Border Gateway Protocol 4 (BGP-4) Send Hold Timer
draft-spaghetti-idr-bgp-sendholdtimer-08
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Replaced".
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|---|---|---|---|
| Authors | Job Snijders , Ben Cartwright-Cox | ||
| Last updated | 2022-08-19 | ||
| Replaced by | draft-ietf-idr-bgp-sendholdtimer | ||
| RFC stream | (None) | ||
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| Consensus boilerplate | Unknown | ||
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draft-spaghetti-idr-bgp-sendholdtimer-08
IDR J. Snijders
Internet-Draft Fastly
Updates: 4271 (if approved) B. Cartwright-Cox
Intended status: Standards Track Port 179 Ltd
Expires: 20 February 2023 19 August 2022
Border Gateway Protocol 4 (BGP-4) Send Hold Timer
draft-spaghetti-idr-bgp-sendholdtimer-08
Abstract
This document defines the SendHoldTimer session attribute for the
Border Gateway Protocol (BGP) Finite State Machine (FSM).
Implementation of a SendHoldTimer should help overcome situations
where BGP sessions are not terminated after it has become detectable
for the local system that the remote system is not processing BGP
messages. For robustness, this document specifies that the local
system should close BGP connections and not solely rely on the remote
system for session closure when BGP timers have expired. 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 20 February 2023.
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Copyright Notice
Copyright (c) 2022 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. Specification of the Send Hold Timer . . . . . . . . . . . . 3
3.1. Session Attributes . . . . . . . . . . . . . . . . . . . 3
3.2. SendHoldTimer_Expires Event Definition . . . . . . . . . 4
3.3. MsgSent Event Definition . . . . . . . . . . . . . . . . 5
3.4. Restarting the SendHoldTimer . . . . . . . . . . . . . . 5
4. Send Hold Timer Expired Error Handling . . . . . . . . . . . 5
5. Operational Considerations . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
9.1. Normative References . . . . . . . . . . . . . . . . . . 6
9.2. Informative References . . . . . . . . . . . . . . . . . 7
Appendix A. Implementation status - RFC EDITOR: REMOVE BEFORE
PUBLICATION . . . . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
This document defines the SendHoldTimer session attribute 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, 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
theorised to have contributed to IP traffic backholing 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 SendHoldTimer. 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 hosts 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 across the
network socket to the remote peer. Historically, many BGP
implementations were unable to handle this situation in a robust
fashion. Previous BGP RFC specifications would not give cause for
the session to be torn down in such situations.
Generally BGP implementation have no visibility into lower-layer
subsystems such as TCP or the peer's current Receive Window.
Therefore, this document relies upon BGP implementations having the
ability to detect whether the TCP socket to a BGP peer is progressing
(data is being transmitted), or persisting in a stalled state.
3. Specification of the Send Hold Timer
BGP speakers are implemented following a conceptual model "BGP Finite
State Machine" (FSM), which is outlined in section 8 of [RFC4271].
This specification updates the BGP FSM as following:
3.1. Session Attributes
The following mandatory session attributes are added to paragraph 6
of Section 8, before "The state session attribute indicates the
current state of the BGP FSM":
9) SendHoldTimer
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10) SendHoldTime (an initial value of 8 minutes is recommended)
3.2. SendHoldTimer_Expires Event Definition
Section 8.1.3 [RFC4271] is extended as following:
Event XX1: SendHoldTimer_Expires
Definition : An event generated when the SendHoldTimer expires.
Status: Mandatory
If the SendHoldTimer_Expires (Event XX1), the local system:
- logs a message with the BGP Error Notification Code "Send Hold
Timer Expired",
- releases all BGP resources,
- sets the ConnectRetryTimer to zero,
- drops the TCP connection,
- increments the ConnectRetryCounter,
- (optionally) performs peer oscillation damping if the
DampPeerOscillations attribute is set to TRUE, and
- changes its state to Idle.
If the DelayOpenTimer_Expires event (Event 12) occurs in the Connect
state, the local system:
- sends an OPEN message to its peer,
- sets the HoldTimer to a large value, and
- sets the SendHoldTimer to a large value, and
- changes its state to OpenSent.
If the DelayOpen attribute is set to FALSE, the local system:
- stops the ConnectRetryTimer (if running) and sets the
ConnectRetryTimer to zero,
- completes BGP initialization
- sends an OPEN message to its peer,
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- sets the HoldTimer to a large value, and
- sets the SendHoldTimer to a large value, and
- changes its state to OpenSent.
A HoldTimer value of 4 minutes is suggested.
A SendHoldTimer value of 8 minutes is suggested.
3.3. MsgSent Event Definition
Section 8.1.5 [RFC4271] is extended as following:
Event XX2: MsgSent
Definition: An event is generated when a KEEPALIVE or UPDATE message is transmitted.
Status: Mandatory
3.4. Restarting the SendHoldTimer
On page 74 [RFC4271] before "If the local system receives an UPDATE
message, and the UPDATE message error handling procedure (see
Section 6.3) detects an error (Event 28), the local system:", add the
following:
If the local system transmits a KEEPALIVE or UPDATE message (MsgSent
(Event XX2)), the local system:
- restarts the SendHoldTimer, and
- remains in the Established state.
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.
5. Operational Considerations
When the local system recognizes a remote peer is not processing any
BGP messages for the duration of the Send Hold Timer, the local
system will not be able to inform the remote peer through a BGP
message as to why the session is being closed (i.e. a NOTIFICATION
message with the "Send Hold Timer Expired" error code).
Even so, BGP speakers SHOULD provide this reason as part of their
operational state; e.g. bgpPeerLastError in the BGP MIB [RFC4273].
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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
This document requests IANA to assign a value named "Send Hold Timer
Expired" in the "BGP Error (Notification) Codes" sub-registry under
the "Border Gateway Protocol (BGP) Parameters" registry.
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>.
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[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/>.
[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>.
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.
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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]
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
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