| Network Working Group | V. Moreno |
| Internet-Draft | Cisco Systems |
| Intended status: Experimental | D. Farinacci |
| Expires: May 8, 2019 | lispers.net |
| A. Rodriguez-Natal | |
| M. Portoles-Comeras | |
| F. Maino | |
| S. Hooda | |
| S. Kondalam | |
| Cisco Systems | |
| November 4, 2018 |
Uberlay Interconnection of Multiple LISP overlays
draft-moreno-lisp-uberlay-00
This document describes the use of the Locator/ID Separation Protocol (LISP) to create multiple independent and survivable network overlays that are interconnected by a transit overlay. The transit overlay is referred to as the "uberlay" and provides connectivity and control plane abstraction between overlays. Structuring the network into multiple network overlays allows each overlay to scale independently. The different network overlays are autonomous from a control and data plane perspective to enable failure survivability across overlays. The hierarchical structure of the multi-overlay network interconnected by an uberlay provides optimizations to the forwarding of unicast traffic as well as the replication of multicast traffic in both the overlay and underlay. This document specifies the mechanisms and procedures for the distribution of control plane information across overlay sites and in the uberlay as well as the lookup and forwarding procedures for unicast and multicast traffic within and across overlays. The specification also defines the procedures to support inter-overlay mobility of EIDs and their integration with the intra-overlay EID mobility procedures defined in draft-ietf-lisp-eid-mobility.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 8, 2019.
Copyright (c) 2018 IETF Trust and the persons identified as the document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
In order to improve scale, enhance resiliency, provide regional failure survivability, and provide fault isolation, a LISP network may be structured as a collection of site-overlays interconnected by a transit area. Each site-overlay is a fully functional overlay network and has its own set of Map Servers and Map Resolvers. Site-overlays share a border xTR with a transit area. Connectivity between site-overlays is provided via the transit area which we will refer to as “The Uberlay”. This specification describes the Control Plane and Forwarding procedures for the implementation of an Uberlay connected multi-overlay LISP network.
LISP related terms, notably Map-Request, Map-Reply, Ingress Tunnel Router (ITR), Egress Tunnel Router (ETR), Map-Server (MS) and Map-Resolver (MR) are defined in the LISP specification [RFC6830].
Terms defining interactions with the LISP Mapping System are defined in [RFC6833].
Terms related to the procedures for signal free multicast are defined in [RFC8378].
The following terms are here defined to facilitate the descriptions and discussions within this particular document.
Site-Overlay - Overlay network at a specific area or domain. This overlay network has a dedicated Mapping System.
Border-xTR - xTR that connects a site-overlay to one or more uberlays.
xTR - LISP Tunnel Router as defined in [RFC6833]. An xTR connects end-points to the site-overlay.
Local Mapping System - Mapping system of the site-overlay
Uberlay - Overlay network that interconnects different site-overlays to each other. The Uberlay has a dedicated Mapping System and creates an overlay amongst the border xTRs which connect different site-overlays.
Uberlay Mapping System - Autonomous mapping system dedicated to the uberlay.
Site-Overlay EIDs - Also referred to as local site-overlay EIDs, these are the EIDs that are connected to xTRs in a particular site-overlay and are registered in their own local site-overlay mapping system. These EIDs will also be registered in the uberlay but not in the remote site-overlay mapping systems.
Remote site-overlay EIDs - These are EIDs connected and registered in site-overlays other than the local site-overlay.
Local site-overlay EIDs - These are EIDs connected and registered in the local site-overlay.
A LISP network can be structured as a collection of LISP site-overlays that are interconnected by one or more LISP Uberlays.
A LISP site-overlay is an overlay network that has its own set of xTRs, its own dedicated Mapping System and it may have a dedicated RLOC space, separate from that of other site-overlays or the uberlay. A LISP uberlay is also an overlay network with its own set of xTRs, its own dedicated Mapping System and it may have its own dedicated RLOC space. When the RLOC spaces are dedicated, RLOC routes in the local underlay do not leak across to the underlay of other site-overlays.
A site-overlay will have xTRs and Border xTRs. The xTRs provide connectivity to the local site-overlay EIDs, which are the EIDs that are locally connected to the overlay-site. The Border xTRs are Re-encapsulating Tunnel Routers (RTRs) that connect the site-overlays to the LISP Uberlay in the transit network. xTRs participate in one site-overlay and one site-overlay only. Border xTRs participate in the mapping system of the site-overlay it resides in and the mapping system of the uberlay it connects the site-overlay to. Border xTRs may be shared by more than one site-overlay.
The different site-overlays can be interconnected by an uberlay. The uberlay consists of a dedicated Mapping System and the set of Border xTRs that connect the participating site-overlays to the Uberlay and the Uberlay Mapping System.
