Internet DRAFT - draft-ietf-lisp-pubsub
draft-ietf-lisp-pubsub
LISP Working Group A. Rodriguez-Natal
Internet-Draft Cisco
Intended status: Standards Track V. Ermagan
Expires: 1 September 2023 Google
A. Cabellos
UPC/BarcelonaTech
S. Barkai
Nexar
M. Boucadair
Orange
28 February 2023
Publish/Subscribe Functionality for the Locator/ID Separation Protocol
(LISP)
draft-ietf-lisp-pubsub-15
Abstract
This document specifies an extension to the request/reply based
Locator/ID Separation Protocol (LISP) control plane to enable
Publish/Subscribe (PubSub) operation.
Status of This Memo
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
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Internet-Drafts are draft documents valid for a maximum of six months
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This Internet-Draft will expire on 1 September 2023.
Copyright Notice
Copyright (c) 2023 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.
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Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Scope of Applicability . . . . . . . . . . . . . . . . . 4
2. Terminology and Requirements Notation . . . . . . . . . . . . 4
3. Deployment Requirements . . . . . . . . . . . . . . . . . . . 4
4. Map-Request PubSub Additions . . . . . . . . . . . . . . . . 5
5. Mapping Request Subscribe Procedures . . . . . . . . . . . . 6
6. Mapping Notification Publish Procedures . . . . . . . . . . . 11
7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
7.1. Security Association between ITR and Map-Server . . . . . 12
7.2. DDoS Attack Mitigation . . . . . . . . . . . . . . . . . 13
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
9.1. Normative References . . . . . . . . . . . . . . . . . . 15
9.2. Informative References . . . . . . . . . . . . . . . . . 15
Appendix A. Sample PubSub Deployment Experiences . . . . . . . . 17
A.1. PubSub as a Monitoring Tool . . . . . . . . . . . . . . . 17
A.2. Mitigating Negative Map-Cache Entries . . . . . . . . . . 17
A.3. Improved Mobility Latency . . . . . . . . . . . . . . . . 18
A.4. Enhanced Reachability with Dynamic Redistribution of
Prefixes . . . . . . . . . . . . . . . . . . . . . . . . 18
A.5. Better Serviceability . . . . . . . . . . . . . . . . . . 19
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 19
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
1. Introduction
The Locator/ID Separation Protocol (LISP) [RFC9300] [RFC9301] splits
IP addresses into two different namespaces: Endpoint Identifiers
(EIDs) and Routing Locators (RLOCs). LISP uses a map and encapsulate
(a.k.a., map-and-encap) approach that relies on (1) a Mapping System
(basically a distributed database) that stores and disseminates EID-
RLOC mappings and on (2) LISP tunnel routers (xTRs) that encapsulate
and decapsulate data packets based on the content of those mappings.
Ingress Tunnel Routers (ITRs) / Re-encapsulating Tunnel Routers
(RTRs) / Proxy Ingress Tunnel Routers (PITRs) pull EID-to-RLOC
mapping information from the Mapping System by means of an explicit
request message. Section 6.1 of [RFC9301] indicates how Egress
Tunnel Routers (ETRs) can tell ITRs/RTRs/PITRs about mapping changes.
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This document presents a Publish/Subscribe (PubSub) extension in
which the Mapping System can notify ITRs/RTRs/PITRs about mapping
changes. When this mechanism is used, mapping changes can be
notified faster and can be managed in the Mapping System versus the
LISP sites.
In general, when an ITR/RTR/PITR wants to be notified for mapping
changes for a given EID-Prefix, the following main steps occur:
(1) The ITR/RTR/PITR builds a Map-Request for that EID-Prefix with
the Notification-Requested bit (N-bit) set and which also
includes its xTR-ID and Site-ID.
(2) The Map-Request is forwarded to one of the Map-Servers that the
EID-Prefix is registered to.
(3) The Map-Server creates subscription state for the ITR/RTR/PITR
on the EID-Prefix.
(4) The Map-Server sends a Map-Notify to the ITR/RTR/PITR to confirm
that the subscription has been created and then waits for an
acknowledgement of the notification.
(5) The ITR/RTR/PITR sends back a Map-Notify-Ack to acknowledge the
successful receipt of the Map-Notify.
(6) When there is a change in the mapping of the EID-Prefix, the
Map-Server sends a Map-Notify message to each ITR/RTR/PITR in
the subscription list.
(7) Each ITR/RTR/PITR sends a Map-Notify-Ack to acknowledge the
received Map-Notify.
This operation is repeated for all EID-Prefixes for which ITRs/RTRs/
PITRs want to be notified. An ITR/RTR/PITR can set the N-bit for
several EID-Prefixes within a single Map-Request. Please note that
the steps above illustrate only the simplest scenario and that
details for this and other scenarios are described later in the
document.
The reader may refer to [I-D.boucadair-lisp-pubsub-flow-examples] for
sample flows to illustrate the use of the PubSub specification.
