LISP Support for Dynamic Anycast Routing
draft-kjsun-lisp-dyncast-00
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| Authors | KJ Sun , Younghan Kim | ||
| Last updated | 2021-08-09 | ||
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draft-kjsun-lisp-dyncast-00
Network Working Group K. Sun
Internet-Draft Y. Kim
Intended status: Informational Soongsil University
Expires: 10 February 2022 9 August 2021
LISP Support for Dynamic Anycast Routing
draft-kjsun-lisp-dyncast-00
Abstract
This draft describes the LISP-based architecture and solutions for
supporting dynamic anycast (Dyncast) routing.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 10 February 2022.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Architecture Overview . . . . . . . . . . . . . . . . . . . . 2
4. Addressing Dyncast Requirements with LISP . . . . . . . . . . 6
4.1. Anycast-based Service Addressing . . . . . . . . . . . . 6
4.2. Instance Affinity . . . . . . . . . . . . . . . . . . . . 6
4.3. Encoding and Signaling of Metric . . . . . . . . . . . . 7
4.4. Dynamic Routing Decisions based using Metrics . . . . . . 7
4.5. Supporting Service Dynamism . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.1. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
In an environment where equivalent services are distributed in
multiple geographic locations, Dynamic-Anycast (Dyncast) enables to
perform resource-efficient anycast routing. To support Dyncast,
according to [draft-liu-dyncast-ps-usecases], a unique service
identifier that can be assigned to multiple instances in multiple
edge environments should be able to be mapped as an actual routable
unicast address. Since this concept is similar to the Location/ID
separation method already used in the LISP design basis, the LISP
protocol can be considered as one of the candidate protocols that can
implement Dyncast. This draft is proposed to design the LISP-based
architecture for Dyncast and analyze the extension method of LISP to
meet the requirements defined in [draft-liu-dyncast-reqs] for
realizing dynamic anycasting between different LISP sites.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document is to be interpreted as described in [RFC2119]. This
document uses the terminology described in [RFC6830],
[draft-liu-dyncast-ps-usecases], [draft-liu-dyncast-reqs].
3. Architecture Overview
Figure 1 describes the Dyncast architecture based on LISP. In the
LISP architecture [draft-ietf-lisp-introduction-13], each edge
network has one or more LISP routers deployed. For anycast address,
[RFC6830] defines that anycast address can be assigned for both
Endpoint ID (EID) and Routing Locator (RLOC) within each of their
address spaces. In this draft, we called EID for dynamic anycasting
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as Dyncast Service ID (DSID), which is assigned to equivalent
services across the multiple LISP sites. Similar to the common EID
definition, the DSID cannot be routed globally by itself, and the
same DSID cannot be assigned to different services. In order to
forward a packet destined for a DSID between LISP edges, the
addresses of the LISP Egress Tunnel Router (ETR) are used as RLOC,
which operates as a Dyncast Binding ID (DBID) from a Dyncast
perspective. Map-server/resolver of the LISP control plane can
manage mapping information for DSID-RLOC mappings together with
existing EID-RLOC mappings. Differences of DSID-RLOC from existing
EID-RLOC mapping table, it that a single DSID can be mapped with
multiple RLOCs from different edge sites together.
For resource-efficient forwarding decisions across multiple service
instances, [draft-li-dyncast-architecture] defines Dyncast Metric
Agent (D-MA) which collects metrics related network and service
instances. Actual packet forwarding is handled in the Dyncast Router
(D-Router) based upon collected metrics with maintaining instance
affinity. In the LISP architecture, the D-Router function can be
implemented on the LISP xTR, and the D-MA can be deployed as a
separate component within the edge for managing service instances, or
it can be deployed in combination with the LISP xTR. The LISP,
control plane is logically centralized and it provides an interface
with each LISP router to exchange mapping information. However, it
does not mean that the LISP control plane is located in a single
physical location, several mechanisms for distributing the mapping
system already have been defined.
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LISP Edge LISP Edge
+----------+ +----------+
| Service | | Service |
| Instance | | Instance |
| (DBID) | | (DBID) |
+----------+ +----------+
| +---------------------+ |
| | LISP Control Plane | |
+----------+"""""+---------------------+" |
| D-MA | " " " |
+----------+ " " " |
| " " " +----------+
| " " " | D-MA |
+----------+" " +--------------------+ "+----------+
| LISP-xTR |DBID" | Core Network |DBID | LISP-xTR |
|(D-Router)|----"-| (RLOC-Space) |------|(D-Router)|
+----------+ " +--------------------+ +----------+
| " |DBID |
| "+--------------------+ |
| | LISP-xTR (D-Router)| |
| +--------------------+ |
+----------+ | +----------+
| Client | +----------+ | Client |
| (EID) | | Client | | (EID) |
+----------+ | (EID) | +----------+
+----------+
LISP Edge
Figure 1: LISP-based Dyncast Architecture
Figure 2 shows an example of LISP-based Dyncast deployment where two
services each deployed two instances at different edges. In this
scenario, two services are assigned an RLOC according to the ETR
address of the LISP site. Both Service_A and Service_B instances
connected to ETR_2 are assigned RLOC2, which is the RLOC of ETR_2, as
a binding ID. In the case of the edge where ETR_2 is located, as an
edge composed only of service instances, the LISP Router function can
be operated by being strongly coupled to the edge computing server.