It is assumed that a single uberlay is used to connect any site-overlays that are part of the same global network. Multiple paths may be realized in the underlay by standard routing procedures, but the uberlay remains a single instance. No provisions are made for multiple uberlays and any multi-path routing calculation that may be required in the overlay to support such an environment. In addition, any communication between site-overlays must happen via the uberlay, which may include a border xTR that is shared by the site-overlays communicating. Multiple adminstrative entities may remain in control of different site-overlays, but the uberlay remains a single overlay servicing the multiple site-overlays connecting to it.
Each site-overlay will have its own set of Map Servers and Map Resolvers (MS/MRs) which operate as an autonomous Mapping System. The Uberlay Mapping System is also autonomous and includes all necessary Map Servers and Map Resolvers. Any of the Mapping Systems, in site-overlays or in the Uberlay, follow the control plane specification in [RFC6833] and may be structured as a Distributed Delegation Tree (DDT) per [RFC8111]for the purposes of horizontal scaling or other optimizations within each Mapping System.
The MS/MRs can be co-located with the border-xTRs of the site-overlay When a Border xTR services more than one site-overlay, and the MS/MRs are instantiated on the Border xTR, logical instances of MS/MRs must be dedicated to each site-overlay.
This specification defines the interaction between the Mapping Systems of the site-overlays and the uberlay to deliver a multi-overlay hierarchical network. The forwarding procedures relevant to the border xTRs are also specified. Figure 1 illustrates the multi-overlay network.
+-------------------------------+ | +-----+ +-----+ +-----+ | | | xTR | | xTR | | xTR | | | +-----+ +-----+ +-----+ | | | | +-------+ | RLOC space 1 | Site Overlay 1 | MS/MR | | (underlay 1) | +-------+ | | | | | | +--------+ +--------+ | +-----| Border |--| Border |----+ +-----| xTR |--| xTR |----+ | +--------+ +--------+ | | | | | | | | +-------+ | Uberlay | Uberlay | MS/MR | | RLOC Space | +-------+ | (Transit Underlay) | | | | | +----------+ | +---------| Border |----------+ +---------| xTR |----------+ | +----------+ | | | | +-------+ | RLOC space 2 | Site Overlay 2 | MS/MR | | (underlay 2) | +-------+ | | | | +-----+ +-----+ +-----+ | | | xTR | | xTR | | xTR | | | +-----+ +-----+ +-----+ | +-------------------------------+ Figure 1. Site-overlays connected via Uberlay
Structuring the LISP network as multiple site-overlays interconnected by an uberlay delivers the following benefits:
A site-overlay maintains state only for its local site-overlay EIDs and RLOCs. Tunnels never cross site-overlay or uberlay boundaries. Remote site-overlay EIDs are reachable at the source site-overlay via a default mapping which will steer all traffic destined to remote site-overlay EIDs to the border xTRs where it can be handed off to the uberlay. The uberlay maintains state for the EIDs of all interconnected site-overlays and will steer traffic from the source site-overlay to the destination site-overlay by encapsulating the traffic from the source site-overlay border xTR to the destination site-overlay border xTR. Thus, forwarding is achieved by concatenating overlays and doing Re-encapsulation at the border xTRs to forward the traffic from the Ingress site-overlay to the Egress site-overlay via the Uberlay.
Inter-site communication is achieved by encapsulating traffic destined to remote site-overlay EIDs. to the border xTRs following the mapping registered for the default EID-prefix, rather than having to maintain state for remote site-overlay EIDs. Traffic will be decapsulated at the border xTRs and a lookup in the uberlay mapping system will determine the site-overlay to which traffic is to be re-encapsulated. The lookup should return the uberlay RLOCs for the border xTRs of the site-overlay where the destination EID is located. At the border xTR of the destination site, traffic will be de-capsulated, a lookup in the local destination site-overlay Mapping System will take place and traffic will be re-encapsulated to the xTR that connects to the destination EID.
Traffic for non-LISP sites, or for EIDs not registered in any site-overlay, will also be forwarded to the border xTR where it will be forwarded or dropped as appropriate.
Local EIDs must be registered by the xTRs into the local Mapping System of the site-overlay. Intra-site communication follows the standard procedures of registration, resolution, caching and encapsulation defined in [I-D.ietf-lisp-rfc6830bis] and [I-D.ietf-lisp-rfc6833bis] amongst the xTRs within the local site-overlay.