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1.1. Scope of Applicability
The PubSub procedure specified in this document is intended to be
used in contexts with controlled access to the Map-Server. How a
deployment controls access to a Map-Server is deployment specific,
and therefore out of the scope of this document. However, the Map-
Resolvers and Map-Servers need to be configured with the required
information to at least ensure the following:
(1) Map-Resolvers MUST verify that an xTR is allowed to (1) set the
N-bit to 1 and (2) use the xTR-ID, Site-ID, and ITR-RLOCs
included in a Map-Request.
(2) Map-Servers MUST only accept subscription requests from Map-
Resolvers that verify Map-Requests as previously described.
2. Terminology and Requirements Notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
The document uses the terms defined in Section 3 of [RFC9300].
3. Deployment Requirements
In addition to the general assumptions and expectations that
[RFC9301] makes for LISP deployments, this document makes the
following deployment requirements:
(1) A unique 128-bit xTR-ID (plus a 64-bit Site-ID) identifier is
assigned to each xTR.
(2) Map-Servers are configured to proxy Map-Replying (i.e., they are
solicited to generate and send Map-Reply messages) for the
mappings they are serving.
(3) A security association (e.g., a PubSubKey) is required between
the ITRs and the Map-Servers (see Section 7.1).
If a requirement is not met, a subscription cannot be established,
and the network will continue operating without this enhancement.
The configuration of xTR-IDs and Site-IDs is out of the scope of this
document. The reader may refer to [I-D.ietf-lisp-yang] for an
example of how these identifiers can be provisioned to LISP nodes.
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4. Map-Request PubSub Additions
Figure 1 shows the format of the updated Map-Request to support the
PubSub functionality. In particular, this document associates a
meaning with one of the reserved bits (see Section 8).
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=1 |A|M|P|S|p|s|R|I| Rsvd |L|D| IRC | Record Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Nonce . . . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . . . Nonce |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source-EID-AFI | Source EID Address ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ITR-RLOC-AFI 1 | ITR-RLOC Address 1 ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ITR-RLOC-AFI n | ITR-RLOC Address n ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ |N| Reserved | EID mask-len | EID-Prefix-AFI |
Rec +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ | EID-Prefix ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Map-Reply Record ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ xTR-ID +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Site-ID +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Map-Request with I-bit, N-bit, xTR-ID, and Site-ID
The following is added to the Map-Request message defined in
Section 5.2 of [RFC9301]:
xTR-ID bit (I-bit): This bit is set to 1 to indicate that 128-bit
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xTR-ID and 64-bit Site-ID fields are present in the Map-Request
message. For PubSub operation, an xTR MUST be configured with an
xTR-ID and Site-ID, and it MUST set the I-bit to 1 and include its
xTR-ID and Site-ID in the Map-Request messages it generates. If
the I-bit is set, but the Site-ID and/or xTR-ID are not included,
a receiver can detect the error because, after processing that
last EID-record, there are no bytes left from processing the
message. In this case, the receiver SHOULD log a malformed Map-
Request and MUST drop the message.
Notification-Requested bit (N-bit): The N-bit of an EID-Record is
set to 1 to specify that the xTR wants to be notified of updates
for that EID-Prefix.
xTR-ID field: If the I-bit is set, this field is added to the Map-
Request message as shown in Figure 1, starting right after the
final Record in the message (or the Map-Reply Record, if present).
The xTR-ID is specified in Section 5.6 of [RFC9301].
Site-ID field: If the I-bit is set, this field is added to the
Map-Request message as shown in Figure 1, following the xTR-ID
field. The Site-ID is defined in Section 5.6 of [RFC9301].
5. Mapping Request Subscribe Procedures
The xTR subscribes for changes, to a given EID-Prefix, by sending a
Map-Request to the Mapping System with the N-bit set on the EID-
Record. The xTR builds a Map-Request according to Section 5.3 of
[RFC9301] but also does the following:
(1) The xTR MUST set the I-bit to 1 and append its xTR-ID and Site-
ID to the Map-Request.
(2) The xTR MUST set the N-bit to 1 for the EID-Record to which the
xTR wants to subscribe.
(3) If the xTR has a nonce associated with the EID-Prefix, it MUST
use this nonce increased by one in the Map-Request. Otherwise,
it generates a nonce following Section 5.2 of [RFC9301]. It is
RECOMMENDED that the xTR uses persistent storage to keep nonce
state. If the xTR does not have persistent storage and does not
have a nonce associated with the EID-Prefix, it MUST reset the
nonce by using the procedure described in Section 7.1 to
successfully create a new security association with the Map-
Server.
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The Map-Request is forwarded to the appropriate Map-Server through
the Mapping System. This document does not assume that a Map-Server
is pre-assigned to handle the subscription state for a given xTR.
The Map-Server that receives the Map-Request will be the Map-Server
responsible for notifying that specific xTR about future mapping
changes for the subscribed mapping records.
