Internet DRAFT - draft-ietf-teas-pce-native-ip
draft-ietf-teas-pce-native-ip
TEAS Working Group A. Wang
Internet-Draft China Telecom
Intended status: Informational B. Khasanov
Expires: August 6, 2021 Yandex LLC
Q. Zhao
Etheric Networks
H. Chen
Futurewei
February 2, 2021
Path Computation Element (PCE) based Traffic Engineering (TE) in Native
IP Networks
draft-ietf-teas-pce-native-ip-17
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
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on August 6, 2021.
Copyright Notice
Copyright (c) 2021 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
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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 Critical Parameters Delivery . . . . . . . 8
7. Deployment Consideration . . . . . . . . . . . . . . . . . . 9
7.1. Scalability . . . . . . . . . . . . . . . . . . . . . . . 9
7.2. High Availability . . . . . . . . . . . . . . . . . . . . 10
7.3. Incremental deployment . . . . . . . . . . . . . . . . . 10
7.4. Loop Avoidance . . . . . . . . . . . . . . . . . . . . . 10
7.5. E2E Path Performance Monitoring . . . . . . . . . . . . . 10
8. Security Considerations . . . . . . . . . . . . . . . . . . . 10
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
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 Path Computation Element
(PCE) architecture described in [RFC4655] , introduced a broader use
applicability for a PCE as a central controller. PCEP Protocol
(PCEP) continues to be used as the protocol between PCE and Path
Computation Client (PCC). Building on that 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:
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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, for traffic requiring a service assurance (prioritized
traffic).
o No changes in a router's forwarding behavior.
o Based on centralized control through a distributed network control
plane.
o Support different network requirements such as high traffic volume
and prefix scaling.
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 a multiple 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.
2. Terminology
This document uses the following terms defined in [RFC5440]:
o PCE: Path Computation Element
o PCEP: PCE Protocol
o PCC: Path Computation Client
Other terms are used in this document:
o CCDR: Central Control Dynamic Routing
o E2E: End to End
o ECMP: Equal-Cost Multipath
o RR: Route Reflector
o SDN: Software Defined Network
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3. CCDR Architecture in Simple Topology
Figure 1 illustrates the CCDR architecture for traffic engineering in
a simple topology. The topology is composed of 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 (lo11 and lo12 are the
loopback address of R1, lo21 and lo22 are the loopback address of
R2).
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, send 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 assured
transport, 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 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, satisfying 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 a large-scale network, such as that
illustrated in Figure 2, the multiple BGP sessions cannot be
established hop by hop 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(RR)+-----------------+
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 | Don'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-loaded 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 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, to build the path to
the BGP next-hop of the advertised prefixes. The path to these
BGP next-hop will also be learned via the IGP protocol, but the
route from the PCEP has the higher preference. Such design can
assure the IGP path to the BGP next-hop can be used to protect the
path assigned by PCE.
o PCE sends the prefixes information to the PCC(edge routers that
have established BGP sessions) for advertising different prefixes
via the specified BGP session.
o The priority traffic may share some links or nodes, if path the
shared links or nodes can meet the requirement of application.
When the priority traffic prefixes were changed but the total
volume of priority traffic does not exceed the physical capacity
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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
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(RR)+-----------------+
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 Critical Parameters Delivery
The PCEP protocol needs to be extended to transfer the following
critical parameters:
o Peer information that is used to build the BGP session
o Explicit route information for 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
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end-to-end dedicated path hop-by-hop, and advertise the prefixes that
are 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.
All above dynamically created states (BGP sessions, Explicit route
and Prefix advertised prefix) will be cleared on the expiration of
the 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
manually or via 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 were 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.
7. Deployment Consideration
7.1. Scalability
In the CCDR architecture, only the edge routers that connect with the
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 domain 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.
The on-path router needs only to keep the specific policy routes for
the BGP next-hop of the differentiated 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.
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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.
If one node on the optimal path fails, 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 a 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 needs to support the necessary
PCEP extension. 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 router to head router) to eliminate any possible
transient traffic loop.
7.5. E2E Path Performance Monitoring
It is necessary to deploy the corresponding E2E path performance
monitoring mechanism to keep assure that the delay, jitter or packet
loss index meet the original path performance aim. The performance
monitoring results should feedback to the PCE to let it accomplish
the re-optimize process, send the update control message to related
PCC if necessary. Traditional OAM methods(ping, trace) can be used.
8. Security Considerations
The setup of BGP sessions, prefix advertisement, and explicit peer
route establishment are all controlled by the PCE. See [RFC4271] and
[RFC4272] for BGP security considerations. Security consideration
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part in [RFC5440] and [RFC8231] should be considered. 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 changes to the forwarding
behavior of the underlay devices. There are no additional security
impacts on these devices.
9. IANA Considerations
This document does not require any IANA actions.
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, Donald Eastlake,
Alvaro Retana, Martin Duke, Magnus Westerlund, Benjamin Kaduk, Roman
Danyliw, Eric Vyncke, Murray Kucherawy, Erik Kline and Jessica Chen
for their supports and comments on this draft.
11. References
11.1. Normative References
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/info/rfc4271>.
[RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis",
RFC 4272, DOI 10.17487/RFC4272, January 2006,
<https://www.rfc-editor.org/info/rfc4272>.
[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>.
[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>.
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[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>.
[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>.
11.2. Informative References
[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>.
[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>.
Authors' Addresses
Aijun Wang
China Telecom
Beiqijia Town, Changping District
Beijing 102209
China
Email: wangaj3@chinatelecom.cn
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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
Huaimo Chen
Futurewei
Boston, MA
USA
Email: huaimo.chen@futurewei.com
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