TEAS Working Group A. Wang
Internet-Draft China Telecom
Intended status: Experimental B. Khasanov
Expires: February 26, 2021 Huawei Technologies
Q. Zhao
Etheric Networks
H. Chen
Futurewei
August 25, 2020
PCE in Native IP Network
draft-ietf-teas-pce-native-ip-11
Abstract
This document defines the architecture for traffic engineering within
native IP network, using multiple BGP sessions strategy and PCE
-based central control mechanism. It uses the Central Control
Dynamic Routing (CCDR) procedures described in this document, and the
Path Computation Element Communication Protocol (PCEP) extension
specified in draft ietf-pce-pcep-extension-native-ip.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. CCDR Architecture in Simple Topology . . . . . . . . . . . . 4
4. CCDR Architecture in Large Scale Topology . . . . . . . . . . 5
5. CCDR Multiple BGP Sessions Strategy . . . . . . . . . . . . . 6
6. PCEP Extension for Key Parameters Delivery . . . . . . . . . 8
7. Deployment Consideration . . . . . . . . . . . . . . . . . . 9
7.1. Scalability . . . . . . . . . . . . . . . . . . . . . . . 9
7.2. High Availability . . . . . . . . . . . . . . . . . . . . 9
7.3. Incremental deployment . . . . . . . . . . . . . . . . . 10
8. Security Considerations . . . . . . . . . . . . . . . . . . . 10
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 11
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
11.1. Normative References . . . . . . . . . . . . . . . . . . 11
11.2. Informative References . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
[RFC8735] describes the scenarios and simulation results for traffic
engineering in the native IP network to provide End-to-End (E2E)
performance assurance and QoS using PCE based centralized control,
referred to as Centralized Control Dynamic Routing (CCDR). Based on
the various scenarios and analysis as per [RFC8735], the solution for
traffic engineering in native IP network should meet the following
criteria:
o Same solution for native IPv4 and IPv6 traffic.
o Support for intra-domain and inter-domain scenarios.
o Achieve End to End traffic assurance, with determined QoS
behavior.
o No upgrade to forwarding behaviour of the router.
o Capable to exploit the power of centrally control and the
flexibility/robustness of distributed control protocol.
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o Coping with the differentiation requirements for large amount
traffic and prefixes.
o Adjust the optimal path dynamically upon the change of network
status. No physical links resources reservation in advance.
Stateful PCE [RFC8231] specifies a set of extensions to PCEP to
enable stateful control of paths such as MPLS-TE Label Switched
Paths(LSP)s between and across PCEP sessions in compliance with
[RFC4657]. It includes mechanisms to achieve state synchronization
between Path Computation Clients(PCCs) and PCEs, delegation of
control of LSPs to PCEs, and PCE control of timing and sequence of
path computations within and across PCEP sessions. Furthermore,
[RFC8281] specifies a mechanism to dynamically instantiate LSPs on a
PCC based on the requests from a stateful PCE or a controller using
stateful PCE. [RFC8283] introduces the architecture for PCE as a
central controller as an extension of the architecture described in
[RFC4655] and assumes the continued use of PCEP as the protocol used
between PCE and PCC.[RFC8283] further examines the motivations and
applicability for PCEP as a Southbound Interface (SBI), and
introduces the implications for the protocol.
This document defines the architecture for traffic engineering within
native IP network, using multiple BGP session strategy, to meet the
above criteria in dynamical and centrally control mode. The
architecture is referred as CCDR architecture. It depends on the
central control (PCE) element to compute the optimal path for
selected traffic, and utilizes the dynamic routing behavior of
traditional IGP/BGP protocols to forward such traffic.
The control messages between PCE and underlying network node are
transmitted via Path Computation Element Communications Protocol
(PCEP) protocol. The related PCEP extensions are provided in draft
[I-D.ietf-pce-pcep-extension-native-ip].
