IDR Working Group A. Wang
Internet-Draft W. Wang
Intended status: Informational China Telecom
Expires: March 10, 2022 G. Mishra
Verizon Inc.
H. Wang
S. Zhuang
J. Dong
Huawei Technologies
September 6, 2021
Analysis of VPN Routes Control in Shared BGP Session
draft-wang-idr-vpn-routes-control-analysis-04
Abstract
This draft analyzes some scenarios and the necessaries for VPN routes
control in the shared BGP session, which can be the used as the base
for the design of related solutions.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 2
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
4. Inter-AS VPN Option B/AB Scenario . . . . . . . . . . . . . . 3
5. Inter-AS VPN Option C Scenario . . . . . . . . . . . . . . . 4
6. Intra-AS VPN RR Deployment Scenario . . . . . . . . . . . . . 5
7. VPN Routes Shared on one PE . . . . . . . . . . . . . . . . . 6
8. Requirements for the solutions . . . . . . . . . . . . . . . 7
9. Security Considerations . . . . . . . . . . . . . . . . . . . 8
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
11. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 8
12. Normative References . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
BGP Maximum Prefix feature [RFC4486] is often used at the network
boundary to control the number of prefixes to be injected into the
network. But for some scenarios when the VPN routes from several
VRFs are advertised via one shared BGP session, there is lack of
appropriate methods to control the flooding of VPN routes within one
VRF to overwhelm the process of VPN routes in other VRFs. That is to
say, the excessive VPN routes advertisement should be controlled
individually for each VRF in such shared BGP session.
The following sections analyzes the scenarios that are necessary to
such mechanism.
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 defined in this draft:
o RD: Route Distinguisher, defined in [RFC4364]
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o RR: Router Reflector, provides a simple solution to the problem of
IBGP full mesh connection in large-scale IBGP implementation.
o VRF: Virtual Routing Forwarding, a virtual routing table based on
VPN instance.
4. Inter-AS VPN Option B/AB Scenario
For inter-AS VPN deployment option B/AB scenario, as described in
Figure 1, there is one BGP session between ASBR1 and ASBR2, which is
used to advertise the VPN routes from VPN1 and VPN2 VRF. Normally
the operator will deploy the BGP maximum prefixes feature under
different address families between the ASBR1 and ASBR2, but the
threshold must be set very high to cope with the situation when all
the VRFs in each family reach their VPN routes limit simultaneously.
In case VPN routes in only one of VRF, for example VPN1 in PE3,
advertises excess VPN routes(with RD set to RD31 and RT import/export
set to RT1. Configurations on other PEs are similar) into the
network, but VPN routes advertisement in other VRFs are in normal,
the prefix bar set between the ASBRs will not take effect. Such
excessive VPN routes will be advertised into the AS1, to PE1 and PE2
respectively.
PE1 in this example, provides the services for VPN2 at the same time.
If it receives the excessive VPN routes for VPN1 from ASBR1, although
such VPN routes have exceeded the limit within the VRF VPN1, it can't
break the BGP session with ASBR1 directly, because the VPN prefix
limit is to prevent a flood from errors or other issues but does not
prevent the device from being overwhelmed and resources exhausted.
All it can do is to receive and process the excessive BGP updates
continuously, parse the excessive VPN routes for VPN1 and drop it,
extract the VPN routes for VPN2 and install it.
Doing so can certainly influence the performance of PE1 to serve the
other VPN services on it, considering that there are hundreds of VRFs
deployed on it.
PE1 should have the capability to control the advertisement of
specified excessive VPN routes from its BGP peer. The ASBR should
also have such capability.
