| Internet-Draft | Unsolicited BFD for Sessionless Applicat | December 2021 |
| Chen, et al. | Expires 6 June 2022 | [Page] |
For operational simplification of "sessionless" applications using BFD, in this document we present procedures for "unsolicited BFD" that allow a BFD session to be initiated by only one side, and be established without explicit per-session configuration or registration by the other side (subject to certain per-interface or per-router policies).¶
We also introduce a new YANG module to configure and manage "unsolicited BFD". The YANG module in this document conforms to the Network Management Datastore Architecture (NMDA) [RFC8342].¶
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.¶
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 6 June 2022.¶
Copyright (c) 2021 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 Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.¶
The current implementation and deployment practice for BFD ([RFC5880] and [RFC5881]) usually requires BFD sessions be explicitly configured or registered on both sides. This requirement is not an issue when an application like BGP [RFC4271] has the concept of a "session" that involves both sides for its establishment. However, this requirement can be operationally challenging when the prerequisite "session" does not naturally exist between two endpoints in an application. Simultaneous configuration and coordination may be required on both sides for BFD to take effect. For example:¶
Clearly it is beneficial and desirable to reduce or eliminate unnecessary configurations and coordination in these "sessionless" applications using BFD.¶
In this document we present procedures for "unsolicited BFD" that allow a BFD session to be initiated by only one side, and be established without explicit per-session configuration or registration by the other side (subject to certain per-interface or per-router policies).¶
With "unsolicited BFD" there is potential risk for excessive resource usage by BFD from "unexpected" remote systems. To mitigate such risks, several mechanisms are recommended in the Security Considerations section.¶
Compared to the "Seamless BFD" [RFC7880], this proposal involves only minor procedural enhancements to the widely deployed BFD itself. Thus we believe that this proposal is inherently simpler in the protocol itself and deployment. As an example, it does not require the exchange of BFD discriminators over an out-of-band channel before the BFD session bring-up.¶
When BGP Add-Path [RFC7911] is deployed at an IXP using the Route Server, multiple BGP paths (when exist) can be made available to the clients of the Router Server as described in [RFC7947]. The "unsolicited BFD" can be used in BGP route selection by these clients to eliminate paths with "inaccessible nexthops".¶
With "unsolicited BFD", one side takes the "Active role" and the other side takes only the "Passive role" as described in [RFC5880].¶
On the passive side, the "unsolicited BFD" SHOULD be explicitly configured on an interface or globally (apply to all interfaces). The BFD parameters can be either per-interface or per-router based. It MAY also choose to use the parameters that the active side uses in its BFD Control packets. The "My Discriminator", however, MUST be chosen to allow multiple unsolicited BFD sessions.¶
The active side starts sending the BFD Control packets as specified in [RFC5880]. The passive side does not send BFD Control packets.¶
When the passive side receives a BFD Control packet from the active side with 0 as "Your Discriminator" and does not find an existing BFD session, the passive side MAY create a matching BFD session toward the active side, if permitted by local configuration.¶
It would then start sending the BFD Control packets and perform necessary procedure for bringing up, maintaining and tearing down the BFD session. If the BFD session fails to get established within certain specified time, or if an established BFD session goes down, the passive side would stop sending BFD Control packets and MAY delete the BFD session created until the BFD Control packets is initiated by the active side again.¶
When an Unsolicited BFD session goes down, an implementation MAY retain the session state for a period of time, which may be configurable. Retaining this state can be useful for operational purposes.¶
The "Passive role" may change to the "Active role" when a local client registers for the same BFD session, and from the "Active role" to the "Passive role" when there is no longer any locally registered client for the BFD session.¶
This document defines a new state variable called Unsolicited Role.¶
bfd.UnsolicitedRole¶
The operational mode of BFD interface when configured for unsolicited behaviour. Options can be either PASSIVE, ACTIVE or NULL (NULL - not initialized) for unsolicited BFD sessions. Default (not configured for unsolicited behaviour) MUST be set to NULL if present on the interface.¶
This section extends the YANG data model for BFD [RFC9127] to cover unsolicited BFD. We import [RFC8349] since the "bfd" container in [RFC9127] is under "control-plane-protocol".¶
Configuration for unsolicited BFD parameters for IP single-hop sessions can be done at 2 levels:¶
For operational data, a new "unsolicited" container has been added for BFD IP single-hop sessions.¶
The tree diagram below uses the graphical representation of data models, as defined in [RFC8340].¶
module: ietf-bfd-unsolicited
augment /rt:routing/rt:control-plane-protocols
/rt:control-plane-protocol/bfd:bfd/bfd-ip-sh:ip-sh:
+--rw unsolicited {bfd-unsol:unsolicited-params-global}?
