-
Notifications
You must be signed in to change notification settings - Fork 2
/
draft-sa-idr-maxprefix.xml
345 lines (321 loc) · 19.3 KB
/
draft-sa-idr-maxprefix.xml
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE rfc SYSTEM "rfc2629.dtd" [
<!ENTITY RFC2234 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.2234.xml">
<!ENTITY RFC2629 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.2629.xml">
<!ENTITY RFC4234 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.4234.xml">
<!ENTITY nbsp " ">
]>
<?xml-stylesheet type='text/xsl' href='rfc2629.xslt' ?>
<?rfc strict="yes" ?>
<?rfc comments="no" ?>
<?rfc inline="no" ?>
<?rfc editing="no" ?>
<?rfc toc="yes" ?>
<?rfc tocompact="yes" ?>
<?rfc tocdepth="3" ?>
<?rfc symrefs="yes" ?>
<?rfc sortrefs="yes" ?>
<?rfc compact="yes" ?>
<?rfc subcompact="no" ?>
<rfc category="std"
ipr="trust200902"
docName="draft-sa-idr-maxprefix-00"
updates="4271"
submissionType="IETF">
<front>
<title abbrev="Revised BGP Maximum Prefix Limits">
Revised BGP Maximum Prefix Limits
</title>
<author fullname="Job Snijders" initials="J." surname="Snijders">
<organization abbrev="NTT">NTT Ltd</organization>
<address>
<postal>
<street>Theodorus Majofskistraat 100</street>
<code>1065 SZ</code>
<city>Amsterdam</city>
<country>The Netherlands</country>
</postal>
<email>[email protected]</email>
</address>
</author>
<author fullname="Melchior Aelmans" initials="M." surname="Aelmans">
<organization>Juniper Networks</organization>
<address>
<postal>
<street>Boeing Avenue 240</street>
<code>1119 PZ</code>
<city>Schiphol-Rijk</city>
<country>The Netherlands</country>
</postal>
<email>[email protected]</email>
</address>
</author>
<date />
<area>Routing</area>
<workgroup>Inter-Domain Routing</workgroup>
<keyword>BGP</keyword>
<keyword>Prefix</keyword>
<abstract>
<t>
This document updates RFC4271 by revising control mechanism which limit the negative impact of route leaks (RFC7908) and/or resource exhaustion in Border Gateway Protocol (BGP) implementations.
</t>
</abstract>
<note title="Requirements Language">
<t>
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 <xref target="RFC2119"/> <xref target="RFC8174"/> when, and only when, they appear in all capitals, as shown here.
</t>
</note>
</front>
<middle>
<section title="Introduction">
<t>
This document updates <xref target="RFC4271" /> by revising control mechanism which limit the negative impact of <xref target="RFC7908">route leaks</xref> and/or resource exhaustion in Border Gateway Protocol (BGP) implementations.
While <xref target="RFC4271" /> described methods to tear down BGP sessions or discard UPDATES after certain thresholds are exceeded, some nuances in this specification were missing resulting in inconsistencies between BGP implementations.
In addition to clarifying "inbound maximum prefix limits", this document also introduces a specification for "outbound maximum prefix limits".
</t>
</section>
<!--
<section title="Application of Control Theory to BGP Operations">
<t>
</t>
</section>
-->
<section title="Changes to RFC4271 Section 6">
<t>
This section updates <xref target="RFC4271" /> to specify what events can result in AutomaticStop (Event 8) in the BGP FSM.
</t>
<t>
The following paragraph replaces the second paragraph of Section 6.7 (Cease), which starts with "A BGP speaker MAY support" and ends with "The speaker MAY also log this locally.":
</t>
<t>
<list style="empty">
<t>
A BGP speaker MAY support the ability to impose a locally-configured, upper bound on the number of address prefixes the speaker is willing to accept from a neighbor (inbound maximum prefix limit) or send to a neighbor (outbound prefix limit).
The limit on the prefixes accepted from a neighbor can be applied before policy processing (Pre-Policy) or after policy processing (Post-Policy).
Outbound prefix limits MUST be measured after policy since the Policy (even a policy of "send all") is run before determining what can be sent.
When the upper bound is reached, the speaker, under control of local configuration, either:
<list style="letters">
<t><!-- option a -->
Discards new address prefixes to or from the neighbor (while maintaining the BGP connection with the neighbor)
</t>
<t> <!-- option b -->
Terminates the BGP connection with the neighbor
</t>
</list>
<!-- OLD : If the BGP speaker decides to terminate its BGP connection with a neighbor because the number of address prefixes received from the neighbor exceeds the locally-configured, upper bound, then the speaker MUST send the neighbor a NOTIFICATION message with the Error Code Cease. -->
If the BGP peer uses option (b) where the limit causes a CEASE Notification, then the CEASE error codes should use:
</t>
</list>
</t>
<texttable>
<ttcol>Subcode</ttcol><ttcol>Symbolic Name</ttcol>
<c>1</c><c>Maximum Number of Prefixes Reached</c>
<c>TBD</c><c>Threshold exceeded: Self-Destructing, Maximum Number of Prefixes Send</c>
</texttable>
<t>
<list style="empty">
<t>
The speaker MAY also log this locally.
