LISP Transport for Policy Distribution

Abstract

This document describes the use of the Locator/ID Separation Protocol (LISP) to encode and transport data models for the configuration of LISP ITRs.¶

1. Introduction

When LISP ITRs are deployed with enough configuration to build a LISP overlay, they may require additional configurations such as security, QoS, and/or traffic forwarding policies. As networks continue to grow, it can be challenging to ensure these configurations are distributed to many ITRs and kept in sync. LISP network operators may wish to re-use their existing LISP architecture to distribute these configurations as opposed to configuring them by hand, using a script, or investing in a configuration management system. The configurations can be distributed via a mapping system that the network operator manages or is managed by a third-party as part of a managed service offering.¶

2. Definition of Terms

LISP related terms are defined as part of the LISP specification [RFC6830], notably EID, RLOC, Map-Request, Map- Reply, Map-Notify, Ingress Tunnel Router (ITR), Egress Tunnel Router (ETR), Map- Server (MS) and Map-Resolver (MR).¶

3. Policy Distribution Use Cases

The ITR could use the mapping system to receive configuration policies for use cases such as:¶

• The RLOC interfaces of an ITR may be connected to WAN links that are policed at sub-line rate by its upstream provider. Using the mapping system, the ITR could receive and apply the QoS policies that would shape traffic to the correct rate on each ITR RLOC interface.¶
• ITRs use the mapping system to receive access-list (ACL) configuration(s) that would allow them to restrict traffic from authorized sources to authorized services.¶
• ITRs receive configurations that determine local forwarding policies, such as specifying ITR RLOCs to be used for egress forwarding on a per-application basis or RLOCs on different ITRs within the same LISP site to maintain application symmetry.¶
• Baseline configurations for common services (e.g., DNS, SSH, Syslog) can be maintained in a mapping system and distributed across multiple ITRs.¶

Policy distribution is not meant to provide zero-touch provisioning for ITRs within a LISP network. At a minimum, the ITR must have a map resolver defined, IP connectivity to the map resolver, and one or more distinguished names defined for receiving specific policies from the mapping system.¶

4. Policy Distribution: Packet Flow Description

The following figure illustrates a reference system used to support packet flow descriptions in this section.¶

                 +----------+         +-+---+
                 |controller|---------|MS/MR|
                 +----------+         +-----+
                                         |
                     _..-._.--._...._.,.-|_.,--._.-_._.-.._
                 .-.'                                      '.-.
                (                  RLOC SPACE                  )
                (                                              )
                 '..'.-._.'--'._.'.-._.'.-._.'.-._.'.-._.'.--.'
                          /                           \
                   (ifaceA)                         (ifaceB)
                  +-+--+--+                         +-+--+--+
                 .| xTR A |.-.                     .| xTR B |.-.
                ( +-+--+--+   )                   ( +-+--+--+   )
               .'   Site A   )                   .'   Site B   )
               (            .                    (             .
               '--'._.'.     )                    '--'._.'.     )
                         '--'                               '--'

The reference system contains two sites, site A and site B, with corresponding xTR-A and xTR-B providing encapsulation and decapsulation services for the overlay traffic. xTR-A uses interface-A to forward and receive encapsulated traffic through the RLOC space; and xTR-B uses interface-B for it.¶

For packet flow purposes the reference system assumes that a network controller provides the policies to a map-server.¶

When an ITR comes up, it requests it's designated policies with it's map-server. The MS may have this policy configured by the administrator via a network controller.¶

5. Mapping System Operations

The mapping system that is used for distributing policy configurations can be managed by either the administrator who owns and operates their own LISP sites or a third-party administrator who offers LISP mapping system functionality as a managed service. A controller or orchestrator could be used to update and optimize policies within the mapping system based on network or ITR telemetry.¶

Within the mapping system, the administrator must define a distinguished name that is specific to an ITR. The distinguished name is associated with the specific policy configurations that the ITR is to receive. Each ITR is configured with the minimal requirements to perform a mapping request procedure as well as a distinguished name that can be matched upon in the mapping system.¶

Map-Servers should be able to receive policy registrations through the Map-Registration process. The Map-Registration must encode the policy following the specification in the policy distribution encoding section.¶

6. Policy Distribution Process

The ITR subscribes to its policy via the Map-Request procedure defined in section 5 of [I-D.ietf-lisp-pubsub]. The PubSub procedure is used to ensure that policies can be updated or audited after an ITR has received them. Policies are published to the ITR from the mapping system using the mapping notification procedure defined in section 6 of [I-D.ietf-lisp-pubsub].¶

EID-to-RLOC mappings used for policy distribution are of the type EID <Distinguished Name> to RLOC <JSON policy specification>. The EID is a distinguished name uniquely identifying a router in the system, while each RLOC record uses JSON encoding to specify the particular policy (or policies) that this router needs to implement.¶

7. Policy Distribution Encoding

When the ITR is configured to receive a policy using a distinguished name, the ITR sends a subscription for the EID record encoded as this Distinguished Name. When a policy has been registered with the Mapping System for this Distinguished Name, the ITR receives a publication with a list of policies as RLOC records and encoded as JSON strings (as defined in section 5.4 of [RFC8060].¶

Example encoding for QoS policy that shapes traffic to 50 percent of the line-rate: EID-Record encoded as distinguished name "policy-ce-router1" RLOC-Record record encoded as JSON string "{ "shape":{ "interface":"ethernet1", "direction":"outbound", "unit":"percent", "value":50 }}"¶

Example encoding for setting the ITR's NTP server to 1.1.1.1: EID-Record encoded as distinguished name "policy-ce-router" RLOC-Record record encoded as JSON string "{ "NTP-address" : "1.1.1.1" }"¶

Multiple ITRs can be configured to use multiple distinguished names for receiving multiple sets policies. This allows for an ITR to receive specific policies and many ITRs to receive policies that can be broadly applied. Referring to the two examples above, an ITR can be configured to use a distinguished name of "policy-ce-router1" to receive a QoS configuration that is specific to that node while also using a distinguished name of "policy-ce-router" to receive configurations that are common to each ITR in the LISP network (e.g., NTP configuration). The use of multiple distinguished names per ITR reduces the amount of configuration within the mapping system.¶

10. References