TEAS Working Group A. Wang
Internet-Draft China Telecom
Intended status: Experimental B. Khasanov
Expires: May 19, 2021 Yandex LLC
Q. Zhao
Etheric Networks
H. Chen
Futurewei
November 15, 2020
PCE in Native IP Network
draft-ietf-teas-pce-native-ip-13
Abstract
This document defines an architecture for providing traffic
engineering in a native IP network using multiple BGP sessions and a
Path Computation Element (PCE)-based central control mechanism. It
defines the Central Control Dynamic Routing (CCDR) procedures and
identifies needed extensions for the Path Computation Element
Communication Protocol (PCEP).
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
7.4. Loop Avoidance . . . . . . . . . . . . . . . . . . . . . 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
[RFC8283], based on an extension of the PCE architecture described in
[RFC4655] , introduced a broader use applicability for a PCE as a
central controller. PCEP is continued to be used as the protocol
between PCE and PCC. Building on this work, this document describes
a solution using a PCE for centralized control in a native IP network
to provide End-to-End(E2E) performance assurance and QoS for traffic.
The solution combines the use of distributed routing protocols and a
centralized controller, referred to as Centralized Control Dynamic
Routing(CCDR).
[RFC8735] describes the scenarios and simulation results for traffic
engineering in a native IP network based on use of a CCDR
architecture. Per [RFC8735], the architecture for traffic
engineering in a native IP network should meet the following
criteria:
o Same solution for native IPv4 and IPv6 traffic.
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o Support for intra-domain and inter-domain scenarios.
o Achieve End to End traffic assurance, with determined QoS
behavior, for traffic requiring a service assurance(prioritized
traffic).
o No changes in a router's forwarding behavior.
o Capability to use the power of centralized control and the
flexibility/robustness of a distributed network control plane.
o Support different network requirements such as large traffic
amount and prefix scale.
o Ability to adjust the optimal path dynamically upon the changes of
network status. No need for physical links resources reservations
to be done in advance.
Building on the above documents, this document defines an
architecture meeting these requirements by using multiple a BGP
session strategy and a PCE as the centralized controller. The
architecture depends on the central control (PCE) element to compute
the optimal path, and utilizes the dynamic routing behavior of IGP/
BGP protocols for forwarding the traffic.
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
Other terms are defined in this document:
o CCDR: Central Control Dynamic Routing
o E2E: End to End
o ECMP: Equal-Cost Multipath
o RR: Route Reflector
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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 accordingly.
+-----+
+----------+ 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
In the Intra-AS scenario, IGP and BGP combined with a PCE are
deployed between R1 and R2. In the inter-AS scenario, only the
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 following:
o Build two BGP sessions between R1 and R2, via the different
loopback addresses on these routers.
o Using the PCE, set the explicit peer route on R1 and R2 for BGP
next hop to different physical link addresses between R1 and R2.
The explicit peer route can be set in the format of a static
route, which is different from the route learned from the IGP
protocol.
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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.
After the above actions, the bi-directional traffic between the PF11
and PF21, and the bi-directional traffic between PF12 and PF22 will
go through different physical links between R1 and R2.
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
the next hop for BGP session 2. In this case, the prefixes that are
advertised by the BGP peers need not be changed.
If, for example, there is bi-directional priority traffic from
another address pair (for example prefix PF13/PF23), and the total
volume of priority 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-directional traffic between PF13/PF23 will go through the same
assigned dedicated physical links as the traffic between PF12/PF22.
Such a decoupling philosophy of the IGP/BGP traffic link and the
physical link achieves a flexible control capability for the network
traffic, achieving the needed QoS assurance to meet the application's
requirement. The router needs only support native IP and multiple
BGP sessions setup via different loopback addresses.
4. CCDR Architecture in Large Scale Topology
When the priority traffic spans across a large scale network, as that
illustrated in Figure 2, the multiple BGP sessions cannot be
established hop by hop, for example, the iBGP within one AS.
For such a scenario, we propose using a Route Reflector (RR)
[RFC4456] to achieve a 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 the same as that described in the CCDR architecture for the
simple topology.
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
priority traffic) to the selected forwarding address.
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+-----+
+----------------+ 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
Generally, 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:
+----------------+-------------+---------------+-----------------+
| 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
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has end to end under-loading links; for Prefix Set No.3, we can let
traffic pass over a determined single path, as 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, and packet loss constraints to meet
the above requirements in a large scale IP-based network only using a
distributed routing protocol, but these requirements can be met with
the assistance of PCE, as that described in [RFC4655] and [RFC8283].
The PCE will have the overall network view, ability to collect the
real-time network topology, and the network performance information
about the underlying network. The PCE can select the appropriate
path to meet the various network performance requirements for
different traffic.
