VPN Prefix Outbound Route Filter (VPN Prefix ORF) for BGP-4
draft-ietf-idr-vpn-prefix-orf-08
| Document | Type | Active Internet-Draft (idr WG) | |
|---|---|---|---|
| Authors | Wei Wang , Aijun Wang , Haibo Wang , Gyan Mishra , Jie Dong | ||
| Last updated | 2024-09-22 | ||
| Replaces | draft-wang-idr-vpn-prefix-orf | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
| Document shepherd | Susan Hares | ||
| Shepherd write-up | Show Last changed 2023-05-12 | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | shares@ndzh.com |
draft-ietf-idr-vpn-prefix-orf-08
IDR Working Group W. Wang
Internet-Draft A. Wang
Intended status: Experimental China Telecom
Expires: 27 March 2025 H. Wang
Huawei Technologies
G. Mishra
Verizon Inc.
J. Dong
Huawei Technologies
23 September 2024
VPN Prefix Outbound Route Filter (VPN Prefix ORF) for BGP-4
draft-ietf-idr-vpn-prefix-orf-08
Abstract
This draft defines a new type of Outbound Route Filter (ORF), known
as the VPN Prefix ORF. The VPN Prefix ORF mechanism is applicable
when VPN routes from different VRFs are exchanged through a single
shared BGP session.
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
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 27 March 2025.
Copyright Notice
Copyright (c) 2024 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
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and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. The general procedures of VPN Prefix ORF mechanism on
sender . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Intra-domain Scenarios and Solutions . . . . . . . . . . 7
4.1.1. Scenario-1 and Solution (Unique RD, One RT) . . . . . 7
4.1.2. Scenario-2 and Solution (Unique RD, Multiple RTs) . . 10
4.1.3. Scenario-3 and Solution (Universal RD) . . . . . . . 12
5. Source PE Extended Community . . . . . . . . . . . . . . . . 14
6. VPN Prefix ORF Encoding . . . . . . . . . . . . . . . . . . . 15
6.1. Source PE TLV . . . . . . . . . . . . . . . . . . . . . . 18
6.2. Source AS TLV . . . . . . . . . . . . . . . . . . . . . . 18
6.3. Route Target TLV . . . . . . . . . . . . . . . . . . . . 18
7. Operation process of VPN Prefix ORF mechanism on receiver . . 19
8. Withdraw of VPN Prefix ORF entries . . . . . . . . . . . . . 20
9. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 20
10. Implementation Considerations . . . . . . . . . . . . . . . . 21
10.1. Implementation Considerations . . . . . . . . . . . . . 22
10.2. Implementation status . . . . . . . . . . . . . . . . . 22
10.3. Experimental topology . . . . . . . . . . . . . . . . . 23
11. Security Considerations . . . . . . . . . . . . . . . . . . . 23
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23
13. Contributor . . . . . . . . . . . . . . . . . . . . . . . . . 24
14. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 24
15. Normative References . . . . . . . . . . . . . . . . . . . . 25
Appendix A. Experimental topology . . . . . . . . . . . . . . . 26
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27
1. Introduction
[I-D.wang-idr-vpn-routes-control-analysis] analyzes the scenarios and
requirements for controlling VPN routes within a shared BGP session.
Furthermore, this draft examines the existing solutions and their
limitations pertaining to these scenarios and proposes a new VPN
Prefix ORF solution to meet the requirements as described in section
8 of [I-D.wang-idr-vpn-routes-control-analysis].
Now, there are several solutions can be used to alleviate these
problem:
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* Route Target Constraint (RTC) as defined in [RFC4684]
* Address Prefix ORF as defined in [RFC5292]
* CP-ORF mechanism as defined in [RFC7543]
* PE-CE edge peer Maximum Prefix
* Configure the Maximum Prefix for each VRF on edge nodes
However, there are limitations to existing solutions:
1) Route Target Constraint
RTC can only filter the VPN routes from the uninterested VRFs, if the
“offending routes” come from the interested VRF, RTC mechanism can't
filter them.
2) Address Prefix ORF
Using Address Prefix ORF to filter VPN routes requires pre-
configuration, but it is impossible to know in advance which prefix
may exceed the predefined threshold.
3) CP-ORF Mechanism
[RFC7543] defines the Covering Prefixes ORF (CP-ORF). A BGP speaker
sends a CP-ORF to a peer in order to pull routes that cover a
specified host address. A prefix covers a host address if it can be
used to forward traffic towards that host address.
CP-ORF is applicable in Virtual Hub-and-Spoke[RFC7024] VPN and also
the BGP/MPLS Ethernet VPN (EVPN)[RFC7432] networks, but its main aim
is also to get the wanted VPN prefixes and can't be used to filter
the overwhelmed VPN prefixes dynamically.
4) PE-CE edge peer Maximum Prefix
The BGP Maximum-Prefix feature is used to control how many prefixes
can be received from a neighbor. By default, this feature allows a
router to bring down a peer when the number of received prefixes from
that peer exceeds the configured Maximum-Prefix limit. This feature
is commonly used for external BGP peers. If it is applied to
internal BGP peers, for example the VPN scenarios, all the VPN routes
from different VRFs will share the common fate. If the number of VPN
routes of a certain VPN exceeds the configured Maximum-Prefix limit,
the BGP session will be shut down, which will effect the operation of
other VPN routes transmitted via this BGP session.
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5) Configure the Maximum Prefix for each VRF on edge nodes
When a VRF overflows, it stops the import of routes and log the extra
VPN routes into its RIB. However, PEs still need to parse the BGP
updates. These processes will cost CPU cycles and further burden the
overflowed PE.
