TEAS Working Group A. Wang
Internet-Draft China Telecom
Intended status: Experimental B. Khasanov
Expires: December 3, 2020 Huawei Technologies
Q. Zhao
Etheric Networks
H. Chen
Futurewei
June 1, 2020
PCE in Native IP Network
draft-ietf-teas-pce-native-ip-07
Abstract
This document defines the framework for traffic engineering within
native IP network, using multiple BGP sessions strategy and PCE
-based central control architecture.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. CCDR Framework in Simple Topology . . . . . . . . . . . . . . 3
4. CCDR Framework 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 . . . . . . . . . . . . . . . . . . . . . . . 10
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 native IP network. To meet the requirements of
various scenarios, the solution for traffic engineering in native IP
network should have the following criteria:
o No complex signaling procedures among network nodes like MPLS-TE.
o End to End traffic assurance, determined QoS behavior.
o Same deployment method for intra-domain and inter-domain.
o No upgrade to forwarding behavior of the router.
o Support native IPv4 and IPv6 traffic in the same solution.
o Can exploit the power of centrally control and flexibility/
robustness of distributed control protocol.
o Coping with the differentiation requirements for large amount
traffic and prefixes.
o Flexible deployment and automation control.
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This document defines the framework for traffic engineering within
native IP network, using multiple BGP session strategy, to meet the
above requirements in dynamical and centrally control mode. The
framework is referred as Central Control Dynamic Routing (CCDR)
framework. 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]: PCE,
PCEP
The following terms are used in this document:
o CCDR: Central Control Dynamic Routing
o E2E: End to End
o ECMP: Equal Cost Multi Path
o RR: Route Reflector
o SDN: Software Defined Network
3. CCDR Framework in Simple Topology
Figure 1 illustrates the CCDR framework 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 differently.
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 framework for this simple topology are the
followings:
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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 traffic between the PF11 and PF21, and
the 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
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 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
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. No complex
signaling procedures like MPLS are introduced, the router needs only
support native IP and multiple BGP sessions setup via different
loopback addresses.
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+-----+
+----------+ 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 framework in simple topology
4. CCDR Framework 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 to use 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 framework for 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
assured 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 framework 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:
+----------------+-------------+---------------+-----------------+
| 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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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 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 framework 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.
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.
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+------------+
| 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 framework 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
the prefixes that contained in the corresponding PCEP message, and
build the end to end dedicated path hop by hop.
The explicit route created by PCE has the higher priority than the
route information created by other protocols, including the route
manually configured.
All above dynamically created states (BGP sessions, Prefix advertised
prefix, Explict route) will be cleared once the connection between
the PCE and network devices is interrupted.
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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] .
The reason that we select PCEP as the southbound protocol instead of
OpenFlow, is that PCEP is suitable for the changes in control plane
of the network devices, while OpenFlow dramatically changes the
forwarding plane. We also think that the level of centralization
that required by OpenFlow is hardly achievable in SP networks so
hybrid BGP+PCEP approach looks much more interesting.
7. Deployment Consideration
7.1. Scalability
In CCDR framework, 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 domain deployment, the PCE 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 framework 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.
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.
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For high availability of PCE/SDN-controller, operator should rely on
existing HA 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 assures calculations of E2E path upon the status of network
condition and the service requirements in real time.
The PCE need consider the explicit route deployment order (for
example, from tail router to head router) to eliminate the possible
transient traffic loop.
CCDR framework described in this draft puts more requirements on the
function of PCE and its communication with the underlay devices.
Service provider should consider more on the protection of PCE and
their communication with the underlay devices, which is described in
document [RFC5440] and [RFC8253]
CCDR framework 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.
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.
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11. References
11.1. 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>.
[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>.
[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>.
[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>.
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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-05 (work in progress), February 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
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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