Internet DRAFT - draft-ietf-idr-bgp-sendholdtimer
draft-ietf-idr-bgp-sendholdtimer
IDR J. Snijders
Internet-Draft Fastly
Updates: 4271 (if approved) B. Cartwright-Cox
Intended status: Standards Track Port 179 Ltd
Expires: 1 September 2024 Y. Qu
Futurewei Technologies
29 February 2024
Border Gateway Protocol 4 (BGP-4) Send Hold Timer
draft-ietf-idr-bgp-sendholdtimer-02
Abstract
This document defines the SendHoldTimer and SendHoldTime session
attributes for the Border Gateway Protocol (BGP) Finite State Machine
(FSM). Implementation of the SendHoldTimer helps overcome situations
where a BGP session 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 session 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.
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
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 1 September 2024.
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Copyright Notice
Copyright (c) 2024 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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Example of a problematic scenario . . . . . . . . . . . . . . 3
3. SendHoldTimer - Changes to RFC 4271 . . . . . . . . . . . . . 3
3.1. Session Attributes . . . . . . . . . . . . . . . . . . . 4
3.2. Timer Event: SendHoldTimer_Expires . . . . . . . . . . . 4
3.3. Changes to the FSM . . . . . . . . . . . . . . . . . . . 4
3.4. Changes to BGP Timers . . . . . . . . . . . . . . . . . . 5
4. Send Hold Timer Expired Error Handling . . . . . . . . . . . 5
5. Operational Considerations . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
9.1. Normative References . . . . . . . . . . . . . . . . . . 7
9.2. Informative References . . . . . . . . . . . . . . . . . 7
Appendix A. Implementation status - RFC EDITOR: REMOVE BEFORE
PUBLICATION . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
This document defines the SendHoldTimer and SendHoldTime session
attributes for the Border Gateway Protocol (BGP) [RFC4271] Finite
State Machine (FSM) defined in section 8.
Failure to terminate a 'stuck' BGP session can result in Denial Of
Service, and the subsequent failure to generate and deliver BGP
WITHDRAW messages to other BGP peers of the local system is
detrimental to all participants of the inter-domain routing system.
This phenomena is theorized to have contributed to IP traffic
blackholing events in global Internet routing system [bgpzombies].
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This specification intends to improve this situation by requiring
sessions to be terminated if the local system has detected that the
remote system cannot possibly have received any BGP messages for the
duration of the SendHoldTime. Through codification of the
aforementioned requirement, operators will benefit from consistent
behavior across different BGP implementations.
BGP speakers following this specification do not exclusively rely on
remote systems robustly closing connections, but will also locally
close connections.
2. Example of a problematic scenario
In implementations lacking the concept of a SendHoldTimer, a
malfunctioning or overwhelmed remote peer 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
peer 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 peer that is advertising a TCP Receive Window (RCV.WND) of size
zero. This 0 window prevents the local system from sending
KEEPALIVE, CEASE, WITHDRAW, UPDATE, or any other critical BGP
messages successfully across the network socket to the remote peer,
and this causes the BGP FSM to stuck.
Generally BGP implementations have no visibility into lower-layer
subsystems such as TCP or the peer's current Receive Window size, and
there is no existing BGP mechanism for such a stuck session to be
torn down. Hence BGP implementations are not able to handle this
situation in a robust and consistent fashion.
This document provides a mechanism for BGP implementations to detect
whether the TCP socket to a BGP peer is progressing (data is being
transmitted), or persisting in a stalled state. In case of a stalled
state, the BGP session can be restarted.
3. SendHoldTimer - Changes to RFC 4271
BGP speakers are implemented following a conceptual model "BGP Finite
State Machine" (FSM), which is outlined in section 8 of [RFC4271].
This specification adds a BGP timer, SendHoldTimer, and updates the
BGP FSM as following:
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3.1. Session Attributes
The following mandatory session attributes for each connection are
added to Section 8, before "The state session attribute indicates the
current state of the BGP FSM":
9) SendHoldTimer
10) SendHoldTime (an initial value of 8 minutes is recommended)
The SendHoldTime determines how long a BGP speaker would stay in
Established state before the TCP connection is dropped because no BGP
messages can be successfully transmitted to its peer. A BGP speaker
can configure the value of the SendHoldTime to each peer
independently.
