RFC 8671 PROPOSED STANDARD BGP · MONITORING · ROUTING
BMP Adj-RIB-Out: Support for Adj-RIB-Out in the BGP Monitoring Protocol (BMP)
Lets BGP monitoring show the routes a router advertises, not only the ones it receives.
RFC EDITOR
Evens, T., Bayraktar, S., Lucente, P., Mi, P., and S. Zhuang, "Support for Adj-RIB-Out in the BGP Monitoring Protocol (BMP)", RFC 8671, DOI 10.17487/RFC8671, November 2019, <https://www.rfc-editor.org/info/rfc8671>.
BIBTEX
@misc{rfc8671,
series = {Request for Comments},
number = 8671,
howpublished = {RFC 8671},
publisher = {RFC Editor},
doi = {10.17487/RFC8671},
url = {https://www.rfc-editor.org/info/rfc8671},
author = {T. Evens and S. Bayraktar and P. Lucente and P. Mi and S. Zhuang},
title = {{Support for Adj-RIB-Out in the BGP Monitoring Protocol (BMP)}},
pagetotal = 9,
year = 2019,
month = nov,
} LINEAGE · FROM THE RFC INDEXOpen full graph →
RFC text
Contents
Internet Engineering Task Force (IETF) T. Evens
Request for Comments: 8671 S. Bayraktar
Updates: 7854 Cisco Systems
Category: Standards Track P. Lucente
ISSN: 2070-1721 NTT Communications
P. Mi
Tencent
S. Zhuang
Huawei
November 2019
Support for Adj-RIB-Out in the BGP Monitoring Protocol (BMP)
Abstract
The BGP Monitoring Protocol (BMP) only defines access to the Adj-RIB-
In Routing Information Bases (RIBs). This document updates BMP (RFC
7854) by adding access to the Adj-RIB-Out RIBs. It also adds a new
flag to the peer header to distinguish between Adj-RIB-In and Adj-
RIB-Out.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8671.
Copyright Notice
Copyright (c) 2019 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 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. Terminology
3. Definitions
4. Per-Peer Header
5. Adj-RIB-Out
5.1. Post-policy
5.2. Pre-policy
6. BMP Messages
6.1. Route Monitoring and Route Mirroring
6.2. Statistics Report
6.3. Peer Up and Down Notifications
6.3.1. Peer Up Information
7. Other Considerations
7.1. Peer and Update Groups
7.2. Changes to Existing BMP Session
8. Security Considerations
9. IANA Considerations
9.1. Addition to BMP Peer Flags Registry
9.2. Additions to BMP Statistics Types Registry
9.3. Addition to BMP Initiation Message TLVs Registry
10. Normative References
Acknowledgements
Contributors
Authors' Addresses
1. Introduction
The BGP Monitoring Protocol (BMP) defines monitoring of the received
(e.g., Adj-RIB-In) Routing Information Bases (RIBs) per peer. The
pre-policy Adj-RIB-In conveys to a BMP receiver all RIB data before
any policy has been applied. The post-policy Adj-RIB-In conveys to a
BMP receiver all RIB data after policy filters and/or modifications
have been applied. An example of pre-policy versus post-policy is
when an inbound policy applies attribute modification or filters.
Pre-policy would contain information prior to the inbound policy
changes or filters of data. Post-policy would convey the changed
data or would not contain the filtered data.
Monitoring the received updates that the router received before any
policy has been applied is the primary level of monitoring for most
use cases. Inbound policy validation and auditing are the primary
use cases for enabling post-policy monitoring.
In order for a BMP receiver to receive any BGP data, the BMP sender
(e.g., router) needs to have an established BGP peering session and
actively be receiving updates for an Adj-RIB-In.
Being able to only monitor the Adj-RIB-In puts a restriction on what
data is available to BMP receivers via BMP senders (e.g., routers).
This is an issue when the receiving end of the BGP peer is not
enabled for BMP or when it is not accessible for administrative
reasons. For example, a service provider advertises prefixes to a
customer, but the service provider cannot see what it advertises via
BMP. Asking the customer to enable BMP and monitoring of the Adj-
RIB-In are not feasible.