Upon receipt of the Map-Request, the Map-Server processes it as
described in Section 8.3 of [RFC9301]. In addition, unless the xTR
is using the procedure described in Section 7.1 to create a new
security association, the Map-Server MUST verify that the nonce in
the Map-Request is greater than the stored nonce (if any) associated
with the xTR-ID (and EID-Prefix, when applicable). Otherwise, the
Map-Server MUST silently drop the Map-Request message and SHOULD log
the event to record that a replay attack could have occurred.
Furthermore, upon processing, for the EID-Record that has the N-bit
set to 1, the Map-Server proceeds to add the xTR-ID contained in the
Map-Request to the list of xTRs that have requested to be subscribed
to that EID-Prefix.
If an xTR-ID is successfully added to the list of subscribers for an
EID-Prefix, the Map-Server MUST extract the nonce and ITR-RLOCs
present in the Map-Request, and store the association between the
EID-Prefix, xTR-ID, ITR-RLOCs, and nonce. Any already present state
regarding ITR-RLOCs and/or nonce for the same xTR-ID MUST be
overwritten. When the LISP deployment has a single Map-Server, the
Map-Server can be configured to keep a single nonce per xTR-ID for
all EID-Prefixes (when used, this option MUST be enabled at the Map-
Server and all xTRs).
If the xTR-ID is added to the list, the Map-Server MUST send a Map-
Notify message back to the xTR to acknowledge the successful
subscription. The Map-Server builds the Map-Notify according to
Sections 5.5 and 5.7 of [RFC9301] with the following considerations:
(1) The Map-Server MUST use the nonce from the Map-Request as the
nonce for the Map-Notify.
(2) The Map-Server MUST use its security association with the xTR
(Section 7.1) to sign the authentication data of the Map-Notify.
The xTR MUST use the security association to verify the received
authentication data.
(3) The Map-Server MUST send the Map-Notify to one of the ITR-RLOCs
received in the Map-Request (which one is implementation
specific).
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As a reminder, the initial transmission and retransmission of Map-
Notify messages by a Map-Server follow the procedure specified in
Section 5.7 of [RFC9301]. Some state changes may trigger an overload
that would impact, e.g., the outbound capacity of a Map-Server. A
similar problem may be experienced when a large number of state
entries are simultaneously updated. To prevent such phenomena, Map-
Servers SHOULD be configured with policies to control the maximum
number of subscriptions and also the pace of Map-Notify messages.
For example, the Map-Server may be instructed to limit the resources
that are dedicated to unsolicited Map-Notify messages to a small
fraction (e.g., less than 10%) of its overall processing and
forwarding capacity. The exact details to characterize such policies
are deployment and implementation specific. Likewise, this document
does not specify which notifications take precedence when these
policies are enforced.
When the xTR receives a Map-Notify with a nonce that matches one in
the list of outstanding Map-Request messages sent with an N-bit set,
it knows that the Map-Notify is to acknowledge a successful
subscription. The xTR processes this Map-Notify, as described in
Section 5.7 of [RFC9301], and MUST use the Map-Notify to populate its
Map-Cache with the returned EID-Prefix and RLOC-set. As a reminder,
following Section 5.7 of [RFC9301], the xTR has to send a Map-Notify-
Ack back to the Map-Server. If the Map-Server does not receive the
Map-Notify-Ack after exhausting the Map-Notify retransmissions
described in Section 5.7 of [RFC9301], the Map-Server can remove the
subscription state. If the Map-Server removes the subscription
state, and absent explicit policy, it SHOULD notify the xTR by
sending a single Map-Notify with the same nonce but with Loc-Count =
0 (and Loc-AFI = 0), and ACT bits set to 5 "Drop/Auth-Failure". It
is OPTIONAL for the xTR to update its map-cache entry for the EID-
Prefix (if any) based on this Map-Notify. This message is
specifically useful for cases where Map-Notifies are successfully
received by an xTR but the corresponding Map-Notify-Acks were lost
when forwarded to the Map-Server. xTR implementations can use this
signal to try to reinstall their subscription state instead of
maintaining stale mappings.
The subscription of an xTR-ID may fail for a number of reasons. For
example, it fails because of local configuration policies (such as
accept and drop lists of subscribers), because the Map-Server has
exhausted the resources to dedicate to the subscription of that EID-
Prefix (e.g., the number of subscribers excess the capacity of the
Map-Server), or because the xTR tried but was not successful in
establishing a new security association (Section 7.1).
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If the subscription request fails, the Map-Server sends a Map-Reply
to the originator of the Map-Request, as described in Section 8.3 of
[RFC9301], with the following considerations:
* If the subscription request fails due to policy (e.g. for
explicitly configured subscriptions, as described later in this
section) the Map-Server MUST respond to the Map-Request with a
Negative Map-Reply (Loc-Count = 0 and Loc-AFI = 0) with ACT bits
set to 4 "Drop/Policy-Denied".
* If the subscription request fails due to authentication (e.g. when
a new security associationg is being established, as described in
Section 7.1), the Map-Server MUST respond to the Map-Request with
a Negative Map-Reply (Loc-Count = 0 and Loc-AFI = 0) with ACT bits
set to 5 "Drop/Auth-Failure".