</t>
</list>
</t>
</section>
<section title="Changes to RFC4271 Section 8">
<t>
This section updates <xref target="RFC4271">Section 8</xref>, the paragraph that starts with "One reason for an AutomaticStop event is" and ends with "The local system automatically disconnects the peer." is replaced with:
</t>
<t>
<list style="empty">
<t>
Possible reasons for an AutomaticStop event are: A BGP speaker receives an UPDATE messages with a number of prefixes for a given peer such that the total prefixes received exceeds the maximum number of prefixes configured (either "Pre-Policy" or "Post-Policy"), or announces more prefixes than through local configuration allowed to.
The local system automatically disconnects the peer.
</t>
</list>
</t>
</section>
<section title="BGP Yang Model Considerations - PERHAPS REMOVE BEFORE PUBLICATION">
<t>
In <xref target="I-D.ietf-idr-bgp-model" /> in container 'prefix-limit', a leaf named "max-prefixes" exists.
The authors recommend the BGP Yang Model to be revised to contain the following leaves:
<list style="hanging">
<t>max-prefixes-inbound-pre-policy</t>
<t>max-prefixes-inbound-post-policy</t>
<t>max-prefixes-outbound</t>
</list>
In addition to the above, the authors suggest that the BGP Yang Model is extended in such a way that per peer per AFI/SAFI pair an operator can specify whether to tear down the session or discard sending or receiving updates.
</t>
</section>
<section title="Changes to RFC4271 Section 9">
<t>
This section updates <xref target="RFC4271" /> by adding a subsection after Section 9.4 (Originating BGP routes) to specify various events that can lead up to AutomaticStop (Event 8) in the BGP FSM.
</t>
<t>
<list style="empty">
<t>
9.5 Maximum Prefix Limits
</t>
<t>
9.5.1 Pre-Policy Inbound Maximum Prefix Limits
</t>
<t>
<list style="empty">
<t>
The Adj-RIBs-In stores routing information learned from inbound UPDATE messages that were received from another BGP speaker <xref target="RFC4271">Section 3.2</xref>.
The pre-policy limit uses the number of NLRIs per Address Family Identifier (AFI) per Subsequent Address Family Identifier (SAFI) as input into its threshold comparisons.
For example, when an operator configures the pre-policy limit for IPv4 Unicast to be 50 on a given EBGP session, and the other BGP speaker announces its 51st IPv4 Unicast NLRI, the session MUST be terminated.
</t>
<t>
Pre-policy limits are particularly useful to help dampen the effects of full table route leaks and memory exhaustion when the implementation stores rejected routes.
</t>
</list>
</t>
<t>
9.5.2 Post-Policy Inbound Maximum Prefix Limits
</t>
<t>
<list style="empty">
<t>
RFC4271 describes a Policy Information Base (PIB) that contains local policies that can be applied to the information in the Routing Information Base (RIB).
The post-policy limit uses the number of NLRIs per Address Family Identifier (AFI) per Subsequent Address Family Identifier (SAFI), after application of the Import Policy as input into its threshold comparisons.
For example, when an operator configures the post-policy limit for IPv4 Unicast to be 50 on a given EBGP session, and the other BGP speaker announces a hundred IPv4 Unicast routes of which none are accepted as a result of the local import policy (and thus not considered for the Loc-RIB by the local BGP speaker), the session is not terminated.
</t>
<t>
Post-policy limits are useful to help prevent FIB exhaustion and prevent accidental BGP session teardown due to prefixes not accepted by policy anyway.
</t>
</list>
</t>
<t>
9.5.3 Outbound Maximum Prefix Limits
</t>
<t>
<list style="empty">
<t>
An operator MAY configure a BGP speaker to terminate its BGP session with a neighbor when the number of address prefixes to be advertised to that neighbor exceeds a locally configured post-policy upper limit.
The BGP speaker then MUST send the neighbor a NOTIFICATION message with the Error Code Cease and the Error Subcode "Threshold reached: Maximum Number of Prefixes Send". Implementations MAY support additional actions.
The Hard Cease action is defined in <xref target="RFC8538" />.
</t>
<t>
Reporting when thresholds have been exceeded is an implementation specific consideration, but SHOULD include methods such as Syslog <xref target="RFC5424"/>.
By definition, Outbound Maximum Prefix Limits are Post-Policy.
</t>
<t>
The Adj-RIBs-Out stores information selected by the local BGP speaker for advertisement to its neighbors.
The routing information stored in the Adj-RIBs-Out will be carried in the local BGP speaker's UPDATE messages and advertised to its neighbors <xref target="RFC4271">Section 3.2</xref>.
The Outbound Maximum Prefix Limit uses the number of NLRIs per Address Family Identifier (AFI) per Subsequent Address Family Identifier (SAFI), after application of the Export Policy, as input into its threshold comparisons.