BMP [RFC7854] only defines Adj-RIB-In being sent to BMP receivers.
This document updates the per-peer header defined in Section 4.2 of
[RFC7854] by adding a new flag to distinguish between Adj-RIB-In and
Adj-RIB-Out. BMP senders use the new flag to send either Adj-RIB-In
or Adj-RIB-Out.
Adding Adj-RIB-Out provides the ability for a BMP sender to send to
BMP receivers what it advertises to BGP peers, which can be used for
outbound policy validation and to monitor routes that were
advertised.
2. Terminology
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. Definitions
Adj-RIB-Out
As defined in [RFC4271], "The Adj-RIBs-Out contains the routes for
advertisement to specific peers by means of the local speaker's
UPDATE messages."
Pre-policy Adj-RIB-Out
The result before applying the outbound policy to an Adj-RIB-Out.
This normally would match what is in the local RIB.
Post-policy Adj-RIB-Out
The result of applying outbound policy to an Adj-RIB-Out. This
MUST convey to the BMP receiver what is actually transmitted to
the peer.
4. Per-Peer Header
The per-peer header has the same structure and flags as defined in
Section 4.2 of [RFC7854] with the addition of the O flag as shown
here:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|V|L|A|O| Resv |
+-+-+-+-+-+-+-+-+
* The O flag indicates Adj-RIB-In if set to 0 and Adj-RIB-Out if set
to 1.
The existing flags are defined in Section 4.2 of [RFC7854], and the
remaining bits are reserved for future use. They MUST be transmitted
as 0, and their values MUST be ignored on receipt.
When the O flag is set to 1, the following fields in the per-peer
header are redefined:
* Peer Address: The remote IP address associated with the TCP
session over which the encapsulated Protocol Data Unit (PDU) is
sent.
* Peer AS: The Autonomous System number of the peer to which the
encapsulated PDU is sent.
* Peer BGP ID: The BGP Identifier of the peer to which the
encapsulated PDU is sent.
* Timestamp: The time when the encapsulated routes were advertised
(one may also think of this as the time when they were installed
in the Adj-RIB-Out), expressed in seconds and microseconds since
midnight (zero hour), January 1, 1970 (UTC). If zero, the time is
unavailable. Precision of the timestamp is implementation-
dependent.
5. Adj-RIB-Out
5.1. Post-policy
The primary use case in monitoring Adj-RIB-Out is to monitor the
updates transmitted to a BGP peer after outbound policy has been
applied. These updates reflect the result after modifications and
filters have been applied (e.g., post-policy Adj-RIB-Out). Some
attributes are set when the BGP message is transmitted, such as next
hop. Post-policy Adj-RIB-Out MUST convey to the BMP receiver what is
actually transmitted to the peer.
The L flag MUST be set to 1 to indicate post-policy.
5.2. Pre-policy
Similar to Adj-RIB-In policy validation, pre-policy Adj-RIB-Out can
be used to validate and audit outbound policies. For example, a
comparison between pre-policy and post-policy can be used to validate
the outbound policy.
Depending on the BGP peering session type -- Internal BGP (IBGP),
IBGP route reflector client, External BGP (EBGP), BGP confederations,
route server client -- the candidate routes that make up the pre-
policy Adj-RIB-Out do not contain all local RIB routes. Pre-policy
Adj-RIB-Out conveys only routes that are available based on the
peering type. Post-policy represents the filtered/changed routes
from the available routes.
Some attributes are set only during transmission of the BGP message,
i.e., post-policy. It is common that the next hop may be null,
loopback, or similar during the pre-policy phase. All mandatory
attributes, such as next hop, MUST be either zero or have an empty
length if they are unknown at the pre-policy phase completion. The
BMP receiver will treat zero or empty mandatory attributes as self-
originated.
The L flag MUST be set to 0 to indicate pre-policy.
6. BMP Messages
Many BMP messages have a per-peer header, but some are not applicable
to Adj-RIB-In or Adj-RIB-Out monitoring, such as Peer Up and Down
Notifications. Unless otherwise defined, the O flag should be set to
0 in the per-peer header in BMP messages.