This draft defines a new type of Outbound Route Filter (ORF), called
the VPN Prefix ORF. This mechanism is event-driven and does not
require pre-configuration. When the number of VPN routes in a VRF
exceeds the prefix limit, the router will identify the VPN prefix
(RD, RT, source PE, etc.) of the offending VPN routes in this VRF and
send a VPN Prefix ORF message to its BGP peer, which contains the
relevant information. If a BGP speaker receives a VPN Prefix ORF
entry from its BGP peer, it will filter the VPN routes it intends to
send according to the entry.
The purpose of this mechanism is to control the outage within the
minimum range and avoid route churn effects when a VRF on a device in
the network overflows.
VPN Prefix ORF is applicable when the VPN routes from different VRFs
are exchanged via one shared BGP session.
2. Conventions used in this document
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 [RFC2119] .
3. Terminology
The following terms are used in this draft:
* RD: Route Distinguisher, defined in [RFC4364]
* ORF: Outbound Route Filter, defined in [RFC5291]
* AFI: Address Family Identifier, defined in [RFC4760]
* SAFI: Subsequent Address Family Identifier, defined in [RFC4760]
* EVPN: BGP/MPLS Ethernet VPN, defined in [RFC7432]
* RR: Router Reflector, provides a simple solution to the problem of
IBGP full mesh connection in large-scale IBGP implementation.
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* VRF: Virtual Routing Forwarding, a virtual routing table based on
VPN instance.
4. The general procedures of VPN Prefix ORF mechanism on sender
The operation of VPN Prefix ORF mechanism on each device is
independent, each of them makes a local judgment to determine whether
it needs to send a VPN Prefix ORF message to its upstream peer.
Operators can configure the algorithms in the devices according to
their own circumstances.
This section describes the procedures for the receiving BGP peer to
receive VPN route information from the sending BGP peer. The VPN
information includes the updated VPN routes and their corresponding
VPN instance identification information. Based on the VPN instance
identification information, the receiving BGP peer determines the
newly added VPN routes. It then checks whether the number of the
newly added VPN routes has caused the number of total VPN routes to
exceed the maximum route limit for the associated VPN instance.
If the route number of the VPN instance, which is identified by the
VPN instance identification information, is reached or exceeds its
limit, it will send the instruction information to the sending BGP
peer, indicating that the sending BGP peer stop sending the
corresponding VPN routes which are identified by the VPN instance
identification information.
The receiving BGP peer and the sending BGP peer are iBGP peers within
the same AS. The VPN instance identification information is RD and
the instruction information is sent through the ROUTE-REFRESH
message.
The instruction information that sends from the receiving BGP peer
includes the followings information:
* The ORF entries that are included in the route-refresh message.
* Set the Action field in the ORF entries to the value that
instructs adding the corresponding filter condition to the
outbound route filter of the sending BGP peer.
* Set the Match field in the ORF entries to the value that instructs
denying the VPN routes updates that match the corresponding ORF
entries.
* The RD value that identifies the above mentioned VPN instance is
added to the type-specific part of the ORF entries.
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When multiple VRFs on a PE are receiving VPN routes with a specific
RD, if one VRF exceeds its limit upon receiving routes with that RD,
then the PE sends a VPN Prefix ORF message, which will prevent other
VRFs that have not exceeded their limits from receiving VPN routes
containing that RD, leading to communication disruptions between
these VRFs and the rejected VPN routes. In order to more finely
control VPN routing, when not all VRFs on a PE that are interested in
VPN routes with a specific RD exceed the limit, the PE MUST not send
a VPN Prefix ORF entry.
The detail procedures for further subdivisions are described below:
a) No quota value is set on PE
On PE, each VRF has a prefix limit. When the PE receives VPN routes
from its BGP peer, PE does the following:
S01. PE extracts the VPN route information from BGP UPDATE message, and
determines the target VRFs for the received VPN routes based on the
RT of the VPN route and the RT-import of VRFs.
S02. If (a target VRF exceeds the limit which caused by VPN routes carry a
certain RD) {
S03. If (not all the other target VRFs have overflowed) {
S04. PE should not trigger the VPN Prefix ORF mechanism, and only
performs VPN route filtering for the target VRF, stopping
the import of VPN routes carrying the specific RD.
S05. } else {
S06. PE should trigger the VPN Prefix ORF mechanism and send a BGP
ROUTE-REFRESH message contains the corresponding VPN Prefix
ORF entry to its peer.
S07. }
S08. }
b) Quota value is set on PE
On PE, each VRF has a prefix limit, and routes associated with each
<RD, source PE> tuple have a pre-configured quota. When the PE
receives VPN routes from its BGP peer, PE does the following:
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S01. PE extracts the VPN route information from BGP UPDATE message, and
determines the target VRFs for the received VPN routes based on
the RT of the VPN route and the RT-import of VRFs.
S02. If (VPN routes associated with <RD, source PE> tuple exceed the quota) {
S03. If (the prefix limit of VRF is not exceeded) {
S04. PE may send a warning message to the operator, and the VPN
Prefix ORF mechanism should not be triggered.
S05. } else {
S06. If (not all the other target VRFs have overflowed) {
S07. PE should not trigger the VPN Prefix ORF mechanism, and
only performs VPN route filtering for the target VRF,
stopping the import of VPN routes carrying the specific RD.
S08. else {
S09. PE triggers the VPN Prefix ORF mechanism and send a BGP
ROUTE-REFRESH message containing the corresponding VPN
Prefix ORF entry to its peer.
