plnog 13: julian lucek: centralized traffic enginnering
DESCRIPTION
Julian Lucek – is a Distinguished Engineer at Juniper Networks, where he has been working with many operators on the design and evolution of their networks. Before joining Juniper Networks in 1999, he worked at BT for several years, at first in the Photonics Research Department and later in the data transport and routing area. During this time he gained a PhD in ultrahigh-speed optical transmission and processing from Cambridge University. He is the holder of several patents in the area of communications technology. He has a Master’s degree in Physics from Cambridge University and holds Juniper Networks Certified Internet Expert (JNCIE) certification number 21. He is co-author of the book “MPLS-Enabled Applications: Emerging Developments and New Technologies”, by Ina Minei and Julian Lucek. This book is now in its third edition. Topic of Presentation: Centralized Traffic Enginnering Language: English Abstract: This presentation discusses the advantages of Centralised Traffic Engineering, compared to Distributed Traffic Engineering or shortest-path routing. We will explore benefits in terms of increased network efficiency and in terms of services that would be difficult or impossible to create using Distributed Traffic EngineeringTRANSCRIPT
Copyright © 2014 Juniper Networks, Inc. 1 Copyright © 2013 Juniper Networks, Inc.
CENTRALISED TRAFFIC ENGINEERING
JULIAN LUCEK [email protected] PLNOG13, SEPTEMBER 2014
Copyright © 2014 Juniper Networks, Inc. 2
Title Only
1
2
AGENDA
3
Motivations for Centralised Traffic Engineering
Key protocol mechanisms: PCEP, BGP-LS
TE Controller Example: NorthStar
Copyright © 2014 Juniper Networks, Inc. 3
WHAT INFORMATION GOES INTO DETERMINING A PATH FOR PACKET TRAFFIC?
Shortest Path
(IGP,LDP)
Distributed TE
(constrained SPF)
+Reservable bandwidth Topology
+
Centralised TE
+Reservable bandwidth Topology
+Complete view of packet demands
Fragmented view of packet demands
Topology
Copyright © 2014 Juniper Networks, Inc. 4
ADVANTAGES OF CENTRALISED CONTROL
Purely distributed computation does not work for all cases. A central entity (TE Controller) with global knowledge can: • Avoid TE “blocking” problems that occur in distributed computation case
• Compute a global optimum for a set of TE paths • Can use more sophisticated algorithms than CSPF • Can make more efficient use of network resources
• Deal with path diversity requirements • Give predictability in path placement • Take account of future requirements, when computing paths
Copyright © 2014 Juniper Networks, Inc. 5
LSP BLOCKING PROBLEM WITH DISTRIBUTED TE
20/100
0/50 0/50
PE1
PE2
PE3
X/Y: X=reserved bw Y=total link bw
• PE1 has already set up the green LSP to PE3, with BW reservation of 20 units.
• PE2 wants to set up an LSP to PE3 with BW=90. It is blocked by presence of green LSP.
• Centralised path computation would solve the problem.
bw=20
P1 P2
P3
bw=90 20/50 20/50
90/100
Copyright © 2014 Juniper Networks, Inc. 6
N O P
L M
DISTRIBUTED TRAFFIC ENGINEERING
I J K
B
X
Z
A
C
Suppose all links are 10G. Assume all links have same metric. A has set up an LSP to X, bw=4 B has set up an LSP to Z, bw=4. If C now needs to set up an LSP to Z, with bw=4, it has to use a non-optimum path.
Copyright © 2014 Juniper Networks, Inc. 7
N O P
L M
CENTRALISED TRAFFIC ENGINEERING
I J K
B
X
Z
A
C
TE Controller has knowledge of all the LSPs needed, so can perform a global optimisation.
Copyright © 2014 Juniper Networks, Inc. 8
AUTONOMOUS OPTIMISATION: FAILURE SCENARIOS
N O P
L M
I J K
B
X
Z
A
C
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DYNAMIC LSP SPLITTING
LSP A-E (7G Auto-Bw Adjusted) LSP A-E (7G)
LSP A-E-2 (5G)
Traffic surges to 10G
LSP A-E-1 (5G) Traffic drops to 4G
LSP A-E (4G)
E
A B
C D
Copyright © 2014 Juniper Networks, Inc. 10
PATH DIVERSITY
PE1
PE2
PE3
PE4
• The two paths must be engineered such that they have no nodes or links in common – including the PEs!
• Difficult to achieve path separacy when each ingress node calculates its own path.
• However, a central controller can calculate both paths to ensure separacy.
Copyright © 2014 Juniper Networks, Inc. 11
P2MP PATH DIVERSITY
Source, S1 Source, S2
Ingress PE1 Ingress PE2
Egress PEs Egress PEs
Receiver Receiver
The two P2MP LSPs have different ingress PEs and must not have any nodes or links in common • Difficult to ensure path separacy when ingress nodes calculate the paths. • However, a central controller can calculate both paths to ensure separacy.