In this case, the D-MA function can be implemented on the ETR to
insert service-instance-related metrics directly into the LISP
protocol packet. In case that a service instance and a client co-
exist like an edge where ETR_3 is located, the D-MA entity can be
independently deployed proximity of the service instance is running,
transparent from the LISP operation for clients. Mapping information
update for DSID is performed through the LISP protocol Map-Register
message, and service-instance-related metric can be delivered through
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in the LISP protocol header or other methods. A method of inserting
service-instance-related metric information into the LISP protocol
will be discussed later. When the ITR_1 receives a packet destined
for the DSID of the service by service request from the Host_1, the
ITR can acquire the RLOC mapped to the requested DSID from the LISP
control-plane through the Map-Request message. At the control plane,
it may select an proper DBID address on the collected metric
information and return it to the ITR or return the DBID list of
multiple service instances with metric information to the ITR so the
ITR selects the proper DBID in the list. A method for determining an
appropriate DBID will be discussed later.
Service_A
+------+
Map-Register D-Router +-|DSID_A|
(DSID_A, DBID2, <metric>) +-------+------+ | +------+
(DSID_B, DBID2, ,metric>) | ETR_2 | D-MA |-|
+-------+------+ | +------+
| +-|DSID_B|
+------------------+ | RLOC2 +------+
Host_1 D-Router | +--------------+ |--+(DBID2) Service_B
+--------+ +-------+ | | LISP | |
| EID_H1 |--| ITR_1 |----| | Control Plane| |
+--------+ +-------+ | +--------------+ |
RLOC1| RLOC-Space |--+ RLOC3
+------------------+ |(DBID3)
D-Router Host_2
Map-Register +-------+ +--------+
(DSID_A, DBID3, <metric>) | ETR_3 |---| EID_H2 |
(DSID_B, DBID3, <metric>) +-------+ +--------+
|
+------+
| D-MA |
+------+
|
+-----+-----+
| |
+------+ +------+
|DSID_A| |DSID_B|
+------+ +------+
Service_A Service_B
Figure 2: LISP-based Dyncast Example Scenario
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4. Addressing Dyncast Requirements with LISP
4.1. Anycast-based Service Addressing
To support Dyncast routing, the system must provide a method for
searching a service identifier allocated as an anycast address and
mapping it to a specific unicast address. From this point of view,
the LISP is a suitable protocol for separating ID/Location of service
and managing mapping information. When the system allocates the same
D-SID to each service instance for service equivalency, the LISP can
define an anycast address space for the DSID and assign it to service
instances created across multiple sites. Also, the DBID can be used
as an RLOC address of LISP xTR that can be routed between edges as
unicast. That is, it is necessary to define a separate space for
anycast address within the existing EID space and to allocate it in
advance so that it can be used in all edge networks where the service
instances are located. In the LISP definition, the EID assigned to
each service has a globally unique value and, in particular,
[RFC6830] defines that anycast address can be assigned within an EID
or RLOC block spaces. In each LISP site, same as the EID which is
defined to enable internal routing, the DSID can be able to be routed
without the DBID encapsulation process to the EID within a single
site.
4.2. Instance Affinity
For Dyncast routing, it is required that the system must set
"Instance Affinity" for one or several service requests to provide
routing to the same service instance for the same flow. In LISP, the
RLOC mapping information for the destination EID is stored in a local
cache called Map-cache in the ITR for a certain period of time, and
it is maintained for a set time-to-live (TTL) time. Therefore,
mapping information for a specific service once requested from a
client is generally maintained in the ITR until the corresponding
session expires and can be delivered to the RLOC stored in the map-
cache entry. However, in order to have a flexible selection of
service instances between different flows at the same point, it is
additionally required to assign different RLOCs for different flows
depending on metrics dynamically changed. For that, it is necessary
to enhance ITR Map-cache to maintain destination RLOC for each flow.
In addition, although the general TTL value in LISP ITR is defined as
24 hours, in Dyncast the system requires a shorter TTL time for
changing network path depending on dynamically updated network-
related and service-instance-related metrics.
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4.3. Encoding and Signaling of Metric
In Dyncast routing, the one of most important requirements is that it
should be able to collect various metrics of service-instances-
related as well as network-related, and include them in-network
routing decisions. For that, it is necessary to define how to
collect these metrics and forward them, and also where to make a
decision. In the LISP environment, since that the entire EID-RLOC
mapping information is managed in the control plane, one possible
scenario is that the D-MA function which collects service-instance-
related metrics updates them to the DSID mapping entry in the LISP
control plane. For that, it can be used an encoding method proposed
in [draft-farinacci-lisp-name-encoding] that defines to insert
specific information such as parameters for a specific EID or RLOC
using an ASCII string. Using that, it is possible to encode a string
that is pre-defined of a specific metric to interpret in the control
plane and send a Map-Request message so that the control plane can
select an appropriate RLOC based on it. In order to insert service-
instance-related metrics, the D-MA must forward the DSID of the
requested service to the LISP ITR so that the metric can be inserted
into the header of the Map-Register message. This metric information
encoded into the Map-Register message can help the LISP control plane
to uses a mechanism to make a routing decision based on the metric
information of the requested or updated BSID.