S10. }
S11. }
S12. }
When the VPN Prefix ORF mechanism is triggered, the device SHOULD
send an alarm information to network operators.
4.1. Intra-domain Scenarios and Solutions
For intra-AS VPN deployment, there are three scenarios:
* RD is allocated per VPN per PE, each VRF only import one RT (see
Section 4.1.1).
* RD is allocated per VPN per PE. Multiple RTs are associated with
such VPN routes, and are imported into different VRFs in other
devices(see Section 4.1.2).
* RD is allocated per VPN, each VRF imports one/multiple RTs(see
Section 4.1.3).
The following sections will describe solutions to the above scenarios
in detail.
4.1.1. Scenario-1 and Solution (Unique RD, One RT)
In this scenario, PE1-PE4 and RR are iBGP peers. RD is allocated per
VPN per PE. The offending VPN routes only carry one RT. We assume
that the network topology is shown in Figure 1.
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+------------------------------------------------------------------------+
| |
| |
| +-------+ +-------+ |
| | PE1 +----------------+ +-----------------+ PE4 | |
| +-------+ | | +-------+ |
| VPN1(RD11,RT1) | | VPN2(RD12,RT2) |
| VPN2(RD12,RT2) | | |
| +-+----+-+ |
| | RR | |
| +-+----+-+ |
| | | |
| | | |
| +-------+ | | +-------+ |
| | PE2 +----------------+ +-----------------+ PE3 | |
| +-------+ +-------+ |
| VPN1(RD21,RT1) VPN1(RD31,RT1) |
| VPN2(RD22,RT2,RT1) VPN2(RD32,RT2) |
| |
| AS 100 |
| |
+------------------------------------------------------------------------+
Figure 1 Network Topology of Scenario-1
When PE3 sends an excessive number of VPN routes with RT1, and both
PE1 and PE2 import VPN routes with RT1, the process of offending VPN
routes will influence performance of VRFs on PEs. PEs and RR should
have appropriate mechanisms to identify and control the advertising
of offending VPN routes.
a) PE1
If quota value is not set on PE1, and each VRF has a prefix limit on
PE1. When the PE1 receives VPN routes from its BGP peer, it does the
following:
S01. If (the prefix limit for VPN1 VRF is exceeded) {
S02. PE1 sends a VPN Prefix ORF message to the RR and a warning message
to the operator. The VPN Prefix ORF message will carry the prefix
limit of VPN1 VRF, with the RD is set to RD31, the RT value is set
to RT1, the source PE is PE3. RR handles the offending VPN routes
and controls the number of VPN routes according to the value of
"Offending VPN routes process method".
S03. } else {
S04. PE1 should not trigger the VPN Prefix ORF mechanism, and only
performs VPN route filtering for the target VRF.
S05. }
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NOTE: When the prefix limit for VPN1 VRF is exceeded, there are no
other VRFs on PE1 that need the VPN routes with RT1. PE1 sends a VPN
Prefix ORF message to the RR and a warning message to the operator.
If each <RD31, source PE3> tuple imported into a VRF has a quota, and
each VRF has a prefix limit. When the PE1 receives VPN routes from
its BGP peer, it does the following:
S01. If (VPN routes associated with <RD31, PE3> tuple exceed the quota) {
S02. If (the prefix limit of VPN1 VRF is not exceeded) {
S03. PE1 sends a warning message to the operator, and the VPN Prefix
ORF mechanism should not be triggered.
S04. } else {
S05. PE1 generates a BGP ROUTE-REFRESH message containing a VPN
Prefix ORF entry with (RD31, the prefix limit of VPN1 VRF,
source PE is PE3, RT is RT1), and send the entry to RR. RR
handles the offending VPN routes according to the value of
"Offending VPN routes process method".
S06. }
S07. }
b) PE2
If quota value is not set on PE2, and each VRF has a prefix limit on
PE2. When the PE2 receives VPN routes from its BGP peer, it does the
following:
S01. If (the prefix limit for VPN1 VRF is exceeded) {
S02. If (the prefix limit for VPN2 VRF is exceeded) {
S03. PE2 sends a VPN Prefix ORF message to the RR and a warning
message to the operator. The VPN Prefix ORF message will
indicate the VRF Prefix Limit = min(prefix limit of VPN1 VRF,
prefix limit of VPN2 VRF), with the RD set to RD31, the RT
value set to RT1. RR handles the offending VPN routes and
controls the number of VPN routes according to the value of
"Offending VPN routes process method".
S04. } else {
S05. PE2 should not trigger the VPN Prefix ORF mechanism, and only
performs VPN route filtering for the target VRF.
S06. }
S07. }
NOTE: PE2 cannot directly trigger the VPN Prefix ORF mechanism when
the prefix limit of VPN1 VRF is exceeded, because VPN2 VRF requires
the VPN routes with RT1. PE2 triggers the mechanism only when the
prefix limits for both the VPN1 and VPN2 VRFs have been exceeded.
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If each <RD31, source PE3> tuple imported into a VRF has a quota, and
each VRF has a prefix limit. When the PE2 receives VPN routes from
its BGP peer, it does the following:
S01. If (VPN routes associated with <RD31, PE3> tuple exceed the quota) {
S02. If (the prefix limit of VPN1 VRF is not exceeded) {
S03. PE2 sends a warning message to the operator, and the VPN Prefix
ORF mechanism should not be triggered.
S04. } else {
S05. If (the prefix limit of VPN2 VRF is not exceeded) {
S06. PE2 should not trigger the VPN Prefix ORF mechanism, and
only performs VPN route filtering for the target VPN1 VRF,
stopping the import of VPN routes with <RD31, PE3>.