* If the subscription request fails due to any other reason, the
Map-Server MUST follow Section 8.3 of [RFC9301] with no changes.
The xTR processes any (Negative) Map-Reply as specified in
Section 8.1 of [RFC9301], with the following considerations: if the
xTR receives a Negative Map-Reply with ACT bits set to 4 "Drop/
Policy-Denied" or 5 "Drop/Auth-Failure" as a response to a
subscription request, it is OPTIONAL for the xTR to update its map-
cache entry for the EID-Prefix (if any) based on this Negative Map-
Reply. If the subscription request fails (for whichever reason), it
is up to the implementation of the xTR to try to subscribe again.
If the Map-Server receives a subscription request for an EID-Prefix
not present in the mapping database, it SHOULD follow the same logic
described in Section 8.4 of [RFC9301] and create a temporary
subscription state for the xTR-ID to the least-specific prefix that
both matches the original query and does not match any EID-Prefix
known to exist in the LISP-capable infrastructure. Alternatively,
the Map-Server can instead determine that such a subscription request
fails, and send a Negative Map-Reply following Section 8.3 of
[RFC9301]. In both cases, the TTL of the temporary subscription
state or the Negative Map-Reply SHOULD be configurable, with a value
of 15-minutes being RECOMMENDED.
The subscription state can also be created explicitly by
configuration at the Map-Server (possible when a pre-shared security
association exists, see Section 7) using a variety of means that are
out of scope. If at the time the explicit subscription is configured
there is no nonce that can be used for the explicit subscription
state (e.g., from a different subscription already established with
the same xTR when a single nonce is kept per xTR-ID), then both the
xTR and Map-Server MUST be configured with the initial nonce to use.
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It is RECOMMENDED to have a configuration option to enable (or
disable) the xTR to accept publication information for EID-Prefixes
the xTR did not explicitly subscribe to. By default, the xTR is
allowed to modify explicitly configured subscription state following
the procedures described in this section, however this MAY be
disabled at the Map-Server via configuration. If the Map-Server is
instructed to not allow xTRs to modify explicitly configured
subscriptions, and an xTR tries to do so, this triggers a Negative
Map-Reply with ACT bits set to 4 "Drop/Policy-Denied" as described
earlier in this section.
The following specifies the procedure to remove a subscription: If a
valid Map-Request with the N-bit set to 1 only has one ITR-RLOC with
AFI = 0 (i.e., Unknown Address), the Map-Server MUST remove the
subscription state for that xTR-ID (unless this is disabled via
configuration, see previous paragraph). If the subscription state is
removed, the Map-Server MUST send a Map-Notify to the source RLOC of
the Map-Request. If the subscription removal fails due to
configuration, this triggers a Negative Map-Reply with with ACT bits
set to 4 "Drop/Policy-Denied" as described earlier in this section;
the Map-Server sends the Negative Map-Reply to the source RLOC of the
Map-Request in this case. Removing subscription state at the Map-
Server can lead to replay attacks. To soften this, the Map-Server
SHOULD keep the last nonce seen per xTR-ID (and EID-Prefix, when
applicable). If the Map-Server does not keep last nonces seen, then
the Map-Server MUST require the xTRs to subscribe using the procedure
described in Section 7.1 to create a new security association with
the Map-Server.
If the Map-Server receives a Map-Request asking to remove a
subscription for an EID-Prefix without subscription state for that
xTR-ID, but covered by a less-specific EID-Prefix for which
subscription state exists for the xTR-ID, the Map-Server SHOULD stop
publishing updates about this more-specific EID-Prefix to that xTR,
until the xTR subscribes to the more-specific EID-Prefix. The same
considerations regarding authentication, integrity protection, and
nonce checks described in this section and Section 7 for Map-Requests
used to update subscription state, apply for Map-Requests used to
remove subscription state.
When an EID-Prefix is removed from the Map-Server (either when
explicitly withdrawn or when its TTL expires), the Map-Server
notifies its subscribers (if any) via a Map-Notify with TTL equal 0.
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6. Mapping Notification Publish Procedures
The publish procedure is implemented via Map-Notify messages that the
Map-Server sends to xTRs. The xTRs acknowledge the reception of Map-
Notifies via sending Map-Notify-Ack messages back to the Map-Server.
The complete mechanism works as follows:
When a mapping stored in a Map-Server is updated (e.g., via a Map-
Register from an ETR), the Map-Server MUST notify the subscribers of
that mapping via sending Map-Notify messages with the most updated
mapping information. If subscription state in the Map-Server exists
for a less-specific EID-Prefix and a more-specific EID-Prefix is
updated, then the Map-Notify is sent with the more-specific EID-
Prefix mapping to the subscribers of the less-specific EID-Prefix
mapping. The Map-Notify message sent to each of the subscribers as a
result of an update event follows the encoding and logic defined in
Section 5.7 of [RFC9301] for Map-Notify, except for the following:
(1) The Map-Notify MUST be sent to one of the ITR-RLOCs associated
with the xTR-ID of the subscriber (which one is implementation
specific).