The excessive VPN routes may carry just one RT(for example in VPN1 on
PE3), or carry more than one RTs(for example in VPN2 on PE3). Such
excessive VPN routes may be imported into one VRF(for example VPN1 on
PE1) or more than one VRFs(for example both VPN2 and VPN3 import the
VPN routes with RD32, which has attached RT2 and RT3 together when
they are advertised)
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+---------------------------+ +------------------------------+
| | | |
| | | |
| +---------+ | | +---------+ |
| | PE1 | | | | PE3 | |
| +---------+ | | +---------+ |
|VPN1(RD11,RT1)\ | | /VPN1(RD31,RT1) |
|VPN2(RD12,RT2) \+---------+ MP-EBGP +---------+/ VPN2(RD32,RT2,RT3)|
|VPN3(RD3 ,RT3) | | | | |
| | ASBR1 |-----------| ASBR2 | |
| | | | | |
| +---------+ +---------+ |
| / | | \ |
| +---------+/ | | \+---------+ |
| | PE2 | | | | PE4 | |
| +---------+ | | +---------+ |
|VPN1(RD21,RT1) | | VPN2(RD42,RT2) |
|VPN2(RD2 ,RT2) | | VPN3(RD3, RT3) |
| AS1 | | AS2 |
+---------------------------+ +------------------------------+
Figure 1: The Option B/Option AB cross-domain scenario
5. Inter-AS VPN Option C Scenario
For inter-AS VPN deployment option C scenario, as that described in
Figure 2, there is one BGP session between RR1 and RR2, which is used
to advertise the VPN routes from all the VRFs that located on the
edge routers(PE1 and PE2). The BGP maximum prefix bar can't also
prevent the excessive advertisement of VPN routes in one VRF, and
such abnormal behavior in one VRF can certainly influence the
performances of PEs to serve other normal VRFs.
PE and RR should all have some capabilities to control the specified
excessive VPN routes to be advertised from its upstream BGP peer.
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MP-EBGP
+------------------------------------------+
| |
+------------+--------------+ +------------+------------------+
| +---+----+ | | +----+----+ |
| +---+ RR1 +---+ | | +----+ RR2 +---+ |
| | +--------+ | | | | +---------+ | |
| | | | | | | |
| |IBGP IBGP| | | |IBGP IBGP| |
| | | | | | | |
| +--+---+ +---+--+ | | +---+---+ +--+--+ |
| | PE1 | | ASBR1|--|--------------|---| ASBR2 | | PE2 | |
| +------+ +------+ | | +-------+ +-----+ |
| AS1 | | AS2 |
+---------------------------+ +-------------------------------+
Figure 2: The Option C cross-domain scenario
6. Intra-AS VPN RR Deployment Scenario
For intra-AS VPN deployment, as depicted in Figure 3, if the RR is
present, the above excess VPN routes advertisement churn can also
occurs. For example, if PE3 receives excessive VPN routes for VPN1
VRF(there may be several reasons for this to occur, for example,
multiple CEs connect to PE3 advertising routes simultaneously causing
a wave of routes, redistribution from VRF to VRF, or from GRT to VRF
on PE3 etc.), it will advertise such excessive VPN routes to RR and
then to PE1. The BGP session between RR and PE3, and the BGP session
between RR and PE1 can't prevent this to occur.
The RD in each VPN may be allocated and unique for each VPN on each
PE(as example VPN1 in Figure 3), or only unique for each VPN(as
example VPN2 in Figure 3).
Each VPN may be associated with one or more RTs. The excessive VPN
routes may have only one RT(for example, the excessive VPN routes
from PE3 has the RD equal to RD31 and RT is set only to RT1)
When PE1 in this figure receives such excessive VPN routes, it can
only process them, among the other normal BGP updates. This can
certainly influence process of VPN routes for other normal services,
the consequences on the receiving PE1 may be the one or more of the
followings:
a) PE1 can't process a given number of routes in time period X
leading to dropping of routes
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b) Delayed processing that may result in an incomplete number of
inputs to the BGP Best Path decision.
c) L3VPN customers experiencing an incorrect VPN specification for
some time period Y.
d) The convergence of control plane processing impacts the traffic
forwarding
PE and RR should all have some capabilities to control the specified
excessive VPN routes to be advertised from its upstream BGP peer.
+-----------------------------------------------+
| +---------+ +---------+ |
| | PE1 | | PE4 | |
| +---------+ +---------+ |
| VPN1(RD11,RT1) \ / VPN2(RD12,RT2)|
| VPN2(RD12,RT2) \+---------+ / |
| | | |
| | RR | |
| | | |
| +---------+ \ |
| / \ |
| +---------+/ +---------+ |
| | PE2 | | PE3 | |
| +---------+ +---------+ |
| VPN1(RD21,RT1) VPN1(RD31,RT1,RT2)|
| VPN2(RD12,RT2) |
| |
| AS100 |
+-----------------------------------------------+
Figure 3: Intra-AS VPN RR deployment scenario
7. VPN Routes Shared on one PE
The scenarios described above are mainly in device level, that is to
say, if the receiving PE has some mechanism to control the excess VPN
routes advertisement from its BGP neighbor, the failure churn effect
can be controlled then. But there are also situations that the
granular control should be took place within the receiving PE itself.
