wdiff rfc9687.original rfc9687.txt

IDR

Internet Engineering Task Force (IETF) J. Snijders
Internet-Draft
Request for Comments: 9687 Fastly
Updates: 4271 (if approved) B. Cartwright-Cox
Intended status:
Category: Standards Track Port 179
Expires: 7 February 2025
ISSN: 2070-1721 Y. Qu
Futurewei
6 August
November 2024

Border Gateway Protocol 4 (BGP-4) Send Hold Timer
draft-ietf-idr-bgp-sendholdtimer-15

Abstract

This document defines the SendHoldtimer, SendHoldTimer, along with the
SendHoldTimer_Expires event, for the Border Gateway Protocol (BGP)
Finite State Machine (FSM). Implementation of the SendHoldTimer
helps overcome situations where a BGP connection is not terminated
after the local system detects that the remote system is not
processing BGP messages. This document specifies that the local
system should close the BGP connection and not solely rely on the
remote system for connection closure when the SendHoldTimer expires.
This document updates RFC4271.

Requirements Language

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. RFC 4271.

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 an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list It represents the consensus of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid the IETF community. It has
received public review and has been approved for a maximum publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of six months RFC 7841.

Information about the current status of this document, any errata,
and how to provide feedback on it may be updated, replaced, or obsoleted by other documents obtained 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 7 February 2025.
https://www.rfc-editor.org/info/rfc9687.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
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(https://trustee.ietf.org/license-info) in effect on the date of
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in the Revised BSD License.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language
3. Example of a problematic scenario . . . . . . . . . . . . . . 3
3. Problematic Scenario
4. Changes to RFC 4271 - SendHoldTimer . . . . . . . . . . . . . 4
3.1.
4.1. Session Attributes . . . . . . . . . . . . . . . . . . . 4
3.2.
4.2. Timer Event: SendHoldTimer_Expires . . . . . . . . . . . 4
3.3.
4.3. Changes to the FSM . . . . . . . . . . . . . . . . . . . 4
3.4.
4.4. Changes to BGP Timers . . . . . . . . . . . . . . . . . . 6
4.
5. Send Hold Timer Expired Error Handling . . . . . . . . . . . 6
5.
6. Implementation Considerations . . . . . . . . . . . . . . . . 6
6.
7. Operational Considerations . . . . . . . . . . . . . . . . . 7
7.
8. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8.
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
10. Acknowledgements
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
10.1.
11.1. Normative References . . . . . . . . . . . . . . . . . . 7
10.2.
11.2. Informative References . . . . . . . . . . . . . . . . . 8
Appendix A. Implementation status - RFC EDITOR: REMOVE BEFORE
PUBLICATION . . . . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9

1. Introduction

This document defines the SendHoldtimer, SendHoldTimer, along with the
SendHoldTimer_Expires event, for the Border Gateway Protocol (BGP)
[RFC4271]
Finite State Machine (FSM) defined in section 8. Section 8 of [RFC4271].

Failure to terminate a blocked BGP connection can result in network
reachability issues, and the subsequent failure to generate and
deliver BGP UPDATE messages to another BGP speaker of the local
system is detrimental to all participants of the inter-domain routing
system. This phenomena is thought to have contributed to IP traffic
blackholing
packet loss events in the global Internet routing system
[bgpzombies].

This specification intends to improve this situation by requiring
that BGP connections be terminated if the local system has detected
that the remote system cannot possibly have processed any BGP
messages for the duration of the SendHoldTime. Through
standardization of the aforementioned requirement, operators will
benefit from consistent behavior across different BGP
implementations.

BGP speakers following this specification do not rely exclusively on
remote systems closing blocked connections, but will connections; they also locally close
blocked connections.

2. Requirements Language

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.

3. Example of a problematic scenario Problematic Scenario

In implementations lacking the concept of a SendHoldTimer, a
malfunctioning or overwhelmed remote speaker may cause data on the
BGP socket in the local system to accumulate ad infinitum. This
could result in forwarding failure and traffic loss, as the
overwhelmed speaker continues to utilize stale routes.

An example fault state: as BGP runs over TCP [RFC9293], it is
possible for a BGP speaker in the Established state to encounter a
BGP speaker that is advertising a TCP Receive Window (RCV.WND) of
size zero. This 0 The size zero of this window prevents the local system
from sending KEEPALIVE, UPDATE, or any other critical BGP messages
across the network socket to the remote speaker.

Generally BGP implementations have no visibility into lower-layer
subsystems such as TCP or the speaker's current Receive Window size,
and there is no existing BGP mechanism for such a blocked connection
to be recognized. Hence BGP implementations are not able to handle
this situation in a consistent fashion.