2. Terminology
This document uses the following terms defined in [RFC5440]:
o PCE
o PCEP
o PCC
The following terms are used in this document:
o CCDR: Central Control Dynamic Routing
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o E2E: End to End
o ECMP: Equal-Cost Multipath
o RR: Route Reflector
o SDN: Software Defined Network
3. CCDR Architecture in Simple Topology
Figure 1 illustrates the CCDR architecture for traffic engineering in
simple topology. The topology is comprised by four devices which are
SW1, SW2, R1, R2. There are multiple physical links between R1 and
R2. Traffic between prefix PF11(on SW1) and prefix PF21(on SW2) is
normal traffic, traffic between prefix PF12(on SW1) and prefix
PF22(on SW2) is priority traffic that should be treated with
priority.
In Intra-AS scenario, IGP and BGP are deployed between R1 and R2. In
inter-AS scenario, only native BGP protocol is deployed. The traffic
between each address pair may change in real time and the
corresponding source/destination addresses of the traffic may also
change dynamically.
The key ideas of the CCDR architecture for this simple topology are
the followings:
o Build two BGP sessions between R1 and R2, via the different
loopback addresses on these routers.
o Send different prefixes via the established BGP sessions. For
example, PF11/PF21 via the BGP session 1 and PF12/PF22 via the BGP
session 2.
o Set the explicit peer route on R1 and R2 respectively for BGP next
hop to different physical link addresses between R1 and R2. Such
explicit peer route can be set in the format of static route to
BGP peer address, which is different from the route learned from
the IGP protocol.
After the above actions, the bi-direction traffic between the PF11
and PF21, and the bi-direction traffic between PF12 and PF22 will go
through different physical links between R1 and R2, each set of
traffic pass through different dedicated physical links.
If there is more traffic between PF12 and PF22 that needs to be
assured , one can add more physical links between R1 and R2 to reach
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the the next hop for BGP session 2. In this cases the prefixes that
advertised by the BGP peers need not be changed.
If, for example, there is bi-direction traffic from another address
pair that needs to be assured (for example prefix PF13/PF23), and the
total volume of assured traffic does not exceed the capacity of the
previously provisioned physical links, one need only to advertise the
newly added source/destination prefixes via the BGP session 2. The
bi-direction traffic between PF13/PF23 will go through the assigned
dedicated physical links as the traffic between PF12/PF22.
Such decouple philosophy gives network operator flexible control
capability on the network traffic, achieve the determined QoS
assurance effect to meet the application's requirement. The router
needs only support native IP and multiple BGP sessions setup via
different loopback addresses.
+-----+
+----------+ PCE +--------+
| +-----+ |
| |
| BGP Session 1(lo11/lo21)|
+-------------------------+
| |
| BGP Session 2(lo12/lo22)|
+-------------------------+
PF12 | | PF22
PF11 | | PF21
+---+ +-----+-----+ +-----+-----+ +---+
|SW1+---------+(lo11/lo12)+-------------+(lo21/lo22)+--------------+SW2|
+---+ | R1 +-------------+ R2 | +---+
+-----------+ +-----------+
Figure 1: CCDR architecture in simple topology
4. CCDR Architecture in Large Scale Topology
When the assured traffic spans across the large scale network, as
that illustrated in Figure 2, the multiple BGP sessions cannot be
established hop by hop, especially for the iBGP within one AS.
For such scenario, we should consider using the Route Reflector (RR)
[RFC4456] to achieve the similar effect. Every edge router will
establish two BGP sessions with the RR via different loopback
addresses respectively. The other steps for traffic differentiation
are same as that described in the CCDR architecture for simple
topology.
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As shown in Figure 2, if we select R3 as the RR, every edge router(R1
and R7 in this example) will build two BGP session with the RR. If
the PCE selects the dedicated path as R1-R2-R4-R7, then the operator
should set the explicit peer routes via PCEP protocol on these
routers respectively, pointing to the BGP next hop (loopback
addresses of R1 and R7, which are used to send the prefix of the
assured traffic) to the selected forwarding address.
