Border Gateway Protocol 4 (BGP-4) Send Hold Timer
draft-spaghetti-idr-bgp-sendholdtimer-00
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| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Job Snijders , Ben Cartwright-Cox | ||
| Last updated | 2021-04-20 | ||
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draft-spaghetti-idr-bgp-sendholdtimer-00
IDR J. Snijders
Internet-Draft Fastly
Updates: 4271 (if approved) B. Cartwright-Cox
Intended status: Standards Track April 20, 2021
Expires: October 22, 2021
Border Gateway Protocol 4 (BGP-4) Send Hold Timer
draft-spaghetti-idr-bgp-sendholdtimer-00
Abstract
This document defines the SendHoldTimer session attribute for the
Border Gateway Protocol (BGP) Finite State Machine (FSM). A session
should be terminated if the TCP receive window is zero for the
duration of the Send Hold Timer, in this situation the peer is
expected to terminate the connection. For robustness, this document
specifies that the local system should also close the connection.
This document updates RFC4271.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
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 October 22, 2021.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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 Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Specification of the Send Hold Timer . . . . . . . . . . . . 3
2.1. Session Attributes . . . . . . . . . . . . . . . . . . . 3
2.2. SendHoldTimer_Expires Event Definition . . . . . . . . . 3
3. Send Hold Timer Expired Error Handling . . . . . . . . . . . 4
4. Implementation status - RFC EDITOR: REMOVE BEFORE PUBLICATION 5
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
This document defines the SendHoldTimer session attribute for the
Border Gateway Protocol (BGP) [RFC4271] Finite State Machine (FSM)
defined in section 8.
As BGP runs over TCP [RFC0793] 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 and thus preventing the local
system from sending KEEPALIVE, CEASE, WITHDRAW, UPDATE, or other
critical messages across the wire. At the moment of writing, most
BGP implementations appear unable to handle this situation in a
robust fashion.
Not terminating 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 [l3outage]
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This specification intends to improve this situation by requiring
sessions to be terminated if the TCP receive window is zero for the
duration of the Send Hold Timer. 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. 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:
2.1. 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
10) SendHoldTime (an initial value of 4 minutes is recommended)
2.2. SendHoldTimer_Expires Event Definition
Section 8.1.3 [RFC4271] is extended as following:
Event XX: SendHoldTimer_Expires
Definition : An event generated when the SendHoldTimer expires.
Status: Mandatory
If the SendHoldTimer_Expires (Event XX), 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,
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- (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,
- sets the HoldTimer to a large value, and
- changes its state to OpenSent.
A HoldTimer value of 4 minutes is suggested.
A SendHoldTimer value of 4 minutes is suggested.
3. Send Hold Timer Expired Error Handling
If a system does not send and receive 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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4. 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".
o OpenBGPD [openbgpd]
While not a BGP implementation, as a result of investigation into
this phenomena, the Linux TCP implementation TCP_USER_TIMEOUT option
was improved, allowing easier termination of TCP sessions which are
not progressing data [TCP_USER_TIMEOUT].
5. Acknowledgements
The authors would like to thank William McCall for their helpful
review of this document.
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.
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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. References
8.1. Normative References
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981,
<https://www.rfc-editor.org/info/rfc793>.
[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>.
8.2. Informative References
[l3outage]
Reuters, "Level 3 problem sparks temporary outage for some
U.S. telecomms", August 2020,
<https://www.reuters.com/article/level-3-communi-outages-
idUSL2N1CB00C>.
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[openbgpd]
Jeker, C., "bgpd send side hold timer", December 2020,
<https://marc.info/?l=openbsd-tech&m=160796802508185&w=2>.
[TCP_USER_TIMEOUT]
Chen, E., "[Idr] TCP & BGP: Some don't send terminate BGP
when holdtimer expired, because TCP recv window is 0",
January 2021, <https://mailarchive.ietf.org/arch/msg/idr/
KOU59BTIvsqv8OHVBIvcVr97fD4/>.
Authors' Addresses
Job Snijders
Fastly
Amsterdam
Netherlands
Email: job@fastly.com
Ben Cartwright-Cox
London
United Kingdom
Email: ben@benjojo.co.uk
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