S07. } else {
S08. PE2 generates a BGP ROUTE-REFRESH message containing a VPN
Prefix ORF entry with (RD31, min(prefix limit of VPN1 VRF,
prefix limit of VPN2 VRF), source PE is PE3, RTs are RT1
and RT2), and send the entry to RR. RR handles the
offending VPN routes according to the value of "Offending
VPN routes process method".
S09. }
S10. }
S11. }
4.1.2. Scenario-2 and Solution (Unique RD, Multiple RTs)
In this scenario, PE1-PE4 and RR are iBGP peers. RDs are allocated
per VPN per PE. Multiple RTs are associated with the offending VPN
routes and are imported into different VRFs on other devices. We
assume the network topology is depicted in Figure 2.
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+------------------------------------------------------------------------+
| |
| |
| +-------+ +-------+ |
| | PE1 +----------------+ +-----------------+ PE4 | |
| +-------+ | | +-------+ |
| VPN1(RD11,RT1) | | VPN2(RD42,RT2) |
| VPN2(RD12,RT2) | | |
| +-+----+-+ |
| | RR | |
| +-+----+-+ |
| | | |
| | | |
| +-------+ | | +-------+ |
| | PE2 +----------------+ +-----------------+ PE3 | |
| +-------+ +-------+ |
| VPN1(RD21,RT1) VPN1(RD31,RT1,RT2) |
| VPN2(RD32,RT2) |
| |
| AS 100 |
| |
+------------------------------------------------------------------------+
Figure 2 Network Topology of Scenario-2
When PE3 sends an excessive number of VPN routes with RT1 and RT2,
while both PE1 and PE2 import VPN routes with RT1, and PE1 also
imports VPN routes with RT2.
a) PE1
If quota value is not set on PE1, and each VRF has a prefix limit on
PE1. Since VPN2 VRF requires the VPN routes with RT1, PE1 cannot
directly trigger VPN Prefix ORF mechanism when the prefix limit of
VPN1 VRF is exceeded. This case is similar to PE2 without quota in
Section 4.1.1, which is modified as follows:
S03. PE1 sends a VPN Prefix ORF message to the RR and a warning
message to the operator. The VPN Prefix ORF message will
indicate the VRF Prefix Limit = min(prefix limit of VPN1
VRF, prefix limit of VPN2 VRF), with the RD set to RD31,
the RT value set to RT1 and RT2, source PE identified as
PE3. RR handles the offending VPN routes and controls the
number of VPN routes according to the value of "Offending
VPN routes process method".
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If each <RD31, source PE3> tuple imported into a VRF has a quota, and
each VRF has a prefix limit. This case is similar to PE2 with quota
in Section 4.1.1, which is modified as follows:
S08. PE1 generates a BGP ROUTE-REFRESH message containing a
VPN Prefix ORF entry with (RD31, min(prefix limit of VPN1
VRF, prefix limit of VPN2 VRF), source PE is PE3, RTs are
RT1 and RT2), and send the entry to RR. RR handles the
offending VPN routes according to the value of "Offending
VPN routes process method".
b) PE2
If quota value is not set on PE2, and each VRF has a prefix limit on
PE2. Since only VPN1 VRF needs to import VPN routes with RT1, this
case is similar to PE1 without quota in Section 4.1.1, which is
modified as follows:
S02. PE2 sends a VPN Prefix ORF message to the RR and a warning message
to the operator. The VPN Prefix ORF message will indicate the VRF
Prefix Limit = prefix limit of VPN1 VRF, with the RD set to RD31,
the RT value set to RT1 and RT2, source PE identified as PE3. RR
handles the offending VPN routes and controls the number of VPN
routes according to the value of "Offending VPN routes process
method".
If each <RD31, source PE3> tuple imported into a VRF has a quota, and
each VRF has a prefix limit. This case is similar to PE1 with quota
in Section 4.1.1, which is modified as follows:
S05. PE2 generates a BGP ROUTE-REFRESH message containing a VPN
Prefix ORF entry with (RD31, prefix limit of VPN1 VRF, source
PE is PE3, RTs are RT1 and RT2), and send the entry to RR. RR
handles the offending VPN routes according to the value of
"Offending VPN routes process method".
4.1.3. Scenario-3 and Solution (Universal RD)
In this scenario, PE1-PE4 and RR are iBGP peers. RD is allocated per
VPN. One/Multiple RTs are associated with the offending VPN routes
and are imported into different VRFs on other devices. We assume the
network topology is shown in Figure 3.
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+------------------------------------------------------------------------+
| |
| |
| +-------+ +-------+ |
| | PE1 +----------------+ +-----------------+ PE4 | |
| +-------+ | | +-------+ |
| VPN1(RD1,RT1) | | VPN2(RD12,RT2) |
| VPN2(RD12,RT2) | | |
| +-+----+-+ |
| | RR | |
| +-+----+-+ |
| | | |
| | | |
| +-------+ | | +-------+ |
| | PE2 +----------------+ +-----------------+ PE3 | |
| +-------+ +-------+ |
| VPN1(RD1,RT1) VPN1(RD1,RT1,RT2) |
| VPN2(RD32,RT2) |
| |
| AS 100 |
| |
+------------------------------------------------------------------------+
Figure 3 Network Topology of Scenario-3
When PE3 sends an excessive number of VPN routes associated with RD1,
RT1 and RT2, and both PE1 and PE2 import VPN routes with RT1, the
process of offending VPN routes can affect the performance of the
VRFs on PEs.
a) PE1
If quota value is not set on PE1, and each VRF has a prefix limit on
PE1. Since VPN2 VRF requires the VPN routes with RT2, PE1 cannot
trigger VPN Prefix ORF mechanism directly when the prefix limit of
VPN1 VRF is exceeded. This case is similar to PE2 without quota in
Section 4.1.1, which is modified as follows:
S03. PE1 sends a VPN Prefix ORF message to the RR and a warning
message to the operator. The VPN Prefix ORF message will
indicate the VRF Prefix Limit = min(prefix limit of VPN1
VRF, prefix limit of VPN2 VRF), with the RD set to RD1,
the RT value set to RT1 and RT2, source PE identified as
PE3. RR handles the offending VPN routes and controls the
number of VPN routes according to the value of "Offending
VPN routes process method".