+-----+
+----------------+ PCE +------------------+
| +--+--+ |
| | |
| | |
| ++-+ |
+------------------+R3+-------------------+
PF12 | +--+ | PF22
PF11 | | PF21
+---+ ++-+ +--+ +--+ +-++ +---+
|SW1+-------+R1+----------+R5+----------+R6+---------+R7+--------+SW2|
+---+ ++-+ +--+ +--+ +-++ +---+
| |
| |
| +--+ +--+ |
+------------+R2+----------+R4+-----------+
+--+ +--+
Figure 2: CCDR architecture in large scale network
5. CCDR Multiple BGP Sessions Strategy
In general situation, different applications may require different
QoS criteria, which may include:
o Traffic that requires low latency and is not sensitive to packet
loss.
o Traffic that requires low packet loss and can endure higher
latency.
o Traffic that requires low jitter.
These different traffic requirements can be summarized in the
following table:
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+----------------+-------------+---------------+-----------------+
| Prefix Set No. | Latency | Packet Loss | Jitter |
+----------------+-------------+---------------+-----------------+
| 1 | Low | Normal | Don't care |
+----------------+-------------+---------------+-----------------+
| 2 | Normal | Low | Dont't care |
+----------------+-------------+---------------+-----------------+
| 3 | Normal | Normal | Low |
+----------------+-------------+---------------+-----------------+
Table 1. Traffic Requirement Criteria
For Prefix Set No.1, we can select the shortest distance path to
carry the traffic; for Prefix Set No.2, we can select the path that
is comprised by under loading links from end to end; For Prefix Set
No.3, we can let all assured traffic pass the determined single path,
no Equal Cost Multipath (ECMP) distribution on the parallel links is
desired.
It is almost impossible to provide an End-to-End (E2E) path
efficiently with latency, jitter, packet loss constraints to meet the
above requirements in large scale IP-based network via the
distributed routing protocol, but these requirements can be solved
with the assistance of PCE, as that described in [RFC4655] and
[RFC8283] because the PCE has the overall network view, can collect
real network topology and network performance information about the
underlying network, select the appropriate path to meet various
network performance requirements of different traffics.
The architecture to implement the CCDR Multiple BGP sessions strategy
are the followings. Here PCE is the main component of the Software
Definition Network (SDN) controller and is responsible for optimal
path computation for priority traffic.
o SDN controller gets topology via BGP-LS[RFC7752] and link
utilization information via existing Network Monitor System (NMS)
from the underlying network.
o PCE calculates the appropriate path upon application's
requirements, sends the key parameters to edge/RR routers(R1, R7
and R3 in Fig.3) to establish multiple BGP sessions and advertises
different prefixes via them. The loopback addresses used for BGP
sessions should be planned in advance and distributed in the
domain.
o PCE sends the route information to the routers (R1,R2,R4,R7 in
Fig.3) on forwarding path via PCEP
[I-D.ietf-pce-pcep-extension-native-ip], to build the path to the
BGP next-hop of the advertised prefixes.
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o If the assured traffic prefixes were changed but the total volume
of assured traffic does not exceed the physical capacity of the
previous E2E path, PCE needs only change the prefixed advertised
via the edge routers (R1,R7 in Fig.3).
o If the volume of assured traffic exceeds the capacity of previous
calculated path, PCE can recalculate and add the appropriate paths
to accommodate the exceeding traffic. After that, PCE needs to
update on-path routers to build the forwarding path hop by hop.