The architecture to implement the CCDR Multiple BGP sessions strategy
is as the follows:
The PCE will be responsible for the optimal path computation for the
different priority classes of traffic:
o PCE collects topology information via BGP-LS [RFC7752] and link
utilization information via the existing Network Monitoring System
(NMS) from the underlying network.
o PCE calculates the appropriate path based upon the application's
requirements, and sends the key parameters to edge/RR routers(R1,
R7 and R3 in Figure 3) to establish multiple BGP sessions. The
loopback addresses used for the 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
Figure 3) on the 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.
o PCE send the prefixes information to the PCC for advertising
different prefixes via the specified BGP session.
o If the priority traffic prefixes were changed but the total volume
of priority traffic does not exceed the physical capacity of the
previous E2E path, the PCE needs only change the prefixed
advertised via the edge routers (R1,R7 in Figure 3).
o If the volume of priority traffic exceeds the capacity of the
previous calculated path, the PCE can recalculate and add the
appropriate paths to accommodate the exceeding traffic. After
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that, the PCE needs to update the 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 sessions deployment
6. PCEP Extension for Key Parameters Delivery
The PCEP protocol needs to be extended to transfer the following key
parameters:
o Peer information that is used to build the BGP session
o Explicit route information to BGP next hop of advertised prefixes
o Advertised prefixes and their associated BGP session.
Once the router receives such information, it should establish the
BGP session with the peer appointed in the PCEP message, build the
end to end dedicated path hop by hop, and advertise the prefixes that
contained in the corresponding PCEP message.
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 other dynamic protocols.
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All above dynamically created states (BGP sessions, Explicit route,
Prefix advertised prefix, ) will be cleared on the expiration of
state timeout interval which is based on the existing Stateful PCE
[RFC8231] and PCECC [RFC8283] mechanism.
Regarding the BGP session, it is not different from that configured
via the manual or NETCONF/YANG. Different BGP sessions are used
mainly for the clarification of the network prefixes, which can be
differentiated via the different BGP nexthop. Based on this
strategy, if we manipulate the path to the BGP nexthop, then the path
to the prefixes that advertised with the BGP sessions will be changed
accordingly. Details of communications between PCEP and BGP
subsystems in the router's control plane are out of scope of this
draft and will be described in a separate draft
[I-D.ietf-pce-pcep-extension-native-ip] .
7. Deployment Consideration
7.1. Scalability
In the CCDR architecture, only the edge routers that connects with
PCE are responsible for the prefixes advertisement via the multiple
BGP sessions deployment. The route information for these prefixes
within the on-path routers is distributed via the BGP protocol.
For multiple domains deployment, the PCE, or the pool of PCEs
responsible for these domains, needs only to control the edge router
to build the multiple EBGP sessions; all other procedures are the
same as within one domain.
Unlike the solution from BGP Flowspec, the on-path router needs only
to keep the specific policy routes for the BGP next-hop of the
differentiate prefixes, not the specific routes to the prefixes
themselves. This lessens the burden of the table size of policy
based routes for the on-path routers; and has more expandability
compared with BGP flowspec or Openflow solutions. 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, whereas
the BGP flowspec or Openflow solutions need 1000 policy routes on
them.
7.2. High Availability
The CCDR architecture is based on the use of the native IP protocol.
If the PCE fails, the forwarding plane will not be impacted, as the
BGP sessions between all the devices will not flap and the forwarding
table remains 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 paths to load balance/hot-standby the priority traffic to
meet the path failure situation.
For ensuring high availability of a PCE/SDN-controllers architecture,
an operator should rely on existing high availability solutions for
SDN controllers, such as clustering technology and deployment.
7.3. Incremental deployment
Not every router within the network will support the PCEP extension
defined in [I-D.ietf-pce-pcep-extension-native-ip] simultaneously.
For such situations, routers on the edge of a domain can be upgraded
first, and then the traffic can be prioritized between different
domains. Within each domain, the traffic will be forwarded along the
best-effort path. A Service provider can selectively upgrade the
routers on each domain in sequence.
7.4. Loop Avoidance
A PCE needs to assure calculation of the E2E path based on the status
of network and the service requirements in real-time.
The PCE needs to consider the explicit route deployment order (for
example, from tail rotuer to head rotuer) to eliminate any possible
transient traffic loop.
8. Security Considerations
The setup of BGP sessions, prefix advertisement, and explicit peer
route establishment are all controlled by the PCE. To prevent a
bogus PCE sending harmful messages to the network nodes, the network
devices should authenticate the validity of the PCE and ensure a
secure communication channel between them. Mechanisms described in
[RFC8253] should be used.
The CCDR architecture does not require the changes of forwarding
behavior on the underlay devices, there will no additional security
impacts on these 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>.
[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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[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., Tan, R., and C. Zhu,
"PCEP Extension for Native IP Network", draft-ietf-pce-
pcep-extension-native-ip-09 (work in progress), October
2020.
Authors' Addresses
Aijun Wang
China Telecom
Beiqijia Town, Changping District
Beijing 102209
China
Email: wangaj3@chinatelecom.cn
Boris Khasanov
Yandex LLC
Ulitsa Lva Tolstogo 16
Moscow
Russia
Email: bhassanov@yahoo.com
Quintin Zhao
Etheric Networks
1009 S CLAREMONT ST
SAN MATEO, CA 94402
USA
Email: qzhao@ethericnetworks.com
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Huaimo Chen
Futurewei
Boston, MA
USA
Email: huaimo.chen@futurewei.com
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