The major primary issue arising from that arises when a BGP speaker being is unable to send a
BGP message to a given remote speaker is that as a result that the affected speaker
subsequently is may end
up operating based on stale with outdated routing information. Failure of the BGP
speaker to send (and thus the remote speaker to receive) BGP messages
on a single BGP session can negatively impact the ability of an
entire autonomous system (or even a group of autonomous systems) to
converge.

4. Changes to RFC 4271 - SendHoldTimer

BGP speakers are implemented following a conceptual model "BGP Finite
State Machine" (FSM), which is outlined in section Section 8 of [RFC4271].
This specification adds a BGP timer, SendHoldTimer, and updates the
BGP FSM as follows:

3.1. indicated in the following subsections.

4.1. Session Attributes

The following optional session attributes for each connection are
added to the list in Section 8, before 8 of [RFC4271] appearing just prior to
"The optional session attributes support different features of the
BGP functionality that have implications for the BGP FSM state
transitions":

NEW

| 14) SendHoldTimer
|
| 15) SendHoldTime

The

SendHoldTime determines how long a BGP speaker will stay in the
Established state before the TCP connection is dropped because no BGP
messages can be transmitted to its peer. A BGP speaker can configure
the value of the SendHoldTime for each peer independently.

3.2.

4.2. Timer Event: SendHoldTimer_Expires

Another timer event is added to Section 8.1.3 of [RFC4271] as
following:
follows:

NEW

3.3.

4.3. Changes to the FSM

The following changes are made to section Section 8.2.2 in of [RFC4271].

In "OpenConfirm State", the handling of Event 26 is revised as
follows:

OLD

NEW

The following paragraph is added to section Section 8.2.2 of [RFC4271] in
"Established State", after the paragraph which that ends "unless the
negotiated HoldTime value is zero.": zero":

NEW

| If the SendHoldTimer_Expires (Event 29) occurs, the local
| system:
|
| - (optionally) sends a NOTIFICATION message with the BGP Error
| Code "Send Hold Timer Expired" if the local system can
| determine that doing so will not delay the following actions
| in this paragraph,
|
| - logs an error message in the local system with the BGP Error
| Code "Send Hold Timer Expired",
|
| - releases all BGP resources,
|
| - sets the ConnectRetryTimer to zero,
|
| - drops the TCP connection,
|
| - increments the ConnectRetryCounter by 1,
|
| - (optionally) performs peer oscillation damping if the
| DampPeerOscillations attribute is set to TRUE, and
|
| - changes its state to Idle.
|
| Each time the local system sends a BGP message, it restarts the
| SendHoldTimer unless the SendHoldTime value is zero or the
| negotiated HoldTime value is zero, in which cases case the
| SendHoldTimer is stopped.
|
| The SendHoldTimer is stopped following any transition out of
| the Established state as part of the "release all BGP
| resources" action.

3.4.

4.4. Changes to BGP Timers

Section 10 of [RFC4271] summarizes BGP Timers. timers. This document adds
another optional BGP timer: SendHoldTimer.

NEW

| SendHoldTime is an FSM attribute that stores the initial value for
| the SendHoldTimer. If SendHoldTime is non-zero non-zero, then it MUST be
| greater than the value of HoldTime, HoldTime; see Section 5 6 of
| [I-D.ietf-idr-bgp-sendholdtimer] [RFC9687] for
| suggested default values.

5. Send Hold Timer Expired Error Handling

If the local system does not send any BGP messages within the period
specified in SendHoldTime, then a NOTIFICATION message with the "Send
Hold Timer Expired" Error Code MAY be sent and the BGP connection
MUST be closed. Additionally, an error MUST be logged in the local
system, indicating the Send "Send Hold Timer Expired Expired" Error Code.

6. Implementation Considerations

Due to the relative rarity of the failure mode that this
specification is designed to address, and also the fact that network
operators may be unfamiliar with the formal specification of BGP
fault detection mechanisms such as HoldTimer, it is likely that a
large number of operators are will be unaware of the necessity of need for an
additional mechanism such as SendHoldtimer. SendHoldTimer.

Accordingly, it is RECOMMENDED that implementations of this
specification enable SendHoldtimer SendHoldTimer by default, without requiring
additional configuration of the BGP speaking BGP-speaking device.

The default value of SendHoldTime for a BGP connection SHOULD be the
greater of:

* 8 minutes; minutes or

* 2 times the negotiated HoldTime

Implementations MAY make the value of SendHoldTime configurable,
either globally or on a per-peer basis, within the constraints set
out in Section 3.4 above. 4.4.

The subcode for NOTIFICATION message "Send Hold Timer Expired" is set
to 0 and is not used, used; no additional data is to be appended to the end
of a "Send Hold Timer Expired" NOTIFICATION message.