+--rw enabled? boolean
+--rw local-multiplier? multiplier
+--rw (interval-config-type)?
+--:(tx-rx-intervals)
| +--rw desired-min-tx-interval? uint32
| +--rw required-min-rx-interval? uint32
+--:(single-interval) {single-minimum-interval}?
+--rw min-interval? uint32
augment /rt:routing/rt:control-plane-protocols
/rt:control-plane-protocol/bfd:bfd/bfd-ip-sh:ip-sh
/bfd-ip-sh:interfaces:
+--rw unsolicited {bfd-unsol:unsolicited-params-per-interface}?
+--rw enabled? boolean
+--rw local-multiplier? multiplier
+--rw (interval-config-type)?
+--:(tx-rx-intervals)
| +--rw desired-min-tx-interval? uint32
| +--rw required-min-rx-interval? uint32
+--:(single-interval) {single-minimum-interval}?
+--rw min-interval? uint32
augment /rt:routing/rt:control-plane-protocols
/rt:control-plane-protocol/bfd:bfd/bfd-ip-sh:ip-sh
/bfd-ip-sh:sessions/bfd-ip-sh:session:
+--ro unsolicited
+--ro role? bfd-unsol:unsolicited-role
¶
<CODE BEGINS> file "ietf-bfd-unsolicited@2021-11-23.yang"
module ietf-bfd-unsolicited {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-bfd-unsolicited";
prefix "bfd-unsol";
// RFC Ed.: replace occurences of YYYY with actual RFC numbers
// and remove this note
import ietf-bfd-types {
prefix "bfd-types";
reference
"RFC 9127: YANG Data Model for Bidirectional Forwarding Detection
(BFD)";
}
import ietf-bfd {
prefix "bfd";
reference
"RFC 9127: YANG Data Model for Bidirectional Forwarding Detection
(BFD)";
}
import ietf-bfd-ip-sh {
prefix "bfd-ip-sh";
reference
"RFC 9127: YANG Data Model for Bidirectional Forwarding Detection
(BFD)";
}
import ietf-routing {
prefix "rt";
reference
"RFC 8349: A YANG Data Model for Routing Management
(NMDA version)";
}
organization "IETF BFD Working Group";
contact
"WG Web: <https://datatracker.ietf.org/wg/bfd/>
WG List: <rtg-bfd@ietf.org>
Editors: Enke Chen (enchen@paloaltonetworks.com),
Naiming Shen (naiming@zededa.com),
Robert Raszuk (robert@raszuk.net),
Reshad Rahman (reshad@yahoo.com)";
description
"This module contains the YANG definition for BFD unsolicited
as per RFC YYYY.