(2) The Map-Server increments the nonce by one every time it sends a
Map-Notify as publication to an xTR-ID for a particular EID-
Prefix.
(3) The Map-Server MUST use its security association with the xTR to
compute the authentication data of the Map-Notify.
When the xTR receives a Map-Notify with an EID not local to the xTR,
the xTR knows that the Map-Notify has been received to update an
entry on its Map-Cache. The xTR MUST keep track of the last nonce
seen in a Map-Notify received as a publication from the Map-Server
for the EID-Prefix. When the LISP deployment has a single Map-
Server, the xTR can be configured to keep track of a single nonce for
all EID-Prefix (when used, this option MUST be enabled at the Map-
Server and all xTRs). If a Map-Notify received as a publication has
a nonce value that is not greater than the saved nonce, the xTR drops
the Map-Notify message and logs the fact a replay attack could have
occurred. The same considerations discussed in Section 5.6 of
[RFC9301] regarding Map-Register nonces apply here for Map-Notify
nonces.
The xTR processes the received Map-Notify as specified in Section 5.7
of [RFC9301], with the following considerations: The xTR MUST use its
security association with the Map-Server (Section 7.1) to validate
the authentication data on the Map-Notify. The xTR MUST use the
mapping information carried in the Map-Notify to update its internal
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Map-Cache. If after following Section 5.7 of [RFC9301] regarding
retransmission of Map-Notify messages, the Map-Server has not
received back the Map-Notify-Ack, it can try to send the Map-Notify
to a different ITR-RLOC for that xTR-ID. If the Map-Server tries all
the ITR-RLOCs without receiving a response, it may stop trying to
send the Map-Notify.
7. Security Considerations
Generic security considerations related to LISP control messages are
discussed in Section 9 of [RFC9301].
In the particular case of PubSub, cache poisoning via malicious Map-
Notify messages is avoided by the use of nonce and the security
association between the ITRs and the Map-Servers.
It is RECOMMENDED to follow guidance from the last paragraph of
Section 9 of [RFC9301] to ensure integrity protection of Map-Request
messages (e.g., to prevent xTR-ID hijacking).
7.1. Security Association between ITR and Map-Server
Since Map-Notifies from the Map-Server to the ITR need to be
authenticated, there is a need for a soft-state or hard-state
security association (e.g., a PubSubKey) between the ITRs and the
Map-Servers. For some controlled deployments, it might be possible
to have a shared PubSubKey (or set of keys) between the ITRs and the
Map-Servers. However, if pre-shared keys are not used in the
deployment, LISP-SEC [RFC9303] can be used as follows to create a
security association between the ITR and the Map-Server.
First, when the ITR is sending a Map-Request with the N-bit set
following Section 5, the ITR also performs the steps described in
Section 6.4 of [RFC9303]. The ITR can then generate a PubSubKey by
deriving a key from the One-Time Key (OTK) and Map-Request's nonce as
follows: PubSubKey = KDF(OTK + nonce), where KDF is the Key
Derivation Function indicated by the OTK Wrapping ID. If OTK
Wrapping ID equals NULL-KEY-WRAP-128, then the PubSubKey is the OTK.
Note that as opposed to the pre-shared PubSubKey, this generated
PubSubKey is different per EID-Prefix to which an ITR subscribes
(since the ITR will use a different OTK per Map-Request).
When the Map-Server receives the Map-Request it follows the procedure
specified in Section 5 with the following considerations: The Map-
Server MUST verify that the OTK has not been used before. If the
Map-Server verifies the OTK and cannot determine that the OTK has not
been used before, the subscription request fails due to
authentication and this triggers a Negative Map-Reply with ACT bits
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set to 5 "Drop/Auth-Failure", as described in Section 5. The xTR
might try again with a different OTK upon reception of this Negative
Map-Reply. Note that a Map-Server implementation might decide to not
keep full past OTKs and instead use some form of hash. In that case,
hash collisions are handled as if the OTK has been reused. Such an
implementation needs to balance the hash length with the rate of
collisions expected for the particular deployment; this is
implementation specific. If the Map-Server has to reply with a Map-
Reply for any other reason (e.g., if PubSub is not supported or a
subscription is not accepted), then it follows normal LISP-SEC
procedure described in Section 5.7 of [RFC9303]. No PubSubKey,
security association, or subscription state is created when the Map-
Server responds with any Map-Reply message.
Otherwise, if the Map-Server has to reply with a Map-Notify (e.g.,
due to subscription accepted) to a received Map-Request, the
following extra steps take place:
* The Map-Server extracts the OTK and OTK Wrapping ID from the LISP-
SEC ECM Authentication Data.
* The Map-Server generates a PubSubKey by deriving a key from the
OTK as described before for the ITR. This is the same PubSubKey
derived at the ITR which is used to establish a security
association between the ITR and the Map-Server.