6.1. Route Monitoring and Route Mirroring
The O flag MUST be set accordingly to indicate if the route monitor
or route mirroring message conveys Adj-RIB-In or Adj-RIB-Out.
6.2. Statistics Report
The Statistics Report message has a Stat Type field to indicate the
statistic carried in the Stat Data field. Statistics report messages
are not specific to Adj-RIB-In or Adj-RIB-Out and MUST have the O
flag set to zero. The O flag SHOULD be ignored by the BMP receiver.
This document defines the following new statistics types:
* Stat Type = 14: Number of routes in pre-policy Adj-RIB-Out. This
statistics type is 64-bit Gauge.
* Stat Type = 15: Number of routes in post-policy Adj-RIB-Out. This
statistics type is 64-bit Gauge.
* Stat Type = 16: Number of routes in per-AFI/SAFI pre-policy Adj-
RIB-Out. The value is structured as: 2-byte Address Family
Identifier (AFI), 1-byte Subsequent Address Family Identifier
(SAFI), followed by a 64-bit Gauge.
* Stat Type = 17: Number of routes in per-AFI/SAFI post-policy Adj-
RIB-Out. The value is structured as: 2-byte Address Family
Identifier (AFI), 1-byte Subsequent Address Family Identifier
(SAFI), followed by a 64-bit Gauge.
6.3. Peer Up and Down Notifications
Peer Up and Down Notifications convey BGP peering session state to
BMP receivers. The state is independent of whether or not route
monitoring or route mirroring messages will be sent for Adj-RIB-In,
Adj-RIB-Out, or both. BMP receiver implementations SHOULD ignore the
O flag in Peer Up and Down Notifications.
6.3.1. Peer Up Information
This document defines the following Peer Up Information TLV type:
* Type = 4: Admin Label. The Information field contains a free-form
UTF-8 string whose byte length is given by the Information Length
field. The value is administratively assigned. There is no
requirement to terminate the string with null or any other
character.
Multiple Admin Labels can be included in the Peer Up Notification.
When multiple Admin Labels are included, the BMP receiver MUST
preserve their order.
The Admin Label is optional.
7. Other Considerations
7.1. Peer and Update Groups
Peer and update groups are used to group updates shared by many
peers. This is a level of efficiency in implementations, not a true
representation of what is conveyed to a peer in either pre-policy or
post-policy.
One of the use cases to monitor post-policy Adj-RIB-Out is to
validate and continually ensure the egress updates match what is
expected. For example, wholesale peers should never have routes with
community X:Y sent to them. In this use case, there may be hundreds
of wholesale peers, but a single peer could have represented the
group.
From a BMP perspective, it should be simple to include a group name
in the Peer Up, but it is more complex than that. BGP
implementations have evolved to provide comprehensive and structured
policy grouping, such as session, AFI/SAFI, and template-based group
policy inheritances.
This level of structure and inheritance of polices does not provide a
simple peer group name or ID, such as wholesale peer.
This document defines a new Admin Label type for Peer Up Information
TLVs (Section 6.3.1) that can be used instead of requiring a group
name. These labels have administrative scope relevance. For
example, labels "type=wholesale" and "region=west" could be used to
monitor expected policies.
Configuration and assignment of labels to peers are BGP
implementation-specific.
7.2. Changes to Existing BMP Session
In case of any change that results in the alteration of behavior of
an existing BMP session (i.e., changes to filtering and table names),
the session MUST be bounced with a Peer Down/Peer Up sequence.
8. Security Considerations
The considerations in Section 11 of [RFC7854] apply to this document.
Implementations of this protocol SHOULD require establishing sessions
with authorized and trusted monitoring devices. It is also believed
that this document does not add any additional security
considerations.
9. IANA Considerations
IANA has assigned the following new parameters to the "BGP Monitoring
Protocol (BMP) Parameters" registry
(https://www.iana.org/assignments/bmp-parameters/).