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If each <RD1, source PE3> tuple imported into a VRF has a quota, and
each VRF has a prefix limit. This case is similar to PE2 with quota
in Section 4.1.1, which is modified as follows:
S08. PE1 generates a BGP ROUTE-REFRESH message containing a VPN
Prefix ORF entry with (RD1, min(prefix limit of VPN1 VRF,
prefix limit of VPN2 VRF), source PE is PE3, RTs are RT1
and RT2), and send the entry to RR. RR handles the
offending VPN routes according to the value of "Offending
VPN routes process method".
b) PE2
If quota value is not set on PE2, and each VRF has a prefix limit on
PE2. Since only VPN1 VRF needs to import VPN routes with RT1, this
case is similar to PE1 without quota in Section 4.1.1, which is
modified as follows:
S02. PE2 sends a VPN Prefix ORF message to the RR and a warning message
to the operator. The VPN Prefix ORF message will indicate the VRF
Prefix Limit = prefix limit of VPN1 VRF, with the RD set to RD1,
the RT value set to RT1 and RT2, source PE identified as PE3. RR
handles the offending VPN routes and controls the number of VPN
routes according to the value of "Offending VPN routes process
method".
If each <RD31, source PE3> tuple imported into a VRF has a quota, and
each VRF has a prefix limit. This case is similar to PE1 with quota
in Section 4.1.1, which is modified as follows:
S05. PE2 generates a BGP ROUTE-REFRESH message containing a VPN
Prefix ORF entry with (RD1, prefix limit of VPN1 VRF, source PE
is PE3, RTs are RT1 and RT2), and send the entry to RR. RR
handles the offending VPN routes according to the value of
"Offending VPN routes process method".
5. Source PE Extended Community
We usually use next hop to identify the source, but it may not be
useful in the following scenarios:
* a PE may have multiple addresses so that its BGP peer may receive
several different next hop addresses from the same source.
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* In Option B inter-domain scenario, the ASBR will change the next
hop.
ORIGINATOR_ID is a non-transitive attribute generated by RR to
identify the source, but ORIGINATOR_ID cannot be advertised outside
the local AS. To address the above scenarios, we have defined a new
Extended Community: Source PE Extended Community (SPE EC), which is
designed to transmit the identifier of source. The value of SPE EC
can be set by source PE, RR or ASBR. Once set and attached to the
BGP UPDATE message, its value should not be altered along the
advertisement path.
The AS number of source PE can be conveyed by Source AS Extended
Community, as defined in [RFC6514]
The format of SPE EC is shown as Figure 4.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x0d | ORIGINATOR_ID :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: ORIGINATOR_ID (cont.) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4 The format of SPE EC
For the RR/ASBR, it should perform as following:
* Check the existence of the SPE EC. If it exists, does not change
it.
* If SPE EC does not exist, check the existence of ORIGINATOR_ID.
If it exists, put it into SPE EC.
* If ORIGINATOR_ID does not exist, put the router-id of source PE
into SPE EC.
6. VPN Prefix ORF Encoding
In this section, we defined a new ORF type called VPN Prefix Outbound
Route Filter (VPN Prefix ORF). The ORF entries are carried in the
BGP ROUTE-REFRESH message as defined in [RFC5291]. A BGP ROUTE-
REFRESH message can carry one or more ORF entries. The ROUTE-REFRESH
message which carries ORF entries contains the following fields:
* AFI (2 octets)
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* SAFI (1 octet)
* When-to-refresh (1 octet): the value is IMMEDIATE or DEFER
* ORF Type (1 octet)
* Length of ORF entries (2 octets)
A VPN Prefix ORF entry contains a common part and type-specific part.
The common part is encoded as follows:
* Action (2 bits): the value is ADD, REMOVE or REMOVE-ALL
* Match (1 bit): the value is PERMIT or DENY
* Offending VPN routes process method (1 bit): if the value is set
to 0, it means all offending VPN routes on the sender of VPN
Prefix ORF message should be withdrawn; if the value is set to 1,
it means the sender of VPN Prefix ORF message refuse to receive
new offending VPN routes. The default value is 0.
* Reserved (4 bits)
VPN Prefix ORF also contains type-specific part. The encoding of the
type-specific part is shown in Figure 5.
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+-----------------------------------------+
| |
| Sequence (4 octets) |
| |
+-----------------------------------------+
| |
| Length (2 octets) |
| |
+-----------------------------------------+
| |
| VRF Prefix Limit (4 octets) |
| |
+-----------------------------------------+
| |
| Route Distinguisher (8 octets) |
| |
+-----------------------------------------+
| |
| Optional TLVs (variable) |
| |
+-----------------------------------------+
Figure 5: VPN Prefix ORF type-specific encoding
* Sequence: identifying the order in which RD-ORF is generated.