* The PubSubKey can now be used to sign and authenticate any Map-
Notify between the Map-Server and the ITR for the subscribed EID-
Prefix. This includes the Map-Notify sent as a confirmation to
the subscription. When the ITR wants to update the security
association for that Map-Server and EID-Prefix, it once again
follows the procedure described in this section.
Note that if the Map-Server replies with a Map-Notify, none of the
regular LISP-SEC steps regarding Map-Reply described in Section 5.7
of [RFC9303] occur.
7.2. DDoS Attack Mitigation
If PubSub is deployed under the scope of applicability defined in
Section 1.1 only known nodes can participate on the PubSub
deployment. DDoS attacks based on replayed messages by unknown nodes
are avoided by the use of nonce and the security association between
the ITRs and the Map-Servers. Misbehaving known nodes may send
massive subscription requests which may lead to exhausting the
resources of a Map-Server. Furthermore, frequently changing the
state of a subscription may also be considered as an attack vector.
To mitigate such issues, Section 5.3 of [RFC9301] discusses rate-
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limiting Map-Requests and Section 5.7 of [RFC9301] discusses rate-
limiting Map-Notifies. Note that when the Map-Notify rate-limit
threshold is met for a particular xTR-ID, the Map-Server will discard
additional subscription requests from that xTR-ID and will fall back
to [RFC9301] behavior when receiving a Map-Request from that xTR-ID
(i.e., the Map-Server will send a Map-Reply).
8. IANA Considerations
This document requests IANA to assign a new bit from the "LISP
Control Plane Header Bits: Map-Request" sub-registry under the
"Locator/ID Separation Protocol (LISP) Parameters" registry available
at [IANA-LISP]. The suggested position of this bit in the Map-
Request message can be found in Figure 1.
+======+===============+==========+=============+===============+
| Spec | IANA Name | Bit | Description | Reference |
| Name | | Position | | |
+======+===============+==========+=============+===============+
| I | Map-Request-I | 11 | xTR-ID Bit | This-Document |
+------+---------------+----------+-------------+---------------+
Table 1: Additions to the Map-Request Header Bits Sub-Registry
This document also requests the creation of a new sub-registry
entitled "LISP Control Plane Header Bits: Map-Request-Record" under
the "Locator/ID Separation Protocol (LISP) Parameters" registry
available at [IANA-LISP].
The initial content of this sub-registry is shown in Table 2:
+====+=============+========+========================+=============+
|Spec|IANA Name |Bit | Description |Reference |
|Name| |Position| | |
+====+=============+========+========================+=============+
|N |Map-Request-N|1 | Notification-Requested |This-Document|
| | | | Bit | |
+----+-------------+--------+------------------------+-------------+
Table 2: Initial Content of LISP Control Plane Header Bits: Map-
Request-Record Sub-Registry
The remaining bits (i.e., Bit positions 2-8) are Unassigned.
The policy for allocating new bits from this sub-registry is
Specification Required (Section 4.6 of [RFC8126]).
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Review requests are evaluated on the advice of one or more designated
experts. Criteria that should be applied by the designated experts
include determining whether the proposed registration duplicates
existing entries and whether the registration description is
sufficiently detailed and fits the purpose of this registry. These
criteria are considered in addition to those already provided in
Section 4.6 of [RFC8126] (e.g., the proposed registration must be
documented in a permanent and readily available public
specification). The designated experts will either approve or deny
the registration request, communicating this decision to IANA.
Denials should include an explanation and, if applicable, suggestions
as to how to make the request successful.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC9300] Farinacci, D., Fuller, V., Meyer, D., Lewis, D., and A.
Cabellos, Ed., "The Locator/ID Separation Protocol
(LISP)", RFC 9300, DOI 10.17487/RFC9300, October 2022,
<https://www.rfc-editor.org/info/rfc9300>.
[RFC9301] Farinacci, D., Maino, F., Fuller, V., and A. Cabellos,
Ed., "Locator/ID Separation Protocol (LISP) Control
Plane", RFC 9301, DOI 10.17487/RFC9301, October 2022,
<https://www.rfc-editor.org/info/rfc9301>.
[RFC9303] Maino, F., Ermagan, V., Cabellos, A., and D. Saucez,
"Locator/ID Separation Protocol Security (LISP-SEC)",
RFC 9303, DOI 10.17487/RFC9303, October 2022,
<https://www.rfc-editor.org/info/rfc9303>.
9.2. Informative References
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Internet-Draft LISP-PubSub February 2023
[I-D.boucadair-lisp-pubsub-flow-examples]
Boucadair, M., "LISP PubSub Flow Examples", Work in
Progress, Internet-Draft, draft-boucadair-lisp-pubsub-
flow-examples-03, 10 February 2023,
<https://datatracker.ietf.org/doc/html/draft-boucadair-
lisp-pubsub-flow-examples-03>.
