Network Working Group J. Dong
Internet-Draft Huawei Technologies
Intended status: Standards Track Z. Li
Expires: January 13, 2022 China Mobile
L. Ou
Y. Luo
China Telcom Co., Ltd.
July 12, 2021
BGP FlowSpec Extensions for Large Scale Prefix based Steering
draft-dong-idr-flowspec-scalable-prefix-steering-01
Abstract
This document describes a mechanism to use BGP FlowSpec RFC5575 as a
scalable way of distributing prefix based traffic steering policies.
The necessary extensions to BGP are also specified.
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
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on January 13, 2022.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Typical Scenario of Prefix based Traffic Steering . . . . . . 3
3. Proposed BGP Extensions . . . . . . . . . . . . . . . . . . . 4
3.1. New Wide Community Atom . . . . . . . . . . . . . . . . . 4
3.2. New Wide BGP Community . . . . . . . . . . . . . . . . . 5
4. Operational Procedures . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. Contributing Authors . . . . . . . . . . . . . . . . . . . . 7
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
9. Normative References . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
Dynamic traffic steering becomes more and more popular in operator
networks. It is desirable that an automatic and scalable mechanism
can be provided to dynamically deploy such policies to network
devices. BGP FlowSpec [RFC8955] provides a flexible mechanism to
specify the matching rules and the corresponding actions for specific
traffic. Due to the flexibility of BGP FlowSpec, the number of
flowspec filtering entries supported in hardware is usually limited,
which is suitable for a small number of complicated traffic matching
and manipulation policies. In some operator networks, there are
requirements of dynamically deploying a large amount of destination
prefix based traffic steering policies, thus some scalable mechanism
for large scale prefix based traffic steering policy is needed.
One possible option is that the controller advertises the destination
prefix based steering policy as normal IP routes directly to the
network devices. Although this seems straightforward, it is
difficult to determine the interaction results of the steering routes
and the existing routes in the devices, and may have unexpected
impacts to the whole network.
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Another option is that the controller advertises the destination
prefix based steering policy as BGP FlowSpec routes to the network
devices. Instead of installing these routes as the BGP FlowSpec
filtering entries, the network devices are instructed by the
controller to download the prefix based steering policies to their
Forwarding Information Base (FIB), so that the number of prefix based
steering policy supported is not limited by the number of BGP
FlowSpec filtering entries.
This document proposes to use the mechanism in the second option, and
specifies the required extensions to BGP protocol.
2. Typical Scenario of Prefix based Traffic Steering
In ISP networks, usually there are multiple paths to a particular
destination. The path with better QoS characteristics such as
latency, loss, jitter, etc., is preferred. Since these QoS
characteristics change from time to time, the decision of path
selection also needs to be changed accordingly.
Figure 1 shows a typical scenario of prefix based traffic steering in
inter-domain ISP networks. As shown in the figure, there are two
transit nodes from AS-1 to the destination Prefix-1 in AS-4, saying
transit node M in AS-2 and transit node N in AS-3. In normal state,
traffic from AS-1 to Prefix-1 goes through transit node M. While
transit node N would be preferred when performance degradation
happens on transit node M. In that case, traffic should be steered
to go through transit node N instead. According to the real time
network performance condition, the traffic steering policy needs to
be changed dynamically. Thus the operator of AS-1 expects an
efficient and convenient mechanism for steering the traffic to
different transit nodes.
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********************************
* +----------+ *
* AS-1 | Policy | *
* |Controller| * AS-2
* +----------+ *
* +---+ +---+ * +-----------+
* /| B |---------| C |-----| Transit M |\ AS-4
* / +---+\ +---+\ * +-----------+ \\
* / | \\ / | \ / \ +---------+
*+---+/ | \\// | * \ / \_| |
*| A | | //\ | * X _| Prefix-1|
*+---+\ | // \\ | * / \ / | |
* \ | / \ | / \ / +---------+
* \ +---+ +---+/ * +-----------+ //
* \| D |---------| E |-----| Transit N |/
* +---+ +---+ * +-----------+
* *
* ISP Network * AS-3
* *
********************************
Figure 1. Scenario of Prefix Based Traffic Steering
3. Proposed BGP Extensions
This section specifies the proposed extension to BGP protocol.
3.1. New Wide Community Atom
A new Wide Community Atoms TLV [I-D.ietf-idr-wide-bgp-communities]
"Bit Flags List Atom" is defined. This atom is an array of units of
32 flags numbered from the most significant bit as bit zero. The
Length field for this TLV is always a multiple of four bytes,
regardless of the number of bits carried, and no padding is required.
Unassigned bits are considered as reserved and MUST be set to zero on
transmission by the originator of this TLV. Bits not contained in
the TLV MUST be assumed to be set to zero.
Type (TBA): Bit Flags List Atom
One flag (bit 31) is defined in this document. When this flag is set
to 1, recursive route lookup SHOULD be performed in the local routing
table identified by the address family of the received route with
this TLV. When this bit is set to 0, recursive route lookup SHOULD
be performed in the global routing table.
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+-------+-------+--------------------------------------------------+
| Bit | Value | Meaning |
+-------+-------+--------------------------------------------------+
| 31 | 0 | recursive route lookup in global table |
| | 1 | recursive route lookup in local table |
| other | - | MUST be zero when sent and ignored upon receipt. |
+-------+-------+--------------------------------------------------+
The assignment of other bits is managed by IANA.
3.2. New Wide BGP Community
A new Registered Wide BGP Community "Download to FIB" is defined. It
is used to instruct the receiving BGP speakers to download the BGP
FlowSpec routes carrying this Wide Community into the FIB, instead of
installing the FlowSpec routes into FlowSpec filtering entries.