Copyright © 2014 Juniper Networks, Inc. 12
BANDWIDTH CALENDARING
Bandwidth Calendaring allows network operators to reserve resources in advance
§ Via NorthStar GUI or via API § Can be a one-off reservation, or a recurring reservation
Copyright © 2014 Juniper Networks, Inc. 13
PROGRAMMABLE PATH COST FUNCTION
Lowest latency path Lowest IGP metric path
Path computation according to application/service requirements: • Lowest metric path • Lowest latency path • Path that avoids particular links or nodes
Copyright © 2014 Juniper Networks, Inc. 14
MAINTENANCE-MODE
Automate re-routing of traffic before a scheduled maintenance window:
Node tagged as going into maintenance mode, affected LSPs are identified by NorthStar. 1
1 3
X X
X
2
2 LSPs are re-computed and re-signaled around the affected node through a PCEP update (all make-before-break). Node is subsequently moved into maintenance mode.
Node is tagged as available again after maintenance window finishes. Optimum LSP paths are restored again through PCEP update and LSP re-signaling
3 Node is tagged as available after maintenance window finishes. Optimum LSP paths are restored through PCEP update and re-signaling.
Copyright © 2014 Juniper Networks, Inc. 15
KEY ATTRIBUTES OF A CENTRALISED CONTROLLER • Has real-time knowledge of topology of network, link attributes and bandwidth availability on each link
• Has real-time knowledge of status and attributes of all TE LSPs in the network
• Has real-time knowledge of the traffic matrix • Has the ability to modify existing LSPs, and to instantiate new LSPs
• Has the ability to exchange information and receive requests for action from northbound applications via APIs
Copyright © 2014 Juniper Networks, Inc. 16
Title Only
Path Computation Element
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PCE: A STANDARDS-BASED APPROACH
§ PCE: Path Computation Element (RFC 4655)
An entity that can calculate paths in the network
§ PCE: Path Computation Element Computes the path
§ PCC: Path Computation Client Receives the path. Signals LSP using RSVP (or sets up SPRING LSP)
§ PCEP: PCE protocol (RFC 5440) For PCE/PCC communication
Components What is it?
PCE PCEP
PCC PCC
PCC
Copyright © 2014 Juniper Networks, Inc. 18
ACTIVE STATEFUL PCE
• The original PCE draft (mid-2000s) were mainly focused on stateless PCE.
• In the last two years, the hot topic has been Active Stateful PCE, as it is in line with the SDN paradigm.
• The PCE has visibility into the network state AND the demands
• The PCE (rather than the routers) is the entity that drives changes • Dictates the order of operations network-wide • Creates new state
Copyright © 2014 Juniper Networks, Inc. 19
LSP TYPES, WHEN USING ACTIVE STATEFUL PCE 1/ “Vanilla” LSP
• Configured on ingress router (i.e. exists in router config file) • Path computed by ingress router using CSPF • Existence of LSP, and associated parameters, reported to PCE for PCE’s info
only – PCE cannot modify the LSP.
2/ Delegated LSP • Configured on ingress router (i.e. exists in router config file) • When first set up, path is computed by ingress router using CSPF • Delegated to PCE – means that PCE can modify parameters from time to time
e.g. bandwidth, ERO
3/ PCE-initiated LSP • PCE decides to create LSP. • Sends set-up request to ingress router via PCEP, with ERO, bandwidth etc • Automatically delegated to PCE –means that PCE can modify parameters over
time • Is ephemeral –does not exist in router’s config file.
Copyright © 2014 Juniper Networks, Inc. 20
ACTIVE STATEFUL PCE FUNCTIONS • Delegation – ability for a PCC to grant control over an LSP • Report (PCRpt)– ability for a PCC to report state of LSPs
• Each LSP Status Report in a PCRpt message can contain the actual LSP's path, bandwidth, operational and administrative status
• Can report all LSPs, delegated and non-delegated, so PCE has full visibility of all LSPs
• Update (PCUpd) – ability of the PCE to update attributes for an LSP delegated to it
• Instantiate/tear down (PCInitiate)– ability for a PCE to create or tear down an LSP
Copyright © 2014 Juniper Networks, Inc. 21
N L
A
M
Y
C
D
Z
To make traffic take path A-L-M-N-Y, send it to L with label stack = {406,607,708}
Path setup
Centralized path
computation
N L
A
M
Y
C
D
Z
407 708
704 807
SPRING (SEGMENT ROUTING)
Copyright © 2014 Juniper Networks, Inc. 22
Title Only
BGP-LS
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BGP-LS BACKGROUND • Mechanism to carry traffic engineering link state info in BGP
• bandwidth availability, link colours (admin-groups), SRLGs etc
• Two major categories of application • 1/ For inter-domain (i.e. inter-area, inter-AS) traffic engineering.