[I-D.haindl-lisp-gb-atn]
Haindl, B., Lindner, M., Moreno, V., Portoles-Comeras, M.,
Maino, F., and B. Venkatachalapathy, "Ground-Based LISP
for the Aeronautical Telecommunications Network", Work in
Progress, Internet-Draft, draft-haindl-lisp-gb-atn-08, 23
September 2022, <https://datatracker.ietf.org/doc/html/
draft-haindl-lisp-gb-atn-08>.
[I-D.ietf-lisp-eid-mobility]
Portoles-Comeras, M., Ashtaputre, V., Maino, F., Moreno,
V., and D. Farinacci, "LISP L2/L3 EID Mobility Using a
Unified Control Plane", Work in Progress, Internet-Draft,
draft-ietf-lisp-eid-mobility-11, 10 January 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-lisp-
eid-mobility-11>.
[I-D.ietf-lisp-yang]
Ermagan, V., Rodriguez-Natal, A., Coras, F., Moberg, C.,
Rahman, R., Cabellos-Aparicio, A., and F. Maino, "LISP
YANG Model", Work in Progress, Internet-Draft, draft-ietf-
lisp-yang-18, 29 August 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-lisp-
yang-18>.
[I-D.moreno-lisp-uberlay]
Moreno, V., Farinacci, D., Rodriguez-Natal, A., Portoles-
Comeras, M., Maino, F., and S. Hooda, "Uberlay
Interconnection of Multiple LISP overlays", Work in
Progress, Internet-Draft, draft-moreno-lisp-uberlay-06, 28
September 2022, <https://datatracker.ietf.org/doc/html/
draft-moreno-lisp-uberlay-06>.
[IANA-LISP]
IANA, "Locator/ID Separation Protocol (LISP) Parameters",
<https://www.iana.org/assignments/lisp-parameters/lisp-
parameters.xhtml>.
[RFC6835] Farinacci, D. and D. Meyer, "The Locator/ID Separation
Protocol Internet Groper (LIG)", RFC 6835,
DOI 10.17487/RFC6835, January 2013,
<https://www.rfc-editor.org/info/rfc6835>.
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Appendix A. Sample PubSub Deployment Experiences
Some LISP production networks have been running different forms of
PubSub for some time. The following subsections provide an inventory
of some experience lessons from these deployments.
A.1. PubSub as a Monitoring Tool
Some LISP deployments are using PubSub as a way to monitor EID-
Prefixes (particularly, EID-to-RLOC mappings). To that aim, some
LISP implementations have extended the LISP Internet Groper (lig)
[RFC6835] tool to use PubSub. Such an extension is meant to support
an interactive mode with lig, and request subscription for the EID of
interest. If there are RLOC changes, the Map-Server sends a
notification and then the lig client displays that change to the
user.
A.2. Mitigating Negative Map-Cache Entries
Section 8.1 of [RFC9301] suggests two TTL values for Negative Map-
Replies: either 15-minute (if the EID-Prefix does not exist) or
1-minute (if the prefix exists but has not been registered). While
these values are based on the original operational experience of the
LISP protocol designers, negative cache entries have two unintended
effects that were observed in production.
First, if the xTR keeps receiving traffic for a negative EID
destination (i.e., an EID-Prefix with no RLOCs associated with it),
it will try to resolve the destination again once the cached state
expires, even if the state has not changed in the Map-Server. It was
observed in production that this is happening often in networks that
have a significant amount of traffic addressed for outside of the
LISP network. This might result on excessive resolution signaling to
keep retrieving the same state due to the cache expiring. PubSub is
used to relax TTL values and cache negative mapping entries for
longer periods of time, avoiding unnecessary refreshes of these
forwarding entries, and drastically reducing signaling in these
scenarios. In general, a TTL-based schema is a “polling mechanism”
that leads to more signaling where PubSub provides an "event
triggered mechanism" at the cost of state.
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Second, if the state does indeed change in the Map-Server, updates
based on TTL timeouts might prevent the cached state at the xTR from
being updated until the TTL expires. This behavior was observed
during configuration (or reconfiguration) periods on the network,
where no-longer-negative EID-Prefixes do not receive the traffic yet
due to stale Map-Cache entries present in the network. With the
activation of PubSub, stale caches can be updated as soon as the
state changes.
A.3. Improved Mobility Latency
An improved convergence time was observed on the presence of mobility
events on LISP networks running PubSub as compared with running LISP
[RFC9301]. As described in Section 4.1.2.1 of
[I-D.ietf-lisp-eid-mobility], LISP can rely on data-driven Solicit-
Map-Requests (SMRs) to ensure eventual network converge. Generally,
PubSub offers faster convergence due to (1) no need to wait for a
data triggered event and (2) less signaling as compared with the SMR-
based flow. Note that when a Map-Server running PubSub has to update
a large number of subscribers at once (i.e., when a popular mapping
is updated) SMR based convergence may be faster for a small subset of
the subscribers (those receiving PubSub updates last). Deployment
experience reveals that data-driven SMRs and PubSub mechanisms
complement each other and provide a fast and resilient network
infrastructure in the presence of mobility events.
