using the EID.
2. Mapping System
- A LISP mapping system maps EIDs to RLOCs.
- The ITR queries the mapping system to find the corresponding RLOC for a given EID.
LISP Components
- ITR (Ingress Tunnel Router):
- Located near the sender, it encapsulates packets with RLOC information.
- ETR (Egress Tunnel Router):
- Located near the receiver, it decapsulates packets and forwards them to the destination EID.
- PITR (Proxy Ingress Tunnel Router):
- Allows non-LISP sites to communicate with LISP sites by acting as a proxy for encapsulation.
- PETR (Proxy Egress Tunnel Router):
- Allows LISP sites to communicate with non-LISP sites by acting as a proxy for decapsulation.
- Map Server (MS):
- Accepts EID-to-RLOC mappings from ETRs.
- Map Resolver (MR):
- Resolves queries from ITRs for EID-to-RLOC mappings.
Advantages of LISP
- Improved Scalability:
- By separating IDs and locators, the size of routing tables in core networks is reduced.
- Mobility:
- Devices can move between networks without changing their EID. Only the RLOC updates, which is reflected in the mapping system.
- Multihoming:
- A device or site can have multiple RLOCs for redundancy and load balancing.
- Traffic Engineering:
- Traffic can be steered dynamically based on policies or network conditions.
- Security:
- The mapping system can be used to validate EID-to-RLOC mappings, reducing spoofing risks.
Use Cases
- Data Center Networks:
- For large-scale environments with many mobile workloads and dynamic IP addressing.
- WANs and the Internet:
- To improve routing scalability across large geographic networks.
- IoT and Mobility:
- For mobile devices or IoT devices that need persistent identities across changing locations.
- Multicast Networks:
- Efficiently handle multicast traffic by mapping groups to locators dynamically.
Comparison to Traditional Routing
| Feature | Traditional Routing | LISP |
|---|---|---|
| Address Function | Combined (ID and Locator) | Separate (EID and RLOC) |
| Routing Table Size | Large | Smaller in core networks |
| Mobility Support | Limited | Native and efficient |
| Scalability | Limited by table growth | Enhanced |
Challenges of LISP
- Adoption Barrier:
- Requires changes to network devices to support LISP components.
- Mapping System Latency:
- Querying the mapping system adds latency to the first packet of a flow.
- Complexity:
- Adds additional layers of encapsulation and configuration.
LISP Protocol Specifications
LISP is described in a set of RFCs:
- RFC 6830: Core architecture and protocol.
- RFC 6833: Control plane for mapping.
- RFC 6834: Data plane for encapsulation.
By decoupling locators and identifiers, LISP addresses modern networking challenges like routing scalability, efficient mobility, and flexible traffic engineering.