* Length: identifying the length of this VPN Prefix ORF entry.
* VRF Prefix Limit: carrying the prefix limt of the overflowed VRF.
* Route Distinguisher: distinguish the different user routes. The
VPN Prefix ORF filters the VPN routes it tends to send based on
Route Distinguisher. If RD is equal to 0, it means all VPN
prefixes.
* Optional TLVs: carry the potential additional information to give
the extensibility of the VPN Prefix ORF mechanism.
Note that if the Action component of an ORF entry specifies REMOVE-
ALL, the ORF entry does not include the type-specific part.
When the BGP ROUTE-REFRESH message carries VPN Prefix ORF entries, it
must be set as follows:
* The ORF-Type MUST be set to 66 (VPN Prefix ORF).
* The AFI MUST be set to IPv4, IPv6, or Layer 2 VPN (L2VPN).
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* If the AFI is set to IPv4 or IPv6, the SAFI MUST be set to MPLS-
labeled VPN address.
* If the AFI is set to L2VPN, the SAFI MUST be set to BGP EVPN.
* The Match field should be set to PERMIT when VRF Prefix Limit =
0xFFFF and RD=0; otherwise, the Match field should be set to DENY.
6.1. Source PE TLV
Source PE TLV is defined to identify the source of the VPN routes.
For the sender of VPN Prefix ORF, it will check the existence of SPE
EC. If it exists, the sender will put it into Source PE TLV.
Otherwise, the value of Source PE TLV should be set to local AS
number and next hop address.
The source PE TLV contains the following types:
* IPv4 Source PE TLV: Type = 1 (suggested), Length = 4 octets, value
= next hop address in IPv4 format.
* IPv6 Source PE TLV: Type = 2 (suggested), Length = 16 octets,
value = next hop address in IPv6 format.
* Source PE identifier TLV: Type = 3 (suggested), Length = 4 octets,
value = the value of ORIGINATOR_ID in Source PE Extended
Community.
6.2. Source AS TLV
Source AS TLV is defined to identify the source AS number of source
PE. The encoding of Source AS TLV is as follow:
Type = 4 (suggested), Length = 4 octets, value = the value of
Source AS in Source AS Extended Community as defined in [RFC6514].
6.3. Route Target TLV
Route Target TLV is defined to identify the RT of the offending VPN
routes. RT and RD can be used together to filter VPN routes when the
source VRF contains multiple RTs, and the VPN routes with different
RTs may be assigned to different VRFs on the receiver. The Route
Target TLV contains the following types:
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Type = 5 (suggested), Length = 8*n (n is the number of RTs that
the offending VPN routes attached) octets, value = the RT of the
offending VPN routes. If multiple RTs are included, there must be
an exact match.
7. Operation process of VPN Prefix ORF mechanism on receiver
The receiver of VPN Prefix ORF entries, which may be a Route
Reflector (RR) or Provider Edge (PE), when receives VPN Prefix ORF
entry from its BGP peer, it does the following:
S01. The receiver check the combination of <AFI/SAFI, ORF-Type, Sequence,
Route Distinguisher> of the received VPN Prefix ORF entry.
S02. If (the combination does not already exist in the ORF-Policy table) {
S03. The receiver adds the VPN Prefix ORF entry to the ORF-Policy table.
S04. } else {
S05. The receiver discards the entry.
S06. }
The filtering conditions for the stored VPN Prefix ORF entries
contain the RD and RT of the source PE.
When all downstream devices send the VPN Prefix ORF entries with the
same filtering condition to the receiver, the receiver SHOULD
generate a VPN Prefix ORF entry that includes this filtering
condition and send it to its upstream devices.
After installing the filter entries for the outbound VPN prefixes,
the RR or ASBR does the following before sending VPN routes:
S01. RR or ASBR check if there are matching filtering conditions in the
ORF-Policy table for the VPN routes.
S02. If (matching filtering conditions does not exist) {
S03. The RR/ASBR sends the VPN routes.
S04. } else {
S05. If (the "Offending VPN routes process method" bit is set to 0) {
S06. The RR/ASBR withdraws all the VPN routes identified by RD, RT
and any relevant information in the optional TLVs within the
entry, and stop sending the corresponding VPN routes to the
sender of the VPN Prefix ORF entry.
S06. } else {
S07. The receiver withdraw the extra VPN routes according to the
value of VRF Prefix Limit, RD, RT and any relevant information
in optional TLVs within the entry, and stop sending the
corresponding VPN routes to the sender of the VPN Prefix ORF
entry.
S06. }
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8. Withdraw of VPN Prefix ORF entries
When the VPN Prefix ORF mechanism is triggered, a warning message
will be generated and sent to the network operators. Operators
should manually configure the network to resume normal operation.
Since devices can record the VPN Prefix ORF entries sent by each VRF,
operators can identify the entries that are needed to be withdrawn
and manually trigger the withdraw process as described in [RFC5291].
9. Applicability
Using the scenario in Section 4.1.1, we demonstrate how to determine
each field when the sender generates a VPN Prefix ORF entry.