Furthermore, experience showed that not all LISP entities on the
network need to implement PubSub for the network to get the benefits.
In scenarios with significant traffic coming from outside of the LISP
network, the experience showed that enabling PubSub in the border
routers significantly improves mobility latency overall. Even if
edge xTRs do not implement PubSub, and traffic is exchanged between
EID-Prefixes at the edge, xTRs still converge based on data-driven
events and SMR-triggered updates.
A.4. Enhanced Reachability with Dynamic Redistribution of Prefixes
There is a need to interconnect LISP networks with other networks
that might or might not run LISP. Some of those scenarios are
similar to the ones described in [I-D.haindl-lisp-gb-atn] and
[I-D.moreno-lisp-uberlay]. When connecting LISP to other networks,
the experience revealed that in many deployments the point of
interaction with the other domains is not the Mapping System but
rather the border router of the LISP site. For those cases the
border router needs to be aware of the LISP prefixes to redistribute
them to the other networks. Over the years different solutions have
been used.
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First, Map-Servers were collocated with the border routers, but this
was hard to scale since border routers scale at a different pace than
Map-Servers. Second, decoupled Map-Servers and border routers were
used with static configuration of LISP entries on the border, which
was problematic when modifications were made. Third, a routing
protocol (e.g., BGP) can be used to redistributed LISP prefixes from
the Map-Servers to a border router, but this comes with some
implications, particularly the Map-Servers needs to implement an
additional protocol which consumes resources and needs to be properly
configured. Therefore, once PubSub was available, deployments
started to adapt it to enable border routers to dynamically learn the
prefixes they need to redistribute without the need of extra
protocols or extra configuration on the network.
In other words, PubSub can be used to discover EID-Prefixes so they
can be imported into other routing domains that do not use LISP.
Similarly, PubSub can also be used to discover when EID-Prefixes need
to be withdrawn from other routing domains. That is, in a typical
deployment, a border router will withdraw an EID-Prefix it has been
announcing to external routing domains, if it receives a notification
that the RLOC-set for that EID-Prefix is now empty.
A.5. Better Serviceability
EID-to-RLOC mappings can have very long TTL, sometimes in the order
of several hours. Upon the expiry of that TTL, the xTR checks if
these entries are being used and removes any entry that is not being
used. The problem with very long Map-Cache TTL is that (in the
absence of PubSub) if a mapping changes, but it is not being used,
the cache remains but it is stale. This is due to no data traffic
being sent to the old location to trigger an SMR based Map-Cache
update as described in Section 4.1.2.1 of
[I-D.ietf-lisp-eid-mobility]. If the network operator runs a show
command on a router to track the state of the Map-Cache, the router
will display multiple entries waiting to expire but with stale RLOC
information. This might be confusing for operators sometimes,
particularly when they are debugging problems. With PubSub, the Map-
Cache is updated with the correct RLOC information, even when it is
not being used or waiting to expire, and this helps with debugging.
Acknowledgments
We would like to thank Marc Portoles, Balaji Venkatachalapathy,
Bernhard Haindl, Luigi Iannone, and Padma Pillay-Esnault for their
great suggestions and help regarding this document.
Many thanks to Alvaro Retana for the careful AD review.
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Thanks to Chris M. Lonvick for the security directorate review, Al
Morton for the OPS-DIR review, Roni Even for the Gen-ART review, Mike
McBride for the rtg-dir review, Magnus Westerlund for the tsv
directorate review, and Sheng Jiang for the int-dir review.
Thanks to John Scudder, Erik Kline, Lars Eggert, Warren Kumari,
Martin Duke, Murray Kucherawy, Éric Vyncke, Robert Wilton,
Zaheduzzaman Sarker, and Roman Danyliw for the IESG review.
This work was partly funded by the ANR LISP-Lab project #ANR-
13-INFR-009 (https://anr.fr/Projet-ANR-13-INFR-0009).
Contributors
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Dino Farinacci
lispers.net
San Jose, CA
USA
Email: farinacci@gmail.com
Johnson Leong
Email: johnsonleong@gmail.com
Fabio Maino
Cisco
San Jose, CA
USA
Email: fmaino@cisco.com
Christian Jacquenet
Orange
Rennes
France
Email: christian.jacquenet@orange.com
Stefano Secci
Cnam
France
Email: stefano.secci@cnam.fr
Authors' Addresses
Alberto Rodriguez-Natal
Cisco
Barcelona
Spain
Email: natal@cisco.com
Vina Ermagan
Google
United States of America
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Email: ermagan@gmail.com
Albert Cabellos
UPC/BarcelonaTech
Barcelona
Spain
Email: acabello@ac.upc.edu
Sharon Barkai
Nexar
Email: sharon.barkai@getnexar.com
Mohamed Boucadair
Orange
Rennes
France
Email: mohamed.boucadair@orange.com
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