3.2. Timer Event: SendHoldTimer_Expires
Another timer event is added to Section 8.1.3 of [RFC4271] as
following:
Event XX1: SendHoldTimer_Expires
Definition: An event generated when the SendHoldTimer expires.
Status: Mandatory
3.3. Changes to the FSM
The following changes are made to section 8.2.2 in [RFC4271].
In "OpenConfirm State", the handling of Event 26 is revised as
follows:
Old Text:
If the local system receives a KEEPALIVE message (KeepAliveMsg
(Event 26)), the local system:
- restarts the HoldTimer and
- changes its state to Established.
Next Text:
If the local system receives a KEEPALIVE message (KeepAliveMsg
(Event 26)), the local system:
- restarts the HoldTimer,
- sets the SendHoldTimer to the default or configured value, and
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- changes its state to Established.
The following paragraph is added to section 8.2.2 in "Established
State", after the paragraph which ends "unless the negotiated
HoldTime value is zero.":
If the SendHoldTimer_Expires (Event XX1), the local system:
- sends a NOTIFICATION message with the BGP Error Code "Send Hold
Timer Expired",
- 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 successfully sends a KEEPALIVE, UPDATE,
and/or NOTIFICATION message, it restarts its SendHoldTimer.
3.4. Changes to BGP Timers
In Section 10 of [RFC4271] summarizes BGP Timers. This document adds
another BGP timer: SendHoldTimer.
SendHoldTime is a mandatory FSM attribute that stores the initial
value for the SendHoldTimer. The suggested default value for
SendHoldTime is 8 minutes. An implementation MAY make it
configurable.
4. Send Hold Timer Expired Error Handling
If a system does not send successive KEEPALIVE, UPDATE, and/or
NOTIFICATION messages within the period specified in the Send Hold
Time, then the BGP connection is closed and a log message is emitted.
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5. Operational Considerations
When the local system recognizes a remote peer is not processing any
BGP messages for the duration of the SendHoldTime, likely the local
system will not be able to inform the remote peer through a BGP
message as to why the session is being closed by sending a
NOTIFICATION. This documents suggests that a NOTIFICATION message
with the "Send Hold Timer Expired" error code is still sent,
meanwhile an error message SHOULD be logged into the local system.
Other mechanisms can be used as well, for example BGP speakers SHOULD
provide this reason as part of their operational state; e.g.
bgpPeerLastError in the BGP MIB [RFC4273].
6. Security Considerations
This specification addresses the vulnerability of a BGP speaker to a
potential attack whereby a BGP peer can pretend to be unable to
process BGP messages and in doing so create a scenario where the
local system is poisoned with stale routing information.
There are three detrimental aspects to the problem of not robustly
handling 'stuck' peers:
* Failure to send BGP messages to a peer implies the peer is
operating based on stale routing information.
* Failure to disconnect from a 'stuck' peer hinders the local
system's ability to construct a non-stale local Routing
Information Base (RIB).
* Failure to disconnect from a 'stuck' peer hinders the local
system's ability to inform other BGP peers with current network
reachability information.
In other respects, this specification does not change BGP's security
characteristics.
7. IANA Considerations
IANA has registered code 8 for "Send Hold Timer Expired" in the "BGP
Error (Notification) Codes" sub-registry under the "Border Gateway
Protocol (BGP) Parameters" registry.
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8. Acknowledgements
The authors would like to thank William McCall, Theo de Raadt, John
Heasley, Nick Hilliard, Jeffrey Haas, and Tom Petch for their helpful
review of this document.
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>.
[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>.
[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>.
[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)",
RFC 9293, DOI 10.17487/RFC9293, August 2022,
<https://www.rfc-editor.org/info/rfc9293>.
9.2. 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>.
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[openbgpd] Jeker, C., "bgpd send side hold timer", December 2020,
<https://marc.info/?l=openbsd-tech&m=160820754925261&w=2>.
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
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Ben Cartwright-Cox
Port 179 Ltd
London
United Kingdom
Email: ben@benjojo.co.uk
Yingzhen Qu
Futurewei Technologies
Santa Clara,
United States
Email: yingzhen.ietf@gmail.com
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