For example, when an operator configures the Outbound Maximum Prefix Limit for IPv4 Unicast to be 50 on a given EBGP session, and were about to announce its 51st IPv4 Unicast NLRI to the other BGP speaker as a result of the local export policy, the session MUST be terminated.
</t>
<t>
Outbound Maximum Prefix Limits are useful to help dampen the negative effects of a misconfiguration in local policy.
In many cases, it would be more desirable to tear down a BGP session rather than causing or propagating a route leak.
</t>
</list>
</t>
</list>
</t>
</section>
<section title="Security Considerations">
<t>
Maximum Prefix Limits are an essential tool for routing operations and SHOULD be used to increase stability.
<!-- comment from sue: This section does not provide the appropriate depth of security to indicate
why maximum prefix provides a tool for limiting attacks or errors to
bring down networks.
-->
</t>
</section>
<section title="IANA Considerations">
<t>
<!-- TDB, find better names? -->
This memo requests that IANA assigns a new subcode named "Threshold exceeded: Self-Destructing, Maximum Number of Prefixes Send" in the "Cease NOTIFICATION message subcodes" registry under the "Border Gateway Protocol (BGP) Parameters" group.
</t>
</section>
<section title="Acknowledgments">
<t>
The authors would like to thank
Saku Ytti and John Heasley (NTT),
Jeff Haas, Colby Barth and John Scudder (Juniper Networks),
Martijn Schmidt (i3D.net),
Teun Vink (BIT),
Sabri Berisha (eBay),
Martin Pels (Quanza),
Steven Bakker (AMS-IX),
Aftab Siddiqui (ISOC),
Yu Tianpeng,
Ruediger Volk (Deutsche Telekom),
Robert Raszuk (Bloomberg),
Jakob Heitz (Cisco),
and Susan Hares (Hickory Hill Consulting)
for their support, insightful review, and comments.
</t>
</section>
<section title="Implementation status - RFC EDITOR: REMOVE BEFORE PUBLICATION">
<t>
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
RFC7942. 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.
</t>
<t>
The below table provides an overview (as of the moment of writing) of which vendors have produced implementation of inbound or outbound maximum prefix limits.
Each table cell shows the applicable configuration keywords if the vendor implemented the feature.
</t>
<texttable anchor="table_ex" title="Maximum prefix limits capabilities per implementation" style="all">
<ttcol align="center" width="20%">Vendor</ttcol>
<ttcol align="center">Inbound Pre-Policy</ttcol>
<ttcol align="center">Inbound Post-Policy</ttcol>
<ttcol align="center">Outbound</ttcol>
<c>Cisco IOS XR</c><c></c><c>maximum-prefix</c><c></c>
<c>Cisco IOS XE</c><c></c><c>maximum-prefix</c><c></c>
<c>Juniper Junos OS</c><c>prefix-limit</c><c>accepted-prefix-limit, or prefix-limit combined with 'keep none'</c><c></c>
<c>Nokia SR OS</c><c>prefix-limit</c><c></c><c></c>
<c>NIC.CZ BIRD</c><c>'import keep filtered' combined with 'receive limit'</c><c>'import limit' or 'receive limit'</c><c>export limit</c>
<c>OpenBSD OpenBGPD</c><c>max-prefix</c><c></c><c></c>
<c>Arista EOS</c><c>maximum-routes</c><c>maximum-accepted-routes</c><c></c>
<c>Huawei VRPv5</c><c>peer route-limit</c><c></c><c></c>
<c>Huawei VRPv8</c><c>peer route-limit</c><c>peer route-limit accept-prefix</c><c></c>
<postamble>First presented by Snijders at <xref target="RIPE77"/></postamble>
</texttable>
</section>
<section title="Appendix: Implementation Guidance">
<t>
1)
make it clear who does what:
if A sends too many prefixes to B
A should see "ABC" in log
B should see "DEF" in log
to make it clear which of the two parties does what
2)
recommended by default automatically restart after between 15 and 30 minutes
</t>
</section>
</middle>
<back>
<references title="Normative References">
<?rfc include="reference.RFC.2119"?>
<?rfc include="reference.RFC.8174"?>
<?rfc include="reference.RFC.4271"?>
<?rfc include="reference.RFC.8538"?>
</references>
<references title="Informative References">
<?rfc include="reference.I-D.ietf-idr-bgp-model"?>
<?rfc include="reference.RFC.5424"?>
<?rfc include="reference.RFC.7908"?>
<reference anchor="RIPE77" target="https://ripe77.ripe.net/wp-content/uploads/presentations/59-RIPE77_Snijders_Routing_Policy_Architecture.pdf">
<front>
<title>Robust Routing Policy Architecture</title>
<author surname="Snijders" fullname="Job Snijders">
<organization>NTT Communications</organization>
</author>
<date month="May" year="2018"/>
</front>
</reference>
</references>
</back>
</rfc>