4.4. Dynamic Routing Decisions based using Metrics
The Dyncast system is required that in must make routing decisions
for all service requests, and this must be done under an
understanding of all metrics. Routing decisions in the LISP can be
done in the control plane or ITR by specifying priority and weight
values for each RLOC. In case that routing decisions are made in the
control plane, the Map-Resolver dynamically sets the priority and
weight values of each mapped DBIDs collected from D-MAs, selects a
proper DBID based on them, and forward it to the requested ITR using
the Map-Reply message. However, since this centralized approach may
not be calculated based on point of requested ITR, the actual routing
path may not be optimal. In case that routing decision is determined
at the ITR, the LISP control plane may return one or more DBID values
for the requested DSID to the ITR, including priority and weight
values based on the collected metrics. After receiving multiple
DBIDs, the ITR stores them in map-cache entry and selects an
appropriate one to forward the data packet. For that, a mechanism
for estimating appropriate priority and weight values based on both
network-related and service-instance-related metrics is required for
the control plane or ITR.
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In the Dyncast architecture described in
[draft-li-dyncast-architecture], the D-Router collects metrics by
exchanging metric information of the service identifier between
another edge D-Routers and make a decision itself. This approach can
minimize the signaling for routing decisions by decentralizing the
authority for the anycast routing decision to an entity in the actual
packet path, but the signaling for collecting metrics between each
D-Router is bound to increase. In contrast, when the LISP is used,
it can reduce effectively signaling of collecting metrics from the
ITR since that the mapping information for D-SID and D-BID can be
managed in a centralized control plane.
4.5. Supporting Service Dynamism
For service dynamism, the Dyncast system should support different
selections for each flow according to a dynamically changing metric
while considering various requirements in the selection of a service
instance. As mentioned in Section 4.2, if the map-cache can be
maintained for each flow, the forwarding path can be dynamically
changed to the different service instances by allocating target DBID
to the map-cache entry per-flow according to dynamic changes of
metrics. In order to refresh the DSID-DBID mapping upon changing
metric, the Solicit Map-Request message can be used to update so that
the ITR can update the weight and priority for the DBID which is
already received from the Map-server. Additionally, as proposed in
[draft-farinacci-lisp-telemetry], telemetry data can be collected
between Encapsulating/Decapsulating xTRs of the current flow, which
is expected to be used for dynamic service path reselection.
5. Security Considerations
TBD
6. References
6.1. Informative References
[draft-farinacci-lisp-name-encoding]
Farinacci, D., "LISP Distinguished Name Encoding", May
2021, <https://datatracker.ietf.org/doc/draft-farinacci-
lisp-name-encoding/>.
[draft-farinacci-lisp-telemetry]
Farinacci, D., Ouissal, S., and E. Nordmark, "LISP Data-
Plane Telemetry", May 2021,
<https://datatracker.ietf.org/doc/draft-farinacci-lisp-
telemetry/>.
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[draft-ietf-lisp-introduction-13]
Cabellos, A. and D. Saucez, "An Architectural Introduction
to the Locator/ID Separation Protocol (LISP)", April 2015,
<https://datatracker.ietf.org/doc/draft-ietf-lisp-
introduction/>.
[draft-li-dyncast-architecture]
Li, Y., Iannone, L., Trossen, D., and P. Liu, "Dynamic-
Anycast Architecture", February 2021,
<https://datatracker.ietf.org/doc/draft-li-dyncast-
architecture/>.
[draft-liu-dyncast-ps-usecases]
Liu, P., Willis, P., and D. Trossen, "Dynamic-Anycast
(Dyncast) Use Cases & Problem Statement", February 2021,
<https://datatracker.ietf.org/doc/draft-liu-dyncast-ps-
usecases/>.
[draft-liu-dyncast-reqs]
Liu, P., Willis, P., and D. Trossen, "Dynamic-Anycast
(Dyncast) Requirements", February 2021,
<https://datatracker.ietf.org/doc/draft-liu-dyncast-
reqs/>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997,
<https://datatracker.ietf.org/doc/rfc2119/>.
[RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The
Locator/ID Separation Protocol (LISP)", RFC 6830, January
2013, <https://datatracker.ietf.org/doc/rfc6830/>.
Authors' Addresses
Kyoungjae Sun
Soongsil University
369, Sangdo-ro, Dongjak-gu
Seoul
06978
Republic of Korea
Phone: +82 10 3643 5627
Email: gomjae@dcn.ssu.ac.kr
Younghan Kim
Soongsil University
369, Sangdo-ro, Dongjak-gu
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Seoul
06978
Republic of Korea
Phone: +82 10 2691 0904
Email: younghak@ssu.ac.kr
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