Download TO FIB:
Type: 0x0001 S = src AS #
F = 0x80 C = 0x00000000
H = 0 T = none
L = 22 octets E = none
R = TBA by IANA P = Type_TBD (Flags 0x00000001)
An example of the Download to FIB Wide BGP community generated by the
policy controller in Figure 1 is as below:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Container Type 1 (1) |1 0 0 0 0 0 0 0| Hop Count: 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length: 22 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Community: Download TO FIB (IANA assigned) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source AS Number: A |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Context AS Number: 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Param TLV (3) | Length: 7 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags (TBD) | Length: 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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4. Operational Procedures
In order to achieve dynamic prefix based traffic steering in the
scenario of Figure 1, the controller of AS-1 constructs a BGP
FlowSpec route which carries the following information:
o Prefix-1 as the Destination Prefix component of BGP FlowSpec NLRI.
o Traffic-Action Extended Community, with the Route Policy
Distribution (RPD) [I-D.ietf-idr-rpd] Flag set. This is to
indicate that the corresponding FlowSpec filtering rules are used
as routing policies.
o NO_ADVERTISE Community [RFC1997]. This indicates that the
receiving BGP speaker MUST NOT advertise this BGP FlowSpec route
to other BGP peers.
o "Redirect to IP" Extended Communities
[I-D.ietf-idr-flowspec-redirect-ip], with the global administrator
field set to the address of transit node N.
o "Download to FIB" Wide BGP Community to indicate that the
receiving BGP speaker SHOULD download this BGP FlowSpec filtering
rule to its FIB.
The controller of AS-1 sends this BGP FlowSpec route to the ASBRs of
AS-1, i.e. router C and E.
On receipt of this BGP FlowSpec route from the controller, the
routers processes the received BGP FlowSpec route as follows:
o Extracts the target prefix Prefix-1 from the Destination Prefix
component in the BGP FlowSpec NLRI.
o Identifies that the RPD Flag in the Traffic-Action Extended
Community is set, so the corresponding filtering rules will be
used as Routing Policies.
o Parses the "Download to FIB" Wide BGP Community, and knows that
this FlowSpec route SHOULD be downloaded into FIB entry, instead
of being installed as FlowSpec filtering entry. And according to
the Flag Bit 31 in the Wide Community Parameters TLV, knows that
the recursive route lookup should be performed in the global
routing table.
o Extracts the redirect IP address from the "Redirect to IP"
Extended Communities, which will be used for the recursive route
lookup.
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After performing the recursive lookup in the designated routing
table, the connected next hop is identified and this route is
downloaded as a FIB entry into the forwarding plane.
5. IANA Considerations
IANA is requested to assign a new code point for the "Bit Flags List
Atom" TLV from the "Wide BGP Communities Atom Types" registry.
IANA is requested to assign a new code point for the "Download to
FIB" Wide BGP Community from the "Registered Wide BGP Communities"
registry.
6. Security Considerations
TBD
7. Contributing Authors
The following individuals gave significant contributions to this
document:
Peng Zhang
China Telecom
15335170018@189.cn
Zhongchao Li
China Telecom
15301588336@189.cn
Dong Shu
China Telecom
15301586130@189.cn
8. Acknowledgements
The authors would like to thank Shunwan Zhuang, Nan Wu and Haibo Wang
for the valuable discussion on this work.
9. Normative References
[I-D.ietf-idr-flowspec-redirect-ip]
Uttaro, J., Haas, J., Texier, M., Karch, A., Ray, S.,
Simpson, A., and W. Henderickx, "BGP Flow-Spec Redirect to
IP Action", draft-ietf-idr-flowspec-redirect-ip-02 (work
in progress), February 2015.
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[I-D.ietf-idr-rpd]
Li, Z., Ou, L., Luo, Y., Lu, S., Mishra, G. S., Chen, H.,
Zhuang, S., and H. Wang, "BGP Extensions for Routing
Policy Distribution (RPD)", draft-ietf-idr-rpd-10 (work in
progress), November 2020.
[I-D.ietf-idr-wide-bgp-communities]
Raszuk, R., Haas, J., Lange, A., Decraene, B., Amante, S.,
and P. Jakma, "BGP Community Container Attribute", draft-
ietf-idr-wide-bgp-communities-05 (work in progress), July
2018.
[RFC1997] Chandra, R., Traina, P., and T. Li, "BGP Communities
Attribute", RFC 1997, DOI 10.17487/RFC1997, August 1996,
<https://www.rfc-editor.org/info/rfc1997>.
[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>.
[RFC8955] Loibl, C., Hares, S., Raszuk, R., McPherson, D., and M.
Bacher, "Dissemination of Flow Specification Rules",
RFC 8955, DOI 10.17487/RFC8955, December 2020,
<https://www.rfc-editor.org/info/rfc8955>.
Authors' Addresses
Jie Dong
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing 100095
China
Email: jie.dong@huawei.com
Zhenqiang Li
China Mobile
No.32 Xuanwumenxi Ave., Xicheng District
Beijing 100032
China
Email: li_zhenqiang@hotmail.com
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Liang Ou
China Telcom Co., Ltd.
109 West Zhongshan Ave,Tianhe District
Guangzhou 510630
China
Email: oul@gsta.com
Yujia Luo
China Telcom Co., Ltd.
109 West Zhongshan Ave,Tianhe District
Guangzhou 510630
China
Email: luoyuj@gsta.com
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