9.1. Addition to BMP Peer Flags Registry
IANA has made the following assignment for the per-peer header flag
defined in Section 4 of this document:
+------+-------------+-----------+
| Flag | Description | Reference |
+======+=============+===========+
| 3 | O flag | RFC 8671 |
+------+-------------+-----------+
Table 1: Addition to the "BMP
Peer Flags" Registry
9.2. Additions to BMP Statistics Types Registry
IANA has made the following assignment for the four statistics types
defined in Section 6.2 of this document:
+-----------+------------------------------+-----------+
| Stat Type | Description | Reference |
+===========+==============================+===========+
| 14 | Number of routes in pre- | RFC 8671 |
| | policy Adj-RIB-Out | |
+-----------+------------------------------+-----------+
| 15 | Number of routes in post- | RFC 8671 |
| | policy Adj-RIB-Out | |
+-----------+------------------------------+-----------+
| 16 | Number of routes in per-AFI/ | RFC 8671 |
| | SAFI pre-policy Adj-RIB-Out | |
+-----------+------------------------------+-----------+
| 17 | Number of routes in per-AFI/ | RFC 8671 |
| | SAFI post-policy Adj-RIB-Out | |
+-----------+------------------------------+-----------+
Table 2: Additions to the "BMP Statistics Types"
Registry
9.3. Addition to BMP Initiation Message TLVs Registry
IANA has made the following assignment per Section 6.3.1 of this
document:
+------+-------------+-----------+
| Type | Description | Reference |
+======+=============+===========+
| 4 | Admin Label | RFC 8671 |
+------+-------------+-----------+
Table 3: Addition to the "BMP
Initiation Message TLVs"
Registry
10. 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>.
[RFC7854] Scudder, J., Ed., Fernando, R., and S. Stuart, "BGP
Monitoring Protocol (BMP)", RFC 7854,
DOI 10.17487/RFC7854, June 2016,
<https://www.rfc-editor.org/info/rfc7854>.
[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>.
Acknowledgements
The authors would like to thank John Scudder and Mukul Srivastava for
their valuable input.
Contributors
The following individuals contributed to this document:
* Manish Bhardwaj, Cisco Systems
* Xianyu Zheng, Tencent
* Wei Guo, Tencent
* Shugang Cheng, H3C
Authors' Addresses
Tim Evens
Cisco Systems
2901 Third Avenue, Suite 600
Seattle, WA 98121
United States of America
Email: tievens@cisco.com
Serpil Bayraktar
Cisco Systems
3700 Cisco Way
San Jose, CA 95134
United States of America
Email: serpil@cisco.com
Paolo Lucente
NTT Communications
Siriusdreef 70-72
2132 Hoofddorp
Netherlands
Email: paolo@ntt.net
Penghui Mi
China
200233
Shanghai
Tengyun Building, Tower A, No. 397 Tianlin Road
Tencent
Email: Penghui.Mi@gmail.com
Shunwan Zhuang
China
100095
Beijing
Huawei Building, No.156 Beiqing Rd.
Huawei
Email: zhuangshunwan@huawei.com
AI ELI5
On this page
PROBLEMBMP only gave access to Adj-RIB-In, the routes a router received. A provider could not see what it advertises to a customer if the customer did not run BMP.
MECHANISMRFC 8671 adds an O flag to the BMP per-peer header (0 for Adj-RIB-In, 1 for Adj-RIB-Out), defines pre-policy and post-policy Adj-RIB-Out, adds four statistics types and an Admin Label TLV for Peer Up.
WHY IT MATTERSA BMP sender can report what it advertises to peers, for outbound policy validation and for monitoring advertised routes. It updates RFC 7854 and is itself updated by RFC 9736.
§1Why Monitor Adj-RIB-Out
The BGP Monitoring Protocol (BMP, RFC 7854) monitors the received Routing Information Bases (RIBs) per peer. Pre-policy Adj-RIB-In conveys the data before any policy is applied; post-policy Adj-RIB-In conveys it after policy filters or modifications.
Being limited to Adj-RIB-In is a problem when the receiving end of a BGP peering is not enabled for BMP or not accessible. For example, a service provider advertises prefixes to a customer but cannot see what it advertises, and asking the customer to enable BMP is not feasible.