7. Operational Considerations

When the local system recognizes that a remote speaker is has not processing
processed any BGP messages for the duration of the SendHoldTime, it
is likely that the local system will not be able to inform the remote
peer through a NOTIFICATION message as to why the connection is being
closed. This documents document suggests that an attempt to send a
NOTIFICATION message with the "Send Hold Timer Expired" error code is Error Code
still be made, if doing so will not delay closing the BGP connection.
Meanwhile
Meanwhile, an error message is logged into in the local system.

Other mechanisms can be used as well, for example example, BGP speakers
SHOULD provide this reason ("Send Hold Timer Expired") as part of
their operational state; e.g. state (for example, bgpPeerLastError in the BGP MIB [RFC4273].

7.
[RFC4273]).

8. Security Considerations

This specification does not change BGP's security characteristics.
Implementing the BGP SendHoldTimer as specified in this document will
enhance network resilience by terminating connections with
malfunctioning or overwhelmed remote peers.

9. IANA Considerations

IANA has registered code value 8 for "Send Hold Timer Expired" in the "BGP
Error (Notification) Codes" registry in within the "Border Gateway
Protocol (BGP) Parameters" registry group.

10. Acknowledgements

The authors would like to thank William McCall, Theo de Raadt, John
Heasley, Nick Hilliard, Jeffrey Haas, Tom Petch, Susan Hares, Keyur
Patel, Ben Maddison, Claudio Jeker, and John Scudder for their
helpful review of this document.

10.

11. References

10.1.

11.1. Normative References
[I-D.ietf-idr-bgp-sendholdtimer]
Snijders, J., Cartwright-Cox, B., and Y. Qu, "Border
Gateway Protocol 4 (BGP-4) Send Hold Timer", Work in
Progress, Internet-Draft, draft-ietf-idr-bgp-
sendholdtimer, <https://datatracker.ietf.org/doc/html/
draft-ietf-idr-bgp-sendholdtimer>.

[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>.

[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/info/rfc4271>.

[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>.

[RFC9293] Eddy, W., Ed., "Transmission Control Protocol (TCP)",
STD 7, RFC 9293, DOI 10.17487/RFC9293, August 2022,
<https://www.rfc-editor.org/info/rfc9293>.

10.2.

11.2. Informative References

[bgpzombies]
Fontugne, R., "BGP Zombies", April 2019,
<https://labs.ripe.net/author/romain_fontugne/bgp-
zombies/>.

[BIRD] Kubecova, K., "BIRD Internet Routing Daemon", October
2023, <https://gitlab.nic.cz/labs/bird/-/commit/
bcf2327425d4dd96f381b87501cccf943bed606e>.

[frr] Lamparter, D., "bgpd: implement SendHoldTimer", May 2022,
<https://github.com/FRRouting/frr/pull/11225>.

[neo-bgp] Cartwright-Cox, B., "What does bgp.tools support", August
2022, <https://bgp.tools/kb/bgp-support>.

[openbgpd] Jeker, C., "bgpd send side hold timer", December 2020,
<https://marc.info/?l=openbsd-tech&m=160820754925261&w=2>.

[RFC4273] Haas, J., Ed. and S. Hares, Ed., "Definitions of Managed
Objects for BGP-4", RFC 4273, DOI 10.17487/RFC4273,
January 2006, <https://www.rfc-editor.org/info/rfc4273>.

Appendix A. Implementation status - RFC EDITOR: REMOVE BEFORE
PUBLICATION

This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in RFC 7942.
The description of implementations in this section is intended to
assist the IETF in its decision processes in progressing drafts to
RFCs. Please note that the listing of any individual implementation
here does not imply endorsement by the IETF. Furthermore, no effort
has been spent to verify the information presented here that was
supplied by IETF contributors. This is not intended as, and must not
be construed to be, a catalog of available implementations or their
features. Readers are advised to note that other implementations may
exist.

According to RFC 7942, "this will allow reviewers and working groups
to assign due consideration to documents that have the benefit of
running code, which may serve as evidence of valuable experimentation
and feedback that have made the implemented protocols more mature.
It is up to the individual working groups to use this information as
they see fit".

* OpenBGPD [openbgpd]

* FRRouting [frr]

* neo-bgp (bgp.tools) [neo-bgp]

* BIRD [BIRD]

Patches to recognize error code 8 were merged into OpenBSD's and the-
tcpdump-group's tcpdump implementations.

Authors' Addresses

Job Snijders
Fastly
Amsterdam
Netherlands
Email: job@fastly.com

Ben Cartwright-Cox
Port 179 Ltd
London
United Kingdom
Email: ben@benjojo.co.uk

Yingzhen Qu
Futurewei Technologies
Santa Clara,
San Jose, CA 95131
United States of America
Email: yingzhen.ietf@gmail.com