Copyright (c) 2021 IETF Trust and the persons
identified as authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject
to the license terms contained in, the Simplified BSD License
set forth in Section 4.c of the IETF Trust's Legal Provisions
Relating to IETF Documents
(http://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC YYYY; see
the RFC itself for full legal notices.";
reference "RFC YYYY";
revision 2021-11-23 {
description
"Initial revision.";
reference
"RFC YYYY: Unsolicited BFD for Sessionless Applications.";
}
/*
* Feature definitions
*/
feature unsolicited-params-global {
description
"This feature indicates that the server supports global
parameters for unsolicited sessions.";
reference
"RFC YYYY: Unsolicited BFD for Sessionless Applications.";
}
feature unsolicited-params-per-interface {
description
"This feature indicates that the server supports per-interface
parameters for unsolicited sessions.";
reference
"RFC YYYY: Unsolicited BFD for Sessionless Applications.";
}
/*
* Type Definitions
*/
typedef unsolicited-role {
type enumeration {
enum unsolicited-active {
description "Active role";
}
enum unsolicited-passive {
description "Passive role";
}
}
description "Unsolicited role";
}
/*
* Augments
*/
augment "/rt:routing/rt:control-plane-protocols/"
+ "rt:control-plane-protocol/bfd:bfd/bfd-ip-sh:ip-sh" {
if-feature bfd-unsol:unsolicited-params-global;
description
"Augmentation for BFD unsolicited parameters";
container unsolicited {
description
"BFD unsolicited top level container";
leaf enabled {
type boolean;
default false;
description
"BFD unsolicited enabled globally for IP single-hop.";
}
uses bfd-types:base-cfg-parms;
}
}
augment "/rt:routing/rt:control-plane-protocols/"
+ "rt:control-plane-protocol/bfd:bfd/bfd-ip-sh:ip-sh/"
+ "bfd-ip-sh:interfaces" {
if-feature bfd-unsol:unsolicited-params-per-interface;
description
"Augmentation for BFD unsolicited on IP single-hop interface";
container unsolicited {
description
"BFD IP single-hop interface unsolicited top level
container";
leaf enabled {
type boolean;
default false;
description
"BFD unsolicited enabled on this interface.";
}
uses bfd-types:base-cfg-parms;
}
}
augment "/rt:routing/rt:control-plane-protocols/"
+ "rt:control-plane-protocol/bfd:bfd/bfd-ip-sh:ip-sh/"
+ "bfd-ip-sh:sessions/bfd-ip-sh:session" {
description
"Augmentation for BFD unsolicited on IP single-hop session";
container unsolicited {
config false;
description
"BFD IP single-hop session unsolicited top level container";
leaf role {
type bfd-unsol:unsolicited-role;
description "Role.";
}
}
}
}
<CODE ENDS>¶
This document registers the following namespace URI in the "IETF XML Registry" [RFC3688]:¶
URI: urn:ietf:params:xml:ns:yang:ietf-bfd-unsolicited¶
Registrant Contact: The IESG.¶
XML: N/A; the requested URI is an XML namespace.¶
This document registers the following YANG module in the "YANG Module Names" registry [RFC6020]:¶
Name: ietf-bfd-unsolicited¶
Namespace: urn:ietf:params:xml:ns:yang:ietf-bfd-unsolicited¶
Prefix: bfd-unsol¶
Reference: RFC YYYY¶
Authors would like to thank Acee Lindem, Greg Mirsky, Jeffrey Haas, Raj Chetan and Tom Petch for their review and valuable input.¶
The same security considerations and protection measures as those described in [RFC5880] and [RFC5881] normatively apply to this document. With "unsolicited BFD" there is potential risk for excessive resource usage by BFD from "unexpected" remote systems. To mitigate such risks, the following measures are mandatory:¶
The YANG module specified in this document defines a schema for data that is designed to be accessed via network management protocols such as NETCONF [RFC6241] or RESTCONF [RFC8040]. The lowest NETCONF layer is the secure transport layer, and the mandatory-to-implement secure transport is Secure Shell (SSH) [RFC6242]. The lowest RESTCONF layer is HTTPS, and the mandatory-to-implement secure transport is TLS [RFC8446].¶
The NETCONF access control model [RFC8341] provides the means to restrict access for particular NETCONF or RESTCONF users to a preconfigured subset of all available NETCONF or RESTCONF protocol operations and content.¶
There are a number of data nodes defined in this YANG module that are writable/creatable/deletable (i.e., config true, which is the default). These data nodes may be considered sensitive or vulnerable in some network environments. Write operations (e.g., edit-config) to these data nodes without proper protection can have a negative effect on network operations. These are the subtrees and data nodes and their sensitivity/vulnerability:¶
/routing/control-plane-protocols/control-plane-protocol/bfd/ip-sh /unsolicited:¶
/routing/control-plane-protocols/control-plane-protocol/bfd/ip-sh /interfaces/interface/unsolicited:¶
Some of the readable data nodes in this YANG module may be considered sensitive or vulnerable in some network environments. It is thus important to control read access (e.g., via get, get-config, or notification) to these data nodes. These are the subtrees and data nodes and their sensitivity/vulnerability:¶
/routing/control-plane-protocols/control-plane-protocol/bfd/ip-sh /sessions/session/unsolicited: access to this information discloses the role of the local system in the creation of the unsolicited BFD session.¶