Figure 4 below describes such scenario. There are four VRFs on PE,
and three of them import the same VPN routes that carry route target
RT3. Such deployment can occur in the inter-VRF communication
scenario. If the threshold of VPN route-limit for these VRFs is set
different, for example, are max-vpn-routes-vrf1, max-vpn-routes-vrf2,
max-vpn-routes-vrf3, max-vpn-routes-vrf4 respectively, and these
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values have the following order, as max-vpn-routes-vrf1<max-vpn-
routes-vrf2< max-vpn-routes-vrf3<max-vpn-routes-vrf4.
If the VPN routes that associates with RT3 is overwhelming, the VRF1
will reach its maximum VPN threshold first. At such stage, the PE
device can't send the control message to its BGP neighbor on behalf
of all the VRFs on it, because other VRFs have still the desire to
receive such VPN routes and have the capacities to store them.
In such situation, the PE device should have some mechanisms to
control the distribution of global VPN routes to its individual VRF
table. Only when all of VRFs on it don't want some VPN routes, then
the PE device can send the VPN routes filter control message to its
BGP neighbor (RR in this example).
+-----------------------------------------------+
| +--------+ |
| | RR |--------------------+ |
| +--------+ | |
| | | |
| | | |
| +--------+ +---+---+ |
| | PE1 | | PE2 | |
| +--------+ +-------+ |
| VPN1(RD21,RT1,RT3) VPN1(RD21,RT1) |
| VPN2(RD22,RT2) VPN3(RD23,RT3) |
| VPN3(RD23,RT3) |
| |
| AS 100 |
+-----------------------------------------------+
Figure 4: The scenario of several VRFs in a PE import VPN routes carries the same RT
.
8. Requirements for the solutions
Based on the above scenarios description, the potential solutions
should meet the following requirements:
a) The control message for the specified VPN routes should be
triggered automatically upon the excessive VPN routes reach its
limit.
b) The control message should be sent only out the device when all
the VRFs on it can't or don't want to process it, or the process of
such excessive routes has exceed its own capability.
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c) For RR devices, such control message should be only flooded to its
upstream BGP neighbor when all its clients can't or don't want to
process it, or the process of such excessive routes has exceed its
own capability.
d) For ASBR devices, such control message should be only flooded to
its upstream BGP neighbor when all its downstream BGP peers can't or
don't want to process it, or the process of such excessive routes has
exceed its own capability.
e) The trigger and removal of such control message should avoid the
possible flapping of excessive VPN routes advertisement.
9. Security Considerations
TBD.
10. IANA Considerations
This document requires no IANA considerations.
11. Acknowledgement
Thanks Robert Raszuk, Jim Uttaro, Jakob Heitz, Shuanglong Chen, Enke
Chen and Srihari Sangli for their valuable comments and discussions
of scenarios described in this draft.
12. 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>.
[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>.
[RFC4486] Chen, E. and V. Gillet, "Subcodes for BGP Cease
Notification Message", RFC 4486, DOI 10.17487/RFC4486,
April 2006, <https://www.rfc-editor.org/info/rfc4486>.
Authors' Addresses
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Aijun Wang
China Telecom
Beiqijia Town, Changping District
Beijing, Beijing 102209
China
Email: wangaj3@chinatelecom.cn
Wei Wang
China Telecom
Beiqijia Town, Changping District
Beijing, Beijing 102209
China
Email: wangw36@chinatelecom.cn
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
Haibo Wang
Huawei Technologies
Huawei Building, No.156 Beiqing Rd.
Beijing, Beijing 100095
China
Email: rainsword.wang@huawei.com
Shunwan Zhuang
Huawei Technologies
Huawei Building, No.156 Beiqing Rd.
Beijing, Beijing 100095
China
Email: zhuangshunwan@huawei.com
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Jie Dong
Huawei Technologies
Huawei Building, No.156 Beiqing Rd.
Beijing, Beijing 100095
China
Email: jie.dong@huawei.com
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