| Internet-Draft | LISP Map Server Reliable Transport | January 2022 |
| Leong, et al. | Expires 22 July 2022 | [Page] |
The communication between LISP ETRs and Map-Servers is based on unreliable UDP message exchange coupled with periodic message transmission in order to maintain soft state. The drawback of periodic messaging is the constant load imposed on both the ETR and the Map-Server. New use cases for LISP have increased the amount of state that needs to be communicated with requirements that are not satisfied by the current mechanism. This document introduces the use of a reliable transport for ETR to Map-Server communication in order to eliminate the periodic messaging overhead, while providing reliability, flow-control and endpoint liveness detection.¶
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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/.¶
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This Internet-Draft will expire on 22 July 2022.¶
Copyright (c) 2022 IETF Trust and the persons identified as the document authors. All rights reserved.¶
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The communication channel between LISP ETRs and Map-Servers is based on unreliable UDP message exchange [I-D.ietf-lisp-rfc6833bis]. Where required, reliability is pursued through periodic retransmissions that maintain soft state on the peer. Map-Register messages are retransmitted every minute by an ETR and the Map-Server times out its state if the state is not refreshed for three successive periods. When registering multiple EID-Prefixes, the ETR includes multiple mapping records in the Map-Register message. Packet size limitations provide an upper bound to the number of mapping records that can be placed in each Map-Register message. When the ETR has more EID-Prefixes to register than can be packed in a single Map-Register message, the mapping records for the EID-Prefixes are split across multiple Map-Register messages.¶
The drawback of the periodic registration is the constant load that it introduces on both the ETR and the Map-Server. The ETR uses resources to periodically build and transmit the Map-Register messages, and to process the resulting Map-Notify messages issued by the Map-Server. The Map-Server uses resources to process the received Map-Register messages, update the corresponding registration state, and build and transmit the matching Map-Notify messages. When the number of EID-Prefixes to be registered by an ETR is small, the resulting load imposed by periodic registrations may not be significant. The ETR will only transmit a single Map-Register message each period that contains a small number of mapping records.¶
In some LISP deployments, a large set of EID-Prefixes must be registered by each ETR (e.g. mobility, database redistribution). Use cases with a large set of EID-Prefixes behind an ETR will result in a much higher load. An example is LISP mobility deployments where EID-Prefixes are limited to host entries. ETRs may have thousands of hosts to register resulting in hundreds of Map-Register and Map-Notify messages per registration period.¶
A transport is required for the ETR to Map-Server communication that provides reliability, flow-control and endpoint liveness notifications. This document describes the use of TCP or SCTP as a LISP reliable transport. The initial application for the LISP reliable transport session is the support of scalable EID prefix registration. The reliable session mechanism is defined to be extensible so that it can support additional LISP communication requirements as they arise using a single reliable transport session between an ETR and a Map-Server. The use of the reliable transport session for EID prefix registration is an alternative and does not replace the existing UDP based mechanism.¶
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].¶
A single LISP reliable transport session may carry information for multiple LISP applications. One such application is the registration of EID to RLOC mappings that operates over a session between an ETR and a Map-Server. Communication over a session is based on the exchange of messages. This document defines a base set of messages to support session establishment and management. It also defines the messages for the EID to RLOC mapping registration application.¶
To support protocol extensibility when new applications, or extensions to existing applications are introduced, the messages are based on a TLV format.¶
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message Data ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message End Marker | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+¶
Reliable transport message format¶
The base message format does not indicate how the peer should deal with the message in cases where the message type is not supported/understood. This is best dealt with by the application. For example, in case an error notification is returned, or an expected acknowledgement message is not received, the application might choose various courses of action; from simply logging that the feature is not supported, all the way to tearing the relationship with the peer down for the feature, or for all LISP features.¶
To ensure backwards compatibility, the map server and ETR MUST communicate via unreliable UDP messages until a TCP session between the two is successfully established.¶
The map server authenticates the ETR with the authentication data contained in the first UDP map-register message it receives from the ETR. Once the ETR is authenticated, the map server performs a passive open by listening on TCP port 4342, and does not qualify the remote port. As a security measure, the map server accepts TCP connections only from those ETRs that have been authenticated via UDP map-register messages.¶
The ETR assumes the active role of the TCP session establishment by connecting to the map server once it has received a UDP map-notify message.¶
When a TCP session goes down, UDP authentication must take place before a new TCP session is established. The map-server will not accept a connection from the ETR until a UDP map-register has been received. Similarly, the ETR will not attempt to establish a session with the map server until an UDP map-notify message has been received.¶
A single reliable transport session is established between the map server and the ETR to cover all communication needs. For example, an ETR that has EID prefix registrations for multiple EID instances and EID address families will only establish a single session with the map server.¶
The error notification message is used to communicate base reliable transport session communication errors. LISP applications making use of the reliable transport session and having to communicate application specific errors must define their own messages to do so. An error notification is issued when the receiver of a message does not recognize the message type or cannot parse the message contents. The notification includes the offending message type and ID and as much of the offending message data as the notification sender wishes to.¶