The border xTRs at a site-overlay should have a local site-overlay RLOC-set and will also have an uberlay RLOC-set. The local site-overlay RLOC-set is in the private site-overlay RLOC space and is used by the border xTRs as the RLOC set for any mappings it may register with the site-overlay Mapping System. The uberlay RLOC-set for the border-xTRs of a particular site-overlay are the RLOCs to reach the site-overlay in the uberlay RLOC space. The border xTR will use the uberlay RLOC-set in any mappings it may register with the uberlay Mapping System. It is possible for a deployment to connect the RLOC spaces of the site-overlays and the uberlay, it is also possible in the scenario of a common RLOC space for the uberlay and local site-overlay RLOC sets to be one and the same. Any implementation of this specification should support disjoint RLOC spaces or joint RLOC spaces.
The border xTRs must register a default EID-prefix as specified in Section 4.3 with the local site-overlay Mapping System. Remote EIDs will be generally reachable by xTRs in a site-overlay using the default EID mapping registered by the border xTRs. This is expected to be the mapping used for most communications to remote site-overlay EIDs. Remote site-overlay EIDs may be registered with the local site-overlay Mapping System for the purposes of supporting inter-overlay EID mobility as specified in Section 6, these mappings will be preferred over the default EID mapping whenever present.
Local EIDs registered with the site-overlay mapping system must also be registered with the Uberlay Mapping System. The registration of the local site-overlay EIDs with the uberlay Mapping System is originated by the Border xTRs. The local site-overlay EIDs SHOULD be aggregated into the shortest covering prefix possible before being registered with the uberlay Mapping System. How this aggregation is achieved is implementation specific.
In order to be able to register the local site-overlay EIDs with the uberlay Mapping System, the border xTRs must subscribe to all EIDs registered in their local site-overlay Mapping System. This is a subscription to 0.0.0.0/0 (or 0::/0) with the N-bit set as specified in [I-D.ietf-lisp-pubsub]. The subscription populates all local site-overlay EID mappings in the map-cache of the border xTRs.
Once received through the subscription, the local site-overlay EIDs in the map-cache at the border xTRs must be registered by the border xTRs with the uberlay Mapping System. The local site-overlay EIDs will be registered using the 'uberlay' RLOC-set for the registering border xTR.
Following [I-D.ietf-lisp-eid-mobility], the border xTRs will also subscribe to any EID prefixes it registers with the uberlay Mapping System. This allows the border xTRs to get Map Notify messages for EID prefixes that may move from their local site-overlay to a remote site-overlay.
Remote site-overlay EIDs may be learnt at a border xTR due to resolution of a remote destination EID or due to a mobility event as specified in Section 6. Remote site-overlay EIDs learnt from the uberlay will be installed in the map-cache of the border xTR with the corresponding remote uberlay RLOC-set for the remote border xTR. When these remote site-overlay EIDs are learnt as a consequence of the map-notify messages defined in the Inter-overlay mobility procedures in Section 6, the EIDs will also be registered with the local site-overlay mapping system using the local site-overlay RLOC-set for the border-xTR. The remote site-overlay EIDs registered with the local site-overlay mapping system will be learnt back at the border xTR because of the border xTR's subscription to all local site-overlay EIDs. This can cause the mapping for the remote EID that is installed in the border xTR map-cache to flip flop between the uberlay RLOC-set and the local site-overlay RLOC-set.
In order to avoid this flip flopping a split horizon procedure must be implemented. When a mapping received at the border xTR (as part of its subscription to all local site-overlay EID prefixes) has the local site-overlay RLOC-set for the border xTR, the mapping received in the subscription corresponds to a remote site-overlay EID and should be ignored by the border xTR. The mapping should not be installed in the map-cache of the border xTR and the EIDs in the mapping should not be advertised to the uberlay.
Intra-site communication follows the standard procedures of registration, resolution, caching and encapsulation defined in [I-D.ietf-lisp-rfc6830bis] and [I-D.ietf-lisp-rfc6833bis] amongst the xTRs within the local site-overlay.
Inter-site communication is achieved by encapsulating traffic destined to remote site-overlay EIDs from the xTRs to the border xTRs. Traffic will be decapsulated at the border xTRs and a lookup in the uberlay mapping system will determine the site-overlay to which traffic is to be re-encapsulated. The lookup should return the uberlay RLOCs for the border xTRs of the site-overlay where the destination EID is located. At the border xTR of the destination overlay-site, traffic will be de-capsulated, and re-encapsulated to the destination xTR, just like an RTR does. The border xTR already has the destination EID in its cache per its subscription to all local site-overlay EIDs.
When receiving encapsulated traffic, a border xTR will de-capsulate the traffic and will do a lookup for the destination EID in its map cache. If the destination EID is present in the map cache, the traffic is forwarded and no lookup takes place. If the destination EID is not present in the cache, the destination EID is not in any local site-overlay connected to the border xTR, in which case the border xTR will issue a map-request to all Uberlay Mapping Systems it is connected to. The criteria to determine which Mapping Systems are Uberlay Mapping Systems is simply to select those Mapping Systems with which the border xTR doesn't hold a subscription to 0.0.0.0/0 (or 0::/0).