Assuming it is an IPv4 network, after PE1-PE4 and RR have advertised
the Outbound Route Filtering Capability, each of PE1-PE4 should send
a VPN Prefix ORF entry that means "PERMIT-ALL" as follows:
* AFI is equal to IPv4
* SAFI is equal to MPLS-labeled VPN address
* When-to-refresh is equal to IMMEDIATE
* ORF Type is equal to VPN Prefix ORF
* Length of ORF entries is equal to 26
* Action is equal to ADD
* Match is equal to PERMIT
* Offending VPN routes process method is equal to 0
* Sequence is equal to 0xFFFFFFFF
* Length is equal to 12
* VRF Prefix Limit is equal to 0xFFFF
* Route Distinguisher is equal to 0
When the VPN Prefix ORF mechanism is triggered on PE1, PE1 generates
a VPN Prefix ORF entry contains the following information:
* AFI is equal to IPv4
* SAFI is equal to MPLS-labeled VPN address
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* When-to-refresh is equal to IMMEDIATE
* ORF Type is equal to VPN Prefix ORF
* Length of ORF entries is equal to 49
* Action is equal to ADD
* Match is equal to DENY
* Offending VPN routes process method is equal to 0
* Sequence is equal to 1
* Length is equal to 35
* VRF Prefix Limit is equal to the prefix limit of VPN1 VRF
* Route Distinguisher is equal to RD31
* Optional TLV:
- Type is equal to 1 (Source PE TLV)
- Length is equal to 4
- value is equal to PE3's IPv4 address
- Type is equal to 4 (Source AS TLV)
- Length is equal to 4
- value is equal to PE3's source AS number
- Type is equal to 5 (Route Target TLV)
- Length is equal to 8
- value is equal to RT1
10. Implementation Considerations
This draft is experimental to determine whether the proposed
mechanism can block the offending routes as expected and whether it
could cause potential network failures. The first subsection
describes implementation considerations for the mechanism. The
second subsection gives a brief description of implementation status.
The third subsection provides a short summary of the experimental
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topology.
10.1. Implementation Considerations
Before originating a VPN Prefix ORF message, the device should
compare the list of RDs and RTs carried by VPN routes to those are
imported by other VRFs on the device. If there is an intersection,
the VPN Prefix ORF message MUST NOT be originated.
In deployment, the quota value can be set with different granularity,
such as by <PE>, <RD, Source AS>, etc. If the quota value is set to
(VRF prefix limit/the number of PEs), whenever a new PE access to the
network, the quota value should be re-evaluated or adjusted
accordingly.
To avoid frequent changes to the quota value, the value SHOULD be set
based on the following formula:
Quota=MIN[(Margins coefficient)*<PE,CE limit>*<Number of PEs within
the VPN, includes the possibility expansion in futures>, VRF Prefixes
Limit]
It should be noted that the above formula is only an example, the
operators can use different formulas based on actual needs in
management plane.
10.2. Implementation status
Currently, H3C has implemented VPN Prefix ORF mechanism related
functions as follows:
* By configuring VRF Prefix limit and quota, achieve the use of RD
and Source PE to control VPN routing.
* Generating, transmitting and processing Type 1 and Type 2 Source
PE TLV.
* Using the Offending VPN routes process method to revoke all
routes.
Besides, we also implemented the following functions based on the
open-source BGP implementation (FRR):
* VPN Prefix ORF mechanism triggered based on VRF limit in intra-
domain and inter-domain scenarios.
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* RD based VPN routing filtering in intra-domain and inter-domain
scenarios.
10.3. Experimental topology
The experiments will test whether the VPN Prefix ORF blocks the
offending routes in the following scenarios:
* Intra-domain as a standalone mechanism,
* Inter-domain as a standalone mechanisms,
* Adding the VPN Prefix ORF to existing mechanisms for intra-domain
VPNs,
* Adding the VPN Prefix ORF to existing mechanisms for intra-domain
VPNs.
11. Security Considerations
This draft does build upon [RFC5291]. A BGP speaker will maintain
the VPN Prefix ORF entries in an ORF-Policy table, this behavior
consumes its memory and compute resources. To avoid the excessive
consumption of resources, [RFC5291] specifies that a BGP speaker can
only accept ORF entries transmitted by its interested peers.
12. IANA Considerations
This document defines a new Outbound Route Filter type - VPN Prefix
Outbound Route Filter (VPN Prefix ORF).
under "BGP Outbound Route Filtering (ORF) Types"
Registry: "VPN Prefix Outbound Route Filter (VPN Prefix ORF)"
Registration Procedure(s): First Come, First Served
Value: 66
This document also define a VPN Prefix ORF TLV type under "Border
Gateway Protocol (BGP) Parameters", four TLV types are defined:
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under "Border Gateway Protocol (BGP) Parameters"
Registry: "VPN Prefix ORF TLV"
Registration Procedure(s): IETF Review
Value range:0-255, value 0 is reserved.
+===========================+=============+===========================+
| Registry | Type | Meaning |
+===========================+=============+===========================+
|IPv4 Source PE TLV | 1(suggested)|IPv4 address for source PE.|
+---------------------------+-------------+---------------------------+
|IPv6 Source PE TLV | 2(suggested)|IPv6 address for source PE.|
+---------------------------+-------------+---------------------------+
|Source PE Identifier TLV | 3(suggested)|ORIGINATOR_ID in Source PE |
| | |Extended Community for |
| | |source PE |
+---------------------------+-------------+---------------------------+
|Source AS TLV | 4(suggested)|Source AS for source PE |
+---------------------------+-------------+---------------------------+
|Route Target TLV | 5(suggested)|Route Target of the |
| | |offending VPN routes |
+---------------------------+-------------+---------------------------+
This document also requests a new Transitive Extended Community Type.
The new Transitive Extended Community Type name shall be "Source PE
Extended Community".
Under "BGP Transitive Extended Community Types:"
Registry: "Source PE Extended Community" type
0x0d(suggested) Source PE Extended Community
13. Contributor
Shunwan Zhuang
Huawei Technologies
Huawei Building, No.156 Beiqing Rd.