+------------+
| Application|
+------+-----+
|
+--------+---------+
+----------+SDN Controller/PCE+-----------+
| +--------^---------+ |
| | |
| | |
PCEP | BGP-LS|PCEP | PCEP
| | |
| +v-+ |
+------------------+R3+-------------------+
PF12 | +--+ | PF22
PF11 | | PF21
+---+ +v-+ +--+ +--+ +-v+ +---+
|SW1+-------+R1+----------+R5+----------+R6+---------+R7+--------+SW2|
+---+ ++-+ +--+ +--+ +-++ +---+
| |
| |
| +--+ +--+ |
+------------+R2+----------+R4+-----------+
Figure 3: CCDR architecture for Multi-BGP deployment
6. PCEP Extension for Key Parameters Delivery
The PCEP protocol needs to be extended to transfer the following key
parameters:
o Peer addresses pair that is used to build the BGP session
o Advertised prefixes and their associated BGP session.
o Explicit route information to BGP next hop of advertised prefixes.
Once the router receives such information, it should establish the
BGP session with the peer appointed in the PCEP message, advertise
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the prefixes that contained in the corresponding PCEP message, and
build the end to end dedicated path hop by hop.
The dedicated path is preferred by making sure that the explicit
route created by PCE has the higher priority (lower route preference)
than the route information created by any other protocols (including
the route manually configured).
All above dynamically created states (BGP sessions, Prefix advertised
prefix, Explicit route) will be cleared on the expiration of state
timeout interval which is based on the existing Stateful PCE
[RFC8231] and PCECC [RFC8283] mechanism.
Details of communications between PCEP and BGP subsystems in router's
control plane are out of scope of this draft and will be described in
separate draft [I-D.ietf-pce-pcep-extension-native-ip] .
7. Deployment Consideration
7.1. Scalability
In CCDR architecture, PCE needs only influence the edge routers for
the prefixes advertisement via the multiple BGP sessions deployment.
The route information for these prefixes within the on-path routers
were distributed via the BGP protocol.
For multiple domains deployment, the PCE or the pool of PCEs that
reponsible for these domains need only control the edge router to
build multiple EBGP sessions, all other procedures are the same that
in one domain.
Unlike the solution from BGP Flowspec, the on-path router need only
keep the specific policy routes to the BGP next-hop of the
differentiate prefixes, not the specific routes to the prefixes
themselves. This can lessen the burden from the table size of policy
based routes for the on-path routers, and has more expandability when
comparing with the solution from BGP flowspec or Openflow. For
example, if we want to differentiate 1000 prefixes from the normal
traffic, CCDR needs only one explicit peer route in every on-path
router, but the BGP flowspec or Openflow needs 1000 policy routes on
them.
7.2. High Availability
The CCDR architecture is based on the distributed IP protocol. If
the PCE failed, the forwarding plane will not be impacted, as the BGP
session between all devices will not flap, and the forwarding table
will remain unchanged.
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If one node on the optimal path is failed, the priority traffic will
fall over to the best-effort forwarding path. One can even design
several assurance paths to load balance/hot-standby the priority
traffic to meet the path failure situation.
For high availability of PCE/SDN-controller, operator should rely on
existing high availability solutions for SDN controller, such as
clustering technology and deployment.
7.3. Incremental deployment
Not every router within the network will support the PCEP extension
that defined in [I-D.ietf-pce-pcep-extension-native-ip]
simultaneously.
For such situations, router on the edge of domain can be upgraded
first, and then the traffic can be assured between different domains.
Within each domain, the traffic will be forwarded along the best-
effort path. Service provider can selectively upgrade the routers on
each domain in sequence.
8. Security Considerations
A PCE needs to assure calculation of E2E path based on the status of
network and the service requirements in real-time.
The PCE needs consider the explicit route deployment order (for
example, from tail router to head router) to eliminate the possible
transient traffic loop.
The setup of BGP session, prefix advertisement and explicit peer
route establishment are all controlled by the PCE. To prevent the
bogus PCE to send harmful messages to the network nodes, the network
devices should authenticate the validity of PCE and keep secures
communication channel between them. Mechanism described in [RFC8253]
should be used to avoid such situation.