Border xTRs may query all Mapping Systems in all uberlays it participates in. The border xTR will then chose based on longest prefix match the more specific EID mapping provided by any of the Mapping Systems. This procedure could also include site-overlay Mapping Systems, however those are not expected to be queried as the border xTR subscribes to all EIDs in the site-overlays and the presence of the mappings in the cache will prevent any lookups. The processing of Map Requests following the multi-domain request logic works as follows:
When following these rules when processing multi-domain requests, the Border xTR guarantees proper discovery and use of destination prefixes, that will be associated with their corresponding overlay fabric. By ignoring the negative replies the procedure works regardless of whether the Mapping Systems of multiple fabrics have consistent configurations or operate individually without being aware of the whole addressing space in the overlay fabric.
Border xTRs will register a mapping to be used as a default mapping to handle the forwarding of traffic destined to any EIDs that are not explicitly registered. These mappings will be registered in the local site-overlay Mapping System of each site-overlay. The RLOCs for the mappings will be the site-overlay RLOCs of the border xTR. This registration is intended to instruct the Mapping System to follow the procedures in [RFC6833] for Negative Map Replies and calculate the broadest non-registered prefix that includes the requested destination EID and issue a map-reply with the calculated EID and the RLOCs registered by the border xTRs. The map-reply may have a shorter TTL to accommodate any changes in the registrations.
The instruction to the Mapping System can be encoded as the registration of a 0.0.0.0/0 (or 0::/0) EID or it can be encoded as the registration of an agreed upon distinguished name such as "Default". In either case, the registration will contain the RLOC set desired for the default handling.
This specification will focus on the procedures necessary to extend signal-free multicast [RFC8378] across multiple site-overlays interconnected with an uberlay. The specification will focus on the extensions of the Sender and Receiver site procedures
The mapping resolution procedures for multicast EIDs at border xTRs fall within the scope of the mechanisms specified in Section 4. The Map-replies obtained from the lookup will follow the behavior specified in [RFC8378] for signal-free multicast.
Forwarding will also follow the General Procedures specified in Section 4 without alteration. It is worth noting that the concatenation of overlays between listener sites, uberlay and sender site-overlays creates a convenient replication structure where the border xTRs act as the replication points to form an optimized end-to-end multi-level replication tree [Ref to Replication Engineering draft].
The receiver and sender site procedures defined in [Ref eid-mobility] apply without change to each site-overlay and to the uberlay. Border xTRs are connected to two or more overlay networks which are following the mobility procedures. An away table is defined at the border xTR for each overlay network it participates in. In order to illustrate the procedures required, this specification describes a scenario where a border xTR has one local site-overlay away table and one uberlay facing away table. The procedures for mobility described in this section are extensible to border xTRs participating in more than two overlays.
When a map notify for an EID is received, an away entry is created on the receiving side table. Any away entries for the specific EID in other tables on the same LISP node (xTR or RTR) must be removed. This general rule addresses convergence necessary for a first move as well as any subsequent moves (moves that take place after the away tables are already populated with entries for the moving EID due to previous moves).
The following set of procedures highlights any additions to the mobility procedures defined in [Ref eid-mobility]:
When supporting multiple Instance IDs as specified in [I-D.ietf-lisp-vpn] the Instance IDs range is divided in two sets. A reuse-set that can be used in each site-overlay and a global-set used across site-overlays and the uberlay.
Instance-IDs that are local to a site-overlay should only provide intra-overlay connectivity and are in the site-overlay mapping system only for VPN use for the xTRs in the site-overlay. When the VPN reaches across site-overlays, then the global-set instance-IDs are in the uberlay mapping system as well as each site-overlay mapping system where the VPN members exist.
This document has no IANA implications
The authors want to thank Kedar Karamarkar, Prakash Jain and Vina Ermagan for their insightful contribution to shaping the ideas in this document.
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997. |
| [RFC3618] | Fenner, B. and D. Meyer, "Multicast Source Discovery Protocol (MSDP)", RFC 3618, DOI 10.17487/RFC3618, October 2003. |
| [RFC4601] | Fenner, B., Handley, M., Holbrook, H. and I. Kouvelas, "Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol Specification (Revised)", RFC 4601, DOI 10.17487/RFC4601, August 2006. |
| [RFC4607] | Holbrook, H. and B. Cain, "Source-Specific Multicast for IP", RFC 4607, DOI 10.17487/RFC4607, August 2006. |