Beijing
Beijing, 100095 China
14. Acknowledgement
Thanks Robert Raszuk, Jim Uttaro, Jakob Heitz, Jeff Tantsura, Rajiv
Asati, John E Drake, Gert Doering, Shuanglong Chen, Enke Chen,
Srihari Sangli and Igor Malyushkin for their valuable comments on
this draft.
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15. Normative References
[I-D.ietf-bess-evpn-inter-subnet-forwarding]
Sajassi, A., Salam, S., Thoria, S., Drake, J., and J.
Rabadan, "Integrated Routing and Bridging in Ethernet VPN
(EVPN)", Work in Progress, Internet-Draft, draft-ietf-
bess-evpn-inter-subnet-forwarding-15, 26 July 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-bess-
evpn-inter-subnet-forwarding-15>.
[I-D.wang-idr-vpn-routes-control-analysis]
Wang, A., Wang, W., Mishra, G. S., Wang, H., Zhuang, S.,
and J. Dong, "Analysis of VPN Routes Control in Shared BGP
Session", Work in Progress, Internet-Draft, draft-wang-
idr-vpn-routes-control-analysis-04, 6 September 2021,
<https://datatracker.ietf.org/doc/html/draft-wang-idr-vpn-
routes-control-analysis-04>.
[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>.
[RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
Communities Attribute", RFC 4360, DOI 10.17487/RFC4360,
February 2006, <https://www.rfc-editor.org/info/rfc4360>.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
2006, <https://www.rfc-editor.org/info/rfc4364>.
[RFC4684] Marques, P., Bonica, R., Fang, L., Martini, L., Raszuk,
R., Patel, K., and J. Guichard, "Constrained Route
Distribution for Border Gateway Protocol/MultiProtocol
Label Switching (BGP/MPLS) Internet Protocol (IP) Virtual
Private Networks (VPNs)", RFC 4684, DOI 10.17487/RFC4684,
November 2006, <https://www.rfc-editor.org/info/rfc4684>.
[RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
"Multiprotocol Extensions for BGP-4", RFC 4760,
DOI 10.17487/RFC4760, January 2007,
<https://www.rfc-editor.org/info/rfc4760>.
[RFC5291] Chen, E. and Y. Rekhter, "Outbound Route Filtering
Capability for BGP-4", RFC 5291, DOI 10.17487/RFC5291,
August 2008, <https://www.rfc-editor.org/info/rfc5291>.
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[RFC5292] Chen, E. and S. Sangli, "Address-Prefix-Based Outbound
Route Filter for BGP-4", RFC 5292, DOI 10.17487/RFC5292,
August 2008, <https://www.rfc-editor.org/info/rfc5292>.
[RFC6514] Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP
Encodings and Procedures for Multicast in MPLS/BGP IP
VPNs", RFC 6514, DOI 10.17487/RFC6514, February 2012,
<https://www.rfc-editor.org/info/rfc6514>.
[RFC7024] Jeng, H., Uttaro, J., Jalil, L., Decraene, B., Rekhter,
Y., and R. Aggarwal, "Virtual Hub-and-Spoke in BGP/MPLS
VPNs", RFC 7024, DOI 10.17487/RFC7024, October 2013,
<https://www.rfc-editor.org/info/rfc7024>.
[RFC7432] Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based
Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February
2015, <https://www.rfc-editor.org/info/rfc7432>.
[RFC7543] Jeng, H., Jalil, L., Bonica, R., Patel, K., and L. Yong,
"Covering Prefixes Outbound Route Filter for BGP-4",
RFC 7543, DOI 10.17487/RFC7543, May 2015,
<https://www.rfc-editor.org/info/rfc7543>.
Appendix A. Experimental topology
The experimental topology is shown in Figure 6.
+--------------------------+ +--------------------------+
| | | |
| | | |
| +---------+ | | +---------+ |
| | PE1 | | | | PE3 | |
| +---------+ | | +---------+ |
| \ | | / |
| \+---------+ EBGP +---------+/ |
| | | | | |
| | ASBR1 |-----------| ASBR2 | |
| | | | | |
| +---------+ +---------+ |
| / | | \ |
| +---------+/ | | \+---------+ |
| | PE2 | | | | PE4 | |
| +---------+ | | +---------+ |
| | | |
| AS1 | | AS2 |
+--------------------------+ +--------------------------+
Figure 6 The experimental topology
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This topology can be used to verify as follows:
* whether the VPN Prefix ORF mechanism could block the offending
routes in intra-domain scenario.
* whether the VPN Prefix ORF mechanism could block the offending
routes in inter-domain scenario.
* whether the VPN Prefix ORF mechanism conflicts with the existing
mechanism and cause failure.
* whether the quota value leads to flapping.
* TBD
Authors' Addresses
Wei Wang
China Telecom
Beiqijia Town, Changping District
Beijing
Beijing, 102209
China
Email: weiwang94@foxmail.com
Aijun Wang
China Telecom
Beiqijia Town, Changping District
Beijing
Beijing, 102209
China
Email: wangaj3@chinatelecom.cn
Haibo Wang
Huawei Technologies
Huawei Building, No.156 Beiqing Rd.
Beijing
Beijing, 100095
China
Email: rainsword.wang@huawei.com
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Gyan S. Mishra
Verizon Inc.
13101 Columbia Pike
Silver Spring, MD 20904
United States of America
Phone: 301 502-1347
Email: gyan.s.mishra@verizon.com
Jie Dong
Huawei Technologies
Huawei Building, No.156 Beiqing Rd.
Beijing
Beijing, 100095
China
Email: jie.dong@huawei.com
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