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = 16 | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Error Code | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Offending Message Type | Offending Message Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Offending Message ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Offending Message Data ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message End Marker | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+¶
Error Notification message format¶
Error Code: An 8 bit field identifying the type of error that occurred. Defined errors are:¶
An error notification cannot be the offending message in another error notification and MUST NOT trigger such a message.¶
EID prefix registration uses the reliable transport session between an ETR and a Map-Server to communicate the ETR local EID database EID to RLOC mappings to the Map-Server. In contrast to the UDP based periodic registration, mapping information over the reliable transport session is only sent when there is new information available for the Map-Server. The Map-Server does not maintain a timer to expire registrations communicated over the reliable transport session. Instead an explicit de-registration (a registration carrying a zero TTL) is needed to delete the state maintained by the Map-Server.¶
The key used to identify registration mapping records in the ETR to Map-Server communication is the EID prefix. The prefix may be specified using an LCAF encoding that includes an EID instance ID.¶
When the reliable transport session goes down, registration mappings learned by the Map-Server are treated as periodic UDP registrations and a timer is used to expire them after 3 minutes. During this period UDP based registrations or the re-establishment of the reliable transport session and subsequent communication of a new mapping can update the EID prefix mapping state.¶
This section defines the LISP reliable transport session messages used to communicate local EID database registrations between the ETR and the Map-Server.¶
The reliable transport registration message is used to communicate EID to RLOC mapping registrations from the ETR to the Map-Server. To increase code reuse, the "Message Data" field uses the same format as the UDP Map-Registers but without the IP and UDP headers. A reliable registration message MUST contain a single mapping-record. The map server MUST discard any reliable registration message that contains more than one mapping record.¶
The reliable transport session is authenticated by means of the session establishment procedure. Thus, although the Map-Register MUST carry the authentication data, it is up to the map server to determine if each individual reliable registration message should be authenticated.¶
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = 17 | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Map-Register message ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... Map-Register message | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message End Marker | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+¶
Registration message format¶
The Acknowledgement message is sent from the Map-Server to the ETR to confirm successful registration of an EID prefix previously communicated by a reliable transport session Registration message. The Registration Acknowledgement message does not carry a mapping record (the map servers view of the mapping). This is accomplished by the LISP reliable transport Map Notification message.¶
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = 18 | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Prefix-Length | EID-Prefix-AFI | EID-Prefix ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message End Marker | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+¶
Registration Acknowledgement message format¶
The Registration Rejection Message is sent by the map server to the ETR to indicate that the registration of a specific EID prefix is being rejected or withdrawn. A rejection refers to a recently-sent registration that is being immediately rejected. A withdrawal refers to a previously accepted registration that is no longer acceptable, perhaps due to a configuration change in the map-server. The ETR must keep track of rejected EID prefixes and be prepared to re-register their mappings when requested through a registration refresh message.¶
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = 19 | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reason | Reserved | Prefix-Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | EID-Prefix-AFI | EID-Prefix ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message End Marker | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+¶
Registration Rejection message format¶
Reason: Code identifying the reason for which the Map-Server rejected or withdrew the registration.¶
Sent by the Map-Server to the ETR to request the (re-)transmission of EID prefix database mapping Registration messages.¶
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = 20 | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Scope |R| Reserved | Prefix-Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | EID-Prefix-AFI | EID-Prefix ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message End Marker | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+¶
Registration Refresh message format¶
Scope: Determines the set of registrations being refreshed.¶
The map-server has the flexibility to control the granularity of the refresh by issuing refresh with different scopes. It can send a single refresh with a coarse scope or send individual refreshes with narrower scope. The ETR MUST be able to process all scopes to ensure the map-server registration states are synchronized with the ETR.¶
Mapping Notification messages communicate the Map-Server view of the mapping for an EID prefix and no longer serve as a registration acknowledgement. Mapping Notifications do not need message level authentication as they are received over a reliable transport session to a known Map-Server. Note that reliable transport Mapping Notification messages do not reuse the UDP Map-Notify message format.¶
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = 21 | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | xTR-ID 128 bits ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | xTR-ID 128 bits ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | xTR-ID 128 bits ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | xTR-ID 128 bits | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | site-ID 64 bits ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | site-ID 64 bits | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Mapping Record ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... Mapping Record | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message End Marker | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+¶