• Traditional approach of loose-hop expansion at border nodes has limitations
• 2/ As a “TE-topology reporting protocol” towards a central controller (e.g. a PCE)
• Much cleaner than using IGP, or CLI-scraping
• Was called BGP Traffic Engineering (BGP-TE) in the earlier drafts • Later changed name to BGP Link State (BGP-LS)
Copyright © 2014 Juniper Networks, Inc. 24
B H D F
E
G J
K
C
A
GIVING CONTROLLER VISIBILITY OF TED VIA IGP PEERING
Central Controller
IGP over GRE
tunnel
IGP over GRE tunnel
Each router only knows TED of its own IGP area(s), so Central Controller needs IGP peering with each area
Copyright © 2014 Juniper Networks, Inc. 25
“Link Attribute” TLVs: carry same info between domains as carried by IGP TE extensions
within a domain
TED NLRI TYPES: NODES AND LINKS “Node
Anchor” TLVs
“Link Descriptor” TLVs
Link NLRI describes “unidirectional link”
Copyright © 2014 Juniper Networks, Inc. 26
B H D F
E
G J
K
C
A
GIVING CONTROLLER VISIBILITY OF TED VIA BGP-LS
Central Controller
Central Controller just needs one BGP-LS session with network
BGP-LS
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Title Only
Putting it all together
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INTERACTION BETWEEN CONTROLLER AND NETWORK (1)
LSP X
LSP Y
Network
TE Controller
BGP-LS peering between TE Controller and at least one node in the network gives TE Controller real-time knowledge of topology and TE parameters of each link.
BGP-LS
Copyright © 2014 Juniper Networks, Inc. 29
INTERACTION BETWEEN CONTROLLER AND NETWORK (2)
LSP X
LSP Y
Network
TE Controller
LSP X and LSP Y were set up via router CLI, not PCEP. However, each LSP ingress router reports existence of its LSPs to the controller via PCEP. In this way, controller is made aware of the existence of such LSPs
PCEP
LSP X
LSP Y
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INTERACTION BETWEEN CONTROLLER AND NETWORK (3)
LSP X
LSP Y
Network
TE Controller
Controller can compute LSP path and install it on ingress router using PCEP. Ingress router confirms successful setup of LSP using PCEP.
PCEP
LSP X
LSP Y
LSP Z
LSP Z
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Title Only
TE Controller Example: Northstar
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Title Only
Routing
BGP-LS
PCEP
Netconf/YANG
Topology Discovery
Path Installation
Path Computation
ANALYZE
PROVISION
OPTIMISE CSPF
Algorithms
NETWORK PROGRAMMABILITY MODEL
ANALYTICS ENGINE
Dynamic feedback loop harvests network
state
Copyright © 2014 Juniper Networks, Inc. 33
Title Only
SOFTWARE-DRIVEN POLICY
Topology Discovery Path Computation Path Installation
NORTHSTAR CONTROLLER
PCEP § LSP discovery IGP-TE, BGP-LS § TED discovery Traffic Statistics
PCEP § Install traffic engineered LSP § One session per LER/PCC
Netconf/XML/YANG BGP-flowspec § Other state injection methods
ANALYZE OPTIMISE PROVISION
Routing Netconf/YANG PCEP Algorithms 3rd party Algorithms
RSVP signaling
OPEN APIs
Copyright © 2014 Juniper Networks, Inc. 34
Title and Bullets
STANDARD APIS FOR 3RD PARTY TOOLS & CUSTOM APPLICATIONS
Topology Discovery Path Computation Path Installation
Topology API Path Comput. API Path Provision API
Routing Netconf/YANG PCEP Junos CSPF Algorithms
Standard, custom, & 3rd party Applications
Built-in Applications, e.g. Bandwidth Calendaring LSP Path Diversity Node Maintenance
REST or Thrift
REST or Thrift
REST or Thrift
Custom and 3rd Party Applications
Copyright © 2014 Juniper Networks, Inc. 35
SUMMARY • TE Controller: Real-time visibility and control of the network. • Solves problems that Distributed TE cannot
• Fully diverse paths • Avoidance of LSP blocking • Globally optimum bin-packing
• APIs for interaction with Northbound applications • Uses standards-based protocols wherever possible
• PCEP • BGP-LS
• For more details: • http://www.juniper.net/us/en/products-services/sdn/northstar-
network-controller/ . • Please get in touch if you would like to see a demo.
Copyright © 2014 Juniper Networks, Inc. 36 Copyright © 2013 Juniper Networks, Inc.
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@JuniperNetworks