RFC 8671 lets a BMP sender report what it advertises to BGP peers. The RFC says this can be used for outbound policy validation and for monitoring advertised routes.
Until now you could only listen to what a router heard. This lets you also listen to what it says to others.
§3Pre-policy and Post-policy Adj-RIB-Out
As defined in RFC 4271, the Adj-RIBs-Out contain the routes for advertisement to specific peers in the local speaker's UPDATE messages. This RFC defines two views of it.
- Pre-policy Adj-RIB-Out: the result before outbound policy. It normally matches what is in the local RIB, though it holds only the routes available for the peering type (IBGP, route reflector client, EBGP, confederation, route server client).
- Post-policy Adj-RIB-Out: the result after outbound policy. It MUST convey to the BMP receiver what is actually transmitted to the peer, including attributes such as next hop that are set at transmission.
Comparing the two can validate and audit outbound policy. Mandatory attributes unknown at the pre-policy stage, such as next hop, MUST be zero or have an empty length, and the BMP receiver treats them as self-originated.
There are two copies of the outgoing list: one before the router's rules are applied, and one showing exactly what was sent.
§4The O Flag in the Per-Peer Header
The per-peer header keeps the structure and flags of RFC 7854 and adds the O flag after V, L and A. O is 0 for Adj-RIB-In and 1 for Adj-RIB-Out. The remaining bits are reserved, MUST be sent as 0 and MUST be ignored on receipt.
The existing L flag still selects policy: it MUST be 1 for post-policy and 0 for pre-policy Adj-RIB-Out.
When O is 1, several fields change meaning to refer to the peer the PDU is sent to: Peer Address, Peer AS and Peer BGP ID. The Timestamp is the time the routes were advertised (or installed in the Adj-RIB-Out); zero means unavailable.
One extra yes/no switch on each message says whether it describes the heard list or the will-say list.
§6Effects on BMP Messages
Route Monitoring and Route Mirroring messages MUST set O to say whether they carry Adj-RIB-In or Adj-RIB-Out. Statistics Reports are not specific to either, so they MUST have O set to zero and the receiver SHOULD ignore it. Peer Up and Down Notifications describe session state, and receivers SHOULD ignore O in them.
Four new statistics types count routes in Adj-RIB-Out: 14 and 15 are 64-bit gauges for pre-policy and post-policy, and 16 and 17 are the per-AFI/SAFI versions, structured as a 2-byte AFI, a 1-byte SAFI and a 64-bit gauge.
A new Peer Up Information TLV, type 4 Admin Label, carries an optional free-form UTF-8 string. Several labels may appear and the receiver MUST preserve their order.
Counting messages get four new counters for the outgoing list, and a router can attach sticky-note labels to each peer.
- 14Pre-policy Adj-RIB-Out — Number of routes, 64-bit gauge.
- 15Post-policy Adj-RIB-Out — Number of routes, 64-bit gauge.
- 16Per-AFI/SAFI pre-policy — 2-byte AFI, 1-byte SAFI, 64-bit gauge.
- 17Per-AFI/SAFI post-policy — 2-byte AFI, 1-byte SAFI, 64-bit gauge.
§7Peer Groups and Session Changes
Implementations use peer and update groups for efficiency, so a single peer can represent hundreds of peers, for example wholesale peers that should never be sent routes with community X:Y. Group names are not simple because policy grouping is structured and inherited. Instead, the Admin Label lets operators tag peers, such as type=wholesale or region=west. How labels are configured and assigned is implementation-specific.
If a change alters the behavior of an existing BMP session (changes to filtering and table names), the session MUST be bounced with a Peer Down/Peer Up sequence.
Instead of listing every peer, you stick labels like "wholesale" on them so you can check the whole bunch at once.
§8Security and IANA
The security considerations of RFC 7854 apply. Implementations SHOULD require sessions with authorized and trusted monitoring devices, and the RFC believes it adds no further security considerations.
IANA assigned flag 3 (the O flag) in the BMP Peer Flags registry, Stat Types 14 to 17, and Initiation Message TLV type 4 (Admin Label).
Only let trusted watchers listen in, just as before.