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

01 Why segment routing?

3 Área Company Name 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.

4 Área Company Name 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

5 Área Company Name 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 (*)

6 Área Company Name 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

02 Show me some scenarios …

8 Core Networks Evolution Telefónica I+D SPRING Use cases CoS-based Traffic Engineering Deterministic non-ECMP Path Load-balancing among non-parallel links Fast Reroute Capacity Planning OAM

9 Core Networks Evolution Telefónica I+D 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)

10 Core Networks Evolution Telefónica I+D 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 Argentina Chile Peru Ecauador

11 Core Networks Evolution Telefónica I+D 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.

12 Core Networks Evolution Telefónica I+D 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 Argentina Chile Peru Ecauador

Do I miss something then?

14 Área Company Name 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

15 Área Company Name PCE with segment routing

16 Área Company Name 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

17 Área Company Name 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

18 Core Networks Evolution Telefónica I+D