Óscar González de Dios PCE, the magic component of Segment Routing Telefónica I+D.

Óscar González de Dios

PCE, the magic component of Segment Routing

Telefónica I+D

01Why segment routing?

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Running a packet-based Network

• Two main philosphies to operate a packet-based network Keep my life simple

• Let the routing decide the path, and let the network distribute the labels I want control, I am smart

• Let me decide where my traffic goes

• Problems of “Keep my life simple” approach The good old times of free unlimited bandwidth are gone Difficult to use several paths Difficult to differentiate among traffics

• OK, so I need to have more control over my traffic Traffic Engineering RSVP-TE allows to set up explicit tunnels and send traffic through them

• Great… but … TE comes with increased complexity Traffic Engineering with RSVP-TE needs lots of tunnels.

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What do we need?

Simplification

1

Scalability

Adapat to changes

3

• Less state in the network

• Less state in the router

• Less tunnels maintained

• No need to signal new paths

• Apply Fast Reroute easily

• Less Protocols in the routers

• No RSVP-TE, no LDP, no T-LDP

2

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Principle of Segment routing

• “Segment Routing enables any node to select any path (explicit or derived from Interior Gateway Protocol (IGP) Shortest Path Tree (SPT) computations) for each of its traffic classes”. (*)

• Let’s identify uniquely “segments” in the network

• At the source, add to the packet the list of segments as labels

• With a simple label lookup at each hop, the packet reaches the destination

(*) http://tools.ietf.org/html/draft-previdi-filsfils-isis-segment-routing-02

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Benefits

• Uses existing MPLS hardware (I hope)

• Maintains few state in the devices (just the forwarding table) Lower CPU/memory requirements in network nodes

• Does not need to maintain tunnels Less complex to operate

• Easy to test any path Allows easy testing

02Show me some scenarios …

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SPRING Use cases

• CoS-based Traffic Engineering

• Deterministic non-ECMP Path

• Load-balancing among non-parallel links

• Fast Reroute

• Capacity Planning

• OAM


CoS-based Traffic Engineering: Example

• There are two main connections from US to Europe: High-capacity, no QoS

requirements and cheap. Low-capacity, minimum delay

and expensive.

• Expensive connections are used for Internet traffic, while cheap connections sends VoIP traffic from VPNs.

• Nowadays there is a manageability problem.

Internet Traffic

VPNs (VoIP)


Load-balancing among non-parallel links + Deterministic non-ECMP Path: Example

• Telefonica International Network

• Multiple links between the peering points and Miami.

• The same from Miami to the different countries.

• RSVP-TE can not be used because of the multiple combinations of links for a two hops path enabling load balancing. Segment Routing would enable this

easily.

• To differentiate services, ECMP is not enough Explicit Path

Miami

Peering Points

Brasil

ArgentinaChile

Peru

Ecauador


Capacity Planning Process

• Segment Routing offers a simple support for explicit path policy.

• One node segment represents the set of ECMP-aware shortest paths.

• Adjacency segments allow to express any explicit path.

• The combination of node and adjacency segment allows to express any path without having to enumerate all the ECMP options.


OAM

• Remote bundle MS sends a packet to R1 which has a rule with

these segment list: {72, 662, 992, 664}

• Remote peering link Node A can monitor the dataplane liveness of

the unidirectional peering link from C to D of AS2 by sending an IP probe with destination address A and segment list {101, 9001}.

• Note: C Node-SID is 101 and C is connected to a peer D with external adjacency segment 9001

Miami

Peering Points

Brasil

ArgentinaChile

Peru

Ecauador

Do I miss something then?

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PCE: the magic component for segment routing

• Segment routing alone does not solve all your problems

• How do I get the list of segments for a path with contraints? PCE is the answer

• How do I optimize the whole network? PCE does it for you

• If there is less state in the network… where is the state? In the PCE It will keep the TED, the labels and the list of paths

• So… all the fuss about segment routing… but without a PCE

A Network with Segment routing without PCE is complex to operate

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PCE with segment routing

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The recipe: PCE for segment routing

• PCEP to query with constraints/inclusion/exclusion

• Syntax to express a SR path (e.g. SR-ERO)

• Stateful PCE to keep track of paths

• Active PCE to create automatically fast reroutes

• Active PCE to reoptimize network

• PCEP for remote instantiation

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Conclusions

• Segment Routing allows to remove complexity from the network devices

• SR enables traffic engineering

• PCE complements Segment Routing Maintains network state Computes optimum paths Takes into account constraints in computation Active stateful PCE can control a network with segment routing

Óscar González de Dios PCE, the magic component of Segment Routing Telefónica I+D.

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