Mapping Notification message format¶
The ETR operates the following per EID prefix, per MS state machine that defines the reliable transport EID prefix registration behavior.¶
There are five states:¶
The following events drive the state transitions:¶
The state machine is:¶
+--------------------+--------------------------------------+ | | Prev State | | Event +-------------------+------------------+ | | No state | Periodic | +--------------------+-------------------+------------------+ | DB creation | -> Periodic | N/A | | [session down] | A1 | | +--------------------+-------------------+------------------+ | DB creation | -> AckWait | N/A | | [session up] | A2 | | +--------------------+-------------------+------------------+ | DB deletion | N/A | -> No state | | | | A3 | +--------------------+-------------------+------------------+ | DB change | N/A | - | | | | A1 | +--------------------+-------------------+------------------+ | Session up | - | -> Stable | | | | A4 | +--------------------+-------------------+------------------+ | Session down | - | N/A | | | | | +--------------------+-------------------+------------------+ | Recv Refresh | - | N/A | | | | | +--------------------+-------------------+------------------+ | Recv Refresh | - | N/A | | [rejected] | | | +--------------------+-------------------+------------------+ | Recv ACK | - | N/A | | | | | +--------------------+-------------------+------------------+ | Recv Rejection | - | N/A | | | | | +--------------------+-------------------+------------------+ | Timer | N/A | - | | | | A5 | +--------------------+-------------------+------------------+¶
xTR per EID prefix per MS state machine¶
+-----------------+-----------------------------------------------+ | | Prev State | | Event +---------------+---------------+---------------+ | | Stable | AckWait | Rejected | +-----------------+---------------+---------------+---------------+ | DB creation | N/A | N/A | N/A | | | | | | +-----------------+---------------+---------------+---------------+ | DB deletion | -> No state | -> No state | -> No state | | | A6 | A6 | | +-----------------+---------------+---------------+---------------+ | DB change | -> AckWait | - | -> AckWait | | | A2 | A2 | A2 | +-----------------+---------------+---------------+---------------+ | Session up | N/A | N/A | N/A | | | | | | +-----------------+---------------+---------------+---------------+ | Session down | -> Periodic | -> Periodic | -> Periodic | | | A7 | A7 | A7 | +-----------------+---------------+---------------+---------------+ | Recv Refresh | -> AckWait | - | -> AckWait | | | A2 | A2 | A2 | +-----------------+---------------+---------------+---------------+ | Recv Refresh | - | - | -> AckWait | | [rejected] | | A2 | A2 | +-----------------+---------------+---------------+---------------+ | Recv ACK | - | -> Stable | -> AckWait | | | | | A2 | +-----------------+---------------+---------------+---------------+ | Recv Rejection | -> Rejected | -> Rejected | - | | | | | | +-----------------+---------------+---------------+---------------+ | Timer | N/A | N/A | N/A | | | | | | +-----------------+---------------+---------------+---------------+¶
xTR per EID prefix per MS state machine¶
Action descriptions:¶
All timer start actions must be jittered.¶
When the reliable transport session is established the ETR moves the state machine into the Stable state without first registering the EID prefix over the reliable transport session. The map server will send a refresh message with a scope of 0 that will trigger the registration message to be sent. Because other applications may be using the reliable session, the refresh message signals the ETR that the map server supports reliable map registration messages. This model will also allow future optimizations where the Map-Server may retain registration state from a previous instantiation of the reliable transport session with the ETR and only request the refresh of EID prefix state beyond some negotiated session progress marker.¶
Aa Map-Server authentication key change is treated as a DB change event and will result in triggering a new Registration message to be transmitted.¶
Received registrations create/update or delete mapping state.¶
A refresh with global scope is sent when a session between the ETR and map-server is first established so the map-server can obtain the complete database contents from the ETR. This refresh is also serving as a capability signaling from the map-server to the ETR that it can support reliable registration.¶
Refresh for rejected registrations sent (R bit set) when a new EID prefix is configured on the Map-Server.¶
Refresh is sent whenever authentication key is changed or EID prefix is deconfigured. Upon reception of the registration map-server can decide whether to acknowledge the registration or issue rejection.¶
Mapping Notification message sent whenever the mapping for a registered or more specific prefix for which notifications are requested changes. ETR acknowledgement or rejection messaging for Mapping Notification is not required because the ETR decides how to process the message based on the registered mapping information. If the mapping information changes the resulting registration will trigger a new Mapping Notification message from the Map-Server.¶
The LISP reliable transport session SHOULD be authenticated. On controlled RLOC networks that can guarantee that the source RLOC address of data packets cannot be spoofed, the authentication check can be a source address validation on the reliable transport packets. When the RLOC network does not provide such guarantees, reliable transport authentication SHOULD be used. Implementations SHOULD support the TCP Authentication Option (TCP-AO) [RFC5925] and SCTP Authenticated Chunks [RFC4895].¶
Assignment of new LISP reliable transport message types is done according to the "IETF Review" model defined in [RFC5266].¶
The initial content of the registry should be as follows.¶
Type Name Reference ----------- ---------------------------------------- -------------- 0-15 Reserved This document 16 Error Notification This document 17 Registration Message This document 18 Registration Acknowledgement Message This document 19 Registration Rejected Message This document 20 Registration Refresh Message This document 21 Mapping Notification Message This document 22-30 Reserved for EID membership distribution TBD 31-64999 Unassigned 65000-65535 Reserved for Experimental Use¶
TCP port 4342 already reserved for LISP CONS that is now obsolete. Repurpose for reliable transport over TCP. Reserve an SCTP port.¶
The authors would like to thank Noel Chiappa, Dino Farinacci, Jesper Skriver, Andre Pelletier and Les Ginsberg for their contributions to this document.¶