CCDR architecture does not require the change of forward behavior on
the underlay devices, then there will no additional security impact
on the devices.
9. IANA Considerations
This document does not require any IANA actions.
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10. Acknowledgement
The author would like to thank Deborah Brungard, Adrian Farrel,
Vishnu Beeram, Lou Berger, Dhruv Dhody, Raghavendra Mallya , Mike
Koldychev, Haomian Zheng, Penghui Mi, Shaofu Peng and Jessica Chen
for their supports and comments on this draft.
11. References
11.1. Normative References
[RFC4456] Bates, T., Chen, E., and R. Chandra, "BGP Route
Reflection: An Alternative to Full Mesh Internal BGP
(IBGP)", RFC 4456, DOI 10.17487/RFC4456, April 2006,
<https://www.rfc-editor.org/info/rfc4456>.
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655,
DOI 10.17487/RFC4655, August 2006,
<https://www.rfc-editor.org/info/rfc4655>.
[RFC4657] Ash, J., Ed. and J. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol Generic
Requirements", RFC 4657, DOI 10.17487/RFC4657, September
2006, <https://www.rfc-editor.org/info/rfc4657>.
[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009,
<https://www.rfc-editor.org/info/rfc5440>.
[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
S. Ray, "North-Bound Distribution of Link-State and
Traffic Engineering (TE) Information Using BGP", RFC 7752,
DOI 10.17487/RFC7752, March 2016,
<https://www.rfc-editor.org/info/rfc7752>.
[RFC8231] Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path
Computation Element Communication Protocol (PCEP)
Extensions for Stateful PCE", RFC 8231,
DOI 10.17487/RFC8231, September 2017,
<https://www.rfc-editor.org/info/rfc8231>.
[RFC8253] Lopez, D., Gonzalez de Dios, O., Wu, Q., and D. Dhody,
"PCEPS: Usage of TLS to Provide a Secure Transport for the
Path Computation Element Communication Protocol (PCEP)",
RFC 8253, DOI 10.17487/RFC8253, October 2017,
<https://www.rfc-editor.org/info/rfc8253>.
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[RFC8281] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path
Computation Element Communication Protocol (PCEP)
Extensions for PCE-Initiated LSP Setup in a Stateful PCE
Model", RFC 8281, DOI 10.17487/RFC8281, December 2017,
<https://www.rfc-editor.org/info/rfc8281>.
[RFC8283] Farrel, A., Ed., Zhao, Q., Ed., Li, Z., and C. Zhou, "An
Architecture for Use of PCE and the PCE Communication
Protocol (PCEP) in a Network with Central Control",
RFC 8283, DOI 10.17487/RFC8283, December 2017,
<https://www.rfc-editor.org/info/rfc8283>.
[RFC8735] Wang, A., Huang, X., Kou, C., Li, Z., and P. Mi,
"Scenarios and Simulation Results of PCE in a Native IP
Network", RFC 8735, DOI 10.17487/RFC8735, February 2020,
<https://www.rfc-editor.org/info/rfc8735>.
11.2. Informative References
[I-D.ietf-pce-pcep-extension-native-ip]
Wang, A., Khasanov, B., Fang, S., and C. Zhu, "PCEP
Extension for Native IP Network", draft-ietf-pce-pcep-
extension-native-ip-06 (work in progress), August 2020.
Authors' Addresses
Aijun Wang
China Telecom
Beiqijia Town, Changping District
Beijing 102209
China
Email: wangaj3@chinatelecom.cn
Boris Khasanov
Huawei Technologies
Moskovskiy Prospekt 97A
St.Petersburg 196084
Russia
Email: khasanov.boris@huawei.com
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Quintin Zhao
Etheric Networks
1009 S CLAREMONT ST
SAN MATEO, CA 94402
USA
Email: qzhao@ethericnetworks.com
Huaimo Chen
Futurewei
Boston, MA
USA
Email: huaimo.chen@futurewei.com
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